H          tfCjgfc* 


i  itiimii 


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UNIVERSITY  OF  CALIFORNIA 

ANDREW 

SMITH 

HALLID1E.: 


1868^^1901 


HANDBOOK 


OF 


CHEMISTRY, 


THEORETICAL,  PRACTICAL,  AND  TECHNICAL 


BY 


F.   A.   ABEL, 


PROFESSOR    OF    CHEMISTRY    AT    THE    ROYAL   MILITARY   ACADEMY,  WOOLWICH;    AND 
ASSISTANT-TEACHER  OF  CHEMISTRY  AT  ST.  BARTHOLOMEW'S  HOSPITAL; 


AND 


C.   L.   BLOXAM, 


FORMERLY   FIRST    ASSISTANT   TO    THE    ROYAL    COLLEGE    OF    CHEMISTRY. 


A   PEEFACE   BY  DR.  HOFMANN: 


AND 


NUMEROUS  ILLUSTRATIONS  ON  WOOD. 


PHILADELPHIA: 

BLANCHARD     AND     LEA 
1854. 


/I 


7T 


PHILADELPHIA: 
T.  K.  AND  P.  G.  COLLINS,  PRINTERS. 


AMERICAN  PUBLISHERS'  NOTICE. 


THE  passage  of  this  volume  through  the  press  has  been  carefully 
superintended  by  a  competent  editor,  to  secure  the  typographical 
accuracy  so  necessary  to  a  work  of  this  nature.  The  very  thorough 
manner  in  which  the  authors  have  carried  out  their  intention  in  its 
preparation,  and  the  recent  date  of  their  labors,  have  rendered  un- 
necessary any  additions  to  the  text.  A  number  of  wood-cuts  have, 
however,  been  introduced,  the  entire  absence  of  illustrations  in  the 
English  edition  appearing  to  be  a  drawback  to  the  utility  of  the 
work  as  a  guide  to  the  student  engaged  in  chemical  operations,  a  pur- 
pose for  which  it  is  especially  designed,  and  will  be  found  eminently 
fitted. 

PHILADELPHIA,  May,  1854. 


103989 


PREFACE  BY  DR.  HOFMANN,  F.R.S. 


I  FEEL  much  pleasure  in  complying  with  the  wish  expressed  by 
Messrs.  Abel  and  Bloxam,  that  I  should  introduce  the  present  volume 
with  a  few  prefatory  remarks. 

The  Authors,  after  having  received  their  chemical  education  in  my 
laboratory,  officiated  for  some  years  as  my  assistants,  and  I  have  had 
ample  opportunities  of  witnessing  their  talents  for  imparting  informa- 
tion, and  smoothing  the  path  of  the  Student,  in  every  department  of 
analysis.  The  present  volume  is  a  synopsis  of  their  experience  in 
laboratory  teaching;  it  gives  the  necessary  instruction  in  chemical 
manipulation,  a  concise  account  of  general  chemistry,  as  far  as  it  is 
involved  in  the  operations  of  the  laboratory,  and  lastly,  qualitative 
and  quantitative  analysis.  The  plan  adopted  in  the  instructions  for 
analysis  is  essentially  that  which  was  first  introduced  by  Baron  Liebig, 
and  which,  modified  in  accordance  with  the  progress  of  science,  and 
with  the  special  requirements  of  the  English  student,  I  have  daily 
practised  myself,  for  the  last  eight  years,  in  this  laboratory. 

I  have  no  doubt  that  the  work  of  Messrs.  Abel  and  Bloxam  will 
fulfil  the  purpose  for  which  it  was  written,  and  will  prove  a  useful 
laboratory  guide  to  the  chemical  student. 

A.  W.  H. 
<•» 

ROYAL  COLLEGE  OF  CHEMISTRY, 
October,  1853. 


PREFACE. 


IT  is  with,  considerable  diffidence  that  the  authors  venture  to  bring 
this  handbook  before  the  public,  at  a  time  when  the  rapid  growth  of 
the  science  of  which  it  treats  has  called  forth  numerous  works  on  all 
its  branches,  from  the  pens  of  chemists  of  the  highest  eminence,  which 
leave  nothing  to  be  desired  in  clearness  of  explanation  or  minuteness 
of  detail.  Although,  however,  the  different  departments  of  chemistry, 
theoretical,  practical,  technical,  and  analytical,  have  been  made  the 
subjects  of  separate  treatises,  which  may  well  rank  as  the  classics  of 
the  science,  there  is  as  yet  no  single  work  which  presents,  even  to 
those  who  can  devote  but  a  comparatively  short  period  to  the  study 
of  this  necessary  branch  of  an  extended  education,  such  a  general 
view  of  practical  chemistry,  in  its  several  relations,  as  shall  enable 
them  to  acquire,  with  the  least  possible  expenditure  of  time,  a  know- 
ledge which  will  either  suffice  for  the  ordinary  applications  of  che- 
mistry to  the  useful  arts,  or  will  serve  as  a  sound  basis  for  the  educa- 
tion of  a  professional  chemist.  To  attain  this  very  desirable  end,  it  is 
obviously  necessary  to  furnish  the  student,  in  many  cases,  with  the 
result  only  of  a  long  chain  of  reasoning,  which  he  would  otherwise 
have  to  elaborate  for  himself,  without  any  advantage  to  compensate 
for  the  sacrifice  of  time. 

It  was  not  the  intention  of  the  authors,  even  if  it  had  been  in  their 
power,  to  write  a  complete  system  of  chemical  philosophy,  but  rather 
to  content  themselves  with  entering  only  so  far  into  theoretical  con- 
siderations as  is  absolutely  essential  in  practice,  and  to  bring  the  laws 
which  determine  the  results  of  chemical  operations  before  the  student, 
in  such  a  form,  that  their  mutual  dependence  might  be  clearly  per- 
ceived, and  that  they  might  readily  fix  themselves  in  the  memory. 
In  carrying  out  this  design,  however,  some  pains  have  been  taken  to 
avoid  giving  a  concise  description  at  the  expense  of  a  clear  and  satis- 
factory explanation. 

The  authors,  having  been  engaged  in  laboratories  where  reference 


Vlll  PREFACE. 


has  been  made  to  them  by  chemical  students  respecting  all  the  trivial 
difficulties  met  with  in  practice,  have  endeavored  to  turn  their  experi- 
ence to  advantage,  in  supplying  information  upon  those  points  which, 
though  apparently  trifling,  form  great  obstacles  in  the  path  of  the 
beginner,  and  are  not  generally  explained  in  treatises  on  scientific 
chemistry,  since  they  are  far  too  unimportant  in  themselves  to  occupy 
pages  which  are  better  filled  with  the  philosophy  of  the  science. 

In  the  sections  devoted  to  chemical  manipulation,  the  various  ope- 
rations are  described,  as  far  as  possible,  in  the  order  in  which  they 
would  occur  in  the  laboratory;  thus,  in  considering  the  preparation  of 
gases,  attention  is  first  directed  to  the  construction  of  the  apparatus, 
the  bending  of  tubes,  perforation  of  corks,  &c.;  next,  the  arrange- 
ments for  collecting  gases  are  noticed;  and  lastly,  the  transference  of 
gases,  and  the  various  operations  which  may  have  to  be  performed 
upon  them. 

Chemical  equations,  which  afford,  at  a  glance,  such  clear  explana- 
tions of  various  processes,  have  been  freely  used  throughout  that  por- 
tion of  the  work  which  treats  of  elementary  chemistry. 

In  describing  the  preparation  of  substances,  details  respecting  the 
necessary  apparatus  have  been  omitted,  since  they  have  been  given 
in  the  sections  on  manipulation.  Since  this  book  is  not  intended  for 
a  complete  work  of  reference,  or  for  an  account  of  all  the  researches 
which  have  been  made  upon  the  subjects  of  which  it  treats,  only  those 
compounds  are  described,  which  appear  to  possess  a  certain  practical 
importance.  The  descriptions  of  the  processes  involved  in  the  differ- 
ent arts  and  manufactures  have  been  stripped,  to  a  great  extent,  of 
their  mechanical  details,  in  order  that  their  chemical  principles  may 
be  more  readily  mastered  by  the  student.  In  the  history  of  the  che^ 
mical  products  obtained  on  a  large  scale,  the  methods  employed  by 
the  practical  chemist  for  ascertaining  their  value  and  for  detecting  the 
impurities  to  which  they  are  liable,  have,  in  most  cases,  been  given. 

There  is  appended  to  the  technical  history  of  the  most  important 
metals,  a  list  of  their  chief  minerals  and  ores,  together  with  a  brief 
outline  of  the  methods  usually  followed  in  assaying  the  ores ;  these 
latter  have  been  given  more  with  the  view  of  imparting  to  the  student 
a  general  idea  of  such  operations,  than  of  enabling  him  to  carry  out, 
by  the  scanty  directions  there  supplied,  operations  which  fall  strictly 
within  the  province  of  the  metallurgist. 

The  reactions  by  which  the  rarer  metals  may  be  distinguished  are 
introduced  into  their  general  history,  to  avoid  unnecessary  complica- 
tion of  the  systematic  course  of  analysis.  When  these  metals  are 


PREFACE.  ix 

supposed  to  exist  in  any  substance  under  examination,  special  methods 
are  always  followed  for  their  detection. 

Some  care  has  been  taken^  by  diligent  comparison  with  the  latest 
monographs,  to  render  the  history  of  elementary  chemistry  a  faithful 
representation,  as  far  as  the  extent  of  the  work  will  allow,  of  the  pre- 
sent state  of  the  science. 

In  the  portion  relating  to  analytical  chemistry,  a  special  description 
of  the  apparatus  and  operations  of  qualitative  and  quantitative  analy- 
sis has  been  given.  The  authors  have  here  made  it  their  chief  aim  to 
be  as  concise  as  possible,  omitting  everything  which  has  no  direct 
bearing  upon  the  systematic  course,  in  order  that  the  student  may  not 
be  discouraged  by  a  superfluity  of  detail,  at  the  commencement  of  a 
study  requiring  so  considerable  an  amount  of  patience. 

Again,  in  constructing  the  systematic  course,  all  unnecessary  inno- 
vation has  been  avoided,  the  older  methods  of  separation  having  been 
retained,  except  in  cases  where  they  yielded  unsatisfactory  results, 
when  they  have  been  replaced  by  others  which  have  been  submitted 
to  the  test  of  experiment ;  however,  in  the  present  progressive  state  of 
analysis,  many  of  the  methods  are  necessarily  very  imperfect;  indeed, 
analytical  tables  must  ever  be  regarded  as  provisional,  and  will  con- 
stantly be  liable  to  be  superseded  by  others  which  are  less  circuitous 
or  more  accurate. 

Under  the  impression  that  the  student  is  far  more  likely  to  retain 
in  his  memory  the  various  methods  of  quantitative  separation  of  sub- 
stances, when  introduced  in  the  form  of  practical  examples,  than  when 
merely  described  in  a  general  manner,  a  number  of  analyses  for  prac- 
tice have  been  selected,  in  which  the  most  important  separations  are 
effected. 

We  have  derived  no  small  gratification  from  the  circumstance  that 
this  work  has  received  the  approbation  of  our  friend  and  former 
teacher,  Dr.  Hofmann. 

LONDON,  October,  1853. 


Xll  CONTENTS. 

DISTILLATION  AND  SUBLIMATION — Theory  of  the  process — Distillation  at  high  temperatures 
— Stills — Worms — Liebig's  condenser — Receivers  —  Frigorific  mixtures  —  Distillation 
at  lower  temperatures,  but  above  212° — Retorts — Flasks  for  distillation — Adapters 
— Joints — Application  of  heat  in  distillation — Sand-bath — Precautions  in  distillation 
— Distillation  at  temperatures  below  212° — Water-bath — Determination  of  boiling- 
points — Fractional  distillation — Sublimation,  \\  38-44. 

DISINTEGRATION — Pestle  and  mortar  —  Crushing  mortar — Pulverization — Levigation — 
Granulation — Precipitation  of  metals,  \\  45,  46. 

SOLUTION — INFUSION — DIGESTION  —  Dishes  —  Beakers— Flasks — Stirrers — Solution  on  a 
small  scale — Lixiviation — Percolators — Saturation,  ||  47-49. 

FILTRATION — Funnels — Filtering-paper — Filters  — Precautions  in  filtering  —  Edulcoration 
— Syringe-bottle — Decantation — Siphon — Pipette — Separation  of  liquids — Separat- 
ing-funnel,  \\  50-52. 

EVAPORATION — Spontaneous  evaporation — Evaporation  in  vacuo — Water-bath — Oil-bath — 
Evaporation  below  ebullition — Evaporation  at  the  boiling-point — Evaporation  to  dry- 
ness — Desiccation — Air-bath — Aspirator — Deliquescence — Drying-tiles,  ||  53,  54. 

CRYSTALLIZATION  ;  by  solution ;  by  fusion — Means  of  promoting  crystallization — Crystal- 
lization by  vaporization,  \\  55,  56. 

IGNITION — Precautions  in  heating  crucibles,  &c. — Crucible-jacket — Ignition  in  qualitative 
analysis,  §  57. 

FUSION — Fluxes — Black  flux — Action  of  fluxes — Crucibles — Precautions  in  fusion,  g$  58, 
59. 

SOURCES  OF  HEAT  IN  THE  LABORATORY — Lamps — Roaring-lamp — Berzelius  and  Mitscher- 
lich's  lamps  —  Argand  oil-lamp  —  Gas-burners  —  Gauze-burner — Furnaces — Drying- 
closet — Black's  furnace — Muffle — Combustion-furnace — Charcoal-chauffer',  \\  60,  61. 

USE  OF  THE  BLOWPIPE  —  Black's  blowpipe — Blowpipe-lamps — Blowpipe-apparatus  — 
Charcoal  supports— Blowpipe-reagents — Intumescence — Decrepitation — Deflagration 
— Detonation — Incandescence — Structure  of  the  blowpipe-flame — Reduction  on  Char- 
coal— Incrustation — Roasting — Colored  beads — Colored  flames,  $%  62-66. 

GLASSBLOWING — Table-blowpipe — Herepath's  blowpipe — Rose's  spirit-blowpipe — Closure 
of  tubes — Sealing  of  tubes — Glass  bulbs — Arsenic  tubes — Combustion- tubes,  \  67. 

ELEMENTARY-  CHEMISTRY. 

CLASSIFICATION  OF  ELEMENTS — Metals  and  non-metallic  substances — Table  of  symbols 
and  equivalents,  §  68. 

OXYGEN— Oxides— Ozone,  \\  69-72. 

HYDROGEN — Precautions  in  preparing  hydrogen — Purification,  \$  73,  74. 

WATER — Circumstances  under  which  water  is  formed — Action  of  spongy  plati- 
num on  gaseous  mixtures — Oxyhydrogen  blowpipe — Drummond  light — Hemming's 
jet — Synthesis  and  analysis  of  water — Ice — Steam — Hydrates — Water  from  different 
sources — Hard  and  soft  waters — Mineral  waters — Distillation  of  water — Binoxide  of 
hydrogen,  \\  75-79. 

NITROGEN — Nitrous  oxide — Nitric  oxide — Nitrous  acid — Peroxide  of  nitrogen,  ||  80-84. 

NITRIC  ACID — Anhydrous  nitric  acid — Hydrated  nitric  acid — Nitrification — Pre- 
paration of  nitric  acid  of  commerce — Nitrates — Action  of  nitric  acid  upon  organic 
substances— Uses,  %$  85,  86. 

ATMOSPHERIC  AIR — Analysis  of  air — Foreign  matters  existing  in  air — Determina- 
tion of  water  and  carbonic  acid — Air  merely  a  mixture,  not  a  combination,  §|  87,  88. 


CONTENTS.  xjii 

NITROGEN  AND  HYDROGEN — Amidogen — Amides,  \  89. 

AMMONIA — Circumstances  under  which  ammonia  is  formed — Solution  of  ammonia 
— Ammonium — Amalgam  of  ammonium — Ammonium-theory  of  Berzelius,  \\  90-92. 

CHLORINE — Bleaching — Disinfecting — Hypochlorous  acid — Euchlorine  —  Chlorous  acid 
— Peroxide  of  chlorine— Chloric  acid  —  Chlorates  —  Chlorochloric  acid — Perchloric 
acid— Chloroperchloric  acid — Millon's  views,  gg  93-95. 

HYDROCHLORIC  ACID — Solution  of  hydrochloric  acid — Uses — Nitro-hydro chloric 
acid — Researches  of  E.  Davy  and  Gay-Lussac — Chloride  of  nitrogen — Chlorides  of 
the  metals,  \\  96,  97. 

BROMINE — Bromic  acid — Hydrobromic  acid — Chloride  of  bromine — Metallic  bromides 
\\  98,  99. 

IODINE — Uses  of  Iodine — lodic  acid — Periodic  acid — Hydriodic  acid — Iodide  of  Nitrogen 
— Chlorides  of  iodine — Bromides  of  iodine — Metallic  iodides — Speculations  of  Dumas 
— Triads  of  elements,  \\  100,  101. 

FLUORINE— Hydrofluoric  acid— Metallic  fluorides,  \  102. 
SULPHUR— Allotropy— Uses  of  sulphur,  §  103. 

SULPHUR  AND  OXYGEN — Hyposulphurous  acid— Sulphurous  acid — Uses  of  sul- 
phurous acid — Hyposulphuric  acid,  §  104. 

SULPHURIC  ACID — Conditions  of  its  formation — Anhydrous  sulphuric  acid 

Nordhausen  sulphuric  acid — Oil  of  vitriol — Manufacture  of  oil  of  vitriol — Theory  of 
the  process — Impurities  of  oil  of  vitriol  —  Other  Hydrates  of  sulphuric  acid  —  Sul- 
phates— Uses  of  sulphuric  acid,  g  105. 

BINARY  THEORY  OF  ACIDS,  g  106. 

Trithonic  acid — Tetrathionic  acid — Pentathionic  acid,  §  107. 

SULPHUR  AND  HYDROGEN — Pentasulphide  of  hydrogen — Hydrosulphuric  acid — 
Sulphur  and  nitrogen — Nitrosulphuric  acid — Sulphate  of  nitric  oxide,  $$  108,  109. 

SULPHUR  AND  CHLORINE — Subchloride  of  sulphur — Chloride  of  sulphur — Sulphur 
and  bromine — Sulphur  and  iodine — Metallic  sulphides  —  Sulphur-acids — Sulphur- 
bases — Sulphur-salts,  g  110. 

SELENIUM — Oxide  of  selenium — Selenious  acid — Selenic  acid — Seleniuretted  hydrogen — 
Chlorides  of  Selenium — Bromides  of  Selenium — Sulphides  of  Selenium- — Metallic 
Selenides,  \\  111,  112. 

PHOSPHORUS — White  phosphorus — Amorphous  phosphorus — Impurities  of  phosphorus 
— Uses  of  phosphorus,  \  113. 

PHOSPHORUS  AND  OXYGEN — Suboxide  of  phosphorus — Hypophosphorous  acid — 
Phosphorous  acid,  \  114. 

PHOSPHORIC  ACID — Anhydrous  phosphoric  acid  — Metaphosphoric,  pyrophospho- 
ric,  and  common  phosphoric  acids — Phosphates — Fleitmann  and  Henneberg's  salts, 
2  115. 

PHOSPHORUS  AND  HYDROGEN — Solid,  liquid,  and  gaseous  phosphuretted  hydrogen 
— Terchloride  of  phosphorus — Pentachloride  of  phosphorus — Oxychloride — Chloro- 
sulphide  —  Bromides  and  iodides  of  phosphorus  —  Phospham — Phosphamide  —  Sul- 
phides and  selenides  of  phosphorus — Phosphides,  \\  116,  117. 

CARBON — Diamond— Graphite — Coal — Origin  and  formation  of  coal — Peat — Lignite — 
Pit-coal — Cannel  coal — Pitch-coal — Cubical  coal — Splint-coal — Caking  coal — Anthra- 
cite— Jet — Decomposition  of  coal — Coal  fires — Inorganic  constituents  of  coal — Valua- 
tion of  fuel — Proximate  and  ultimate  analysis  of  coal,  \\  118-120. 


XIV  CONTENTS. 

ARTIFICIAL  VARIETIES  OF  CARBON — Coke — wood — charcoal — Charbon-roux — 
Cylinder-charcoal — Tests  of  the  quality  of  charcoal — Lampblack — Animal-charcoal 
— Ivory-black— Decolorizing  and  disinfecting  properties  of  charcoal — General  pro- 
perties of  carbon— Uses  of  carbon,  §§  121,  122. 

CARBON  AND  OXYGEN  —  Carbonic  oxide  —  Chlorocarbonic  acid  —  Carbonic  oxide 
series — Carbonic  acid — Liquid  and  solid  carbonic  acid — Determination  of  the  com- 
position of  carbonic  acid — Carbonates — Uses  of  carbonic  acid— Aerated  waters  — 
Fire-annihilator,  |§  123,  124. 

LIGHT  CARBURETTED  HYDROGEN — Marsh-gas — Fire-damp — Explosions  in  coal- 
mines— Davy's  safety-lamp — Coal-gas — Valuation  of  coal-gas — Manufacture  of  coal- 
gas— Analysis  of  coal-gas— Oil-gas— Water-gas,  \\  125-128. 

OLEFIANT  GAS — Bicarburetted  hydrogen  of  Faraday,  §  129. 

Cyanogen — Cyanogen  series — Mellon,  §  130. 

Chlorides  of  carbon — Bisulphide  of  carbon — Carbides,  §§  131-133. 

BORON — Boracic  acid — Lagoons — Borates — Boron  and  nitrogen — Terchloride  of  Boron — 
Terfluoride  of  boron— Sulphide  of  boron,  §g  134,  135. 

SILICON— Silicic  acid— Kock-crystal— Opal— Silicates— Uses  of  silicic  acid,  §|  136, 137. 

GLASS — Relations  of  the  different  ingredients  in  glass — Devitrification — Materials 
for  glass-making — Varieties  of  glass — Colored  glasses — Artificial  gems  —  Enamels, 
|138. 

Silicon  and  hydrogen — Terchloride  of  silicon — Silicon  and  bromine — Terfluoride 
of  silicon — Hydrofluo silicic  acid — Silicon  and  sulphur — Chlorosulphide  of  silicon,  §  139. 
THE  METALS — General  considerations,  \  140. 

POTASSIUM — Suboxide  of  potassium — Potassa — Hydrate  of  potassa — Uses  of  potassa, 
\\  141-143. 

NITRATE  OF  POTASSA — Occurrence  in  nature — Conditions  of  its  formation — Nitri- 
fication— Artificial  production  of  nitrates — Saltpetre-plantations — Preparation  and 
purification  of  nitre — Uses  of  nitre — Examination  (refraction)  of  nitre — Gay-Lussac's 
method — Pelouze's  method,  \%  144-148. 

GUNPOWDER — Theoretical  considerations — Most  advantageous  composition  — 
Gunpowder  of  different  countries — Manufacture  of  gunpowder — The  ingredients — 
Nitre  —  Sulphur  —  Charcoal — Theoretical  considerations  respecting  charbon  roux  — 
Pulverization  and  mixture  of  the  ingredients — Revolutionary  process — Granulation 
of  the  powder — Waltham  Abbey  process— Champy  process — Glazing — Desiccation — 
Properties  of  gunpowder,  $  149. 

Nitrite  of  potassa — Chlorate  of  potassa  —  Uses — Lucifer  matches — Percussion 
powder — Perchlorate  of  potassa — Hypochlorite  of  potassa — Eaude  Javelle — Bromate, 
iodates,  and  periodate  of  potassa,  §§  150-154. 

Sulphate  of  potassa — Bisulphate  of  potassa — Phosphates  of  potassa,  §  155. 

CARBONATE  OF  POTASSA — Impurities  of  commercial  potashes — Pearlash — Bicar- 
bonate of  potassa — Silicates  of  potassa,  $  156,  157. 

Peroxide  of  potassium — Chloride,  bromide,  and  iodide  of  potassium — Valuation 
of  iodide  of  potassium — Fluoride  of  potassium,  $$  158,  159. 

Sulphide  of  potassium — Hydrosulphate  of  sulphide  of  potassium — Bisulphide  and 
polysulphides  of  potassium — Hepar  sulphuris — Theory  of  the  preparation  of  milk  of 
sulphur — Silicofluoride  of  potassium,  %%  160,  161. 
SODIUM — Minerals  containing  sodium — Suboxide  of  sodium,  §  162. 

SODA — Hydrate  of  soda — Nitrate  of  soda — Hypochlorite  of  soda — Chloride  of 
soda — Bleaching  liquid  of  Labarraque — Chlorate  of  soda — Hyposulphite  and  sulphite 
of  soda — Glauber's  salt — Bisulphate  of  soda,  \\  163-167. 


CONTENTS.  •  XV 

PHOSPHATES  OF  SODA — Triphosphate — Common  phosphate — Acid  phosphate 

Pyrophosphates — Metaphosphate — Fleitmann  and  Henneberg's  salts,  §  168. 

CARBONATE  OF  SODA — Barilla — Blanquette — Salicor — Kelp — Manufacture  of  car- 
bonate of  soda  from  common  salt — Balling  process — Composition  of  black  ash  and 
soda  waste — Economical  relations  of  Leblanc's  process — Properties  and  uses  of  car- 
bonate of  soda — Carbonate  of  potassa  and  soda — Sesquicarbonate  and  bicarbonate 
of  soda,  |g  169-172. 

BORATE  OF  SODA — Borax — Tincal — Refining  of  Tincal — Manufacture  of  Borax — 
Octohedral  borax — Vitrified  borax — Uses  of  borax — Valuation  of  tincal — Silicates  of 
soda— Peroxide  of  sodium,  gg  173,  174. 

CHLORIDE  OF  SODIUM — Extraction  of  salt,  in  England,  France,  Germany,  and 
Russia — Graduating  works — Schlotage — Soccage — Uses  of  chloride  of  sodium — Salt- 
glazing,  \  175. 

Bromide,  iodide,  and  fluoride  of  sodium — Sulphides  of  sodium — Lapis  lazuli — 
Ultramarine,  §  176. 

LITHIUM— Lithia— Extraction  of  lithia  from  lepidolite— Salts  of  lithia,  §  177. 

AMMONIUM — Oxide  of  ammonium — Nitrite,  nitrate,  sulphite,  sulphate,  bisulphate,  and 
phosphates  of  ammonia — Microcosmic  salt — Carbonate  of  ammonia — Bicarbonate  of 
ammonia — Phosphate  of  soda  and  ammonia,  $g  178-181. 

CHLORIDE  OF  AMMONIUM — Manufacture  of  sal-ammoniac — Uses — Sulphides  of 
ammonium — Hydrosulphate  of  sulphide  of  ammonium — Liquor  fumans  Boylii,  \\ 
182-184. 

BARIUM — Baryta — Hydrate  of  baryta — Nitrate,  chlorate,  sulphite,  sulphate,  seleniate, 
phosphates,  carbonates,  and  borates  of  baryta,  \\  185-189. 

Binoxide  of  barium — Chloride  of  barium — Sulphides  of  barium — Silicofluoride  of 
barium,  $$  190-192. 
STRONTIUM — Strontia — Hydrate,  nitrate,  sulphate,  and  carbonate  of  strontia — Binoxide 

of  strontium — Chlorides  of  strontium,  $  193. 

CALCIUM — Lime — Lime-burning — Quicklime — Slaking  of  lime — Hydrate  of  lime — Uses 
— Mortar — Theory  of  the  hardening  of  mortar — Hydraulic  mortars  and  cements — 
Modus  operandi  of  cement — Roman  cement — Puzzolano — Ransome's  vitrified  cement 
—Hydraulic  mortar  of  Tournay,  gg  194,  195. 

Nitrate  of  lime — Hypochlorite  of  lime — Chloride  of  lime — Manufacture  of  bleach- 
ing-powder — Uses  of  chloride  of  lime — Sulphite  and  bisulphite  of  lime — Sulphate  of 
lime — Gypsum — Uses  of  sulphate  of  lime — Plaster  of  Paris — Stucco,  §§  196-198. 

PHOSPHATE  OF  LIME — Bone-earth — superphosphate  of  lime  as  manure — Carbon- 
ate of  lime — Natural  varieties — Petrifying  springs — Stalactites — Uses  of  carbonate  of 
lime — Carbonate  of  lime  and  soda — Binoxide  of  calcium,  $$  199,  200. 

Chloride  of  calcium — Oxychloride  of  calcium — Fluorspar — Sulphides  of  calcium 
—Phosphide  of  calcium,  §§  201,  202. 

MAGNESIUM — Magnesia — Hydrate  of  magnesia — Nitrate  and  hypochlorite  of  magnesia 
— Sulphate  of  magnesia — Manufacture  of  Epsom  salts — Sulphate  of  magnesia  and 
potassa — Sulphate  of  magnesia  and  ammonia,  $$  203-205. 

Phosphates  of  magnesia — Triple  phosphate — Ammoniaco-magnesian  phosphate — 
Phosphate  of  magnesia  and  potassa — Carbonate  of  magnesia — Magnesia  alba — Heavy 
carbonate — Dolomite — Borates  and  silicates  of  magnesia — Meerschaum,  talc,  asbestos 
— Chloride  of  magnesium — Sulphide  of  magnesium,  $$  206-208. 

ALUMINUM — Alumina — Corundum — Ruby,  emerald,  amethyst,  sapphire — Hydrates  of 
alumina — Aluminates — Nitrate  of  alumina,  \  209. 


*V1  CONTENTS. 

SULPHATE  OP  ALUMINA — ALUMS — Common  alum — Manufacture  of  alum — Alum- 
stone — Roman  alum — Alum-slate — Reaching  of  alum — Cubical  alum — Uses  of  alum — 
Soda-alum — Ammonia-alum — Phosphates  of  Alumina — Wavellite,  $g  210,  211. 

SILICATES  OF  ALUMINA — Feldspars — Pumice-stone — Mica — Hornblende — Basalt 
— Granite — Clays — Kaolin — Properties  and  varieties  of  clay — Earthenware  and  por- 
celain— Glazing — Colored  glazes — Fire-bricks — Crucibles — Manufacture  of  English 
porcelain — Sevres  China — Porcelaine  tendre — Berlin  porcelain,  \\  212,  213. 

Aluminum  with  chlorine,  fluorine,  and  sulphur,  g  214. 

GLTJCINTJM — Glucina — Preparation,  from  emerald  of  Limoges — Salts  of  glucina — Reac- 
tions of  glucina,  §  215. 

THORINUM— Thorina— Reactions  of  thorina,  \  216. 

YTTRIUM,  ERBIUM,  and  TERBIUM— Yttria-VErbia— Terbia— Extraction  from  gadoli- 
nite — Salts  of  Yttria,  erbia,  and  terbia — Reactions  of  Yttria,  erbia,  and  terbia,  §217. 

CERIUM,  LANTHANIUM,  and  DIDYMIUM— Extraction  from  cerite— Oxide  of  cerium- 
Salts  of  oxide  of  cerium — Sesquioxide,  chloride,  and  sulphide  of  cerium — Oxides  and 
salts  of  lanthanium  and  didymium — Reactions  of  the  oxides  of  cerium,  lanthanium, 
and  didymium,  $218. 

ZIRCONIUM — Zirconia — Extraction  from  hyacinth — Salts  and  reactions  of  zirconia,  g  219. 

CHROMIUM — Oxide  and  sesquioxide  of  chromium — Nitrate  and  sulphate  of  sesquioxide 
of  chromium — Chrome-alums — Carbonate  of  sesquioxide  of  chromium — Protosesqui- 
oxide  of  chromium,  §g  220,  221. 

Chromic  acid — Chromate,  bichromate,  and  terchromate  of  potassa — Chlorochro- 
mate  of  potassa — Chromates  of  soda,  ammonia,  and  sesquioxide  of  chromium — Per- 
chromic  acid — Nitride,  chloride,  and  sesquichloride  of  chromium — Chlorochromic  acid 
— Fluoride  and  sulphides  of  chromium,  gg  222,  223. 

URANIUM — Minerals  containing  uranium — Suboxide  and  oxide  of  uranium — Sulphate  of 
oxide  of  uranium — Protosesquioxide  and  sesquioxide  of  uranium — Nitrate  and  sul- 
phate of  sesquioxide  of  uranium — Extraction  of  uranium  from  pitchblende — Uranate 
of  potassa — Chlorides  of  uranium— Reactions  of  sesquioxide  of  uranium,  \  224. 

IRON — Preparation  of  pure  iron — General  properties  of  iron — Passive  state — Oxide  of 
iron — Nitrate  of  oxide  of  iron — Green  vitriol — Manufacture  of  green  vitriol — Uses — 
Carbonate  of  oxide  of  iron,  g§  225-227. 

SESQUIOXIDE  OF  IRON — Uses  of  sesquioxide  of  iron — Nitrate  and  sulphates  of 
sesquioxide  of  iron — Iron-alum — Phosphate  and  silicates  of  sesquioxide  of  iron,  $  228. 
Magnetic  oxide  of  iron — Ferric  acid — Ferrates — Nitride,  chloride,  sesquichloride, 
and  bromides  of  iron — Iodide  and  sesqui-iodide  of  iron,  g§  229,  230. 

SULPHIDE  OF  IRON — Sesquisulphide  of  iron — Magnetic  pyrites — Bisulphide  of 
iron — Iron-pyrites — Subphosphide  of  iron — Iron  with  carbon,  boron,  and  silicon,  §§ 
231,  232. 

METALLURGY  OF  IRON — Meteoric  stones — Ores  of  iron — Manufacture  of  iron — 
Preparation  of  the  ores — Extraction  of  the  metal — Manufacture  of  pig-iron — Blast 
furnace — Theory  of  the  reduction  of  iron — Conversion  of  pig-iron  into  bar-iron — Re- 
fining— Cold-short  iron — Puddling — Different  varieties  of  cast-iron — Wrought-iron — 
Steel — Natural  steel — Blistered  steel — Shear-steel — Cast-steel — Tempering  of  steel — 
Assay  of  iron-ores,  \  233. 

MANGANESE — Oxide  of  manganese — Sulphate  of  manganese— Phosphate,  carbonates, 
and  silicates  of  manganese — Sesquioxide  of  manganese — Sulphate  of  the  sesquioxide 
— Manganese-alums — Red  oxide  of  manganese — Binoxide  of  manganese — Uses  of 
binoxide  of  manganese,  |§  234-236. 


CONTENTS. 

Manganic  acid — Manganates — Chameleon  mineral — Permanganic  acid — Perman- 
ganate of  potassa,  &c. — Chloride,  sesquichloride,  and  sulphides  of  manganese,  $% 
237,  238. 

ZINC — Purification  of  commercial  zinc — Granulated  zinc — Suboxide  and  oxide  of  zinc — 
Zinc- white — Nitrate,  sulphate,  carbonate,  and  silicate  of  zinc — Binoxide  of  zinc,  §g 
239-241? 

Chloride  and  sulphide  of  zinc — Metallurgy  and  uses  of  zinc — Assay  of  ores  of 
zinc,  $%  242,  243. 

NICKEL — Preparation  of  pure  nickel— Oxide  of  nickel — Nitrate,  sulphate,  and  carbonate 
of  nickel— Sesquioxide  of  nickel,  \\  244,  245. 

Chloride  and  sulphide  of  nickel — Metallurgy  of  nickel — Minerals  containing 
nickel — Extraction  of  nickel  from  speiss,  \\  246,  247. 

COBALT — Oxide  of  cobalt — Nitrate,  sulphate,  and  carbonates  of  cobalt — Sesquioxide  of 
cobalt — Intermediate  oxides  of  cobalt— gg  248,  249. 

Chlorides  and  sulphides  of  cobalt — Technical  history  of  cobalt — Zaffre — Smalt — 
The-nard's  blue,  $%  250,  251. 

VANADIUM — Oxide  and  binoxide  of  vanadium — Vanadic  acid — Terchloride  and  bisul- 
phide of  vanadium — Reactions  of  vanadium,  \  252. 

CADMIUM — Oxide  of  cadmium — Nitrate,  sulphates,  and  carbonates  of  cadmium — Chlo- 
ride and  sulphide  of  cadmium,  §  253. 

COPPER — Suboxide  of  copper — sulphate  of  suboxide  of  copper — Oxide  of  copper — Ver- 
diter — Ammoniacal  oxides  of  copper,  \\  254,  255. 

Nitrate  and  ammonio-nitrate  of  copper — Sulphate  of  copper — Manufacture  of 
blue  vitriol — Ammoniated  sulphate  of  copper — Uses  of  blue  vitriol — Tests  for  im- 
purities— Basic  sulphates  of  copper-^-Ammonio-sulphate  of  copper — Carbonates  of 
copper — Malachite — Silicate  of  copper,  \  256. 

Binoxide  of  copper — Cupric  acid — Copper  and  hydrogen — Copper  and  nitrogen — 
Chlorides  of  copper — Oxychlorides — Brunswick  green,  $$  257,  258. 

Sulphides  of  copper — Copper- glance — Sulphide  of  copper — Oxysulphide — Cop- 
per pyrites — Variegated  copper  ore — Phosphides  of  copper,  \  259. 

METALLURGY  OF  COPPER — Ores  of  copper — Smelting  of  copper  ores — Brankart's 
process  —  Process  of  Rivot  and  Phillips  —  Napier's  process — Uses  of  copper — En- 
graving— Alloys  of  copper  and  zinc — Brass,  &c. — Alloys  of  copper  and  tin^-Bronze 
— gun-metal — Casting  of  guns — Bell-metal,  &c. — German  silver — Tinned  copper — 
Pins— Assay  of  copper-ores,  \\  260-262. 

BISMUTH — Purification  of  commercial  bismuth — Suboxide  and  teroxide  of  bismuth- 
Nitrates  of  bismuth — Flake-white — Sulphates  and  carbonate  of  bismuth — Bismuthic 
acid,  \\  263,  264. 

Terchloride  of  bismuth  —  Oxychloride  of  bismuth — Pearl-white — Sulphides  of 
bismuth— Metallurgy  of  bismuth — Minerals  of  bismuth — Extraction  from  its  ores — 
Uses— Fusible  alloy— Assay  of  ores  of  bismuth,  §§  265,  266. 

GOLD  —  Preparation  of  pure  gold  —  Oxide  of  gold  —  Hyposulphite  of  gold  and  soda  — 
Purple  of  Cassius — Auric  acid — Aurates — Fulminating  gold — Aurosulphite  of  potassa 
— Chloride  and  terchloride  of  gold— Aurum  potabile — Aurochlorides — Sulphides  of 
gold,  \\  267-269. 

METALLURGY  OF  GOLD — Distribution — Alluvial  gold — Extraction  of  gold — Gold- 
washing — Gold-dust — Extraction  by  fusion— Amalgamation  of  gold-ores — Refining  of 
gold — Parting  by  sulphuric  acid — Gold  for  coin — Jeweller's  gold— Gold-leaf— Gilding 
—Electro-gilding— Assay  of  alloys  of  gold— Touchstone— Assay  by  cupellation— 
2 


XV111  CONTENTS. 

Quartation — Determination  of  gold  in  auriferous  sand — Assay  of  ores  containing  gold 
— Calculation  of  gold  in  gold  quartz,  \\  270,  271. 

PLATINUM — Purification  of  commercial  platinum — Malleable  platinum  —  Spongy-pla- 
tinum— Platinum-black — Circumstances  under  which  platinum  vessels  are  damaged 
— Oxide  of  platinum  —  Binoxide  of  platinum — Fulminating  platinum — Platinates — 
Nitrate  and  sulphate  of  binoxide  of  platinum — Platinum  with  hydrogen,  g§  272,  273. 

Protochloride  of  platinum  —  Ammoniated  chloride  —  Green  salt  of  Magnus  — 
Reiset's  platinum-bases — Platosammonium — Gros's  base — Raewsky's  base — Bichlo- 
ride of  platinum — Preparation  of  bichloride  of  platinum  from  platinum-residues — 
Double-salts  of  bichloride  of  platinum  with  other  chlorides — Sulphides  of  platinum, 
\\  274,  275. 

METALLUBGY  OF  PLATINUM — Extraction  of  platinum  from  the  ore — Uses  of  pla- 
tinum, \  276. 

PALLADIUM — Uses — Oxide  and  binoxide  of  palladium — Chlorides  of  palladium — Re- 
actions, §  277.  ,  .  %, 

RHODIUM— Oxides  and  chlorides  of  rhodium— Reactions,  §  278. 
IRIDIUM — Oxides  of  iridium— Chlorides — Reactions  of  iridium,  g  279. 

OSMIUM — Oxide,  sesquioxide,  and  binoxide  of  osmium — Osmious  acid — Osmic  acid — 
Chlorides  of  osmium — Reactions,  §  280. 

RUTHENIUM — Oxides  of  ruthenium — Ruthenic  acid — Chlorides  of  ruthenium — Re- 
actions— Relations  between  the  metals  existing  in  platinum-ores,  \  281. 
Analysis  of  the  ores  of  platinum,  $  282. 

TIN — Preparation  of  pure  tin — Oxide  of  tin — sulphate  and  nitrate  of  oxide  of  tin — Stannic 
acid — Stannates — Metastannic  acid — Metastannates,  \\  283-285. 

Chloride  of  tin — Oxychloride  of  tin — Valuation  of  chloride  of  tin — Bichloride  of 
tin — Chlorostannates — Sulphide  and  bisulphide  of  tin — Mosaic  gold,  $  286. 

METALLURGY  OF  TIN — Ores  of  tin — Smelting  of  tin  ores — Extraction  of  tungsten 
from  the  ores  of  tin — Refining  of  tin  by  liquation — Uses  of  tin — Tinfoil — Manufac- 
ture of  tin-plates — Alloys  of  tin — Assay  of  tin-ores,  §  287. 

ANTIMONY — Purification  of  antimony — Suboxide  of  antimony — Teroxide  of  antimony — 
Nitrate  and  sulphates  of  teroxide  of  antimony — Anomalous  composition  of  the  salts 
of  this  base,  %  288,  289. 

Antimonic  acid — Antimoniates  of  potassa,  soda,  ammonia,  and  teroxide  of  anti- 
mony (antimonious  acid) — Metantimonic  acid — Metantimoniates  and  bi-metantimo- 
niates  of  potassa,  soda,  and  ammonia,  g  290. 

Antimoniuretted  hydrogen — Terchloride  of  antimony — Oxychlorides  of  antimony 
— Pentachloride  of  antimony — Bromide,  iodide,  and  fluoride  of  antimony,  \  291. 

Tersulphide  of  antimony  —  Glass  of  antimony — Crocus  —  Liver  of  antimony — 
Pentasulphide  of  antimony — Sulphantimoniates — Kermes  mineral — Alloys  of  anti- 
mony, \\  292,  293. 

METALLURGY  OF  ANTIMONY  —  Minerals  of  antimony — Extraction  of  antimony 
from  its  ores — Assay  of  ores  of  antimony — Pharmaceutical  preparations  of  antimony, 
\\  294,  295. 

ARSENIC — Fly-powder — Arsenious  acid — Arsenites — Scheele's  green — Schweinfurt  green 
—Arsenic  acid— Arseniates,  \\  296-299. 

Arseniuretted  hydrogen — Terchloride  of  arsenic — Sulphides  of  arsenic — Realgar 
— Yellow  orpiment — Sulpharsenious  acid — Sulpharsenic  acid — Arsenides — Pharma- 
ceutical preparations  of  arsenic,  \\  300,  301. 


CONTENTS.  % 

TUNGSTEN — Wolfram — Binoxide  of  tungsten — Tungstic  acid — Blue  oxide  of  tungsten 

Tungstates — Chlorides,  sulphides,  and  phosphides  of  tungsten — Reactions  of  tungsten, 
g  302. 

MOLYBDENUM — Oxide  and  binoxide  of  molybdenum — Molybdic  acid — Deportment  with 
phosphoric  acid — Chlorides  and  sulphides  of  molybdenum — Reactions,  §  303. 

TELLURIUM— Tellurous  acid  — Telluric  acid— Telluretted  hydrogen  — Chlorides  and 
sulphides  of  tellurium — Reactions  of  tellurium,  g  304. 

TITANIUM — Minerals  containing  titanium — Extraction  from  rutile — Oxide  and  sesqui- 
oxide  of  titanium — Titanic  acid — Nitrides,  chlorides,  and  sulphide  of  titanium — Re- 
actions, g  305. 

MERCURY — Purification  of  commercial  quicksilver — Suboxide  of  mercury — Nitrates, 
sulphate,  and  <«,hromate  of  suboxide  of  mercury,  \\  306,  307. 

Oxide  of  mercury — Oxy-amidide  of  mercury — Salts  of  oxy-amidide  of  mercury — 
Nitrates  and  sulphates  of  oxide  of  mercury — Turbith  mineral — Carbonates  of  mer- 
cury, \  308. 

Nitride  of  mercury — Subchloride  of  mercury — Preparation  of  calomel — Chloride 
of  mercury — Double  compounds  of  chloride  of  mercury — Uses  of  corrosive  sublimate 
— Oxychlorides  of  mercury — Amido-chloride — White  precipitate,  \\  309,  310. 

Bromides  of  mercury — Iodides  of  mercury — Sulphides  of  mercury — Vermilion — 
Manufacture  of  vermilion — Cinnabar,  \\  311,  312. 

AMALGAMS  of  potassium,  sodium,  and  ammonium — Amalgams  of  iron,  zinc,  and 
bismuth — Amalgam  for  electrical  machines — Amalgam  of  gold — Preparation  of  pow- 
dered gold — Amalgams  of  platinum,  copper,  and  tin — Silvering  of  looking-glasses — 
Amalgams  of  lead  and  silver,  §  313. 

METALLURGY  OF  MERCURY — Occurrence  in  nature — Extraction  of  mercury  from 
its  ores — Assay  of  ores  of  mercury — Pharmaceutical  preparation  of  mercury,  g  314. 

LEAD — Preparation  of  pure  lead — Lead  pyrophorus — Saturn's  tree — Suboxide  of  lead — 
Massicot — Litharge — Uses — Nitrites,  nitrates,  and  sulphate  of  lead — Carbonate  of 
lead — Manufacture  of  white  lead — Uses  and  adulterations — Silicates  of  lead — Chro- 
mates  of  lead— Chrome-yellow,  §g  315-317. 

Binoxide  of  lead — Plumbates — Minium — Uses  of  red-lead — Chloride  and  oxy- 
chlorides  of  lead — Bromide  and  iodide  of  lead — Sulphide  and  selenide  of  lead, 
\\  318-320. 

METALLURGY  OF  LEAD — Ores  of  lead — Smelting  of  galena — Refining  of  argenti- 
ferous lead — Pattinson's  process  —  Cupellation  —  Uses  of  lead — Alloys — Plumber's 
solder — Tea-lead — Type-metal — Lead-shot — Manufacture  of  shot — Assay  of  galena, 
\\  321,  322. 

SILVER — Preparation  of  pure  silver — Suboxide  of  silver— Oxide  of  silver — Fulminating 
silver — Nitrite  of  silver — Nitrate  of  silver — Lunar-caustic — Ammonio-nitrate  of  silver 
—  Uses  of  nitrate  of  silver — Hyposulphate,  sulphate,  and  carbonate  of  silver  — 
Binoxide  of  silver,  \\  323-325. 

CHLORIDE  OF  SILVER — Reduction  of  silver  from  the  chloride — Bromide,  iodide, 
and  fluoride  of  silver — Sulphide  and  carbides  of  silver,  \  326. 

METALLURGY  OF  SILVER  —  Ores  of  silver — Extraction  of  silver — Extraction  by 
Cupellation — Amalgamation-process — Method  adopted  at  Freiberg — American  amal- 
gamation process — Mexican  method  of  extraction,  \  327. 

TECHNICAL  HISTORY  OF  SILVER — Alloys  of  silver  and  copper — Standard  silver — 
alloys  of  silver  and  gold— Plating— Electroplating— Silvering  upon  glass— Assay  of 
silver  ores,  §  328. 


X*  CONTENTS. 

TANTALUM — Oxide  of  tantalum — Tantalic  acid — Chloride  and  sulphide  of  tantalum — 
Niobium — Niobic  acid — Chloride  and  sulphide  of  Niobium — Pelopium — Pelopic  acid 
— Chloride  and  sulphide  of  pelopium — Ilmenium — Ilmenic  acid — Extraction  of  tan- 
talum, niobium,  and  pelopium  from  tantalites  and  yttro-tantalites,  §  329. 
PHYSICAL  PROPEKTIES  OF  THE  METALS,  §  330. 


ANALYTICAL  CHEMISTRY. 

Definitions  of  qualitative  and  quantitative,  proximate  and  ultimate  analysis — Apparatus 

and  reagents  used  in  qualitative  analysis,  \\  331-333. 
ANALYTICAL  CLASSIFICATION  OF  METALS,  §  334. 

EEACTIONS  OF  THE  OXIDES  OF  THE  FIRST  GROUP — Potassa — Soda — Oxide  of  ammonium, 
|  335. 

REACTIONS  OF  THE  OXIDES  OF  THE  SECOND  GROUP — Baryta — Strontia — Lime,  Magnesia, 

o     OO/? 

g   OOO. 

REACTIONS  OF  THE  OXIDES  OF  THE  THIRD  GROUP — Alumina — Sesquioxide  of  Chromium — 
Oxide  and  sesquioxide  of  iron — Oxides  of  Cobalt,  Nickel,  Manganese,  and  Zinc,  $  337. 

REACTIONS  OF  THE  OXIDES  OF  THE  FOURTH  GROUP  —  Oxides  of  Mercury,  Copper,  and 
Cadmium — Teroxide  of  Gold — Binoxide  of  Platinum — Oxide  and  Binoxide  of  tin — 
Teroxide  of  Antimony — Antimonic  Acid — Arsenious  and  Arsenic  Acids,  \  338. 

REACTIONS  OF  THE  OXIDES  OF  THE  FIFTH  GROUP — Oxide  of  Lead,  Suboxide  of  Mercury, 
Oxide  of  Silver,  §  339. 

ANALYTICAL  CLASSIFICATION  OF  INORGANIC  ACIDS,  g  340. 

REACTIONS  OF  THE  ACIDS  OF  THE  FIRST  GROUP — Sulphuric,  Phosphoric,  Boracic,  and 
Silicic  acids,  \  341. 

REACTIONS  OF  THE  ACIDS  OF  THE  SECOND  GROUP — Sulphurous,  Chromic,  Hydrofluoric,  and 
Carbonic  acids,  §  342. 

REACTIONS  OF  THE  ACIDS  OF  THE  THIRD  GROUP — Hydrochloric,  Hydrobromic,  Hydriodic, 
Hydrosulphuric,  Hydrocyanic,  Hydrosulphocyanic,  Hydroferrocyanic,  and  Hydro- 
ferricyanic  acids,  $  343. 

REACTIONS  OF  THE  ACIDS  OF  THE  FOURTH  GROUP  —  Nitric,  Chloric,  and  Hypochlorous 
acids,  \  344. 

ANALYTICAL  CLASSIFICATION  OF  ORGANIC  AC!DS,  §  345. 

REACTIONS  OF  ACIDS  OF  THE  FIRST  GROUP — Tartaric,  Tannic,  and  Gallic  Acids,  §  346. 

REACTIONS  OF  ACIDS  OF  THE  SECOND  GROUP — Citric  and  Uric  Acids,  §  347. 

REACTIONS  OF  ACIDS  OF  THE  THIRD  GROUP — Benzoic,  Succinic,  and  Acetic  Acids,  \  348. 

SYSTEMATIC  COURSE  OF  QUALITATIVE  ANALYSIS — Preparation  of  substances  for  analysis 
— Preliminary  examination  for  bases — Solution  of  substances  for  analysis — Treat- 
ment with  general  reagents — Analytical  tables  for  detection  of  bases — Preliminary 
examination  for  acids — General  examination  for  acids — Tables  for  detection  of  acids 
—Special  tests  for  acids,  3J  349-356. 

Qualitative  analysis  of  insoluble  substance;  of  alloys  and  amalgams,  §g  357,  358. 

QUANTITATIVE  ANALYSIS — Apparatus  used  in  quantitative  analysis — Balances,  &c.,  $  359. 

OPERATIONS  IN  QUANTITATIVE  ANALYSIS — Weighing — Solution — Evaporation — Ignition — 
Precipitation — Washing  of  precipitates — Weighing  of  precipitates — Ignition  of  pre- 
cipitates, §  360. 

Determination  of  Oxide  of  Silver,  Suboxide  and  Oxide  of  Mercury,  and  Oxide  of  Lead — 
Valuation  of  Cinnabar,  33  361-365. 


CONTENTS.  Xxl 

Determination  of  Teroxide  of  Bismuth  and  Oxide  of  Copper — Wet  assay  of  copper-ores — 
Determination  of  Oxide  of  Cadmium,  Teroxide  of  Gold,  Binoxide  of  Platinum,  Oxide 
and  Binoxide  of  Tin,  Teroxide  of  Antimony,  Antimonic  Acid,  Arsenious  and  Arsenic 
Acids,  |g  366-374. 

Determination  of  Alumina,  Sesquioxide  of  Chromium,  Oxide  and  Sesquioxide  of  Iron, 
Oxides  of  Cobalt,  Nickel,  Manganese,  and  Zinc,  §$  375-382. 

Determination  of  Baryta,  Strontia,  Lime,  and  Magnesia,  \\  383-386. 

Determination  of  Potassa,  Soda,  and  Oxide  of  Ammonium,  \\  387-889. 

Determination  of  Sulphuric,  Phosphoric,  Boracic,  and  Silicic  Acids,  gg  390-393. 

Determination  of  Sulphurous,  Chromic,  Hydrofluoric,  Carbonic,  and  Oxalic  Acids,  gg  394, 
398.  s  }*  * 

Determination  of  Hydrochloric,  Hydrobromic,  Hydriodic,  and  Hydrosulphuric  Acids, 
gg  399-402. 

Determination  of  Nitric  and  Chloric  Acids,  gg  403,  404. 

QUANTITATIVE  ANALYSIS  ;  SPECIAL  METHODS — Analysis  of  common  salt — Calculation  of 
analyses,  g  405. 

Analysis  of  common  phosphate  of  soda — Determination  of  water  of  crystallization  and  of 
constitution,  g  406. 

Analysis  of  heavy  spar,  g  407. 

Analysis  of  Rochelle  salt — Separation  of  potassium  and  sodium,  g  408. 

Analysis  of  marble,  g  409. 

Analysis  of  limestones — Separation  of  lime,  magnesia,  Sesquioxide  of  iron,  alumina,  and 
silica,  g  410. 

Analysis  of  alum — Separation  of  alumina  and  potassa,  g  411. 

Analysis  of  chrome-iron  ore — Separation  of  iron  and  chromium,  g  412. 

Analysis  of  clay — Separation  of  iron,  alumina,  silica,  lime,  and  magnesia,  g  413. 

Analysis  of  wavellite — Separation  of  alumina  and  phosphoric  acid,  g  414. 

Analysis  of  iron-ores — Margueritte's  process — Preparation  of  standard  solution  of  per- 
manganate of  potassa — Determination  of  the  relative  quantities  of  the  oxides  of  iron, 

l*i& 

Analysis  of  manganiferous  spathic  iron-ore — Separation  of  iron  and  manganese,  g  416. 

Analysis  of  crystallized  sulphate  of  copper,  g  417. 

Analysis  of  calamine — Separation  of  cadmium  and  zinc,  \  418. 

Analysis  of  copper-pyrites — Separation  of  copper  and  iron,  g  419. 

Analysis  of  tartar-emetic,  g  420. 

Analysis  of  pewter — Separation  of  tin,  antimony,  copper,  and  bismuth,  g  421. 

Analysis  of  fusible  alloy — Separation  of  tin,  lead,  and  bismuth,  g  422. 

Analysis  of  type-metal — Separation  of  antimony,  lead,  and  bismuth,  g  423. 

Analysis  of  brass,  bronze,  and  gun-metal — Separation  of  tin,  lead,  copper,  and  zinc,  g  424. 

Analysis  of  German  silver — Separation  of  copper,  zinc,  and  nickel,  g  425. 

Analysis  of  Britannia  metal — Separation  of  tin,  antimony,  copper,  and  lead,  g  426. 

Analysis  of  standard  silver — Separation  of  copper  and  silver — Centigrade  determination 
of  silver,  g  427. 

Analysis  of  standard  gold — Separation  of  gold,  silver,  and  copper,  g  428. 

Analysis  of  amalgams — Separation  of  mercury  and  zinc — Separation  of  mercury  and  tin, 
gg  429,  430. 

Analysis  of  speiss-cobalt — Separation  of  arsenic,  cobalt,  nickel,  and  iron,  g  431. 

Valuation  of  manganese-ores,  g  432. 

Chlorimetry — Valuation  of  chloride  of  lime,  g  433. 

Alkalimetry— Valuation  of  potash  and  soda— Fresenius  and  Will's  alkalimetrical  appa- 
ratus, g  434. 


XX11  CONTENTS. 

Acidimetry — Estimation  of  the  strength  of  dilute  nitric  acid,  g  435. 

Analysis  of  gunpowder,  §  436. 

Analysis  of  glass — Analysis  of  insoluble  silicates — Determination  of  alkalies  in  insoluble 

silicates — Brunner's  method  of  analyzing  silicates,  §  437. 
Analysis  of  cast-iron,  §  438. 
Analysis  of  ultramarine,  §  439. 
Separation  of  chlorine,  bromine,  and  iodine,  $  440. 

Analysis  of  mineral  waters — Clark's  method  for  determining  the  hardness  of  waters,  \  441. 
Analysis  of  soils,  §  442. 

Analysis  of  the  ashes  of  vegetables,  \  443.  .&£%  it 

Analysis  of  the  ashes  of  animal  substances,  $  444. 


LIST  OF  ILLUSTRATIONS. 


FIGS.  PAGE 

1,  2.  Hydrometer   ....  >.!<  ...  ^  .  .  35 

3.  Globe  to  determine  the  density  of  vapors  .  j"v  <  '*tifci  'V^  .  37 

4.  Cube      .\..    ,  >,£     .v^         .            .  .  ,v  ..*.  .  OHM  63 

5.  Regular  octohedron        .            .            .  .  .  .,.'•.  .  ib. 

6.  Khombic  dodecahedron  ....  ->,»-•  .  .  ib. 

7,8.  Right  square  prisms  .             .             .  .  .  .  •.-.-.  -•:  .  ib. 

9,10.  Right  square-based  octohedron        .  .  '••?•*•»  .   :«;v  .  ib. 

11.  Right  rectangular  prism             .....  '**•>  ».  .  64 

12.  Right  rhombic  prism      .             .             .  «v  ''    »u  '  .  .-!;.  .  ib. 

13.  Rectangular-based  octohedron   .             ,',"  ;.>-,•;  .  •:••<**$[  .  .  ib. 

14.  Right  rhombic-based  octohedron            *  .  -  .  •],  '•*<<.  »    ;  .  ib. 

15.  Oblique  rectangular  prism        '  *' .      •    «  .  .  .  .  .  .  .  .  .  ib. 

16.  Oblique  rhombic  prism  .             .  ^          ..  v,   .  .  .  ..  »r  i,  iMk*!.  ib. 

17.  Oblique  rectangular-based  octohedron  .  "«  t  .  ,  .  .  <»•*:  .  ib. 

18.  Oblique  rhombic-based  octohedron         •  ;"  .  •  ,  ?>  :'« •".  •  ib. 

19.  Doubly  oblique  rectangular  prism          ......  55 

20.  Doubly  oblique  rhombic  prism  ...  ib. 

21.  Doubly  oblique  rectangular-based  octohedron   .  •   g  .  .  ib. 

22.  Doubly  oblique  rhombic-based  octohedron  .  .  #vrs  .  .  ib. 

23.  Regular  six-sided  prism             .            •  •  .•  Va  .  .  ib. 

24.  Regular  dodecahedron   .             .             .  .  .  .  .  .  ib. 

25.  Rhombohedron  .........  ib. 

26.  Scalene  dodecahedron    ...            .  .  .  .  .  .  ib. 

27.  Cube,  solid  angles  truncated      .            .  .  .  .  .  ib- 

28.  "                "       replaced  by  faces      .  .  .  .  .  ib. 

29.  "     original  planes  nearly  obliterated  .  .  .  .  •     „•  ib. 

30.  31,  32.  Hemihedral  crystals       .  .  .  .  .  :  r   ib. 

33.  Graham's  diffusion  tube              .             .  ,*...>  .  .     ,;'     .  57 

34.  Safety  tube        .            .                         .  .  .  .  /<  r  V  60 

35.  Cork  borer         .            .            .         :  .  -'.-.-  .>  ;.  £  .   %  /    .  61 
36,37.  Bent  tubes    .            .            .  •    -,   '•  ,.  .  •* <•'•«;  .   '-  *  62 
38,  39.  Washing  bottles  for  gas        .             .  ,  .  ^-k  •   .«  ..  «  65 

40.  Making  caoutchouc  joint            .  .  '  „  .  .  .  .  ib. 

41.  Siphon  eudiometer          .             .             .  V     '  .     .  j^      .  .  .71 

42.  Transferring  gases          .             .             .  ;  .   ;  .  |  .    :  .  .  72 

43.  Liebig's  potassa  apparatus         .            .  .  .  .  .  .74 

44.  Pipette   .             .            .   "         .             .  .  .  .  .  •  ib. 

45.  Thilorier's  apparatus      •            .             .  .  .v  .  •     %  75 

46.  Liebig's  condenser         .            .            .  '  .  .  •    >  .78 


XXIV  LIST  OP  ILLUSTRATIONS. 

FIGS.  PAGE 

47.  Retort  hood "  .  V  ~  .        81 

48.  Sublimation        .             .             ...             .  .  .  .  .84 

49.  Pouring  by  glass  rod      .             .          :  ;            .  .  .  '    ..-       89 
60.  Washing  bottle  for  solids            .            .            i  ,  ..  .  .92 

51.  Pipette   .           '.            ;"           .           V           »   ^  •  **  •  -        93 

52.  Separating  funnel           .             .            .             .  .  .  .  .        ib. 

53.  Evaporation  by  sulphuric  acid  .            .    *    '.    .    '  i    .  •*.  '  .'  .         94 

54.  Desiccating  box              .             .                     '   t  T  F    F  .95 

55.  Berzelius's  lamp             .                      "  .'            .  .  .  .  .       102 

56.  Gauze  gas-burner          .            .        '    .            .  .  .  .  .103 

57.  Ring  gas-burner             v    •    —^-4.    -•-.**«*»   -.--V—  .  .  .  .        ib. 

58.  Combustion  furnace       ........       104 

59.  "            ««          screen        .            .            .  .  .  ib. 

60.  Common  blowpipe          .  *         .             .   •          .  .  •  .  .  ' ~'-4       105 

61.  Black  and  Wolla§ton's  blowpipe             A''1    *'*  >'  ^JV>-  .  lj^:  '  .        ib. 

62.  Nature  of  flame             *  .         .            .            .  .  •  /  +  •  .       108 

63.  "            blowpipe  flame           .            .  •          .  .  •  *Sjt*-f  .  .        ib. 

64.  Preparation  of  hydriodic  acid   .             .-          .  .-  .  .  .151 

65.  Sulphuric  acid  chamber              .             .             .  •  .  .  .  .160 

66.  Preparation  of  carbonic  oxide  .             .           4***  .  .  .  .       196 

67.  Analysis  of  carbonic  acid           .             .  •          .  .   ••  .  .  .       200 

68.  Preparation  of  bisulphide  of  carbon     .             .  •  .  .  .  .213 

69.  "           of  hydrofluosilicic  acid       ...  .  .  .227 

70.  Test-tube  holder            .  -         .            .            .  «'  .  .  .497 

71.  Berlin  crucible  .            .            .            .            .  •  ^  .  .  .        ib. 

72.  Washing  bottle  .             .             .             .             .  •  .«  .  .  ib. 

73.  Spirit-lamp         .             .-..-.  .  .  .  .        ib. 

74.  Cork  borers        .            .            .                       '  ¥**•  .  .  .        ib. 

75.  Sulphuretted  hydrogen  apparatus          .  •  .  .  .  .        ib. 

76.  Fresenius  and  Babo's  test  for  arsenic    ......       526 

77.  Marsh's  test  for  arsenic             .  *t                     .  .  .  .  .528 

78.  Graduated  burette         -.  *                     .            .  .  .  .  .616 

79.  Fresenius  and  Will's  carbonic  acid  apparatus  .   *  .  .       617 


INTRODUCTION. 


EXPERIMENTAL  SCIENCE  may  be  conveniently  divided  into  PHYSICS  and 
CHEMISTRY. 

PHYSICAL  SCIENCE  treats  of  the  changes  of  matter,  without  any  regard  what- 
ever to  its  internal  constitution. 

Thus,  the  laws  of  gravitation  and  cohesion,  which  belong  to  physical  science, 
only  concern  matter  irrespective  of  its  composition. 

CHEMISTRY,  on  the  other  hand,  makes  us  acquainted  with  the  composition  of 
different  forms  of  matter,  and  with  the  changes  which  they  are  capable  of  in- 
ducing in  each  other. 

Water,  considered  with  regard  to  its  physical  properties,  is  a  colorless,  mobile 
liquid,  boiling  at  212°,  and  freezing  at  32°,  almost  incapable  of  compression, 
and  so  forth.  Chemically  speaking,  water  is  described  as  a  compound  of  so  much 
hydrogen  and  oxygen,  capable  of  entering  into  certain  combinations,  and  of  in- 
ducing certain  changes  in  other  forms  of  matter. 

The  science  of  chemistry  is  usually  divided  into  two  branches — inorganic  and 
organic  chemistry.  As  a  convenient  mode  of  classifying  our  knowledge  this 
division  is  useful,  but  as  a  natural  and  absolute  separation  it  has  no  existence ; 
for  the  two  classes  of  substances,  inorganic  and  organic,  so  merge  into  each 
other — so  many  so-called  organic  substances  are  found  capable  of  being  prepared 
by  inorganic  methods,  that  the  boundary-line  is  day  by  day  becoming  fainter, 
and  will,  perhaps,  in  time,  vanish  altogether.  Probably  one  of  the  safest  defini- 
tions that  can  be  given  of  organic  chemistry,  as  distinguished  from  inorganic,  is 
contained  in  the  statement,  that  the  former  branch  of  the  science  treats  of  those 
substances  which  are  the  products,  either  directly  or  indirectly,  of  the  vital  pro- 
cess in  animals  or  vegetables;  and  such  a  definition  will  be  tacitly  admitted 
throughout  this  work. 


SPECIFIC    GRAVITY. 

§  1.  The  specific  gravity  of  a  substance  is  the  term  used  to  express  the  rela- 
tion which  exists  between  the  weights  of  equal  volumes  of  this  substance,  and 
of  some  standard  body  arbitrarily  selected. 

Pure  water  at  the  temperature  of  60°  F.  (15°. 5  C.)  is  the  standard  to  which 
the  specific  gravities  of  solids  and  liquids  are  referred,  whilst  gases  are  compared 
with  pure  and  dry  atmospheric  air. 

Since  we  have  here  to  compare  the  weights  of  equal  volumes,  and  as  altera- 
tions of  volume  always  attend  upon  variations  of  temperature  and  barometric 
pressure,  it  is  of  course  highly  important  that  these  conditions  (the  latter  of  the 
two,  especially  in  the  case  of  gases)  be  taken  into  consideration. 
3 


34  INTRODUCTION. 

The  determination  of  the  specific  gravities  of  substances  is  an  operation  of 
considerable  importance  to  the  practical  chemist,  and  it  will  not,  therefore,  be 
out  of  place  to  describe,  at  the  outset,  the  methods  of  ascertaining  the  specific 
gravities  of  solids,  liquids,  and  gases. 

DETERMINATION   OF   THE     SPECIFIC   GRAVITY  OF  A   SOLID 
MASS   INSOLUBLE   IN   WATER. 

§  2.  The  mass  is  accurately  weighed  in  the  ordinary  balance.  It  is  then 
attached  to  a  fine  silken  thread  (which  may  be  covered  with  a  thin  film  of  wax 
to  prevent  variation  in  weight)  or  a  horsehair,  and  suspended  to  the  hook  at  the 
bottom  of  the  specific-gravity-pan  of  the  balance ;  the  latter  is  then  brought  into 
equilibrium  by  adding  the  requisite  weights ;  the  surface  of  the  mass  having 
been  carefully  wetted  with  a  brush  to  remove  all  air-bubbles  (or,  which  is  better 
in  some  cases,  having  been  heated  in  the  water  and  allowed  to  cool  below  the 
surface),  it  is  now  completely  immersed  in  pure  water  at  60°  F.  (15°. 5  C.), 
and  the  balance  again  brought  into  equilibrium;  the  weight  which  it  has  been 
found  requisite  to  remove  for  this  purpose  is  that  of  an  amount  of  water  equal 
in  volume  to  the  mass ;  and  the  specific  gravity  may  now  be  calculated  by  the 
following  simple  proportion  :— 

Weight  of  an  equal  j    .    (  Weight  of")    . .  ^ 

volume  of  water  j    '   |    the  mass  j 
where  x  will  be  the  specific  gravity  required.1 

If  the  mass  be  lighter  than  water,  it  must  be  attached  to  some  heavy  body  of 
known  specific  gravity,  and  the  determination  conducted  with  this  combination 
just  as  with  the  simple  mass,  a  modification  being  of  course  requisite  in  the 
calculation. 

"DETERMINATION  OF  THE  SPECIFIC  GRAVITY  OF  A  SOLID  MASS 
SOLUBLE  IN  WATER. 

•§  3.  If  the  substance,  the  specific  gravity  of  which  is  required,  be  soluble  in 
water,  the  latter  is  replaced  by  some  other  liquid  of  known  specific  gravity,  which 
is  incapable  of  acting  upon  the  substance  (e.  g.  alcohol,  pyroxylic  spirit,  &c.) ;  the 
specific  gravity  is  then  taken  in  the  usual  way,  and  the  result  calculated  by  the 
following  proportion : — 

Weight  of  an  equal  volume  of  )     .     (  Weight  of  \    . .   J  Sp.  Gr.  of  ) 

the  liquid  employed  j       -   (  the  mass    j    '  '    \  the  liquid  j    ' 

where  x  represents  the  specific  gravity  of  the  substance  operated  upon. 

DETERMINATION   OF   THE    SPECIFIC   GRAVITY   OF  A    SUBSTANCE 
IN   THE    STATE   OF   POWDER. 

§  4.  If  the  substance  be  in  a  state  of  minute  division,  it  will  of  course  be  im- 
practicable to  determine  its  specific  gravity  by  either  of  the  above  methods ;  a 
pretty  close  approximation  to  the  truth,  however,  may  be  obtained  by  placing  a 
quantity,  say  100  grs.  of  the  powder,  in  a  small  dry  bottle,  previously  weighed, 
and  capable  of  containing  a  known  weight,  say  1000  grs.  of  the  liquid  to  be 
employed,  at  60°  F.  (15°. 5  C.)  There  should  be  a  mark  upon  the  neck  of  the 
bottle,  showing  the  level  to  which  it  is  to  be  filled  with  the  liquid.  The  weight 
of  the  powder  and  bottle  having  been  accurately  ascertained,  the  latter  is  filled  to 
the  required  level  with  the  liquid  (the  choice  of  which  is  regulated  by  the  nature 

1  In  general,  for  practical  purposes,  it  is  convenient  to  refer  the  specific  gravity  to 
1000,  since  decimals  may  then,  to  a  great  extent,  be  dispensed  with. 


SPECIFIC    GRAVITY. 


35 


of  the  solid  to  be  operated  upon)  at  60°  F.  (15°. 5  C.),  and  the  weight  again  as- 
certained. The  liquid  should  be  poured  upon  the  powder  by  small  portions  at  a 
time,  and  well  agitated,  to  remove  air-bubbles  (or,  in  some  cases,  it  might  be 
slightly  heated,  and  allowed  to  cool  before  weighing).  By  subtracting  the  weight 
of  the  liquid  which  has  been  poured  into  the  bottle,  from  the  total  weight  of  the 
liquid  which  the  latter  is  known  to  be  capable  of  containing,  we  obtain  the  weight 
of  a  volume  of  liquid  equal  to  that  of  the  powder  employed,  and  from  this  da- 
tum the  specific  gravity  is  calculated  as  usual. 

DETERMINATION   OF   THE    SPECIFIC   GRAVITY   OF  A  LIQUID. 

§  5.  The  instrument  employed  for  determining  the  specific  gravity  of  a  liquid 
is  a  small  light  bottle  (the  weight  of  which  is  known),  capable  of  containing  a 
known  weight  of  water  at  60°  F.  (15°. 5  C.)  when  filled  to  a  certain  level  previ- 
ously ascertained,  and  carefully  marked.  The  bottle  sold  by  the  instrument- 
makers  for  this  purpose,  is  generally  provided  with  a  perforated  stopper  through 
which  the  excess  of  liquid  escapes.  The  operation  by  which  the  specific  gravity 
is  obtained  is  exceedingly  simple.  The  bottle  is  filled  to  the  required  level  with 
the  liquid  to  be  examined,  at  the  temperature  of  60°  F.  (15°. 5  C.),  and  weighed. 
(When  the  temperature  of  the  liquid  is  below  this  point,  it  is  generally  raised  by 
clasping  the  bottle  in  the  hand,  or  immersing  it  in  warm  water;  if  the  tempera- 
ture be  higher  than  60°,  the  bottle  may  be  surrounded  with  a  strip  of  wet  blot- 
ting-paper, and  cooled  in  a  current  of  air.)  To  obtain  the  specific  gravity,  it  is 
merely  necessary  to  divide  the  weight  of  the  liquid  by  the  known  weight  of  wa- 
ter which  the  bottle  is  capable  of  containing.  (It  is  scarcely  necessary  to  remark, 
that  the  presence  of  bubbles  of  air  upon  the  sides  of  the  bottle  must  be  care- 
fully avoided,  and  that  the  exterior  of  the  latter  must  be  well  wiped  before 
weighing.) 

In  order  to  obtain  quickly  an  approximation  to  the  specific  gravity  of  a  liquid, 
an  instrument  known  as  the  hydrometer  is  frequently  employed ;  it  consists  of  a 
glass  tube  of  small  diameter,  forming  the  stem,  to  the  lower  extremity  of  which 
two  bulbs  are  attached.  The  upper  of  these  bulbs  is  simply  filled  with  air,  whilst 
the  lower  contains  some  heavy  substance  (mercury  or  shot),  the  weight  of  which 
is  regulated  according  to  the  purpose  for  which  the  hy- 
drometer is  intended,  being,  of  course,  heavier  when 
the  hydrometer  is  to  be  employed  for  liquids  of  high 
density.  When  the  hydrometer  is  placed  in  any  liquid, 
it  will  assume  an  upright  position,  with  more  or  less  of 
its  stem  projecting  above  the  surface;  it  is  obvious 
that,  following  the  ordinary  law  with  regard  to  floating 
bodies,  the  height  of  the  stem  above  the  surface  will 
depend  upon  the  specific  gravity  of  the  liquid,  and  it  is 
only  necessary  that  the  stem  be  graduated,  in  order  that 
we  may  at  once  read  off  the  specific  gravity.  The  zero 
of  the  scale  is  usually  obtained  by  floating  the  hydro- 
meter in  pure  distilled  water  at  60°  F.  (15°. 5  C.),  and 
marking  upon  its  stem  (or  upon  a  scale  attached  to  it) 
the  level  to  which  it  sinks;  the  same  experiment  being 
repeated  with  another  liquid  of  known  specific  gravity, 
a  second  starting-point  is  obtained,  and  the  space  be- 
tween these  two  points  is  divided  into  an  arbitrary 
number  of  degrees,  to  which  those  on  all  parts  of  the  scale  are  of  course  equal. 
Since  the  stem  of  the  hydrometer  of  extensive  range  would  be  inconveniently 
long,  separate  instruments  are  adapted  to  different  portions  of  the  scale.  In  the 
graduation  commonly  used  in  this  country,  the  degrees  correspond  to  grains,  and 


Fig.  1.          Fig.  2. 


36  INTRODUCTION. 

the  specific  gravity  is  thus  read  off  at  once.  This  method  is  adopted  in  the 
urinometer,  employed  for  determining  the  specific  gravity  of  urine. 

The  liquid  to  be  examined  by  the  hydrometer,  is  placed  in  a  tall  jar,  of  a  dia- 
meter somewhat  greater  than  that  of  the  large  bulb  of  the  instrument ;  the  tem- 
perature is  then  adjusted  (or  is  carefully  observed  with  a  view  to  subsequent 
correction),  and  the  hydrometer  steadily  floated  in  the  liquid ;  after  pressing  the 
hydrometer  down,  and  allowing  it  to  regain  its  level,  the  mark  to  which  it  sinks 
is  noted.  (Since  the  surface  of  the  liquid  around  the  stem  is  bounded  by  a  curve, 
the  operator  must  observe  that  portion  of  the  curve  which  has  been  taken  in  the 
determination  of  the  zero,  and  which  he  can  ascertain  for  himself,  by  placing  the 
instrument  in  distilled  water.) 

The  tables  containing  the  corrections  to  be  made  for  variations  of  temperature, 
often  effect  a  saving  of  time,  with  a  slight  sacrifice  of  accuracy,  since  they  render 
any  adjustment  of  the  temperature  unnecessary. 

DETERMINATION  OF  THE  SPECIFIC  GRAVITY  OF  A  GAS  OR  VAPOR. 

§  6.  The  operation  by  which  the  specific  gravities  of  gases  and  vapors  are  de- 
termined, is  more  complicated  than  those  for  solids  and  liquids,  and  is,  in  com- 
parison with  these  latter,  seldom  called  into  requisition.  It  will  therefore  be 
necessary  to  give  here  merely  an  outline  of  the  process,  leaving  the  minute  de- 
tails to  be  acquired  from  experience. 

The  specific  gravity  of  an  aeriform  substance  is  ascertained  by  comparing  the 
weight  of  a  certain  volume,  with  that  of  an  equal  volume  of  perfectly  dry  and 
pure  atmospheric  air,  of  the  same  temperature  and  pressure. 

If  the  substance  be  a  gas  at  the  ordinary  temperature,  the  operation  is  executed 
as  follows : — 

A  light  glass  globe  of  considerable  size,  fitted  with  a  good  stopcock,  is  care- 
fully dried,  exhausted  of  air,  and  weighed ;  it  is  then  placed  in  connection  with 
a  system  of  tubes  destined  to  purify  and  dry  the  air,  which  is  then  allowed  to 
flow  gradually  in  till  the  globe  is  filled ;  the  temperature  and  barometric  pressure 
having  been  carefully  observed,  the  stopcock  is  closed,  and  the  globe  again 
weighed  j  it  must  afterwards  be  exhausted  a  second  time,  filled  with  the  gas  to 
be  examined  (in  a  state  of  perfect  dryness  and  purity),  and,  the  temperature  and 
barometer  having  been  again  observed,  the  weight  determined.  If  the  pressure 
and  temperature  had  not  varied  during  the  experiment,  we  have  now  the  data 
for  calculating  the  specific  gravity  directly,  viz :  the  weights  of  equal  volumes  of 
atmospheric  air  and  of  the  gas  under  the  same  conditions.  If,  however,  the 
temperature  or  pressure  exhibited  a  difference  in  the  two  weighings,  it  will  be 
necessary  to  reduce  both  gases  (by  calculation)  to  the  same  temperature  and 
pressure,  before  the  specific  gravity  can  be  deduced. 

The  calculations  necessary  for  correcting  gases  for  temperature  and  pressure 
are  given  in  the  method  of  determining  the  density  of  the  vapor  of  volatile  sub- 
stances, in  which  such  calculations  are  most  frequently  necessary.  (§  8) 

DETERMINATION    OF   THE    DENSITY    OF    THE    VAPORS     OF    VOLA- 
TILE  SUBSTANCES. 

§  7.  A  light  glass  globe  (the  diameter  of  which  is  about  three  inches),  having 
a  long  neck  about  half-an-inch  in  diameter  (which  is  softened  in  the  blowpipe- 
flame  at  about  two  inches  from  the  globe,  and  drawn  out  at  an  angle  of  about 
100,°  to  a  long  open  point),  is  carefully  dried,  and  weighed;1  a  quantity  (not 

1  In  very  accurate  experiments,  the  globe  must  be  filled  with  dry  air  previously  to 
•weighing,  by  alternate  exhaustion  and  readmission  of  air  through  a  tube  containing 
chloride  of  calcium. 


SPECIFIC    GRAVITY.  37 

less  than  100  grs.)  of  the  volatile  substance,  is  then  introduced,  by  warming 
the  globe  and  dipping  the  extremity  of  the  beak  into  the  liquid  (if  a  solid, 
liquefied  by  fusion)  ;  the  globe  is  now  attached  to  a  handle  or 
stand,  and  immersed,  with  the  point  projecting  above  the  sur-          Fig.  3. 
face,  in  a  bath  of  water  or  oil,  the  temperature  of  which  must 
be  then  raisedj  considerably  higher  (by  40°  or  50°  F.=25°  or 
30°  C.)  than  the  boiling  point  of  the  volatile  substance.     The 
bath  should  be  provided  with  a  thermometer,  by  which  the 
temperature  is  indicated.     The  flame  below  the  bath  is  so  regu- 
lated, that  the  latter  shall  remain  at  a  nearly  constant  temper- 
ature.     A  jet  of   vapor,  of  course,  issues  rapidly  from  the 
orifice  of  the  neck  of  the  globe  ;    as  soon  as  the  vapor  has 
ceased  to  escape  (which  may  best  be  ascertained,  in  most  cases, 
by  applying  a  light),  the  orifice  is  hermetically  sealed  by  the 
blowpipe,  the  thermometer  and  barometer  being  observed  at  the 
time  of  sealing  (if  any  drops  have  condensed  in  the  point  of  the 
neck,  they  should  be  chased  out  with  a   spirit-flame  before 
sealing).     The  globe  is  removed  from  the  bath,  well  cleansed, 
allowed  to  cool,  and  very  accurately  weighed.     The  point  of  the  neck  is  now 
scratched  with  a  file,  and  broken  off  under  mercury,  when,  in  consequence  of  the 
condensation  of  the  vapor,  the  mercury  will  enter,  and  (unless  an  exceedingly 
volatile  substance  has  been  employed)  will  entirely  fill  the  globe.     If  the  ex- 
periment has  not  been  very  carefully  performed,  a  bubble  of  air  will  remain  in 
the  globe.     The  mercury  is  poured  from  the  globe  into  a  graduated  jar,  and 
accurately  measured;  also,  if  a  bubble  of  air  was  observed  in  the  globe,  the 
latter  is  again  (completely)  filled  with  mercury,  and  the  volume  ascertained. 
We  have  now  the  data  for  the  determination  of  the  specific  gravity. 

§  8.  In  order  to  illustrate  the  method  of  calculating  the  results,  let  us  con- 
sider an  example  where  it  was  required  to  determine  the  density  of  the  vapor  of 
turpentine : — 

Weight  of  the  globe  filled  with  dry  air  at  60°  F.  and  30 

in.  bar 3000.304     grs. 

Weight  of  the  globe  filled  with  vapor  of  turpentine  at 

350°  F.  and  29.6  in.  bar.  (temperature  and  pressure 

at  the  moment  of  sealing  the  point)         .         .         .  3027.474       " 
Volume  of  mercury  which  entered  the  globe  on  breaking 

the  point  at  60°  F.  and  29.6.  in.  bar.      .         .         .       29.50     cub.  in. 
Volume  of  mercury  which  exactly  fills  the  globe  (i.  e. 

capacity  of  the  globe) 30.00         " 

Difference,  being  the  residual  air  (weighed  with  the  vapor) 

at  60°  F.  and  29.6  in.  bar 0.50        " 

100  cubic  inches  of  dry  air  at  60°  F.  and  30  in.  bar. 

weigh.      \^%     .     ^  ..       .         .       ;,.,,,     .         .       31.012     grs. 

From  the  proportion 

100  :  30.00  ::  31.012  :  z=9.304 

we  find  the  weight  of  the  (30  cub.  in.  of)  air  contained  in  the  globe  to  be  9.304 
grs. 
Hence, 

Weight  of  globe  and  air 3009.304 

"          air       ,nv         ,^;  1^     .         .         .         .         9.304 

"          empty  globe    .     ^    : :,  ' '^f     :  .^     .  3000.000 
In  order  to  ascertain  the  actual  volume  of  vapor  which  was  weighed  in  the 
globe,  we  must  deduct  from  the  total  contents  of  the  globe  (30  cub.  in.),  the 


38  INTRODUCTION. 

volume  of  the  air  which  had  not  been  expelled.  We  find,  from  the  above  account 
of  the  experiment,  that  the  volume  of  the  residual  air  at  60°  F.  and  29.6  in. 
bar.  was  0.50  cub.  in.  But  this  air  was  inclosed  with  the  vapor  in  the  globe  at 
a  temperature  of  350°  F.,  the  barometric  pressure  being=29.6  in.,  and  it  is, 
therefore,  necessary  to  ascertain  what  expansion  it  must  have  suffered  at  that 
temperature.  This  is  determined  by  a  calculation  based  upon  the  following  law, 
which  is  the  result  of  many  careful  observations : — 

All  gases  expand  alike  for  an  equal  increase  of  temperature,  and  this  expansion 
amounts  to  Tl^  of  the  volume  which  the  gas  would  occupy  at  0°  F.  for  every 
degree  of  the  Fahrenheit  scale. 

This  law  applies  also  to  vapors  when  remote  from  their  condensing  points,  in 
which  case  they  are  subject  to  the  same  laws  as  the  permanent  gases. 

Now,  according  to  this  statement,  460  volumes  of  any  gas  at  0°  F.,  would 
become  461  vols.  at  1°  F. ;  460  +  2=462  vols.  at  2°  F.,  and  so  on.  Thus  the 
460  vols.  would  have  expanded  to  460  +  60,  or  520  vols.  at  60°  F.,  and  to 
460+350,  or  810  vols.  at  350°  F. 

Vols.  at  60°.     Vols.  at  350°.     Vol.  at  60°    Vol.  at  350°. 

520  ~     :       810       ::       0.5       :       *=0.78  cub.  in. 

Hence  it  appears  that  the  air  remaining  in  the  globe  would,  at  the  time  of  seal- 
ing the  point,  occupy  a  volume  =0.78  cub.  in.,  which  must  therefore  be  de- 
ducted from  the  total  contents  of  the  globe. 

30.00  cub.  in.— 0.78  cub.  in. =29.22  cub.  in. 

The  volume  of  turpentine  vapor  weighed  in  the  globe  was,  then,  (at  350°  F. 
and  29.6  in  bar.)=29.22  cubsin. 

In  order,  however,  to  obtain  the  specific  gravity,  it  is  necessary  to  reduce  this 
volume  to  the  standard  temperature  and  pressure,  viz :  60°  F.  and  30  in.  bar. 

The  correction  for  temperature  is  effected  as  in  the  former  case,  the  proportion 
being  of  course  reversed  : — 

Vols.  at  350°    Vols.  at  60°          Cub.  in.  Cub.  in. 

810       :       520       ::       29.22     :     cc=18.76 

18.76  cub.  in.  then,  would  be  the  volume  occupied  by  these  29.22  cub.  in.  of 
vapor  at  350°  F.,  supposing  that  it  would  bear  cooling  to  60°  F.  without  lique- 
faction. 

A  correction  must  also  be  made  for  the  difference  of  atmospheric  pressure, 
which,  of  course,  influences  the  volume  of  the  vapor.  This  correction  is  based 
upon  the  well-known  law  of  Mariotte,  lhat  the  volume  of  a  gas  is  inversely  as 
the  pressure,  which  holds  good  also  with  regard  to  vapors  removed  from  their 
points  of  liquefaction. 

Bar.          Bar.  Cub.  in.  Cub.  in. 

30     :     29.6    ::    18.76    :    *=18.51 

The  volume,  therefore,  which  the  vapor  (weighed  in  the  globe)  would  have  at 
60°  F.,  and  30  in.  bar.,  is  18.51  cub.  in. 

What,  then,  was  the  weight  of  this  volume  of  vapor  ?  We  shall  ascertain 
this  by  deducting  the  weight  of  the  residual  air  from  that  of  the  total  contents 
of  the  sealed  globe.  The  volume  of  the  residual  air  at  60°  F.  and  29.6  in.  bar. 
was  0.50  cub.  in. : — 

Bar.       .    Bar.  Cub.  in.  Cub.  in. 

30     :     29.6    ::    0.50     :     x=0.49 

At  30  in.  bar.  then,  this  would  occupy  0.49  cub.  in.,  and  would  weigh 
0.152  gr. 


SPECIFIC    GRAVITY. 

Weight  of  globe  and  contents  (turpentine  vapor  and  re- 
sidual air) 3027.474  grs. 

"        Empty  globe 3000.000    " 

"         Turpentine  vapor  and  residual  air  .        •„         .  27.474    " 

"         Residual  air  0.152    " 


Weight  of  18.51  cub.  in.  of  turpentine  vapor,  at  60°  F. 

and  30  in.  bar.      .      '   .  " '     .       '-.         .  27.322    « 

Now,  18.51  cub.  in.  of  air,  of  the  same  temperature  and  pressure,  weigh 
5.740  grs. 

Grs.  Grs. 

5.740     :     27.322    ::    1     :     *=4.76 

4.76,  therefore,  is  the  specific  gravity  required. 

CONVERSION   OF   THERMOMETRIC   DEGREES. 

§  9.  It  is  very  often  necessary,  in  chemical  calculations,  to  convert  a  tempera- 
ture expressed  in  degrees  of  one  thermometric  scale  into  the  corresponding  tem- 
perature on  another  scale,  and  we  may  here  point  out  the  method  of  effecting 
such  conversion. 

The  two  scales  commonly  used  in  laboratories  are  those  of  Fahrenheit  and 
Celsius,  which  latter  is  also  known  as  the  centigrade  scale.  The  zero  of  the 
Fahrenheit  scale  is  the  lowest  temperature  produced  by  a  mixture  of  ice  and 
salt,  which  is  32°  below  the  melting-point  of  ice,  and  212°  below  the  boiling- 
point  of  water.  The  centigrade  scale,  on  the  other  hand,  starts  from  the  melt- 
ing-point of  ice  (0°),  and  makes  the  boiling  point  of  water=100°,  so  that 
100°  C.  correspond  to  180°  F.  (the  number  of  degrees  between  32°  and  212°), 
or  10°  C.  to  18°  F.,  or,  to  simplify  it  still  further,  5°  C.==9°  F.;  the  calculation 
is  now  very  simple,  if  we  remember  that,  since  the  Fahrenheit  scale  commences 
32°  F.  lower  than  that  of  Celsius,  we  must  subtract  32  from  all  Fahrenheit  de- 
grees before  reduction,  and  must  add  this  number  to  all  degrees  which  have  been 
converted  from  the  centigrade.  To  illustrate  this  by  examples,  let  us  suppose  it 
required  to  find  the  degree  upon  the  centigrade  scale  corresponding  to  60°  F. 

60°  —  32°  =  28° 
and       9°    :      5°  :  :  28°  :  z=15°.5 

60°  F.  therefore,  correspond  to  15°. 5  C. 

Again,  to  find  the  Fahrenheit  degree  corresponding  to  80°  C. 

5°     :     9°     ::     80°     :     a=144° 
144°     +    32°    =    176° 

which  is  the  temperature  required.  Hence,  we  may  deduce  the  following  rules 
for  the  conversion  of  thermometric  degrees : — 

To  reduce  Fahrenheit  to  centigrade  degrees,  subtract  32°,  multiply  by  5,  and 
divide  by  9  (  (F.— 32°).f ). 

To  reduce  centigrade  to  Fahrenheit,  multiply  ~by  9,  divide  by  5,  and  add  32° 


40  INTRODUCTION. 


DEFINITION  OF  CHEMICAL  TEEMS 
IN  CONSTANT  USE. 


§  10.  THERE  are  a  few  terms  constantly  employed  in  every  page  of  chemical 
works,  of  which  it  is  highly  necessary  to  have  a  clear  apprehension  in  the  outset; 
we  proceed  to  define  them  as  generally  as  possible. 

An  ACID  is  a  substance  possessing  a  sour  taste,  the  power  of  reddening  most 
vegetable  blues,  such  as  litmus  (acid  reaction),  and  a  tendency  to  combine  with 
bases,  of  which  it  destroys,  in  greater  or  less  degree,  the  characteristic  properties. 
It  is  this  total  or  partial  annihilation  of  characteristic  properties  which  is  implied 
in  the  term  neutralization,  and  acids  are  said  to  neutralize  bases,  or  vice  versa. 

Substances  which  do  not  affect  test-papers  are  said  to  be  neutral. 

A  monobasic  acid  is  one  which  requires  only  one  equivalent  of  a  basic  protox- 
ide to  form  a  neutral  salt ;  whilst  a  bibasic  acid  requires  two,  and  a  tribasic  acid, 
three  equivalents  of  such  bases. 

§  11.  An  INORGANIC  BASE  is  a  metallic  oxide  (i.  e.  a  combination  of  a  metal 
with  oxygen),  which  is  capable  of  combining  with  acids,  and  of  destroying,  in 
greater  or  less  degree,  their  characteristic  properties. 

An  alkali  is  an  inorganic  base  which  is  soluble  in  water;  it  possesses  a  pecu- 
liar acrid  taste,  and  is  capable  of  restoring  the  blue  colour  to  litmus  which  has 
been  reddened  by  an  acid,  or  of  imparting  a  brown  tint  to  turmeric-paper.  (Al- 
kaline reaction.) 

§  12.  A  SALT  is  a  combination  of  an  acid  with  a  base  (oxy-acid  salts),  or  of 
a  salt-radical  with  a  metal  (haloid  salts'). 

This  definition  calls  for  an  explanation  of  the  term  salt-radical. 

A  SALT-RADICAL  is  a  substance  capable  of  combining  with  hydrogen  to  form 
an  acid,  or  with  a  metal  to  form  a  salt.  The  element  chlorine  is  the  type  of  this 
class  of  substances. 

Sulphate  of  potassa,  composed  of  sulphuric  acid  and  potassa,  may  serve  as  an 
example  of  an  oxy-acid  salt;  and  chloride  of  sodium  is  the  type  of  haloid  salts. 
(dxj,  the  sea.) 

A  neutral  salt  of  a  monobasic  acid  is  that  which  contains  as  many  equivalents 
of  the  acid  as  there  are  of  oxygen  in  the  base ;  the  neutral  salts  of  bibasic  and 
tribasic  acids  contain  respectively  one-half,  and  one-third,,  as  many  equivalents 
of  acid  as  there  are  of  oxygen  in  the  base.  A  double  salt  is  a  combination  of 
two  salts;  thus,  alum  is  a  double  salt,  composed  of  sulphate  of  alumina  and 
sulphate  of  potassa. 


ON  EQUIVALENTS. 

§  13.  It  is  almost  impossible  to  give  any  definition  of  the  term  equivalent 
which  would  not  be  open  to  exception,  since  there  are  so  many  opinions  with 
regard  to  the  conditions  by  which  the  application  of  the  term  should  be  regu- 
lated. 

One  of  the  neatest,  and  at  the  same  time,  most  general  definitions  which  can 
be  given,  is  the  following : — 


ON    EQUIVALENTS.  41 

THE  EQUIVALENTS  of  elementary  bodies  (§  68)  represent  the  smallest  propor- 
tions in  which  they  enter  into  combination  with  each  other. 

The  numbers  representing  these  equivalents  are,  of  course,  referred  to  some 
standard  number,  taken  to  represent  the  equivalent  of  one  of  the  elements.  In 
England,  the  standard  is  hydrogen,  which  is  made  =  1 ;  on  the  Continent,  how- 
ever, the  equivalents  are  sometimes  referred  to  oxygen,  which  is  represented  by 
100.  The  two  scales  are  distinguished  as  the  oxygen  and  hydrogen  scales.  The 
equivalent  of  oxygen  (8)  upon  the  hydrogen-scale  represents,  then,  according  to 
our  definition,  the  smallest  weight  of  this  body  which  is  known  to  enter  into 
combination  with  other  elements.  It  is  necessary,  however,  to  bear  in  mind  that 
this  is  no  absolute  assertion ;  it  is  not  affirmed  that  8  grains,  or  8  parts  of  what- 
ever magnitude,  are  the  smallest  absolute  weight  of  oxygen  which  will  enter  into 
combination,  but  it  is  merely  proposed  to  take  8  as  representing  the  smallest 
relative  quantity  of  oxygen  which  can  combine  with  other  elements ;  as  repre- 
senting, in  fact,  the  atom  of  oxygen,  or  that  quantity  so  small  that  it  cannot  be 
divided.  It  is  on  this  view  of  the  nature  of  equivalents  that  they  have  been 
sometimes  called  the  atomic  weights;  but,  by  those  who  maintain  the  infinite 
divisibility  of  matter,  they  are  usually  termed  equivalents,  or  combining  propor- 
tions, the  fitness  of  which  latter  term  will  be  obvious. 

We  cannot  better  illustrate  the  meaning  of  the  term  equivalent,  than  by  de- 
scribing the  method  of  determining  that  of  copper. 

A  weighed  quantity  of  perfectly  pure  black  oxide  of  copper  is  heated  in  a 
stream  of  hydrogen  gas ;  the  latter,  combining  with  the  oxygen  derived  from  the 
oxide  of  copper,  forms  water,  which  is  converted  into  vapor,  and  metallic  copper 
remains;  this  last  is  accurately  weighed;  the  experiment  thus  conducted  shows 
that  100  parts  of  the  black  oxide  of  copper  contain  79.84  parts  of  copper,  and 
20.16  of  oxygen,  whence  we  ascertain,  by  a  proportion,  that  8  parts  (or  one 
equTvaTent)  of  oxygen  are  combined  with  81.7  of  copper.  But  we  have  not  yet 
proved  that  31.7  is  the  equivalent  of  copper,  for  the  black  oxide  might  contain 
more  or  less  than  one  equivalent  of  copper  for  one  equivalent  of  oxygen ;  and  now, 
we  must  pass  from  experiment  to  hypothesis ;  we  must  assume  a  certain  composi- 
tion for  this  oxide,  and  the  equivalent  is  then  at  once  deduced.  The  black  oxide 
of  copper  is  generally  assumed  to  contain  single  equivalents  of  copper  and  oxy- 
gen; first,  because  it  is  the  more  natural  assumption;  secondly,  because  it  pre- 
sents a  striking  analogy  to  many  other  oxides  for  which  a  similar  composition  is 
assumed ;  and  lastly,  because  there  actually  exists  another  oxide  of  copper  (the 
red  oxide),  which,  from  analogy,  and  from  a  certain  tendency  to  decompose  into 
metallic  copper  and  the  black  oxide,  is  assumed  to  contain  two  equivalents  of 
copper  to  one  equivalent  of  oxygen.  Upon  similar  principles  is  the  determina- 
tion of  the  equivalents  of  other  metals  effected. 

The  equivalent  of  a  compound  body  is  the  sum  of  the  equivalents  of  its 
elements. 

In  order  to  exhibit  the  principles  upon  which  the  determination  of  the  equiva- 
lent of  a  compound  body  is  effected,  we  will  suppose  it  required  to  ascertain  the 
equivalent  of  sulphuric  acid. 

For  this  purpose,  it  is  necessary  to  analyze  some  pure  and  well-defined  com- 
bination of  the  acid  with  a  substance  of  known  atomic  weight.  Let  us  suppose 
the  sulphate  of  oxide  of  copper  to  be  employed.  It  will  be  found  to  contain, 
for  every  equivalent,  or  39.7  parts,  of  oxide  of  copper,  40  parts  of  sulphuric 
acid ;  and  if  we  assume  that  this  salt  consists  of  single  equivalents  of  acid  and 
base,  the  number  of  40  will  represent  the  equivalent  of  sulphuric  acid.  The 
assumption  proceeds  here  chiefly  upon  considerations  of  convenience  and  simpli- 
city in  the  first  instance ;  and,  in  subsequent  cases,  may,  of  course,  be  supported 
by  analogy. 

By  analyzing  compounds  of  sulphuric  acid  with  other  bases,  it  will  be  found 


42  INTRODUCTION. 

that  either  40  parts,  or  some  very  simple  multiple  of  this  quantity,  are  required 
to  form  a  neutral  salt.  Moreover,  it  may  easily  be  shown  that  40  parts  of  sul- 
phuric acid  can  be  replaced  by  54  parts,  or  one  equivalent,  of  nitric  acid,  and 
by  22  parts,  or  one  equivalent,  of  carbonic  acid. 

It  will  be  seen  that  the  number  40  is  the  sum  of  one  equivalent  of  sulphur, 
16,  and  three  equivalents  of  oxygen,  24. 

It  is  highly  necessary  to  remember  that  combination  takes  place,  whether 
between  elements  or  compounds,  either  in  the  proportions  of  their  equivalents,  or 
in  multiples  of  those  proportions,  and  never  in  submultiples,  so  that  fractions  of 
equivalents  never  enter  into  chemical  notation;  the  law  thus  expressed,  joined 
with  the  announcement  that  individual  compounds  always  contain  exactly  the 
same  proportions  of  their  elements,  is  usually  designated  the  law  of  definite  and 
multiple  proportions.1 

It  will  be  evident,  from  what  has  been  already  said,  that  if  we  know  the  ele- 
ments of  which  any  compound  is  made  up,  and  the  number  of  equivalents  of  each 
element,  we  may  at  once  calculate  the  percentage  composition ;  and  this  is  one 
of  the  uses  to  which  a  knowledge  of  equivalent  numbers  can  be  applied. 

Another  use  of-  equivalents  in  practical  chemistry  depends  upon  the  circum- 
stance that  the  equivalents  of  elements,  or  compounds  belonging  to  the  same 
group,  as  regards  their  chemical  relations  (the  relation  of  acids  to  acids,  bases 
to  bases,  &c.),  represent  the  proportions  in  which  such  elements  or  compounds 
replace  each  other  in  any  particular  combination  to  form  another  combination  of 
the  same  order;  for  example,  the  equivalents  of  potassium  and  sodium  (39  and 
23)  represent  the  proportions  in  which  these  elements  unite  with  the  same 
quantity  of  oxygen  to  form  the  alkalies  potassa  and  soda,  the  equivalents  of  which 
(47  and  31),  again,  represent  the  proportions  in  which  they  unite  with  the  same 
quantity  of  sulphuric  acid  to  form  the  sulphates  of  potassa  and  soda ;  thus,  by 
applying  our  knowledge  of  the  equivalents  of  these  alkalies,  we  at  once  ascer- 
tain how  much  of  either  of  them  would  be  required  to  neutralize  a  given  quantity 
of  sulphuric  acid. 

(A  table  of  equivalents  will  be  found  at  §  68.) 


ATOMIC  THEORY. 

§  14.  We  have  already  alluded  to  the  existence  of  two  views  respecting  the 
divisibility  of  matter;  according  to  one  of  these,  matter  is  capable  of  infinite 
division,  while  the  other  would  lead  us  to  believe  that  there  exist  certain  ulti- 
mate particles,  of  which  all  matter  is  made  up,  and  which  are  incapable  of  fur- 
ther division;  these  particles  are  termed  atoms  (a  priv.  and  T-E^I-W),  and  the 
theory  based  upon  the  hypothesis  of  their  existence,  is  generally  known  as  the 
Atomic  Theory  of  Dalton,  who  was  the  first  to  propound  it  in  a  definite  form. 

This  theory  allows  us  to  account  for  the  various  phenomena  of  combination 
and  decomposition  in  a  much  more  elegant  and  satisfactory  manner  than  that  of 
infinite  divisibility ;  for  if  the  equivalent  numbers  be  supposed  to  express  the 
relations  between  the  weights  of  atoms  of  different  substances,  the  law  of  multi- 
ple proportions  follows  at  once ;  since,  by  the  definition,  fractions  of  these  cannot 
enter  into  combination ;  and  hence  the  quantities  of  any  element  existing  in  a 
series  of  compounds  must  always  be  multiples,  by  some  whole  number,  of  the 
equivalent  weights. 

The  substitution  of  one  body  for  another,  equivalent  for  equivalent,  is  also 
very  easily  explained  upon  this  theory. 

1  Very  good  examples  of  this  are  seen  in  the  series  of  compounds  of  oxygen  with 
nitrogen  and  sulphur,  to  which  we  refer. 


ON    CHEMICAL    AFFINITY.  43 

Another  necessary  consequence  would  be  the  law,  that  the-  equivalent  of  a 
compound  body  is  the  sum  of  the  equivalents  of  its  components,  for  since  the 
atoms  are  indivisible,  the  compound  atom  produced  by  their  union  must  have 
their  joint  weight. 

On  this  theory,  the  equivalent  volumes  of  gases  would  actually  represent  the 
spaces  occupied  by  their  atoms. 

The  phenomenon  of  isomerism  would  also  be  explicable  by  assuming  a  differ- 
ent arrangement  of  the  atoms  of  which  isomeric  substances  are  composed. 

With  regard  to  the  size  and  shape  of  atoms,  much  discussion  has  taken  place, 
but  it  is  evident  that  these  points  (especially  the  latter)  cannot  be  settled  until 
we  succeed  in  obtaining  particles  of  matter  so  small  that  we  cannot  effect  any 
further  division  ;  and,  moreover,  they  are  decidedly  of  secondary  importance  in  a 
chemical  point  of  view. 

We  should  wish  the  mind  of  the  student  to  be  impressed  with  the  fact,  that 
the  atomic  theory  is  merely  a  collection  of  laws,  based  upon  a  pure  assumption 
of  the  finite  divisibility  of  matter,  thus  differing  widely  from  the  doctrine  of 
equivalents,  which  is  really  the  result  of  experiment,  and  the  generalization  of 
facts. 


COMBINATION    BY    VOLUME. 

§  15.  When  gases  enter  into  combination,  the  volumes  of  the  combining  gases 
always  stand  in  a  very  simple  ratio  to  each  other,  and  if  the  resulting  compound 
be-  also  gaseous,  its  volume  bears  a  simple  relation  to  that  of  its  components. 
(In  most  cases,  a  certain  condensation  takes  place,  the  volume  of  the  compound 
gas  being  less  than  the  sum  of  the  volumes  of  its  constituents.)  Thus,  one 
volume  of  oxygen,  combining  with  two  volumes  of  hydrogen,  produces  two 
volumes  of  water  in  the  state  of  gas;  again,  one  volume  of  chlorine  combines 
with  one  volume  of  hydrogen,  to  form  two  volumes  of  hydrochloric  acid  gas. 

The  following  are  two  well-established  laws  with  regard  to  the  combination  of 
gases  by  volume  : — 

1.  When  two  volumes  of  one  gaseous  element  combine  with  one  volume  of 
another  element,  the  resulting  gas  occupies  two  volumes.. 

2.  When  equal  volumes  of  elementary  gases  combine,  the  volume  of  the  com- 
pound yas  is  the  sum  of  the  volumes  of  its  constituents. 

From  what  has  been  said  with  regard  to  equivalent  weights,  it  follows  that 
the  proportions  by  volume  in  which  the  different  gases  combine  are  perfectly 
constant j  these  proportions,  which,  as  we  have  already  mentioned,  are  exceed- 
ingly simple,  are  usually  termed  the  equivalent  volumes  of  the  gases. 

This  simple  relation  which  we  observe  between  the  volumes  in  which  elementary 
gases  unite,  is  explained  by  the  circumstance  that  the  specific  gravities  of  gases 
are  either  the  same  as  their  equivalents,  or  stand  in  some  very  simple  ratio  to 
them  (of  course,  it  is  here  supposed  that  the  specific  gravity  and  the  equivalent 
are  referred  to  the  same  standard). 


CHEMICAL    AFFINITY. 

§  16.  CHEMICAL  AFFINITY  may  be  defined  as  an  attraction  exerted  at  insensi- 
ble distances,  between  particles  of  matter  of  different  kinds,  the  result  of  which 
is  the  formation  of  new  particles  possessed  of  attributes  different  from  those  of 
their  components. 

This  definition  at  once  exhibits  the  points  of  difference  between  chemical 
attraction  and  the  forces  of  gravitation  and  cohesion. 


44  INTRODUCTION. 

Gravitation  is  exerted,  at  all  distances,  between  masses  of  matter,  without 
regard  to  their  nature,  and  differs,  therefore,  in  toto,  from  affinity. 

Cohesion  differs  less  widely  from  affinity,  since  it  acts  only  at  very  minute 
distances.  This  force,  however,  is  exerted  more  frequently,  and  with  greater 
energy,  between  similar  particles  of  matter  than  between  particles  of  different 
kinds. 

Moreover,  the  operation  of  these  forces  is  not  attended  with  any  material 
alteration  in  the  properties  of  the  matter. 

The  fall  of  an  apple  to  the  earth  is  the  result  of  gravitation,  the  force  which 
binds  the  particles  of  the  fruit  together  is  cohesion,  while  the  ultimate  particles 
or  elements  of  which  the  apple  consists  are  united  by  chemical  attraction  or 
affinity. 

The  operation  of  chemical  affinity,  or  combination,  does  not  take'place  between 
substances  without  reference  to  the  class  to  which  they  belong.  Thus,  elements 
are  very  seldom  found  to  combine  with  other  than  elements,  or  quasi-elements; 
so  rarely,  in  fact,  do  elements  enter  into  direct  combination  with  compound 
substances,  that,  when  this  is  the  case,  it  is  considered  to  afford  ground  for  sus- 
pecting that  the  element  in  question  may  hereafter  prove  to  be  a  compound  body. 
Thus,  acids  are  never  found  to  combine  with  the  metals,  but  always  with  their 
oxides.  Sulphur,  chlorine,  cyanogen,  and  the  like,  never  combine  with  metallic 
oxides,  only  with  metals. 

The  affinity  of  the  metals  for  the  non-metallic  elements  is  generally  much 
greater  than  their  affinity  for  each  other. 

Generally  speaking,  the  more  opposite  the  chemical  relations  of  bodies,  the 
more  powerful  the  affinity  between  them. 

The  operation  of  affinity  is  usually  attended  with  eyolution  of  heat;  all  cases 
of  combustion  are  simply  examples  of  chemical  combination,  attended  with 
evolution  of  heat  and  light. 

It  will  appear  from  our  definition  of  affinity,  that,  since  this  attraction  is 
exerted  only  at  insensible  distances,  its  force  will  be  in  some  degree  proportioned 
to  the  state  of  division  of  the  masses  of  matter  between  which  it  is  exerted; 
accordingly,  we  observe  occasionally  that  masses  which  will  not  act  upon  each 
other,  combine  energetically  when  reduced  to  powder;  thus,  a  mass  of  sulphur, 
even  at  a  moderately  high  temperature,  will  not  act  upon  mercury,  but  if  they 
be  well  triturated  together  in  a  mortar,  at  the  same  temperature,  combination 
takes  place. 

But  this  effect  of  mechanical  division  in  promoting  chemical  attraction,  is 
much  more  strikingly  exemplified  when  the  cohesion  of  one  or  more  of  the  com- 
bining substances  is  diminished — i.e.  when  it  is  reduced  to  the  liquid  state; 
oxalic  acid  in  the  solid  form  will  not  act  upon  hydrated  lime,  but  if  a  solution 
of  oxalic  acid  be  poured  upon  lime,  or  vice  versa — or,  above  all,  if  they  be  mixed 
in  a  state  of  solution,  immediate  combination  ensues,  and  oxalate  of  lime  is 
formed. 

This  attractive  force  is  not  only  influenced  to  a  great  extent  by  the  state  of 
division,  but  it  also  suffers  very  important  modifications  under  various  other 
conditions,  the  chief  of  which  we  shall  endeavor  to  indicate. 

The  affinities  of  various  substances  for  each  other  are  modified  to  a  very  great 
extent  by  the  temperature  at  which  these  affinities  are  exercised.  Thus,  hydro- 
gen will  not  conibine  with  oxygen  at  the  ordinary  temperature,  but,  at  a  some- 
what elevated  temperature,  very  energetic  combination  takes  place.  Again,  to 
take  a  more  complicated  example,  carbonate  of  baryta,  digested  at  a  low  tem- 
perature with  sulphate  of  soda,  yields  sulphate  of  baryta  and  carbonate  of  soda; 
but  if  these  latter  be  boiled  together,  the  decomposition  is  reversed,  we  obtain 
sulphate  of  soda  and  carbonate  of  baryta. 

In  general,  however,  the  cause  of  this  relation  of  affinity  to  temperature  may 


ON    CHEMICAL   AFFINITY.  45 

be  traced  to  a  difference  in  the  state  of  the  product  or  products  of  the  action  of 
such  affinity  at  the  different  temperatures.  A  familiar  example  of  this  is  found 
in  the  decomposition  of  oxide  of  mercury  by  heat,  which  takes  place  at  a  tem- 
perature at  which  both  of  its  constituents  have  a  tendency  to  assume  the  gaseous 
state,  and  we  may  suppose  that  this  very  tendency,  this  molecular  repulsion,  in 
fact,  determines  the  separation  of  the  elements.  Another  very  striking  example 
is  seen  in  the  action  of  chloride  of  ammonium  upon  carbonate  of  lime;  if  this 
latter  be  boiled  with  solution  of  chloride  of  ammonium,  it  is  well  known  that 
carbonate  of  ammonia  is  formed  and  volatilized,  whilst  chloride  of  calcium  re- 
mains in  solution;  whereas,  if  these  substances  (viz.  carbonate  of  ammonia  and 
chloride  of  calcium)  be  mixed  in  a  state  of  solution  at  the  ordinary  temperature, 
carbonate  of  lime  is  precipitated,  and  chloride  of  ammonium  remains  in  solution. 
The  difference,  in  this  case,  appears  to  arise  from  the  tendency  of  the  particles 
of  carbonate  of  ammonia  to  assume  the  gaseous  form  at  high  temperatures. 

Finally,  we  may  cite,  as  an  important  example  of  this  modification  of  affinity, 
the  decomposing  action  of  very  weak  but  fixed  acids  (e.g.  silicic  and  boracic 
acids),  at  high  temperatures,  upon  the  salts  of  more  powerful  acids,  which  are 
capable  of  assuming  the  gaseous  form  (e.  g.  sulphuric  and  nitric). 

The  action  of  the  force  of  affinity,  therefore,  as  will  be  seen  by  the  foregoing 
examples,  is  modified  to  a  most  remarkable  extent,  according  to  the  cohesive 
force  with  which  the  particles  of  the  resulting  compound  are  held  together;  in 
fact,  this  influence  of  cohesion  is  so  generally  observed,  when  it  results  in  the 
passage  from  the  liquid  to  the  solid  state,  that  some  authors  have  laid  down  the 
rule,  that  when  any  two  or  more  solutions  are  mixed,  the  direction  of  the  force 
of  affinity  will  tend  to  the  production  of  that  compound  which  is  the  least  solu- 
ble (i.  e.  possesses  most  cohesive  power)  under  the  circumstances  in  which  it  is 
called  into  existence.  Examples  of  this  form  of  affinity  will  be  seen  in  every 
page  of  chemical  works. 

Light  even  exerts  sometimes  an  important  influence  upon  chemical  combina- 
tion and  decomposition;  the  most  familiar  examples  of  this  action  are,  the  com- 
bination of  hydrogen  and  chlorine,  which  takes  place  instantaneously  under  the 
influence  of  -solar  light,  and  the  decomposition  of  nitric  acid  into  peroxide  of 
nitrogen  and  oxygen,  which  the  rays  of  the  sun  are  capable  of  inducing.  » 

The  powerful  effect  of  electricity  in  modifying  chemical  affinity,  to  such  an 
extent  as  to  effect  the  decomposition  of  the  most  stable  combinations,  is  well 
seen  in  the  resolution  of  water  into  its  elements  (hydrogen  and  oxygen),  by 
means  even  of  a  feeble  galvanic  current,  whereas,  on  the  other  hand,  the  com- 
bination of  hydrogen  and  oxygen  to  produce  water,  may  likewise  be  induced  by 
an  electric  spark  passed  through  the  mixture  of  the  gases. 

Certain  solid  substances  possess  a  most  remarkable  power  of  inducing  combi- 
nation ;  this  is  especially  the  case  with  metals,  and  above  all,  with  platinum, 
which  may  be  obtained  by  particular  processes,  in  the  forms  of  platinum-sponge 
and  platinum-black,  these  being  simply  platinum  in  a  state  of  minute  division : 
if  either  of  these  be  introduced  into  a  mixture  of  oxygen  and  hydrogen  gashes, 
in  the  proportions  in  which  they  combine  to  form  water,  the  metal  becomes  at 
once  redhot,  and  the  combination  takes  place  with  explosion.  This  action  is 
generally  referred  to  a  specific  power,  possessed  by  the  platinum,  of  condensing 
the  gases  within  the  minute  pores  upon  its  surface,  and  of  thus  bringing  them 
within  the  sphere  of  mutual  attraction;  but  why  this  power  should  reside  espe- 
cially with  the  metal  in  question,  has  not  been  fully  explained. 

The  affinities  possessed  by  a  substance  in  its  nascent  state,  i.  e.  at  the  moment 
of  its  elimination  from  a  compound,  are  often  much  more  energetic  than  under 
ordinary  circumstances. 

This  is  especially  noticed  in  the  powerful  oxidizing  action  of  mixtures  capable 
of  yielding  oxygen ;  e.  g.  of  binoxide  of  manganese  and  sulphuric  acid ;  and  in 


46  INTRODUCTION. 

the  increased  affinity  for  oxygen  which  is  possessed  by  nascent  hydrogen,  as 
evolved  by  the  action  of  zinc  upon  liquids  containing  free  sulphuric  or  hydro- 
chloric acid. 

Other  circumstances  might  be  adduced,  which  are  capable  of  altering  the 
direction  of  this  force;  but  the  above  comprise  the  chief  modifying  agencies  to 
which  chemical  attraction  is  subjected  in  practice,  and  the  others  will  be  more 
advantageously  studied  in  individual  examples. 

Enough,  we  trust,  has  been  said,  to  show  that  affinity  is  subject  to  so  many 
modifications  that  its  results  can  be  predicted  only  to  a  very  limited  extent;  and, 
therefore,  that  it  is  preferable  for  the  student  of  chemistry  to  acquire  a  know- 
ledge of  the  laws  of  the  action  of  this  force  from  experience  of  its  effects,  rather 
than  to  rest  any  faith  in  such  general  laws  and  tables  of  affinity  as  were  popular 
among  the  chemists  of  a  former  day,  and  which,  though  they  might  be  faithful 
guides  in  some  cases,  left  almost  as  much  to  unlearn,  in  exceptions,  as  they 
taught  in  rules. 


CHEMICAL  DECOMPOSITION. 

§  17.  The  causes  which  induce  chemical  decomposition  may  be  conveniently 
considered  under  two  divisions :  the  first,  comprising  those  cases  of  decomposition 
which  do  not  take  place  in  consequence  of  an  opposition  of  affinities,  and  which 
are  therefore  purely  phenomena  of  decomposition  unattended  by  recombination ; 
and  the  second  division  embracing  such  decompositions  as  result  from  the  affinity 
of  the  decomposing  agent,  or  of  one  of  its  constituents,  for  some  constituent  of 
the  body  which  is  decomposed. 

The  decompositions  belonging  to  the  first  class  are  chiefly  those  effected  by 
the  physical  agents,  heat,  light,  and  electricity.  The  power  of  heat  to  induce 
decomposition  has  already  been  noticed  in  one  very  simple  example  (that  of 
oxide  of  mercury ;  see  Affinity) ;  but  this  action  of  heat  is  so  universally  and 
readily  available,  that  it  is  constantly  applied  in  the  laboratory;  its  results  are 
so  varied  that  it  is  scarcely  possible  (and  we  know  not  whether  it  would  be 
usefpl)  to  classify  them,  but  we  may  remark  that  they  consist  very  seldom  in  the 
separation  of  the  ultimate  elements  of  any  compound,  but  usually  in  the  produc- 
tion of  certain  combinations  which  are  more  volatile  or  more  stable  than  the 
original  material.  When  organic  substances  are  decomposed  by  the  action  of 
heat  alone,  they  are  usually  said  to  be  subjected  to  destructive  distillation,  and 
are  resolved  into  compounds  much  less  complex  (i.  e.  containing  a  smaller 
number  of  equivalents)  than  the  substance  from  which  they  originated. 

Electricity  is  an  important  agent  of  decomposition,  and  has  somewhat  recently 
received  a  very  interesting  application  in  certain  researches  upon  organic  sub- 
stances. Decompositions  by  electricity  are  usually  effected  by  means  of  the 
galvanic  battery,  and  their  results  may,  to  a  great  extent,  be  predicted.  It  does 
not  come  within  the  scope  of  this  elementary  work  to  give  a  complete  history  of 
the  electro- chemical  theory,  as  that  system  of  laws  is  termed  according  to  which 
the  results  of  the  action  of  electric  currents  can  be  determined  by  a  priori  con- 
siderations ;  but  the  leading  principles  of  this  theory  are  of  sufficient  importance 
to  call  for  a  passing  notice. 

It  is  found  that  when  bodies  are  decomposed  by  a  galvanic  current  (or,  as  it 
is  termed,  subjected  to  electrolysis)  one  of  the  constituents  is  invariably  disen- 
gaged at  the  wire  in  connection  with  the  positive  pole  of  the  battery,  and  the 
other  at  the  negative  pole;  to  take  an  example  which  has  been  already  alluded 
to,  the  decomposition  of  water  by  the  galvanic  current,  we  find  that  the  hydrogen 
is  always  disengaged  at  the  negative,  and  the  oxygen  as  invariably  at  the 
positive  end  of  the  battery.  Now,  it  will  be  remembered  that  bodies  in  a  like 


CHEMICAL    NOMENCLATURE.  47 

electric  state  do  not  attract  each  other,  but  only  those  which  are  in  a  dissimilar 
condition  •  hence,  since  hydrogen  is  attracted  by  the  negative  pole  of  the  battery, 
and  oxygen  by  the  positive,  it  follows  that  hydrogen  is,  with  respect  to  oxygen, 
an  electro-positive  element,  and  vice  versa;  in  the  same  manner,  it  is  found  that 
the  metals  are  disengaged  at  the  negative  pole  of  the  battery,  and  the  non- 
metallic  bodies  with  which  they  are  in  combination,  at  the  positive;  or,  if  the 
salts  or  oxygen-acids  be  operated  upon,  that  the  bases  are  eliminated  at  the 
negative,  and  the  acids  at  the  positive  pole. 

Agreeably  to  this  distinction,  all  the  elements  and  some  compounds  are 
arranged  in  two  series,  the  members  of  which  are  respectively  positive  and  nega- 
tive in  relation  to  each  other. 

The  chief  features  of  the  electro-chemical  theory,  therefore,  are,  that  the  class 
of  electro-positive  substances  (or  those  which  are  disengaged  at  the  negative  end 
of  the  battery)  comprehends  hydrogen,  the  metals,  and  their  basic  oxides,  whilst 
oxygen,  chlorine,  and  most  of  the  non-metallic  elements,  together  with  the  acids, 
are  the  chief  members  of  the  other  class.  It  must,  however,  be  borne  in  mind, 
that  this  distinction  is  only  relative,  and  that  one  substance  may  be  electro-posi- 
tive to  a  second,  and  negative  to  a  third  body ;  thus  sulphur  is  electro-negative 
with  respect  to  silver,  and  electro-positive  in  relation  to  chlorine  (which  stands 
higher  on  the  electro-negative  scale  than  sulphur). 

The  decomposing  influence  of  light  may  be  traced  in  its  action  upon  the  salts 
of  silver,  upon  nitric  acid,  &c. 

In  some  cases,  decomposition  may  result  from  a  mere  mechanical  shock,  as  in 
the  case  of  certain  detonating  compounds,  which  explode  when  lightly  touched ; 
in  these  cases,  it  would  seem  that  the  affinity  between  the  elements  is  so  slight, 
that  the  least  external  disturbance  is  sufficient  to  upset  the  equilibrium. 

It  will  immediately  occur  to  the  mind  of  the  more  advanced  student,  that 
there  are  some  decompositions  effected  by  causes  which  are  yet  unknown;  of 
this  description  are  fermentation  and  the  so-called  effects  of  catalysis  (decom- 
position by  contact)  concerning  which  no  decisive  result  has  at  present  been 
arrived  at. 

True  chemical  decomposition,  resulting  from  the  operation  of  affinity,  may 
take  place  in  a  variety  of  ways. 

The  simplest  case  is  that  in  which  a  substance  seizes  one  constituent  of  a  com- 
pound for  which  it  has,  under  existing  circumstances,  a  greater  affinity  than  the 
other  constituents  have ;  this  case  is  often  termed  one  of  simple  elective  decompo- 
sition. Examples  of  this  form  of  decomposition  are.  seen  in  the  reduction  of 
certain  metallic  oxides  by  hydrogen,  or  carbon,  at  high  temperatures,  and  in  the 
evolution  of  carbonic  acid  by  the  action  of  stronger  acids  upon  the  carbonates. 

Another  case  is  that  which  is  popularly  termed  double  elective  decomposition, 
wherein  two  substances  act  simultaneously  upon  a  third,  each  appropriating  one 
of  the  constituents  of  this  third  body.  The  formation  of  the  chlorides  of  boron 
and  silicon,  by  the  simultaneous  action  of  chlorine  and  carbon  upon  boracic  and 
silicic  acids,  are  cases  in  point. 

Double  decomposition  is  said  to  take  place  when  an  interchange  of  constituents 
is  effected  between  two  compounds ;  as  when  sulphate  of  potassa  and  nitrate  of 
baryta  yield  sulphate  of  baryta  and  nitrate  of  potassa. 


CHEMICAL    NOMENCLATURE. 

§  18.  Before  proceeding  to  the  study  of  individual  chemical  compounds,  we 
must  acquaint  ourselves  with  the  methods  adopted  in  order  to  render  the  name 
of  a  substance  in  some  way  expressive  of  its  constitution. 

The  combinations  of  all  simple  electro-negative  substances  (and  even  of  com- 


48  INTRODUCTION. 

pounds  resembling  them  in  their  chemical  relations)  with  metals  or  non-metallic 
bodies,  are  generally  distinguished  by  the  termination  ide.  Thus  we  have  ox- 
ides, chlorides,  sulphides,  cyanides,  &c. 

When  these  compounds  contain  single  equivalents  of  their  elements,  they  are 
often  distinguished  by  the  prefix  proto.  Thus,  the  terms  protoxide,  protochlor- 
ide,  &c.,  indicate  compounds  of  single  equivalents  of  the  metal  or  non-metallic 
substance,  with  oxygen,  chlorine,  &c.  In  the  following  pages,  however,  we  have 
preferred  to  omit  this  prefix,  and  to  designate  all  such  compounds  by  the  simple 
names,  oxide,  chloride,,  &c.,  since  all  compounds  containing  more  than  one  equiva- 
lent of  either  constituent  are  distinguished  by  their  appropriate  prefixes. 

In  order  to  express  a  compound  of  this  description  containing  more  than  one 
equivalent  of  the  electro-negative  constituent,  we  make  use  of  the  prefixes  bi, 
ter,  penta,  sesqui,  &c. ;  thus,  the  compound  of  two  equivalents  of  chlorine  with 
one  equivalent  of  tin  is  termed  the  bichloride  of  tin ;  that  of  three  equivalents 
of  oxygen  with  two  equivalents  of  iron  (i.  e.  of  1  $  equivalents  with  one  equiva- 
lent), the  sesquioxide  of  iron,  &c.  Where  there  are  more  than  one  equivalent 
of  the  electro-positive  constituent  combined  with  one  equivalent  of  the  electro- 
negative, the  prefix  sub  is  employed ;  the  compound  of  two  equivalents  of  mercury 
with  one  equivalent  of  chlorine  is  known  as  the  subchloride  of  mercury,  and  so 
forth. 

The  prefix  per  is  usually  employed  to  designate  that  combination  of  a  metal 
with  an  electro-negative  body  which  contains  the  greatest  quantity  of  the  latter, 
except  in  the  case  of  oxides,  where  it  'is  applied  to  the  highest  oxide  which  does 
not  possess  acid  properties. 

Acids  derive  their  name  from  their  characteristic  element.  In  the  case  of 
hydrogen-acids,  the  name  of  this  element  is  simply  coupled  with  an  abbreviation 
for  hydrogen,  as  in  the  case  of  hydrochloric  acid,  hydrosulphuric  acid,  &c.  Oxy- 
gen-acids of  the  same  element  are  distinguished,  according  to  the  amount  of 
oxygen  which  they  contain,  by  particular  prefixes  and  terminations.  The  chief 
acid  of  the  series  terminates  in  ic,  and  is  without  a  prefix ;  this  is  the  case  with 
sulphuric,  phosphoric,  arsenic,  nitric  acids,  &c.  The  acid  which  ranks  next  to 
this  generally  terminates  in  ous  without  prefix,  as  phosphorous  acid,  arsenious 
acid,  &c. ;  but  where  an  intermediate  acid  has  been  discovered  after  these  names 
were  established,  its  name,  in  general,  terminates  in  ic,  and  is  distinguished  by 
the  prefix  hypo,  indicating  that  it  contains  less  oxygen  than  the  principal  acid; 
an  example  of  this  is  hyposulphuric  acid.  An  acid  containing  more  oxygen  than 
the  chief  acid  is  known  by  the  prefix  hyper,  as  hyperchloric  acid,  which  contains 
more  oxygen  than  chloric  acid. 

In  the  same  way,  acids  in  ous  containing  less  oxygen  than  the  chief  acid  in 
ous,  are  distinguished  by  the  prefix  hypo;  hyposulphurous  and  hypophosphorous 
acids  will  serve  as  illustrations. 

Salts  receive  names  which  indicate  both  the  acid  and  the  base  of  which  they 
are  composed.  Salts  formed  by  acids  in  ic  are  distinguished  by  the  termination 
ate;  the  terms  sulphate  and  phosphate  imply  the  salts  of  sulphuric  and  phos- 
phoric acids ;  when  the  acid  terminates  in  ous,  the  salts  receive  ite  ;  the  sulphites 
and  phosphites  are  the  salts  of  sulphurous  and  phosphorous  acids.  If  the  acid 
have  a  prefix,  it  is  of  course  retained  in  the  name  of  the  salt. 

In  naming  a  salt  of  the  oxide  of  any  metal,  the  word  oxide  is  usually  omitted, 
for  the  sake  of  brevity ;  thus,  sulphate  of  copper  should  strictly  be  sulphate  of 
oxide  of  copper,  and  the  word  oxide  must  always  be  understood  in  naming  salts 
of  oxygen  acids.  Salts  formed  by  the  combination  of  acids  with  suboxides  are 
usually  known  by  the  prefix  sub;  thus,  subsulphate  of  copper  implies  the  sulphate 
of  suboxide  of  copper.  In  the  same  way,  the  salts  of  peroxides  and  sesquioxides 
are  usually  distinguished  by  the  prefixes  per  and  sesqui. 

Salts  which  contain  more  acid  than  is  requisite  to  form  a  neutral  salt  with  the 


CHEMICAL   NOTATION.  49 

amount  of  base  present,  are  termed  add  salts,  whilst  those  in  which  the  base 
predominates  are  designated  basic.  If  the  amount  of  acid  be  twice  as  great  as 
is  necessary  to  form  a  neutral  salt,  the  compound  is  distinguished  by  the  prefix  li, 
as  bisulphate  of  potassa  (KO.S03,HO.S03),  bitartrate  of  potassa  (KO.HO.T). 

Combinations  of  water  with  other  compounds  are  termed  hydrates. 

Substances  which  are  not  combined  with  water  are  said  to  be  anhydrous. 

Compounds  possessing  the  same  composition,  but  differing  in  their  chemical 
properties,  are  said  to  be  isomeric ;  or,  if  the  compounds  in  question  are  simi- 
larly constituted,  as  regards  the  proportion  of  their  elements,  but  differ  in  the 
actual  number  of  equivalents  which  they  contain,  they  are  termed  polymeric.1 


CHEMICAL  NOTATION. 

§  19.  In  order  to  exhibit,  concisely  and  distinctly,  the  manner  in  which  sub- 
stances act  upon  each  other,  giving  rise  to  new  forms  of  combination,  chemists 
make  use  of  certain  universal  symbols  and  formulae,  which,  when  connected  by 
particular  signs,  are  made  to  represent  all  possible  combinations.  We  shall  pro- 
ceed to  elucidate  some  of  the  most  important  principles  of  this  valuable  system 
of  notation. 

Each  element  is  represented  by  its  own  symbol,  which  is  sometimes  the  initial 
letter,  sometimes  the  characteristic  letters  taken  from  the  English  or  Latin  de- 
signation of  the  element,  and  this  symbol  represents  one  equivalent  of  such 
element;  thus,  N  represents  one  equivalent  of  nitrogen,  Na  (natrium)  one 
equivalent  of  sodium,  Fe  (ferrum)  one  equivalent  of  iron,  &c. 

When  more  than  one  equivalent  of  an  element  is  to  be  expressed,  it  is  effected 
by  placing  a  small  figure  beneath  and  to  the  right  of  the  symbol";  thus,  two 
equivalents  of  nitrogen  are  represented  by  Na,  four  equivalents  of  sulphur  by 
S4,  &c. 

In  order  to  indicate  a  combination  of  two  or  more  elements,  the  symbols  re- 
presenting such  elements  are  simply  arranged  side  by  side;  sulphuric  acid,  a 
compound  of  one  equivalent  of  sulphur  and  three  equivalents  of  oxygen,  is 
represented  by  S03;  starch,  containing  twelve  equivalents  of  carbon,  ten  equiva- 
lents of  hydrogen,  and  ten  equivalents  of  oxygen,  is  written  ClaH10010. 

Some  compounds,  however,  are  denoted  by  particular  symbols;  thus,  cyanogen 
(CaN)  is  usually  represented  by  Cy,  tartaric  acid  (CSH4010)  by  T,  oxalic  acid 
(C203)  by  0,  &c.  In  the  last  two  cases,  of  organic  acids,  the  electro-negative 
mark  (-)  is  used  as  the  sign  of  acidity.  Organic  bases,  in  like  manner,  are  dis- 
tinguished by  the  electro-positive  sign  (+). 

In  writing  a  combination  of  two  or  more  compounds,  they  are  usually  sepa- 
rated by  points  or  commas;  thus,  the  formula  of  sulphate  of  alumina,  composed 
of  alumina  (Ala03)  and  sulphuric  acid  (S03)  is  written  A1303.3S03;  and  alum, 
containing  sulphate  of  alumina,  sulphate  of  potassa,  and  water,  is  expressed  by 
the  formula  KO.S03,A1303.3S03+24HO. 

To  express  more  than  one  equivalent  of  a  compound,  the  elements  of  which 
are  not  separated  by  a  point,  a  large  figure  is  simply  placed  to  the  left  of  the 
compound,  as  in  the  example  of  sulphate  of  alumina;  but  when  the  elements 
are  separated  by  a  point,  the  compound  must  be  inclosed  in  a  parenthesis,  and 
the  coefficient  must  be  placed  outside  and  to  the  left;  thus,  two  equivalents  of 
sulphate  of  alumina  are  expressed  by  2(A1303.3S03). 

1  Urea  (C2H4N202)  is  isomeric  with  cyanate  of  ammonia  (NH4O.C2NO)  and  the  oil  of 
spiraea  (hydride  of  salicyle  C,4H50VH)  with  hydrated  benzoic  acid  (C14H503.HO).     On 
the  other  hand,  cyanic  acid  (C2NO),  fulminic  acid  (C4N202),  and  cyanuric  acid  (C6N303) 
are  polymeric  compounds. 
4 


50  INTRODUCTION. 

The  sign  +  generally  indicates  either  a  state  of  mixture  merely,  or  a  lower 
order  of  combination;  the  expression  KO.S03+BaO.N05  implies  that  sulphate 
of  potassa  is  mixed  with  nitrate  of  baryta.  The  water  contained  in  alum 
exists  in  a  more  loosely  combined  state  than  the  sulphuric  acid  and  alumina. 

The  sign  of  equation  =  is  used  to  imply  that  the  elements  or  compounds 
placed  before  such  sign  would  give  rise  to  those  which  follow  it;  thus,  in  the 
case  of  sulphate  of  potassa  and  nitrate  of  baryta,  sulphate  of  baryta  and  nitrate 
of  potassa  would  be  produced,  and  the  reaction  (as  it  is  termed)  would  be  ex- 
pressed by  the  equation 

BaO.N05+KO.S03=BaO.S03-f-KO.N05. 

In  complicated  reactions,  greater  simplicity  is  often  attained  by  means  of  dia- 
grams, in  which  the  rearrangement  of  the  various  elements  is  indicated  bylines; 
thus,  to  represent  the  preceding  reaction  in  a  diagram  : — 

Nitrate  of  baryta      fBar^a-        ^    -Sulphate  of 


Sulphate  of  potassa  ]  ST?  \   AT.A          . 

[  Potassa_  _\,  Nitrate  of  potassa. 

(A  list  of  symbols  will  be  found  at  §  68.) 


CRYSTALLIZATION.  51 


PHENOMENA  EELATING  TO  THE  PHYSICAL 
CONDITION  OF  BODIES. 


THE  fundamental  principles  of  chemical  philosophy  having  been  explained, 
there  still  remain  to  be  considered,  before  entering  upon  the  special  study  of 
chemical  operations,  certain  phenomena  relating  rather  to  the  physical  condition 
of  bodies,  an  acquaintance  with  which  will  be  found  necessary  to  the  proper 
comprehension  of  their  chemical  history. 


SOLUTION. 

§  20.  SOLUTION  consists  in  the  diffusion  of  one  substance  (whether  solid, 
liquid,  or  gaseous)  through  a  liquid,  in  such  a  manner  as  to  produce  a  homoge- 
neous mass.  This  may  be  the  effect  either  of  true  chemical  combination  or  of 
mechanical  mixture. 

When  solution  depends  upon  the  formation  of  a  chemical  compound,  heat  is 
generally  evolved;  whilst  if  it  be  a  purely  mechanical  process,  either  no  change 
of  temperature  takes  place,  or  a  depression  is  observed. 

In  the  solution  of  hydrate  of  potas^a  (fused  potassa)  in  water,  a  considerable 
amount  of  heat  is  disengaged,  since  the  hydrate  combines  with  the  water; 
whereas  nitrate  of  potassa,  when  dissolved  in  water,  gives  rise  to  a  considerable 
fall  of  temperature. 

When  a  solution  has  taken  up  as  much  of  the  dissolved  body  as  it  is  capable 
of  doing,  the  solution  is  said  to  be  saturated. 

Generally  speaking,  heat  promotes  the  solution  of  solids  and  retards  that  of 
gases ;  but  some  solids  are  less  soluble  at  high  temperatures ;  this  is  the  case 
with  lime,  and  with  sulphate  of  soda. 

If  a  hot  solution  contains  more  of  the  dissolved  body  than,  when  cold,  it 
would  be  capable  of  retaining,  the  excess  of  the  dissolved  body  will  be  deposited 
as  the  solution  cools;  and,  if  it  be  a  solid,  generally  in  the  form  of  crystals,  which 
are  larger  and  more  distinct,  the  more  slowly  they  have  been  deposited. 

Whenever  a  separation  of  a  solid  body  from  a  solution  takes  place,  it  is  termed 
precipitation,  and  the  solid  which  separates  is  called^a  precipitate. 


CRYSTALLIZATION. 

§  21.  CRYSTALLIZATION  is  the  spontaneous  arrangement  of  the  particles  of 
solid  bodies  in  regular  geometric  forms. 

A  tendency  to  such  an  arrangement  is  generally  observed  in  solids  which  are 
gradually  deposited  from  a  state  of  solution,  but  sometimes  in  those  which  have  con- 
densed into  the  solid  from  the  gaseous  form,  or  in  masses  solidified  after  fusion. 

When  the  particles  of  a  solid  substance  are  not  arranged  in  regular  geometric 
forms,  it  is  said  to  be  amorphoits;  when  it  crystallizes  in  two  distinct  forms,  which 
cannot  be  referred  to  the  same  primitive  form,  it  is  termed  dimorphous. 


52  INTRODUCTION. 

If  two  substances  are  found  to  be  capable  of  crystallizing  in  the  same  geometric 
form,  or  in  forms  which  may  be  referred  to  the  same  primitive,  they  are  desig- 
nated isomorphous — a  term  also  applied  to  substances  which,  though  themselves 
incapable  of  crystallizing,  are  found  to  replace  each  other  in  particular  combina- 
tions without  materially  altering  their  crystalline  form.  This  last  sense  of  the 
term  isomorphous,  is  that  in  which  it  is  most  frequently  received,  and  may  be 
illustrated  by  the  three  alkalies,  potassa,  soda,  and  oxide  of  ammonium,  which 
replace  each  other  in  the  class  of  salts  known  as  the  alums,  without  altering 
the  crystalline  form  of  the  latter.  The  alums  are  double  salts,  composed  of  an 
alkaline  sulphate  and  a  sulphate  of  some  basic  sesquioxide,  combined  with  a 
large  amount  of  water  of  crystallization;  the  alums  have  all  the  same  crystal- 
line form.  The  observation  of  this  isomorphism  is  often  useful  in  enabling  us 
to  decide  upon  the  atomic  constitution  of  certain  compounds. 

FORMS  OE  CRYSTALS,  &c. — We  enter  upon  the  subject  of  crystallography  with 
some  considerable  hesitation,  as  it  is  not  within  the  province  of  this  work  to  dis- 
cuss any  subject  belonging  strictly  to  physics;  and,  moreover,  as  crystallography 
may  at  the  present  day  be  regarded  as  forming  of  itself  an  important  branch  of 
natural  science.  ,  Since,  however,  it  is  usual,  and  frequently  of  very  great  im- 
portance, to  pay  some  attention  to  the  physical  structure  of  the  various  solid  com- 
pounds with  which  the  chemist  meets,  both  in  nature  and  in  his  laboratory — 
since  he  is  thereby  frequently  enabled  to  discriminate,  with  the  greatest  nicety 
and  rapidity,  between  different  substances,  or,  at  any  rate,  to  read  therein  some- 
thing concerning  their  nature  which  may  aid  him  considerably  in  his  subsequent 
researches;  and,  as  we  shall  also  repeatedly  make  use  of  certain  crystallographical 
terms  in  the  description  of  elements  and  their  compounds,  we  propose  to  give  as 
brief  and  general  an  outline  of  this  subject  as  we  imagine  will  meet  the  wants  of 
the  student. 

Most  solid  substances  have  a  certain  characteristic  form  in  which  they  crystal- 
lize; this  form  is,  however,  not  always  peculiar  to  themselves,  since  many  sub- 
stances, widely  different  in  their  chemical' character,  crystallize  in  forms  similar 
to  each  other.  We  have  already  made  mention  of  a  property  possessed  by  some 
substances  of  crystallizing  in  two  distinct  forms.  Examples  of  dimorphous  bodies 
are  carbon  and  sulphur. 

If  a  smart  blow  be  applied  to  a  cube  of  rock-salt,  or  a  prism  of  calcareous 
spar,  and  the  smallest  fragments  resulting  from  the  fracture  of  the  two  crystals 
examined,  they  will  be  found  to  be  identical  in  form  with  the  original  masses. 
(The  tendency  possessed  by  crystalline  forms  to  split  in  certain  directions  is  termed 
their  cleavage!)  All  crystals  are  therefore  built  up  of  small  particles  possessing  a 
regular  form,  either  identical  with  that  of  the  crystal  itself,  or  standing  in  some 
simple  relation  to  it.  We  are  not  only  enabled  to  reduce  a  crystal,  by  cleavage, 
to  smaller  forms,  as  already  described,  but  it  is  also  possible,  by  attending  to 
certain  precautions  (§  55),  to  add  to  the  size  of  a  crystal,  without  in  any  way 
altering  its  form.  These  facts,  added  to  certain  optical  properties  possessed  by 
many  crystals,  prove  that  crystalline  bodies  possess  a  certain  regular  structure. 

All  crystalline  forms  exhibit  faces  or  planes;  edges,  or  lines  of  contact  of  two 
planes,  and  points  or  angles,  which  are  formed  by  the  meeting  of  three  or  more 
planes. 

An  imaginary  line  drawn  from  one  angle  to  an  opposite  one,  passing  from  side 
to  side,  or  from  end  to  end,  through  the  centre  of  a  crystal,  is  called  its  axis.  The 
particles  of  a  crystal  may  therefore  be  conceived  to  be  symmetrically  arranged 
round  an  axis  of  this  description.  A  slight  consideration  will  show  that  various 
crystals  may  possess  a  different  numbers  of  axes,  which  have  different  lengths, 
and  cross  each  other  at  different  angles. 

When  a  crystal  is  examined  as  to  its  form,  it  is  held  in  such  a  manner  that 
one  of  the  axes  is  situated  vertically  in  front  of  the  observer's  eye ;  if  the  axis 


FORMS  OF  CRYSTALS.  53 

of  a  crystal  vary  in  length,  the  longest  is  chosen  for  this  vertical  axis;  if  they  are 
equal,  any  one  may  be  chosen.  The  axis  thus  placed,  is  called  the  principal 
axis,  while  the  others  are  called  secondary. 

All  crystalline  forms  may,  according  to  the  nature  of  their  axes,  be  arranged 
in  six  systems.  These  systems  embrace  what  are  called  the  primary  forms  of 
crystals,  from  which  the  secondary  forms  are  produced.  The  meaning  of  the 
latter  term  may  be  explained  in  a  few  words. 

If  a  crystal  be  allowed  to  grow  in  such  a  manner  that  each  plane,  angle,  and 
edge  is  equally  increased,  it  is  self-evident  that,  however,  large  the  crystal  be- 
comes, its  form  will  remain  the  same.  If,  however,  from  some  cause,  only  one 
portion  of  the  crystal  be  added  to  (if,, for  example,  a  crystal  be  not  regularly 
turned  about,  as  directed  at  §  55),  the  form  of  the  crystal  will  undergo  a  change. 
Now,  if  this  alteration  of  the  form  of  a  crystal  be  effected  in  a  certain  regular 
manner,  new  figures  will  result,  which  will  stand  in  a  direct  geometrical  relation 
to  the  form  of  crystal  from  which  they  were  produced.  Such  forms  are  called 
secondary  forms,  belonging,  of  course,  to  the  same  system  as  their  original  or 
primary  form.  It  is  evident  that  a  great  variety  of  forms  may  be  produced  in 
this  way,  by  the  systematic  removal,  to  a  greater  or  less  extent,  of  angles,  edges, 
and  planes. 

We  will  now  confine  ourselves  to  a  brief  description  of  the  principal  forms 
belonging  to  the  six  different  systems,  generally  accepted  in  crystallography. 

I.  The  regular  system  includes  those  crystals  which  have  three  equal  axes,  at 
right  angles  with  each  other. 

The  principal  forms  of  this  system  are  : — 

4.  The  cube,  which  is  inclosed  by  six  equal  square  planes. 

5.  The  regular  octohedron,  inclosed  by  eight  equilateral  triangles. 

6.  The  rhombic  dodecahedron,  inclosed  by  twelve  equal  rhombic  planes. 
In  the  figures,  the  directions  of  the  three  axes  are  shown  by  the  letters  a — a. 


Fig.  4. 


Fig.  5. 


Fig.  6. 


II.  The  square  prismatic  system.  The  crystals  of  this  system  also  have  three 
axes,  which  are  at  right  angles  with  each  other;  one  of  these,  however — the  ver- 
tical axis — is  either  longer  or  shorter  than  the  other  two.  Of  this  system,  the 
principal  forms  are  : — 


Fig.  7.          Fig.  8. 


Fig.  9. 


Fig.  10. 


a — a  principal  axis,     b — b  secondary  axes. 


54 


INTRODUCTION. 


7.  The  right  square,  prism,  of  which  the  secondary  axes  terminate  in  the 
centres  of  the  lateral  planes. 

8.  The  right  square  prism,  of  which  the  secondary  axes  terminate  at  the 
edges  of  the  lateral  planes. 

9.  The  right  square-based  octahedron,  of  which  the  directions  of  the  axes 
correspond  to  those  of  prism  7. 

10.  A  similar  octohedron,  of  which,  however  the  directions  of  the  axes  cor- 
respond to  those  of  prism  8. 

III.  The  crystals  belonging  to  the  right  prismatic  system,  have,  like  those  of  the 
former  systems,  three  axes  at  right  angles  to  each  other;  they  are,  however,  all  of 
unequal  lengths.  This  will  be  observed  in  the  following  forms  of  this  system : — 

11.  The  right  rectangular  prism,  with  the  secondary  axes  terminating  in 
the  centres  of  the  lateral  planes. 

12.  The  right  rhombic  prism,  of  which  the  secondary  axes  terminate  at  the 
edges  of  the  lateral  planes. 

13.  The  rectangular-based  octohedron,  with  axes  corresponding  to  those  of 
prism  11. 

14.  The  right  rhombic-based  octohedron,  with  the  axes  corresponding  to 
those  of  prism  12. 

Fig.  11.          Fig.  12.  Fig.  13.          Fig.  14. 


a>  a, 

a — a  principal  axis,     b — b,  c — c,  secondary  axes. 

IV.  The  crystals  of  the  oblique  prismatic  system  have,  like  the  foregoing,  three 
axes,  but  they  are  no  longer  all  at  right  angles.  The  two  secondary  axes  of  these 
are  at  right  angles,  but  the  principal  axis  is  perpendicular  to  one  of  these,  and 
oblique  to  the  other.  This  system  is  represented  by  the  following  forms,  of 
whjch  the  axes  stand  in  the  same  relation  to  each  other  as  those  of  the  forms 
given  of  the  former  system  : — 

15,  the  oblique  rectangular  prism  ;  16,  the  oblique  rhombic  prism  ;  17,  the 

oblique  rectangular-based  octohedron  ;  18,  the  oblique  rhombic-based  octohedron. 


Fig.  15. 


Fig.  16.          Fig.  17. 


Fig.  18. 


a — a  principal  axis,     b — b,  c — c,  secondary  axes. 

Y.  In  the  crystals  of  this,  which  may  be  called  the  doubly-oblique  prismatic 
system,  all  the  three  axes  are  oblique  to  each  other.  This  system  is  represented 
in  the  figure,  by  two  prisms,  19  and  20,  and  two  octohedra,  21  and  22. 


FORMS   OP   CRYSTALS, 
Fig.  19.  Fig.  20.        Fig.  21. 


55 


Fig.  22. 


a — a  principal  axis,     b — b,  c — c,  secondary  axes. 

VI.  The  rhombohedral  system.  The  forms  of  this  system  differ  considerably 
from  those  of  the  foregoing,  by  containing  four  axes,  instead  of  three.  Of  these 
four,  the  vertical  or  principal  axis  is  perpendicular  to  the  other  three,  which  lie 
all  in  the  same  plane,  are  equal,  and  inclined  to  each  other  at  an  angle  of  60°. 
The  examples  here  given  of  the  forms  belonging  to  this  system  are :  23,  the  regular 
six-sided  prism;  25,  the  rhombohedron ;  24  and  26;  two  species  of  dodecahedra. 


Fig.  23.        Fig.  24. 


Fig.  25.         Fig.  26. 


a — a  principal  axis,     b — b  secondary  axes. 

It  has  been  already  explained  how  the  so-called  secondary  forms  may  be  de- 
rived from  primary  forms ;  the  following  figure,  showing  the  passage  of  the  cube 
to  the  octohedron  may  serve  to  render  this  point  more  intelligible. 


Fig.  27. 


Fig.  28. 


There  is  ane  other  important  class  of  crystals  that  demands  some  slight  expla- 
nation, this  is  the  hemihedral  class.  If  the  alternate  planes  or  faces  of  a  crystal 
be  allowed  to  grow  excessively,  it  will  be  found  that  the  other  planes  gradually 
become  diminished,  and  at  length  they  are  perfectly  obliterated,  a  new  form  of 
crystal  being  the  result.  This  kind  of  action  is  shown  in  the  conversion  of  the 
octohedron  into  the  tetrahedron. 


Fig.  30. 


Fig.  31. 


Fig.  32. 


56  INTRODUCTION. 

The  foregoing  statements  will  at  once  convince  the  student  of  the  great  im- 
portance of  possessing  some  means  of  submitting  crystals  to  an  accurate  measure- 
ment, in  order  to  ascertain  to  what  system  they  belong.  Several  instruments 
have  been  constructed  for  measuring  the  angles  of  crystals ;  they  have  received 
the  name  of  goniometers. 

WATER  OF  CONSTITUTION  AND  CRYSTALLIZATION. — Crystalline  salts  fre- 
quently contain  water  in  two  different  states  of  combination,  which  are  distin- 
guished by  the  terms  water  of  constitution  (or  sometimes  basic  water,  or  water 
of  hydratiori),  and  water  of  crystallization. 

The  water  of  crystallization  is  much  less  intimately  combined  with  the  salt 
than  the  water  of  constitution,  and  is  therefore  more  easily  expelled. 

In  order  to  exhibit  this  difference,  the  water  of  hydration  is  usually  expressed 
by  its  chemical  formula  (HO),  and  is  incorporated  in  the  formula  of  the  salt ; 
whilst  the  water  of  crystallization  is  represented  by  the  mechanical  symbol  (Aq), 
and  is  connected  with  the  formula  by  the  sign-f ,  as  will  be  seen  in  the  exam- 
ples given  below. 

The  reason  for  applying  the  term  water  of  crystallization  to  that  portion  of  the 
combined  water  which  is  most  easily  expelled,  is  found  in  the  influence  which  it 
exerts  upon  the  crystallization  of  the  salt.  Most  salts  containing  water  of  crys- 
tallization lose  their  crystalline  form  upon  its  expulsion,  and  crumble  to  an  amor- 
phous powder. 

This  water  of  crystallization  is  retained  by  different  salts  with  very  different 
degrees  of  force,  but  rare  are  the  cases  where  it  cannot  be  entirely  expelled  at  a 
temperature  of  212°  R  (100°  C.) 

Many  salts  lose  this  water  by  simple  exposure  to  air  of  ordinary  dryness ;  and 
as  the  escape  of  the  water  is  usually*  attended  by  a  peculiar  opaque  appearance 
assumed  by  the  surface  of  the  crystals,  such  salts  are  said  to  be  efflorescent.  The 
ordinary  phosphate  of  soda  (2NaO.HO.P05+24Aq)  and  the  sulphate  of  soda 
(NaO.S08+10Aq)  are  familiar  examples  of  such  salts. 

Other  salts  effloresce  only  in  perfectly  dry  air,  or  in  vacuo,  as  will  be  more  fully 
explained  in  the  section  upon  desiccation. 

Those  salts  which  do  not  effloresce  at  ordinary  temperatures,  generally  do  so 
when  exposed  to  a  moderate  degree  of  heat,  and  in  most  cases  lose  the  whole  of 
their  water  of  crystallization  at  212°  F.  (100°  C.);  this  loss  of  water  is  fre- 
quently attended  with  an  alteration  in  the  color  as  well  as  in  the  form  of  the 
salt;  the  well-known  blue  crystals  of  sulphate  of  copper  (blue  vitriol,  CuO.  S03, 
HO+4Aq)  for  example,  crumble  down  to  a  nearly  white  powder  when  heated 
in  the  water-bath,  the  four  equivalents  of  water  of  crystallization  being  thus  eli- 
minated. 

A  salt  is  sometimes  met  with  in  crystals  of  different  form,  containing  different 
quantities  of  water  of  crystallization. 

Thus,  ordinary  borax  (biborate  of  soda,  Na0.2B08+10Aq)  crystallizes  in 
six-sided  prisms,  containing,  as  indicated  by  the  formula,  ten  equivalents  of  wa- 
ter of  crystallization,  whilst  octohedral  borax  contains  but  five  equivalents. 

Again,  the  common  phosphate  of  soda  (2NaO.HO.P05)  crystallizes  in  two 
different  forms,  containing  respectively  14  and  24Aq,  whilst  two  forms  of  the 
sulphate  of  soda  are  known  with  8  and  10  equivalents  of  water. 

When  heat  is  applied  to  salts  containing  water  of  crystallization,  they  some- 
times dissolve  in  this  water,  undergoing,  as  it  is  termed,  the  aqueous  fusion ;  when 
the  water  of  crystallization  has  been  expelled,  they  generally  become  solid  again, 
and  undergo  the  true  or  igneous  fusion  when  the  temperature  is  still  further  in- 
creased. The  behavior  of  phosphate  of  soda  (2NaO.HO.P05+24Aq),  when 
heated,  affords  a  good  example  of  this. 

Crystals  destitute  of  water  of  crystallization,  do  not,  of  course,  undergo  the 


DIFFUSION  OF  GASES. 


57 


aqueous  fusion;  when  such  crystals  (as,  for  example,  chloride  of  sodium,  NaCl, 
nitrate  of  potassa,  KO.N05)  are  heated,  the  water  mechanically  inclosed  within 
them  is  converted  into  vapor,  which,  in  its  endeavor  to  escape,  splits  the  crystal 
asunder,  producing  a  cracking  sound,  which  has  gained  for  this  phenomenon  the 
name  of  decrepitation. 

The  water  of  constitution  contained  in  salts  is,  as  already  mentioned,  not  so 
easily  expelled  as  the  water  of  crystallization,  and  cannot  generally  be  separated 
without  some  alteration  in  the  chemical  nature  of  the  salt,  whence  this  form  of 
combined  water  has  received  its  present  designation.  The  alteration  in  the  na- 
ture of  the  salt  sometimes  amounts  merely  to  a  diminution  of  solubility,  some- 
times to  a  true  chemical  decomposition  and  production  of  a  new  compound. 

The  green  crystals  of  sulphate  of  iron  (green  vitriol)  have  the  composition 
FeO.S03.HO+6Aq;  if  these  are  heated  to  212°  F.  the  6  Aq  are  expelled, 
and  the  salt  falls  to  a  nearly  white  powder;  but  if  the  crystals  are  heated  to 
redness,  the  whole  of  the  water  is  expelled,  and  FeO.S03,  almost  insoluble  in 
water,  remains.  Again,  if  the  crystals  of  phosphate  of  soda  (2NaO.HO.P05 
-}-24Aq)  are  heated  to  redness,  they  lose  their  twenty-five  equivalents  of  water, 
and  become  2NaO.P05,  a  totally  different  salt  from  the  former,  and  called 
pyrophosphate  of  soda.  (The  constitutional  water,  in  this  instance,  should 
strictly  be  called  basic  water.) 

The  water  of  constitution  may  also  sometimes  be  replaced  by  some  neutral 
salt,  thus  giving  rise  to  the  production  of  a  double  salt ;  for  instance,  in  the  sul- 
phate of  iron  (FeO.S03.HO-{-6Aq),  the  one  equivalent  of  water  of  constitu- 
tion may  be  replaced  by  sulphate  of  potassa  (KO.S03),  and  the  formula  of  the 
double  sulphate  of  potassa  and  oxide  of  iron  is  FeO.S03,KO.S03+6Aq. 


DIFFUSION   OF   GASES. 

§  22.  The  diffusive  power  of  gases  is  the  tendency  which  they  possess  to  inter- 
mix, even  through  very  small  apertures,  and  in  opposition  to  the  force  of  gravi- 
tation.    Thus,  if  two  bottles  be  filled,  the  one  with  hydrogen, 
the  other  with  carbonic  acid  gas,  which  is  many  times  heavier,     Fig.  33. 
and  be  connected  by  means  of  a  glass  tube,  however  narrow,  and 
arranged  even  so  that  the  heavier  gas  must  rise  if  it  mix  with 
the  lighter,  we  find  that,  after  a  few  hours,  the  two  gases  will  be 
contained  in  both  bottles  in  the  same  proportions.     The  rate  of 
diffusion  of  a  gas  represents  the  velocity  with  which  it  passes 
through  very  minute   apertures,  as   compared  with  the  rate  of 
passage  of  some  other  standard  gas  through  apertures  of  the  same 
size. 

This  diffusion  of  gases  takes  place  through  all  porous  bodies  (e.  g. 
dry  membrane,  plaster  of  Paris,  dry  cork,  unglazed  earthenware), 
and  through  the  smallest  crevices;  so  that  gases  should  never  be 
kept  for  any  length  of  time  in  cracked  vessels,  or  in  jars  closed 
with  plain  corks. 

Gases  differ  very  considerably  in  their  rates  of  diffusion,  which 
vary  inversely  as  the  square  roots  of  the  densities  (specific  gravi- 
ties) of  the  gases.  Thus,  the  densities  of  hydrogen  and  oxygen 
are  to  each  other  as  1  :  16 ;  the  square  roots  of  these  numbers  are 
respectively  1  and  4 ;  the  rates  of  diffusion  will  therefore  be  as  4 
(for  hydrogen)  :  1  (for  oxygen). 

The  superior  diffusive  power  of  hydrogen  over  air  may  be  well 
illustrated  by  means  of  Graham's  diffusion  tube,  which  consists  of 


LIB*4*. 
/>V     OF  THE  ^ 

|  -UNIVERSITY) 

V  f 


58  INTRODUCTION. 

a  glass  tube  (Fig.  33),  about  half  an  inch  in  diameter  and  twelve  inches  long, 
closed  at  one  end  with  a  plate  of  plaster  of  Paris,  of  about  one-sixth  of  an  inch 
in  thickness ;  if  this  tube  be  perfectly  dried,  filled  with  hydrogen,  and  its  open 
extremity  immersed  in  water,  the  gas  will  diffuse  through  the  pores  of  the  plas- 
ter so  much  more  rapidly  than  air  will  enter,  that  the  water  may  be  seen  to  rise 
in  the  tube  to  the  height  of  several  inches. 

This  law  of  diffusion  appears  to  afford  an  explanation  of  the  uniform  com- 
position of  atmospheric  air,  and  of  the  non-accumulation  of  injurious  impurities 
in  the  atmosphere. 


CHEMICAL  MANIPULATION. 


APPARATUS  NECESSARY  FOR  THE  PREPARATION 

OF  OASES. 

THE  conditions  for  the  evolution  of  gases  are  various.  Some  are  evolved  at 
common  temperatures,  while  others  require  various  degrees  of  heat  to  effect  their 
disengagement.  The  form  of  apparatus  employed  for  their  preparation  varies 
considerably  in  consequence. 

APPARATUS   FOR   THE   DISENGAGEMENT   OF   GASES   WITH   THE 

AID   OF   HEAT. 

§  23.  Iron  bottles,  such  as  those  in  which  mercury  is  imported,  having  a  piece 
of  iron  pipe  about  two  feet  in  length  firmly  screwed  into  the  opening,  are  gene- 
rally used  when  the  temperature  required  to  disengage  a  gas  amounts  to  a  red 
heat,  as  in  the  preparation  of  oxygen  from  binoxide  of  manganese.  The  most 
convenient  mode  of  conducting  the  gas  disengaged  in  this  apparatus  to  its  reser- 
voir, is  by  fixing  a  piece  of  wide  glass  tube  into  the  end  of  the  iron  pipe,  by 
means  of  a  cork,  in  the  manner  to  be  presently  described,  and  tying  upon  this  a 
piece  of  vulcanized  Indian-rubber  tubing  of  sufficient  length. 

Gases  which  are  obtained  by  distillation  are  conveniently  prepared  in  tubulated 
glass  retorts;  the  form  of  apparatus  being,  in  fact,  almost  the  same  as  that 
employed  in  ordinary  distillation,  to  be  described  under  that  head;  the  retort  is 
connected,  in  the  ordinary  manner,  with  such  purifying  or  collecting  apparatus 
as  circumstances  may  require. 

The  apparatus  most  generally  in  use  for  the  preparation,  on  a  moderate  scale, 
of  gases  requiring  heat  for  their  disengagement,  consists  of  flasks  of  various 
descriptions,  appropriately  fitted  with  corks,  bent  tubing,  and  caoutchouc  con- 
nectors, to  the  purifying  and  collecting  apparatus. 

It  will  be  necessary  to  enter  a  little  into  detail  respecting  the  various  portions 
of  this  kind  of  apparatus,  and  the  mode  of  constructing  it. 

FLASKS. — Various  forms  of  flasks  are  used  as  gas-generators,  but  those  most 
commonly  employed  are  the  Florence  oil  or  wine  flasks,  and  the  thin  flat- 
bottomed  German  flasks,  the  necks  of  which  latter  terminate  in  a  thick  rim  of 
glass.  The  priacipal  advantage  of  the  former  is  their  cheapness ;  in  many  cases 
the  oil-flasks  are  far  too  small ;  the  wine-flasks  (which  are  not  so  frequently  met 
with)  are  generally  very  narrow  in  the  neck,  which  is  a  serious  obstacle  to  their 
use  in  cases  where  it  is  necessary  to  introduce  a  safety  or  funnel-tube  in  addition 
to  the  conducting-tube. 

In  selecting  Florence  flasks  for  use,  particular  attention  should  be  paid  to  the 
following  precautions :  that  they  be  thin  at  the  bottom,  and  as  uniform  in  sub- 
stance as  possible;  that  they  contain  no  air-bubbles  of  any  considerable  size; 


60        APPARATUS  FOR  THE  PREPARATION  OF  GASES. 

and  that  the  necks  be  wide,  tolerably  uniform  in  bore  throughout,  and  stout  at 
their  orifices.1  It  is  advisable  to  fuse  the  sharp  edges  of  the  mouths  of  these 
flasks,  by  very  gradually  heating  them  in  the  blowpipe-flame. 

The  flat-bottomed  Florence  flasks  are  of  but  little  use  in  the  disengagement  of 
gases,  as  they  are  generally  very  thick  at  the  bottom,  and  consequently  unable 
to  stand  any  sudden  change  of  temperature. 

In  selecting  the  flat-bottomed  hard  glass  flas7cs,  the  above  precautions  should 
likewise  be  attended  to ;  the  necks  of  these  should  not,  however,  be  chosen  too 
wide,  as  they  frequently  exceed  those  of  the  Florence  flasks  so  much  in  width 
as  to  render  it  difficult  to  fit  them  properly  with  corks. 

CORKS. — The  conducting- funnel  and  safety- tubes  are  fitted  into  the  flasks  by 
means  of  corks.  Since,  in  the  preparation  of  gases,  it  is  of  the  utmost  import- 
ance that  the  apparatus  should  be  perfectly  tight,  great  care  must  be  bestowed 
upon  the  choice  of  proper  corks.  They  should  be  compact,  and  at  the  same 
time,  elastic ;  or  such  as  will  admit  of  being  rendered  so  by  pressure,  without 
splitting. 

TUBING. — In  selecting  tubing  for  the  various  connecting  portions  of  an  appa- 
ratus of  this  description,  care  should  be  taken  that  its  diameter  be  such  as  to 
admit  of  the  introduction  of  the  requisite  number  of  tubes  into  the  cork,  at  a 
proper  distance  from  each  other,  and  that  the  thickness  of  the  glass  is  in  such 
proportion  to  its  diameter,  that  it  may  be  bent  in  a  proper  manner,  and  possess 
sufficient  strength  to  resist  the  amount  of  pressure  applied  in  introducing  it  into 
the  corks. 

SAFETY-TUBES  are  essential  portions  of  all  apparatus  for  generation  of  gases. 
The  most  simple  form  of  safety-tube  consists  of  a  long  piece  of  tubing 
Fig.  34.  introduced  through  the  cork,  into  the  flask  or  generating  vessel,  so  that 
the  lower  extremity  may  be  covered  to  about  an  inch  by  the  liquid 
contained  therein,  and  protruding  above  the  flask  to  the  height  of  from 
one  to  three  feet,  or  even  higher,  according  to  the  pressure  to  which 
the  liquid  in  the  vessel  is  liable  to  be  subjected  by  the  generation  of 
the  gas. 

The  length  of  such  tubes  is  sometimes  very  inconvenient ;  in  which 
case,  however,  they  may  be  advantageously  replaced  by  Welter's  safety- 
tube  (Fig.  34),  in  which  a  small  quantity  of  mercury  or  other  liquid  is 
made  to  act  as  a  valve.     It  is  inserted  into  the  cork  of  the  flask  or  ves- 
sel, so  as  to  protrude  into  the  latter  about  half  an  inch.     The  funnel- 
tube,  to  be  presently  described,  also  acts,  simultaneously,  as  a  safety-tube. 
When  but  little  or  no  liquid  is  used  in  the  preparation  of  a  gas,  the 
operator  may  substitute  for  the  above  safety-tube,  a  piece  of  tubing  of 
about  five  or  six  inches  in  length,  passing  a  little  way  through  the  cork 
into  the  generating  vessel,  and  closed  at  the  other  extremity  by  means 
of  a  small  caoutchouc  cap,  or  plug  of  cork,  which  is  easily  forced  off  when  the 
pressure  becomes  excessive,  or  may  be  removed  by  the  operator,  if  absorption 
takes  place. 

FUNNEL-TUBES  should  be  selected  of  sufficient  length  to  be  introduced  so  far 
into  the  generating  vessel  as  to  be  covered  by  the  liquid  inside  to  the  extent  of 
about  half  an  inch,  and  to  protrude  some  distance  beyond  the  cork,  as  above 
mentioned. 

§  24.  METHOD  OF  FITTING  UP  APPARATUS  FOR  THE  GENERATION  OF 
GASES. — It  now  becomes  necessary  to  give  some  description  of  the  manner  in 
which  an  apparatus  of  this  kind  should  be  constructed ;  the  directions  will  be 

1  A  good  method  of  removing  the  oil  from  Florence  flasks  is  to  boil  a  strong  solution 
of  common  carbonate  of  soda  in  them  for  some  time,  and  afterwards  to  wash  them 
repeatedly  in  water. 


APPARATUS  FOR  THE  PREPARATION  OP  GASES. 


61 


given  in  general  terms,  so  as  to  be  applicable  to  the  fitting  up  of  any  apparatus 
consisting  of  glass  vessels,  tubes,  and  corks. 

OPERATIONS  WITH  THE  CORKS. — In  fitting  a  cork  to  a  vessel,  it  should  be 
first  softened,  either  by  pressure  between  the  fingers,  or,  if  large,  by  rolling  it 
under  the  foot,  or  by  gentle  hammering.  In  order  that  the  apparatus  may  be 
tight,  it  is  necessary  that  the  cork  thus  softened  should  require  a  gentle  pressure 
for  its  insertion,  and  be  slightly  conical.  In  case  it  is  somewhat  too  large  for 
insertion,  its  size  may  be  reduced  either  by  cutting  with  a  very  sharp  knife,  or 
by  filing  a  portion  off  by  means  of  a  fine  rasp.  Great  care  must,  however,  be 
taken  in  these  operations,  that  the  conical  form  of  the  cork  be  perfectly  pre- 
served, or  it  will  be  impossible  to  make  it  fit  'tightly.  In  fitting  a  cork  into  a 
flask,  tube,  or  bottle,  these  must  invariably  be  held  close  to  the  aperture ;  as 
otherwise,  should  the  pressure  applied  in  introducing  the  cork  be  so  great  as  to 
break  the  glass,  the  most  serious  consequences  to  the  operator  may  result.  It 
is,  indeed,  always  most  prudent  to  hold  the  glass  apparatus  in 
a  cloth  during  this  operation.  Fig.  35. 

Perforations  must  next  be  made  in  the  corks,  for  the  introduc- 
tion of  the  necessary  tubes.  The  cork  is  pierced  in  the  proper 
place,  by  means  of  a  small  raf-tailjile,  care  being  taken  to  bore 
it  straight  through;  the  size  of  the  hole  may  be  then  increased 
to  any  extent  by  filing,  and  substituting  a  larger  file  as  the 
aperture  increases. 

In  order  to  obtain  a  perforation  of  equal  bore  throughout,  it 
is  necessary  to  introduce  the  file  alternately  at  the  opposite  ends 
of  the  cork.  A  very  convenient  implement  for  making  these  per- 
forations is  the  cork-borer  (Fig.  35),  particularly  when  large 
holes  are  required ;  great  care  must,  however,  be  taken  in  boring 
them,  to  maintain  the  borer  in  a  perfectly  straight  direction. 
When  the  cork  is  very  thick,  it  is  advisable  to  bore  half  through 
on  the  one  side,  and  then  to  draw  out  the  borer  and  complete  the 
perforation  in  the  proper  place  from  the  other  side.  Should  the 
perforation  required  not  correspond  in  size  to  any  of  the  cork- 
borers  at  hand,  the  next  size  smaller  should  be  chosen,  and  the 
perforation  afterwards  increased  to  the  proper  dimensions  by 
means  of  a  rat-tail  file.  When  more  than  one  perforation  has  to 
be  made  in  a  cork,  care  must  be  taken  that  the  holes  be  perfectly 
parallel,  and  that  a  partition  of  cork  of  sufficient  thickness  be 
left  between  them;  likewise,  that  the  perforations  are  not  made 
too  close  to  the  side  of  the  cork.  If  these  precautions  are  not 
attended  to,  the  cork  is  easily  torn  and  rendered  unfit  for  use 
on  inserting  the  tube,  or  on  fitting  it  into  the  vessel. 

§  25.  OPERATIONS  WITH  TUBING. — A  piece  of  tubing  of  proper  bore  and 
diameter  having  been  selected  for  use,  the  first  operation  to  be  performed  with  it, 
is  that  of  cutting  it  into  lengths  for  the  various  portions  of  the  apparatus.  To 
this  end,  a  deep  mark  is  made  in  the  glass,  by  means  of  a  sharp  three-edged  file, 
at  the  spot  where  the  tube  is  to  be  divided,  and  it  may  then  be  broken  with  a 
jerk.  Should  the  tube  be  rather  large  and  thick,  it  becomes  necessary  to  con- 
tinue the  file-mark  completely  round  the  glass.  It  is  very  difficult  to  cut  off 
large  tubes  smoothly  with  the  file  alone;  sometimes  the  file-mark  may  be  con- 
tinued into  a  crack  with  a  redhot  iron,  and  led  round  the  tube.  Another  plan 
is  to  clasp  the  tube  (where  it  is  marked)  with  an  iron  wire,  bent  into  the  form 
of  a  hook,  and  heated  to  bright  redness.  If  the  hot  glass  be  then  moistened 
with  water,  a  crack  is  produced,  which  may  be  afterwards  led  round  the  tube. 

The  tube  thus  cut  into  lengths,  now  requires  to  be  bent  in  order  to  receive 
the  proper  form  for  the  necessary  conducting  tubes.  For  all  ordinary  gas-appa- 


62 


APPARATUS  FOR  THE  PREPARATION  OP  GASES. 


ratus,  the  tube  has  to  be  bent  at  right  angles;  but  for  syringe-bottles,  small  tube- 
apparatus,  &c.,  it  requires  bending  at  more  or  less  acute  angles;  the  mode  of 
manipulating  is,  however,  in  all  cases  the  same. 

For  ordinary,  and  even  for  tolerably  hard  glass  tubing,  provided  it  be  not 
very  large  or  thick,  a  simple  spirit-lamp,  or  bat's-wing  gas-jet,  may  be  used  as  the 
source  of  heat.  The  tube  is  supported  on  each  side  of  the  portion  to  be  heated, 
and  held  over  the  flame  for  a  short  time,  being  turned  round  continually,  in 
order  that  it  may  become  uniformly  heated,  and  also  moved  slightly  backwards 
and  forwards  so  as  to  heat  a  sufficient  surface.  When  the  tube  has  become 
thoroughly  heated,  it  is  introduced  into  the  upper  portion  of  the  flame,  and  con- 
tinually moved  about  as  before  until  it  is  soft  to  the  touch,  and  has  been  uni- 
formly heated  to  the  length  of  about  an  inch,  or  even  more,  if  a  very  round 
bend  is  required;  by  a  gradual  pressure,  the  requisite  inclination  is  then  given. 
The  principal  precautions  to  be  observed  in  bending  tubes,  are :  not  to  have  the 


Fig.  36. 


Fig.  37. 


glass  too  soft,  and  to  heat  it  uniformly,  or  the  bend  may  become  distorted  and  flat- 
tened at  the  convex  portion  (Fig.  36) ;  to  give  no  other  than  a  downward  direction 
to  the  hand,  so  that  the  two  extremities  of  the  tube  remain  in  corresponding  direc- 
tions ;  to  heat  a  sufficient  length  of  the  tube,  so  that  the  bend  may  not  be  at  a  sharp 
angle,  but  round  (Fig.  37);  to  apply  only  a  very  slight  pressure  in  bending,  other- 
wise, as  soon  as  the  tube  becomes  too  cool  to  yield,  it  will  snap.  If  a  very  round 
bend  is  required,  one  portion  of  the  glass  must  be  bent  first  as  far  as  admissible, 
without  affecting  the  bore  of  the  tube  or  distorting  it;  the  neighboring  portions 
are  then  heated,  and  the  bend  continued  in  the  same  manner  until  the  requisite 
curve  is  attained.  Very  thin  tubes  must  always  be  bent  very  round,  or  else  the 
convex  portion  of  the  bend  is  certain  to  become  flattened,  and  so  thin  as  to  be 
very  fragile  when  cool,  and  the  concave  portion  will  bend  in  folds,  and  become 
otherwise  distorted.  If  gas  is  at  hand/,  the  ordinary  fish-tail  burner  affords  a 
most  convenient  flame  for  making  round  bends,  as  a  large  surface  of  tube  may 
be  heated  by  it  at  one  time.  Unless  the  tube  has  been  heated  too  powerfully, 
no  difficulty  will  be  found  in  removing,  when  cool,  any  carbon  that  may  have 
been  deposited  upon  it  by  the  gas.  Should  the  tube  to  be  bent  be  of  larger 
dimensions,  and  consist  of  glass  not  easily  fusible,  the  table  or  the  Herapath 
mouth-blowpipe  must  be  employed  for  heating  it,  the  same  precautions  being 
observed  as  above  directed.1 

Before  introducing  tubes  into  the  corks,  it  is  necessary  to  round  the  sharp 
edges  of  the  extremities  of  the  former,  which  would  otherwise  cut  and  injure  the 

1  Should  the  bend  required  be  so  near  one  extremity  of  the  tube  as  to  preclude  the 
possibility  of  supporting  the  short  end  with  the  fingers,  or  should  it  be  even  at  the  very 
extremity,  the  force  necessary  on  this  side  must  be  applied  by  pressing  against  the  glass 
with  an  iron  rod ;  the  latter  should,  however,  not  be  applied  until  the  moment  that  the 
curvature  is  to  be  made,  nor  retained  in  contact  with  the  glass  so  long  as  to  reduce  its 
temperature  below  the  point  of  softness,  as  there  would  be  great  risk  of  cracking  the 
glass  under  those  circumstances. 


APPARATUS  FOR  THE  PREPARATION  OF  GASES.  63 

perforations  prepared  for  their  reception.  This  is  effected  by  fusing  the  extremi- 
ties, either  in  the  flame  of  an  ordinary  lamp  or  by  the  blowpipe.  This  operation 
requires  considerable  care,  on  account  of  the  great  facility  with  which  tubes  crack 
at  the  extremities.  It  is  necessary  first  to  heat  the  tube  gradually,  as  directed 
above,  to  the  extent  of  about  an  inch  from  the  termination,  and  to  remove  it 
slowly  from  the  flame  until  the  extreme  end  only  remains  therein.  As  soon  as 
the  edge  becomes  faintly  redhot,  the  tube  should  be  entirely  removed,  as  other- 
wise it  will  contract  at  the  extremity,  which  is  sometimes  very  inconvenient. 
After  having  heated  a  tube,  the^  operator  must  be  careful  to  avoid  placing  the 
heated  portion  upon  any  cold  surface,  such  as  the  table,  until  it  has  cooled  down 
considerably.  The  force  applied  in  pushing  the  tube  into  the  cork  must  be  very 
gradual  and  gentle;  the  best  plan  is  to  screw  it  in;  it  is  also  advisable,  when 
the  tubes  fit  rather  tightly  in  the  perforations,  or  when  the  former  are  rather 
large,  to  grease  them  slightly  at  the  extremity  first  introduced. 

When  the  tubes  are  properly  inserted,  the  cork  is  fitted  into  the  vessel  with 
great  care;  it  being  held  firmly  between  the  thumb  and  two  first  fingers,  and 
screwed  round,  a  gradual  downward  pressure  being  simultaneously  applied. 

The  cork  having  been  thus  pressed  into  the  vessel  as  far  as  possible,  it  is  re- 
quisite to  ascertain  whether  the  fitting  is  air-tight.  Should  the  cork  contain 
more  than  one  tube,  it  is  necessary,  in  order  to  do  so,  to  close  the  exterior  open- 
ings of  all  but  one.  The  mouth  is  then  applied  to  the  open  tube,  a  portion  of 
the  air  sucked  out  of  the  vessel,  and  the  tongue  immediately  placed  against  the 
opening.  If  the  apparatus  is  tight,  the  tongue  will  be  forced  into  the  aperture. 
Or,  instead  of  sucking  out  the  air,  an  extra  portion  may  be  forced  into  the  vessel 
from  the  mouth,  and  the  tongue  then  pressed  against  the  opening  to  prevent  its 
escaping  from  that  quarter.  If  there  be  any  leakage  in  the  vessel,  the  air  will 
be  heard  to  issue  from  the  place  at  which  the  leakage  exists,  and  the  pressure 
against  the  tongue  will  gradually  diminish.  By  the  latter  test,  the  precise  spot 
at  which  the  apparatus  is  defective  may  be  easily  ascertained. 

It  is  always  preferable,  if  possible,  to  fit  up  an  apparatus  perfectly  air-tight  with 
good  corks  alone;  should  this,  however,  not  be  practicable  (which  is  frequently 
the  case  when  the  corks  are  large,  or  the  openings  of  the  vessels  not  perfectly 
round),  recourse  must  be  had  to  luting. 

§  26.  LUTES. — Various  substances  may  be  employed  as  luting  to  corks.  The 
most  convenient  are,  almond-paste,  linseed-meal  (or  a  mixture  of  both),  white- 
lead,  and  plaster  of  Paris.  If  the  leakage  of  a  cork  be  but  slight,  and  in  the 
substance  of  the  cork  itself,  it  may  be  stopped  by  the  application  of  a  solution  of 
sealingwax  in  spirits  of  wine,  which  penetrates  into  and  fills  up  the  small  pores. 
But  if  the  leakage  be  found  to  exist  at  any  point  where  the  cork  touches  the 
glass,  it  is  advisable  to  cover  the  whole  cork  with  one  of  the  lutes  above  men- 
tioned. The  compactness  and  adhesiveness  of  linseed  and  almond  lute  is  much 
increased  by  the  addition  of  a  little  alkali  to  the  water  with  which  the  meal  is 
mixed.  It  is  also  advantageous  to  dissolve  a  small  portion  of  glue  in  the  water 
employed  in  making  plaster  of  Paris  luting. 

If  the  gas  to  be  generated  may  be  at  once  collected,  without  undergoing  any 
purification,  the  apparatus  generally  consists  of  a  flask  containing,  tightly  fitted, 
by  means  of  a  cork,  a  funnel  or  safety-tube,  and  a  delivery-tube,  which  last  is 
either  bent  twice  downwards  (the  short  end,  which  fits  into  the  cork,  at  a  right 
angle,  and  the  long  end  at  a  more  or  less  obtuse  angle) ;  or  it  is  bent  once,  in 
the  form  of  the  siphon,  the  bend  being  a  very  round  one,  and  the  short  arm 
fixed  into  the  cork. 

If  the  gas  is  to  be  collected  over  a  pneumatic  trough,  the  long  end  of  the  tube 
is  bent  upwards  at  the  extremity,  at  an  angle  of  about  65°.  The  same  form  of 
tube  may  be  used  if  the  gas  is  to  be  collected  in  gas-holders ;  but  it  will  be 


64  PURIFICATION   OP   GASES. 

found  far  more  convenient  to  shorten  the  delivery-tube,  and  attach  it  to  a  piece 
of  vulcanized  Indian-rubber  tubing  of  sufficient  length. 

Very  frequently,  the  gases  require  purification  previously  to  collection  or  use  j 
in  that  case,  the  long  arm  of  the  delivery-tube  is  likewise  bent  at  right  angles, 
and  connected  with  such  purifying  apparatus  as  will  be  presently  described. 

If  only  a  small  quantity  of  gas  requiring  heat  for  its  disengagement  is  to  be 
prepared,  much  saving  of  time  and  material  is  effected  by  the  use  of  a  test-tube, 
or  very  small  flask,  in  the  place  of  the  larger  flask,  into  which  is  fitted,  by  means 
of  a  perforated  cork,  the  short  arm  of  a  tube  bent  in  the  form  of  a  siphon,  the 
extremity  of  the  long  arm  being  bent  upwards,  as  described  above.  This  little 
apparatus  may  be  conveniently  held  over  a  spirit-lamp  by  means  of  a  test-tube 
holder,  and  requires  no  safety-tube,  as  it  may  be  removed  from  the  water  into 
which  the  delivery-pipe  dips,  the  moment  the  evolution  of  gas  ceases. 

APPARATUS     FOR     THE    GENERATION     OF    GASES     AT    ORDINARY 

TEMPERATURES. 

§27.  When  no,  application  of  heat  is  necessary  to  aid  the  evolution  of  a  gas, 
two  different  forms  of  vessels  may  be  employed  as  generators,  namely,  the 
Woulfe's  bottle,  and  corked  wide-mouthed  bottles. 

THE  WOULFE'S  BOTTLE. — This  very  convenient  piece  of  apparatus  consists 
of  a  bottle  with  two  or  three  separate  openings,  which  may  be  fitted  with  corks 
of  the  ordinary  size.  It  presents  a  great  advantage  over  common  glass  bottles, 
as  two  or  three  tubes  may  be  fitted  into  it  perfectly  air-tight,  with  great  ease. 
When  required  for  generating  gas,  it  need  only  have  two  openings,  one  for  the 
funnel  or  safety-tube,  and  the  other  for  the  delivery-tube.  Great  care  should  be 
taken  that  the  interior  of  the  necks  of  these  bottles  be  perfectly  cylindrical. 
When  Woulfe's  bottles  cannot  be  obtained,  wide-mouthed  bottles  may  be  substi- 
tuted, provided  they  can  be  fitted  with  good  bungs,  to  which  tubes  may  be 
adapted  in  the  manner  before  directed.  The  principal  difficulty  attending  their 
use,  is  that  of  fitting  them  air-tight,  since  large  corks  can  be  but  rarely  obtained 
free  from  flaws,  or  sufficiently  elastic  to  allow  of  proper  softening.  It  is  there- 
fore almost  always  necessary  in  their  use  to  have  recourse  to  luting. 

ARRANGEMENTS   FOR  PURIFYING   GASES. 

§  28.  It  is  frequently  necessary  to  subject  the  gases  to  purification  previously 
to  collecting  them,  in  order  to  remove  trifling  admixtures  of  other  gases,  or  par- 
ticles of  liquids  which  are  frequently  held  in  mechanical  suspension.  This  is 
effected,  either  by  allowing  the  gas  to  pass  through  liquids  of  various  descrip- 
tions, or  over  solids;  the  former  being  contained  in  common  or  in  Woulfe's 
bottles,  properly  fitted  up  with  connecting- tubes,  &c.;  the  latter,  in  tubes  of 
various  forms. 

If  a  Woulfe's  bottle  with  three  necks  is  employed,  the  centre  neck  is  fitted 
with  a  safety-tube,  passing  nearly  to  the  bottom  of  the  vessel ;  into  the  neck  on 
the  one  side  is  fitted  a  tube  bent  at  right  angles,  and  reaching  likewise  nearly  to 
the  bottom  of  the  vessel,  while  "the  third  neck  also  contains  a  tube  bent  at  right 
angles,  but  protruding  into  the  vessel  only  about  half  an  inch  beyond  the  cork. 
With  the  latter  tube  is  connected  (in  a  manner  to  be  presently  described)  either 
another  purifying  vessel,  or  the  delivery-tube.  Should  the  Woulfe's  bottle  only 
have  two  necks,  it  is  advisable  to  fit  into  one  a  piece  of  tube  sufficiently  wide  to 
admit  conveniently  the  delivery-tube  of  the  generator.  This  wide  tube  should 
reach  to  within  about  half  an  inch  of  the  bottom,  and  be  cut  off  obliquely,  or 
slightly  notched  at  the  lower  extremity.  This  not  only  acts  as  a  safety-tube, 
but  also  presents  a  movable  joint,  which  is  very  convenient,  since  the  gene- 


PURIFICATION   OF   GASES. 


65 


rating  apparatus  may  be  turned  about,  or  detached  from  the  remainder,  with 
great  ease. 

Fig.  38.  w-    90 

a 


Fig.  40. 


In  the  absence  of  Woulfe's  bottles,  such  wide-mouthed  bottles  as  have  been 
described  already  may  be  fitted  up  in  a  similar  manner,  and  answer  the  purpose 
very  well,  provided  the  fittings  are  perfectly  tight. 

CONNECTION  BY  MEANS  OF  CAOUTCHOUC  JOINTS. — The  bottles  just  de- 
scribed, having  been  properly  charged  with  the  purifying  agent  (with  which  they 
should  not  be  more  than  half  filled),  are  connected  with  the  generating  appa- 
ratus (and  with  each  other,  if  more  than  one  be  required)  by  means  of  caout- 
chouc connecting  pieces.  These  little  tubes,  which  are  indispensable  to  every 
gas-apparatus,  since  they  impart  to  it  the  necessary  flexibility  to  permit  of  the 
individual  portions  being  moved  about  and  disconnected  from  the  remainder  with 
ease,  are  very  easily  made  of  sheet  caoutchouc,  about  the  tenth  or  twelfth  of  an 
inch  thick,  in  the  following  manner :  A  piece  of  this  caoutchouc  of  the  required 
length  is  gently  warmed,  so  as  to  render  it  per- 
fectly flexible  and  soft;  it  is  then  put  round  a 
piece  of  glass  tubing  or  rod,  not  quite  the  size 
of  the  intended  connector.  The  portions  that 
project  on  either  side  are  pressed  together  so  as 
to  adhere  pretty  .closely ;  they  are  then  cut  off 
with  a  very  sharp  pair  of  scissors.  The  two 
edges  are  thus  obtained  perfectly  clean,  and  ad- 
hering slightly  to  each  other  j  they  are  now 
pressed  closely  together,  care  being  taken  not  to 
soil .  the  cut  edges.  When  this  operation  is 
neatly  and  properly  performed,  the  two  fresh  surfaces  join  accurately  together, 
and  provided  they  are  perfectly  clean,  they  will  adhere  to  each  other  so  firmly, 
that  the  tube  will  tear  quite  as  easily  at  any  other  place  as  at  the  junction.  It 
will  frequently  happen  that  the  connector  will  adhere  so  firmly  to  the  glass  on 
which  it  is  made,  as  to  render  it  extremely  difficult  to  remove  it  without  fracture. 
The  application  of  a  small  quantity  of  flour,  or  other  fine  powder,  to  the  inner 
surface  of  the  caoutchouc  will  prevent  this;  or  should  this  have  been  neglected, 
a  drop  of  water,  held  to  the  one  extremity  of  the  tube,  will  be  immediately 
sucked  in  between  it  and  the  glass,  when  it  may  then  be  removed  with  great 
ease.  Should  there  be  any  slight  defect  in  the  connector,  it  is  well  to  make  a 
5 


66 


COLLECTION    OF   GASES. 


second  one  upon  it,  the  joint  of  which  should  be  made  on  the  opposite  side  to 
that  of  the  inner  one;  the  two  tubes  may  be  made  to  join  at  the  extremities,  by 
clipping  a  small  quantity  off;  this  must  not  be  done  at  one  cut,  as  the  tube 
would  then  be  closed  at  the  ends,  but  the  scissors  should  move  round  the  tube. 

Small  pieces  of  vulcanized  Indian  rubber  tubing,  which  is  now  made  of  almost 
any  dimensions,  answer  the  purpose  of  these  connectors  exceedingly  well ;  they 
may  not  adhere  to  the  glass  quite  so  tightly,  a  defect  which  may,  however,  be 
remedied,  by  tying  them  firmly  upon  the  tubes  at  each  extremity. 

In  connecting  the  various  portions  of  a  gas-apparatus  by  means  of  these  joints, 
the  ends  of  the  glass  tubes  should  be  about  the  sixth  or  eighth  of  an  inch  distant 
from  each  other,  inside  the  connector,  in  order  to  impart  to  the  apparatus  a  proper 
degree  of  flexibility. 

The  tying  of  these  joints  upon  the  glass  tubes,  should  they  need  it,  requires 
some  care.  The  best  material  for  tying  is  silken  cord,  of  moderate  thickness. 
The  force  employed  in  tightened  and  tying  the  cord  round  the  connector  should 
be  very  moderate ;  as,  otherwise,  the  safety  of  the  inclosed  glass  tube  is  endan- 
gered. 

It  is  sometimes  necessary  to  pass  gases  over  solids  of  different  descriptions,  in 
the  state  of  lumps  or  powder.  These  solids  are  contained  in  straight  tubes,  or 
in  tubes  bent  in  the  form  of  the  letter  U.  The  straight  tubes  are  employed  of 
various  diameters  (from  f  to  J  inch)  and  lengths,  according  to  the  substance 
they  are  to  contain,  and  are  fitted  at  each  extremity  with  a  good  cork,  containing 
a  piece  of  narrow  glass  tubing  about  two  inches  in  length,  and  protruding  about 
one-eighth  of  an  inch  through  the  cork;  these  serve  to  connect  them,  with  the 
aid  of  caoutchouc  joints,  to  any  form  of  apparatus.  It  is  advisable  to  place 
against  the  inner  extremity  of  each  narrow  tube  a  small  piece  of  cotton-wool  or 
asbestos,  in  order  to  prevent  any  particles  of  the  solid  in  the  tube  from  being 
carried  out  by  the  current  of  gas.  If  the  solid  is  in  powder,  the  tube  should 
not  be  filled  too  full,  in  order  that  a  small  passage  may  be  formed  between  the 
upper  part  of  the  latter  and  the  powder,  by  knocking  the  tube  lengthwise  upon 
the  table. 

Should  the  solid  used  be  in  the  state  of  lumps,  they  should  be  of  moderate 
size,  smaller  fragments  being  introduced  alternately  with  larger,  in  order  that  no 
large  space  may  be  left  in  the  tube. 

If  it  is  necessary  to  weigh  these  tubes,  it  is  better  to  cut  the  corks  off  even 
with  the  tube,  and  to  coat  them  with  sealingwax,  to  prevent  their  absorbing 
moisture,  and  thus  altering  the  weight  of  the  apparatus. 

The  U-tubes  are  only  employed  for  solids  in  the  state  of  lumps,  and  are  filled 
and  fitted  up  in  the  same  manner  as  the7  straight  tubes,  excepting  that  the  narrow 
tubes  which  are  fitted  into  the  corks  are  not  straight,  but  bent' at  right  angles. 

APPARATUS   FOR   COLLECTING    GASES. 

§  29.  Gases  are,  with  few  exceptions,  collected  over  water,  unless  the  dry  gas 
be  required,  when  mercury  is  employed  in  its  stead. 

When  a  gas  is  prepared  in  any  considerable  quantity,  or  it  is  wished  to  pre- 
serve it  for  any  length  of  time,  it  is  collected  in  gasometers,  or  gas-holders. 

The  former  have  been  almost  entirely  superseded  in  the  laboratory  by  the 
Pepys's  gas-holder;  we  shall,  therefore,  confine  ourselves  to  a  brief  description  of 
the  latter. 

THE  GAS-HOLDER. — This  apparatus  consists  of  a  closed  cylindrical  vessel, 
usually  of  copper,  which  is  surmounted  by  a  circular,  shallow  trough  of  the  same 
diameter,  resting  upon  four  pillars.  Into  the  centre  of  the  bottom  of  the  trough 
is  fixed  a  pipe,  which  passes  through  the  top  of  the  gas-vessel,  and  reaches  nearly 
to  the  bottom. 


COLLECTION   OF   GASES.  67 

% 

Another  pipe  is  introduced  into  the  bottom  of  the  trough,  near  to  the  side, 
which  also  passes  into  the  top  of  the  gas-vessel,  where  it  terminates.  Both  these 
pipes  may  be  opened  or  closed  at  pleasure,  by  means  of  stopcocks  placed  between 
the  trough  and  the  gas-chamber.  Another  stopcock  is  fixed  into  the  side  of  the 
latter,  as  close  as  possible  to  the  top,  and  a  short,  wide  pipe  is  fixed  obliquely 
into  the  side  of  the  chamber  near  the  bottom,  in  such  a  manner  that  the  upper 
edge  of  the  pipe  inside  shall  be  situated  about  half  an  inch  lower  than  the  lowest 
edge  of  the  outer  extremity.  This  pipe  is  closed  by  means  of  a  screw-plug.  In 
addition  to  this,  the  gas-chamber  is  provided  with  a  glass  gauge,  which  serves  to 
indicate  the  amount  of  its  gaseous  contents. 

The  gas-holder  is  filled  with  water  by  closing  the  pipe  at  the  bottom,  opening 
the  three  cocks,  and  then  pouring  water  into  the  trough.  After  the  lateral  cock 
lias  been  closed,  the  last  traces  of  air  are  allowed  to  escape  through  the  water  in 
the  tray.  The  other  stopcocks  are  then  closed,  and  if  the  vessel  be  perfectly 
tight,  the  water  will  not  flow  out  upon  removal  of  the  plug.  This  vessel  is  filled 
with  gas  by  introducing  the  delivery-tube  of  the  apparatus  into  the  pipe  at  the 
bottom ;  the  bubbles  of  gas,  as  they  issue  from  it,  will  displace  the  water.  The 
gas-holder  should  be  so  placed  that  the  water  may  flow  into  a  tub  as  it  is  expelled. 
When  the  gas-bubbles  issue  from  the  pipe,  the  holder  is  quite  full ;  the  delivery- 
tube  is  then  removed,  and  the  pipe  closed  by  means  of  the  screw-plug.  The 
lateral  stopcock  is  used  to  pass  the  gas  through  a  jet;  or  any  other  form  of 
apparatus. 

In  cases  where  a  greater  pressure  of  water  may  be  required  to  force  the  gas 
through  any  apparatus,  a  long  tube-funnel  is  screwed  into  the  opening  of  the 
central  pipe  in  the  trough,  and  kept  full  of  water,  which  subjects  the  gas  in  the 
chamber  to  considerable  pressure. 

Great  care  should  be  taken  to  keep  the  trough  filled  with  water,  and  to  disturb, 
the  moment  it  takes  place,  the  rotary  motion  frequently  acquired  by  the  water 
when  it  descends  rapidly  through  the  pipe,  in  order  to  prevent  the  gas  becoming 
mixed  with  air,  which  is  carried  down  with  the  water  in  considerable  quantity, 
directly  the  above  motion  is  set  up.  A  piece  of  wood  placed  in  the  water  will 
prevent  this  occurring,  by  being  drawn  to  the  centre  the  moment  rotation  takes 
place. 

In  order  to  collect  gas  in  a  jar  from  such  a  gas-holder,  it  is  filled  with  water, 
and  placed  over  the  shorter  tube  in  the  tray ;  the  longer  tube  is  then  opened,  so 
that  the  water  may  exert  some  pressure  upon  the  gas,  which  is  thus  forced  up 
through  the  shorter  tube  into  the  jar. 

GAS-BAGS  AND  BLADDERS. — It  is  frequently  necessary  to  receive  the  gas  in 
bladders  or  bags.  These  are  generally  filled,  as  above  described,  from  the  gas- 
holder. The  size  of  the  bladders  required  is  very  various.  When  the  opening 
of  a  bladder  is  softened  by  means  of  warm  water,  it  may  be  easily  fitted  upon  a 
brass  cap,  which  may  be  screwed  to  a  stopcock.  It  is  necessary  always  to  soak 
bladders  in  warm  water  before  use,  in  order  to  soften  them,  and  thus  to  facilitate 
the  removal  of  the  whole  of  the  air  from  them.  Gas-bags  are  now  generally 
made  of  water-proof  Indian-rubber  material,  the  seams  being  rendered  perfectly 
air-tight  by  means  of  caoutchouc. 

WThen  gases  are  prepared  in  smaller  quantities,  they  are  collected  in  glass 
vessels  of  various  descriptions,  over  water  or  mercury,  contained  in  vessels 
called  pneumatic  troughs. 

THE  PNEUMATIC  TROUGH  is  a  vessel,  generally  of  copper  or  iron,  of  such 
dimensions  that  large  jars  may  be  moved  about  and  filled  with  water  in  it;  vari- 
ous supports  and  shelves  are  fixed,  or  made  so  as  to  slide  backwards  and  forwards 
below  the  surface  of  the  water,  upon  which  the  gas-receivers  may  be  placed.  If 
the  gas  is  soluble  in  water,  it  is  necessary  to  collect  it  over  mercury,  in  a  vessel 
called 


68  COLLECTION    OF   GASES. 

* 

THE  MERCURIAL  TROUGH,  which  is  similar  in  construction  to  the  water- 
trough,  but  very  much  smaller,  on  account  of  the  great  weight  and  expense  of 
mercury.  It  is  usually  made  of  Berlin  porcelain,  cast-iron,  or  wood.  When 
manipulating  with  a  mercurial  trough,  it  is  always  necessary  that  the  latter  should 
stand  in  a  tray,  and  the  mercury  should  not  be  allowed  to  remain  in  the  trough 
when  not  in  use,  but  be  poured  back  into  its  bottle  through  a  strainer. 

The  vessels  used  for  collecting  gases  for  experiments  are  of  various  forms. 
The  principal  are  gas-cylinders,  stoppered  gas-jars,  capped  jars,  and  wide-mouthed 
bottles.  When  the  quantity  of  gas  to  be  operated  upon  is  but  very  small,  it  is 
most  conveniently  collected  in  test-tubes. 

GAS-CYLINDERS  should  be  about  twelve  inches  in  height,  two  to  four  inches 
in  diameter,  of  moderate  thickness,  and  ground  at  the  edges,  so  as  to  admit  of 
being  closed  by  a  plate  of  ground  glass. 

TUBES  of  various  sizes,  plain,  or  graduated,  are  frequently  employed  in  pneu- 
matic experiments  (particularly  in  the  analysis  of  gases).  These  tubes  should  be 
of  a  bore  sufficiently  narrow  to  enable  the  operator  to  close  their  orifice  with  the 
thumb. 

STOPPERED  GAS-JARS  are  useful  of  various  sizes.  They  should  not  be  too 
narrow  in  proportion  to  their  height;  they  are  provided  with  openings  at  the 
top,  into  which  glass  stoppers  are  accurately  ground.  These  jars  may  also  be 
very  tightly  closed  by  means  of  good  corks. 

CAPPED  JARS  are  of  the  same  description  as  the  foregoing,  the  opening  being 
fitted  with  a  brass  cap,  into  which  a  stopcock  may  be  screwed.  These  jars  are 
particularly  convenient  for  transferring  gases. 

STOPPERED  BOTTLES  of  various  sizes,  are  frequently  employed  for  collecting 
gases  and  preserving  them  for  some  time.1  Great  care  should  be  taken  that  the 
stoppers  of  these  bottles  fit  accurately.  In  order  to  prevent  their  becoming  fixed 
in  the  bottles,  it  is  advisable  to  grease  them  slightly  with  tallow  or  pomatum. 
The  same  precaution  should  }>e  adopted  in  the  case  of  stoppered  gas-jars. 

There  are  various  methods  for  loosening  stoppers  when  they  become  fixed  in 
bottles  or  jars.  The  most  simple  is  that  of  tapping  the  stopper  on  each  side 
alternately  with  the  handle  of  a  file  or  chisel,  the  iron  portion  of  the  tool  being 
held  closely  in  the  hand.  Should  they  not  be  loosened  by  this  means,  a  gentle 
heat  may  be  applied  to  the  neck  for  a  few  moments  and  the  tapping  repeated. 
An  excellent  plan  consists  in  fitting  a  wooden  lever  (furnished  with  holes  of  dif- 
ferent sizes)  on  to  the  stopper,  and  exerting  a  gradual  force  until  it  is  loosened. 

In  some  cases,  particularly  if  the  bottle  contain  liquids,  it  is  advantageous  to 
heat  the  neck  by  friction  instead  of  by  flame,  to  accomplish  which  a  piece  of  stout 
cord  is  passed  once  round  the  neck,  and  drawn  to  and  fro. 

If  the  stopper  has  been  fixed  in  a  bottle  by  the  crystallization  of  any  substance, 
it  may  frequently  be  removed  by  placing  a  drop  or  two  of  a  solvent  round  the 
edge  of  the  stopper,  and  allowing  it  to  remain  for  a  day  or  so. 

§  30.  One  or  two  precautions  are  necessary  in  the  preparation  and  collection  of 
gases.  It  is  advisable  that  they  should  not  be  generated  too  rapidly,  as,  when 
purification  is  necessary,  much  of  the  gas  evolved  may  escape  the  action  of  the 
purifier;  and  there  is  also  danger,  when  the  gas  is  evolved  with  effervescence,  of  the 
liquid  in  the  generator  rising  so  high  as  to  pass  over  through  the  conducting-tube 
into  the  gas-holder,  or  any  other  portion  of  the  apparatus  with  which  it  may  be 

1  Stoppered  bottles  filled  with  any  gas  which  it  is  wished  to  preserve  therein  for  some 
time,  should  be  placed  in  an  inverted  position,  with  their  necks  immersed  in  water.  A 
strip  of  stout  vulcanized  Indian-rubber  fixed  tightly  across  the  open  mouth  of  the  bottle 
before  it  is  filled,  and  moved  to  one  side  when  the  stopper  is  being  introduced,  may  be 
afterwards  slipped  across  the  top  of  the  latter,  upon  which  it  strains  with  sufficient  force 
to  prevent  the  stopper  being  loosened  by  a  slight  accidental  blow,  or  by  a  slight  expansion 
of  the  gas  within  the  bottle. 


COLLECTION   OP   GASES.  69 

connected.  The  addition  of  an  acid  for  the  disengagement  of  a  gas  should,  there- 
fore, be  always  gradual,  particularly  in  cases  where  the  chemical  action  is  accom- 
panied by  the  disengagement  of  much  heat.  When  the  application  of  heat  is  neces- 
sary for  the  disengagement  of  a  gas,  it  should  always  be  applied  gradually,  and 
only  raised  as  the  evolution  of  gas  diminishes  in  rapidity.  When  gases  are  pre- 
pared in  flasks  or  retorts,  these  are  supported  by  the  ring  of  a  retort-stand,  or  by 
a  tripod-stand,  over  the  gas-burner  or  lamp  by  which  they  are  heated.  It  is  ad- 
visable, particularly  when  the  vessel  contains  a  liquid,  to  place  between  it  and 
the  ring  or  stand,  a  small  copper  or  iron  tray  (or  sand-lath),  similar  in  form  to 
a  shallow  scale-pan,  and  filled  about  one-half  with  dry  sand  of  moderate  fineness. 
The  retort  or  flask  is  pressed  down  into  the  sand,  so  as  to  be  well  covered  with  it. 
This  contrivance  serves  greatly  to  regulate  the  heat,  and  render  its  application 
uniform  over  the  whole  surface  of  the  bottom.  A  square  piece  of  moderately 
fine  wire  gauze,  slightly  depressed  in  the  centre,  for  the  better  reception  of  the 
flask  or  retort,  may  also  be  employed,  particularly  if  the  gas  is  disengaged  merely 
from  a  solid  substance.  Great  care  should  be  taken  not  to  allow  the  sides  of  the 
vessel  to  become  too  hot,  as  portions  of  liquid,  converted  into  vapor  by  the  heat, 
•will  frequently  condense  in  the  cool  part  of  the  neck,  or  upon  the  cork,  and 
trickle  down  the  sides  of  the  vessel,  which,  if  too  hot,  would  immediately  crack 
upon  coming  in  contact  with  the  cooler  liquid. 

Before  proceeding  to  the  collection  of  a  gas,  it  is  first  necessary  to  ascertain 
whether,  and  to  what  extent,  the  gas  is  soluble  in  water.  If  its  solubility  be 
trifling,  cold  water  may  be  employed,  and  warm  or  hot  water  if  the  gas  be  more 
soluble.  The  mercurial  trough  is  used  if  the  gas  to  be  collected  is  exceedingly 
soluble  in  water,  or  if  it  is  wished  to  obtain  the  gas  perfectly  dry.  Tubes  or 
cylinders  are  generally  employed  for  collecting  gases  over  mercury.  In  filling 
these  with  mercury,  they  should  be  held  in  a  sloping  position,  and  the  liquid 
metal  poured  in  very  gradually.  The  retention  of  air  within  the  tube  or  cylinder, 
by  its  adhesion  to  the  glass  surface,  should  be  avoided  as  much  as  possible.  The 
best  method  of  accurately  filling  the  vessel,  is  to  pour  the  mercury  in  through  a 
small  funnel,  into  the  neck  of  which  is  fitted  a  long  glass  tube  of  narrow  bore, 
reaching  to  within  a  quarter  of  an  inch  of  the  bottom  of  the  vessel.  By  this 
method  the  risk  of  fracture  of  the  latter  by  the  weight  of  the  falling  mercury  is 
avoided,  and  the  retention  of  air  prevented  by  the  slow  and  regular  advance 
of  the  column  of  metal  up  the  sides  of  the  vessel.  In  inverting  its  opening 
over  the  troughj  the  tube  or  cylinder  must  be  firmly  grasped  with  the  one  hand, 
while  the  other  is  employed  in  retaining  the  mercury  in  the  vessel,  the  mouth 
of  which,  if  sufficiently  small,  is  closed  with  the  thumb,  or  if  not,  with  a 
cushion  of  caoutchouc. 

Before  collecting  a  gas,  the  portions  evolved  during  the  first  two  or  three 
minutes  should  be  allowed  to  escape,  since  they  are  contaminated  with  the  air 
contained  in  the  apparatus.  In  accurate  experiments,  a  small  portion  of  the 
gas  should  be  collected  in  a  tube,  and  a  test  of  its  purity  applied,  before  it  is 
suffered  to  pass  into  the  vessel  prepared  for  its  reception. 

§  31.  Some  gases  which  are  soluble  in  water,  and  which  have  a  corrosive  action 
upon  mercury  (e.  g.  chlorine),  require  to  be  collected  ly  displacement,  as  it  is 
termed  (i.  e.  in  vessels  filled  with  air,  which  they  are  made  to  displace).  This 
method  is  also  frequently  adopted  when  mercury  is  not  at  hand,  and  it  is  neces- 
sary to  collect  a  gas  in  the  dry  state.  Wide-mouthed  stoppered  bottles,  or  gas- 
cylinders,  are  employed  for  collecting  gases  by  displacement ;  the  mode  of  pass- 
ing the  gas  into  the  receiver  varies  according  to  its  density.  With  gases  heavier 
than  air,  the  delivery-tube,  in  connection  with  the  generating  apparatus,  is  made 
of  sumcient  length  to  pass  down  to  the  bottom  of  the  bottle  or  cylinder.  The 
first  portions  of  the  gas,  as  they  issue  from  the  apparatus,  will  diffuse  themselves 
with  more  or  less  rapidity  through  the  air  in  the  receiver;  after  a  time,  however, 


70  DETONATION   OF   GASES. 

the  atmospheric  air  becomes  almost  perfectly  expelled.  The  current  of  gas 
passing  into  the  receiver  should  be  as  rapid  as  possible;  it  is  also  advisable  to 
close  the  mouth  of  the  latter  partially,  by  means  of  a  glass  plate,  to  guard 
against  the  diffusion  of  the  gas  into  the  external  air.  When  it  is  believed  that 
the  receiver  is  filled  with  the  gas  as  perfectly  as  possible,1  the  delivery-tube 
should  be  disconnected  from  the  apparatus,  and  gradually  taken  out  with  one 
hand,  while  with  the  other  hand  the  operator  should  hold,  close  to  the  mouth  of 
the  vessel,  the  stopper  or  glass  plate,  with  which  the  former  is  closed  the  instant 
the  extremity  of  the  tube  is  withdrawn. 

If  the  (jas  be  lighter  than  air,  the  bottle  or  cylinder  in  which  it  is  to  be  col- 
lected.must  be  fixed  in  an  inverted  position  over  the  extremity  of  the  delivery- 
tube,  which  is  of  sufficient  length  to  pass  up  to  the  bottom  of  the  vessel.  The 
mouth  of  the  receiver  should  be  partially  closed,  by  means  of  a  piece  of  card- 
board, or  a  loosely  fitting  cork,  through  which  the  tube  passes.  When  the 
bottle  or  cylinder  is  properly  charged,  it  is  slowly  raised  till  above  the  opening 
of  the  delivery-tube,  when  the  cardboard  or  cork  is  rapidly  removed,  and  re- 
placed by  the  stopper  or  glass-plate,  the  vessel  being  maintained  in  the  inverted 
position  until  its  mouth  is  properly  closed. 

§  32.  COMBUSTION  OF  GASES. — It  is  frequently  necessary  to  burn  a  gas  as 
it  is  disengaged.  For  this  purpose,  the  delivery-tube  of  the  apparatus  is  replaced 
by  a  jet,  which  is  generally  made  of  glass  tubing.  A  piece  of  narrow  tube  of 
hard  glass  is  heated  in  the  manner  described  previously,  at  such  a  distance  from 
the  one  extremity  as  to  enable  the  manipulator  to  hold  the  shorter  end  with  the 
fingers  during  the  operation.  When  the  heated  portion  of  the  tube  has  become 
soft,  it  is  drawn  cut.  The  short  end  is  then  separated  from  the  longer  one  by 
means  of  a  sharp  61e,  at  about  the  centre  of  the  portion  drawn  out,  and  the 
elongated  extremity  of  the  latter  is  fused  at  the  edges,  by  being  held  for  a  short 
time  in  the  flame  of  a  spirit-lamp. 

On  applying  a  light  to  the  gas  issuing  from  the  jet,  it  will  inflame  and  burn 
steadily,  provided  the  evolution  of  gas  be  regular,  and  not  too  rapid.  It  is 
always  necessary  to  allow  the  gas  to  escape  into  the  air  for  two  or  three  minutes, 
before  applying  a  flame  to  the  jet,  in  order  that  all  the  atmospheric  air  may  be 
expelled;  unless  this  be  strictly  attended  to,  the  most  serious  consequences  may 
result,  explosive  mixtures  being  formed  by  most  inflammable  gases  with  the 
oxygen  of  the  atmosphere.  It  is  also  advisable,  even  after  having  waited  some 
time,  to  envelop  the  principal  portion  of  the  apparatus  in  a  cloth,  before  apply- 
ing a  light  to  the  jet.  If  a  combustible  or  explosive  gas  is  to  be  ignited,  it 
should  be  collected  in  stout  glass  vessels,  and  the  precaution  should  always  be 
taken,  to  wrap  the  vessel  in  a  cloth,  previously  to  setting  fire  to  the  gas;  it 
should  also  invariably  be  firmly  held  by  the  hand,  or  otherwise  fixed,  in  order 
that  the  concussion  produced  by  the  combustion  or  explosion  may  not  overturn 
the  vessel. 

DETONATION  OF  GASES — The  power  possessed  by  the  electric  spark  of  induc- 
ing the  combination  of  gases,  has  been  applied  with  great  success  in  analytical 
experiments. 

It  is  not  our  intention  to  enter  into  any  minute  details  respecting  eudiometry 
(as  this  method  of  analysis  is  termed),  but  to  confine  ourselves  to  a  brief  descrip- 

1  The  period  when  the  vessel  is  properly  charged  with  gas,  may  be  ascertained  with 
sufficient  accuracy  for  ordinary  purposes,  either  by  the  intensity  of  color  of  the  gas  in 
the.  receiver  (as  with  chlorine),  or  by  ascertaining  whether  the  gas  is  issuing  from  the 
mouth  of  the  vessel  in  a  sufficiently  pure  state  to  exhibit  strikingly  any  one  of  its  chemical 
properties.  Thus,  in  collecting  carbonic  acid  by  displacement,  when  the  vessel  is  con- 
sidered charged,  a  lighted  taper  should  be  held  near  its  side,  a  little  below  the  opening 
whence  the  air  is  expelled.  If  the  receiver  is  properly  filled,  the  taper  will  be  instantly 
extinguished  by  the  carbonic  acid  as  it  streams  over  down  the  side  of  the  vessel. 


COMBUSTION   IN   GASES.  71 

tion  of  the  manner  in  which  the  detonation  of  gases  is  effected,  and  the  apparatus 
employed  for  the  purpose.  Grases  are  generally  detonated  over  mercury,  the 
explosion  being  effected  in  an  instrument  termed  an  eudiometer. 

EUDIOMETERS. — There  are  two  kinds  of  eudiometers  in  general  use.  The 
ordinary  straight  eudiometer  is  a  graduated  glass  tube,  of  about  half  an  inch  to 
an  inch  in  diameter,  near  the  closed  end  of  which  are  inserted,  while  the  glass 
is  soft,  two  pieces  of  moderately-stout  platinum  wire,  at  opposite  sides,  in  such  a 
manner  that  their  extremities  inside  the  tube  approach  each  other  within  a  con- 
venient distance  for  the  passage  of  the  electric  spark.  To  one  of  the  wires  is 
attached  a  small  metal  chain,  passing  to  the  ground,  or  fixed  at  the  other  ex- 
tremity to  the  outside  of  the  Leyden  jar. 

When  this  eudiometer  has  been  charged  with  the  gas  to  be  detonated,  it  is 
held  firmly  in  the  hand,  or  secured  by  a  heavy  support,  the  open  end  below  the 
mercury  being  pressed  down  with  some  force  upon  a  cushion  of  caoutchouc,  and 
the  detonation  is  then  effected  by  approaching  the  charged  jar  or  disk  to  the 
outer  extremity  of  one  of  the  wires.  It  is  well- to  wipe  the  glass  in  the  vicinity 
of  the  wires  with  a  warm,  dry  cloth,  before  passing  the  spark.  Two  persons  are 
generally  required  to  perform  the  operation;  the  one  to  hold  the  tube  firmly,  the 
other  to  detonate.  When  the  gas  has  been  detonated,  the  pressure  exerted  upon 
the  caoutchouc  cushion  must  be  very  gradually  diminished,  in  order  to  permit 
the  mercury  to  enter  the  tube  gently  (to  fill  up  the  vacuum  left  by  the  explo- 
sion). The  amount  of  gas  introduced  into  a  tube  for  deto- 
nation must  vary  according  to  the  amount  of  expansion 
attending  the  explosion.  The  eudiometer  should  never  be 
more  than  two-thirds  filled  with  gas. 

Ure's  siphon  eudiometer  consists  of  a  tube  with  wires 
inserted  as  above,  but  which  is  bent  in  the  form  of  the 
letter  U;  the  open  limb  being  somewhat  longer  than  the 
other.  The  gas  having  been  introduced  into  the  closed 
limb,  a  portion  of  the  mercury  is  removed  from  the  open 
end  by  means  of  a  small  pipette,  so  as  to  equalize  the  mer- 
Qury  in  the  two  limbs.  The  open  limb  is  then  firmly 
grasped,  and  the  opening  closed  with  the  thumb j  one  of 
the  wires  may  then  be  approached  to  the  charged  electro- 
phorus-disk,  and  the  gas  inflamed,  the  spark  being  con- 
ducted away  by  the  thumb,  which  touches  the  other  wire. 
If  the  charge  be  given  from  a  jar,  this  wire  must  be  con- 
nected with  the  chain  attached  to  the  outside  of  the  jar. 

§  33.  COMBUSTION  IN  GASES. — Substances  are  generally  introduced  into 
gases,  for  combustion,  by  means  of  small  metal  (^deflagrating)  spoons,  fixed  to  a 
piece  of  iron  wire,  which  passes  at  the  other  extremity  through  a  small  metal 
disk,  provided  in  its  centre  with  a  cork  or  stuffing-box.  When  the  spoon  is  intro- 
duced into  a  bell-jar  or  wide  bottle,  the  disk  falls  upon  the  opening  from  which 
the  stopper  has  been  removed,  and  prevents  the  escape  of  gas,  unless  there  be 
much  pressure  from  inside  in  consequence  of  the  formation  of  vapors,  when  the 
disk  will  be  forced  up.1 

The  wire  with  the  spoon  attached  should  never  reach  lower  in  the  vessel  than 
two-thirds  of  its  depth.  Some  substances  (steel  watch-springs,  &c.)  may  be 

1  In  the  combustion  of  phosphorus  in  oxygen,  care  should  be  taken  that  the  former  be 
perfectly  dry  before  introduction.  A  small  piece  of  phosphorus  should  be  used  for  the 
experiment,  and  the  gas  should  be  contained  in  a  large  jar.  When  substances  incombus- 
tible under  ordinary  circumstances  are  to  be  burnt  in  oxygen  (such*  as  watch-springs  and 
metal  wires),  their  lower  end  should  be  heated  and  dipped  in  sulphur,  or  a  piece  of  Ger- 
man tinder,  wood,  or  cork,  should  be  attached  to  it.  These  are  inflamed  immediately 
before  the  wire  or  watch-spring  is  introduced  into  the  gas. 


72  MEASUREMENT   OF   GASES. 

attached  to  a  simple  wire  by  means  of  thread,  or  of  very  fine  iron-wire,  and  thus 
lowered  into  the  vessel.  Before  projecting  a  powder  into  a  gas,  the  stopper  of 
the  vessel  containing  the  latter  should  be  first  replaced  by  a  glass  plate,  and  the 
powder  introduced  gradually,  care  being  taken  to  prevent  any  of  it  from  falling 
against  the  sides  of  the  vessel,  as  the  heat  disengaged  by  its  combustion  will,  in 
such  cases,  frequently  crack  the  glass.  A  small  quantity  of  water  should  be 
left  at  the  bottom  of  the  vessel. 

§  34.  TRANSFERENCE  OF  GASES. — It  is  frequently  necessary  to  transfer  gases 
from  one  vessel  to  another.  The  manner  in  which  a  gas  is  transferred  from  a 
gas-holder  to  another  vessel,  has  been  already  described.  Bell-glasses,  which 
cannot,  like  bottles,  be  closed  at  the  openings  through  which  the  gas  was  ad- 
mitted, are  transferred,  when  filled,  from  the  pneumatic  trough  to  the  table, 
upon  a  common  plate  or  saucer,  in  which  sufficient  water  is  retained  to  cover  the 
mouth  of  the  jar.  The  depth  of  the  plate  or  saucer  need  be  but  very  slight,  as 
the  smallest  quantity  of  water  surrounding  the  mouth  of  the  jar  is  sufficient  to 
prevent  the  gas  from  escaping.  'Gas-cylinders  are  transferred  from  the  trough 
by  closing  the  mouth  with  a  ground-glass  plate. 

In  transferring  a  gas  from  one  jar  to  another,  the  jar  into  which  the  gas  is 
decanted  is  filled  with  water,  and  placed,  inverted,  upon  the  shelf  of  the  trough, 
so  that  only  about  one-third  of  its  edge  rests  thereupon;  the  jar  containing  the 

gas  to  be  transferred  is  then  depressed  into 

Fig.  42.  the  trough  by  the  right  hand,  and  so  inclined 

pi  that  the  gas  may  pass  up  into  the  first-men- 

U  tioned  jar.     Much  care  is  required  in  trans- 

ferring gases  from  large  into  small  jars  or 
bottles.     It  is  advisable,  in  these  cases,  to 
introduce  the  beak  of  a  funnel,  inverted  under 
the  water,  into  the  vessel  to  be  filled,  in  or- 
1=^       der  that  the  gas,  as  it  escapes  in  great  bub- 
§|        bles  from  the  large  jar,  may  ascend  more 
easily  into  the  smaller  opening  of  the  vessel 
to  be  filled,  by  which  means  the  risk  of  loss 
will  be  much  lessened.     When  the  vessels 

containing  the  gases  are  larger  than  those  which  are  to  receive  them,  it  is  also 
very  advantageous  to  transfer  the  gas  first  into  a  lipped  vessel,  and  from  thence 
into  the  smaller  vessel,  as  the  former,  of  whatever  dimensions  it  may  be,  only 
delivers  small  bubbles  of  gas  from  the  lip. 

§  35.  MEASUREMENT  OF  GASES. — The  apparatus  necessary  for  measuring 
gases  are,  the  pneumatic  or  mercurial  trough,  graduated  jars  and  tubes,  plumb- 
lines,  supports,  a  thermometer,  and  a  barometer. 

In  selecting  graduated  apparatus,  it  is  always  advisable  that  they  should  be 
graduated  to  one  standard.  Thus,  if  the  tubes  and  jars  be  graduated  in  cubic 
inches  and  their  fractions,  the  measures  should  be  divided  into  pints,  ounces, 
&c. ;  or,  if  the  tubes  be  graduated  to  the  continental  scales,  the  measures  should 
be  so  likewise,  since  this  saves  much  calculation. 

The  measurement  of  gases  should  be  effected  upon  a  very  firm  and  level  table 
or  shelf,  which,  in  a  well-conducted  laboratory,  should  be  reserved  exclusively 
for  these  operations. 

If  the  bulk  of  a  gas,  contained  in  any  ungraduated  vessel,  has  to  be  measured, 
it  is  transferred,  in  the  manner  above  described,  into  a  graduated  vessel,  and 
the  space  which  it  occupies  therein  ascertained. 

If  the  gas  is  contained  in  a  jar  or  bottle,  it  is  transferred  into  a  graduated  jar, 
which  is  then  depressed  in  the  well  of  the  trough  until  the  surface  of  the  water 
or  mercury  surrounding  the  jar  corresponds  to  that  within  it,  great  care  being 
taken  to  hold  the  jar  in  an  upright  position,  so  that,  if  the  latter  be  graduated 


SOLUTIONS   OF   GASES.  73 

upon  the  opposite  sides,  the  graduations  indicated  by  the  surface  on  each  side 
correspond  accurately.  In  reading  off  the  graduations  indicated,  the  eye  of  the 
operator  should  be  brought  as  nearly  as  possible  to  a  level  with  the  surface  of 
the  liquid  in  the  jar.  If  the  gas  is  contained  in  tubes,  the  operation  is  pretty 
much  the  same. 

In  reading  off  the  graduation  indicated  by  the  surface  of  liquid  in  a  jar  or 
tube,  attention  must  be  paid  to  the  following  circumstances. 

When  the  liquid  used  moistens  the  side  of  the  vessel  (as  water),  the  surface 
of  the  former  will  be  elevated  where  it  is  in  contact  with  the  vessel;  should 
mercury  be  used  (which  does  not  moisten  the  glass),  there  will  be  a  depression 
of  the  surface -round  the  sides;  it  is  in  both  cases  necessary,  for  correct  measure- 
ment, that  the  eye  be  brought  to  a  level  with  the  general  surface  of  the  liquid. 

In  order  to  secure  the  position  of  the  vessel,  in  which  the  gas  is  measured, 
being  perfectly  upright,  it  is  well  to  suspend  two  plumbrlines  (which  may  con- 
sist of  any  heavy  body  attached  to  a  string)  in  the  neighborhood  of  the  trough — 
the  one  opposite  to  the  position  taken  by  the  operator,  the  other  to  his  right  or 
left  side — the  vessel  should  be  so  placed  that  the  sides  are  parallel  to  the  plumb- 
lines. 

In  reading  off  any  bulk  of  gas,  when  accuracy  is  required,  it  is  necessary  to 
note  the  state  of  the  thermometer  and  barometer  at  the  time,  and  the  tempera- 
ture of  the  air  and  water  should  agree  within  a  degree  or  two  at  the  time  of 
operating.  It  is  then  necessary  that  the  volume  of  gas  observed  should  be  sub- 
mitted to  certain  corrections  for  temperature  and  pressure  of  air,  in  order  that 
the  results  obtained  at  different  periods  may  be  compared.  For  the  methods  of 
effecting  such  corrections,  the  reader  is  referred  to  the  method  of  taking  the 
specific  gravity  of  vapors  (§  8). 

There  is  but  little  difficulty  in  measuring  out  larger  quantities  of  a  gas  for 
any  specific  purpose.  A  graduated  jar  is  tilled  with  water,  and  the  gas  passed. 
or  transferred  into  it  in  the  ordinary  manner,  until  it  contains  nearly  the  re- 
quired quantity.  The  remainder  must  then  be  added  very  gradually,  by  means 
of  a  lipped  vessel  or  delivery- tube  with  a  narrow  opening,  so  that  the  amount  of 
gas  introduced  at  one  time  is  but  small.  Observations  must  be  made  from  time 
to  time,  whether  a  sufficient  quantity  has  been  introduced,  by  lowering  the  jar 
into  the  well  of  the  trough,  and  reading  off  in  the  usual  manner. 

Great  care  is  required  in  measuring  out  smaller  quantities  of  gases  into  tubes 
when  much  accuracy  is  necessary;  the  gas  must  be  delivered  into  them  slowly 
and  in  much  smaller  quantities;  but  in  other  respects  the  operation  is  the  same 
as  above  described. 

§  36.  SOLUTIONS  OF  GASES  in  various  liquids  are  of  great  use  in  the  labora- 
tory as  reagents;  it  will  therefore  be  well  to  say  a  few  words  upon  the  method 
of  preparing  them. 

If  the  quantity  of  gas  to  be  absorbed  be  considerable,  it  is  advisable  to  divide 
the  solvent  into  three  or  four  portions,  introducing  each  into  a  Woulfe's,  or 
wide-mouthed  bottle,  and  connecting  these  with  each  other  and  the  generating 
apparatus,  in  the  manner  directed  for  the  construction  of  a  purifying  apparatus 
(§  28).  If  the  gas  be  very  soluble  in  the  liquid  employed,  the  bubbles,  as  they 
enter  the  first  bottle,  will  be  perfectly  absorbed,  or  they  will  be  reduced  con- 
siderably in  size  as  they  leave  the  delivery-tube,  and  will  gradually  decrease  as 
they  pass  upwards  through  the  fluid.  As  soon  as  the  liquid  in  the  first  bottle 
is  nearly  saturated,  the  bubbles  will  decrease  but  slightly  in  size  as  they  pass 
upwards,  and  a  portion  of  the  gas  will  pass  over  into  the  second  bottle,  where  it 
will  in  turn  be  perfectly  absorbed,  and  thus  the  operation  is  continued  until  the 
bubbles,  as  they  pass  through  the  liquid  in  the  last  vessel,  no  longer  decrease  in 
size.  It  is  advisable  to  attach  a  tube  to  the  last  bottle,  by  which  any  gas  that 


74  CONDENSATION   OP   GASES. 

is  not  absorbed  may  be  conducted  into  a  glass  vessel  containing  a  quantity  of 
the  same  solvent,  or  any  other  liquid  that  may  absorb  the  gas  more  freely. 

When  the  quantity  of  gas  to  be  absorbed,  or  liquid  to  be  saturated,  is  smaller, 
the  latter  should  be  contained  in  a  tall  narrow  jar,  and  the  delivery-tube  be 
allowed  to  pass  to  within  a  quarter  of  an  inch  of  the  bottom ;  the  bubbles  of  gas, 
in  ascending,  are  thus  brought  into  contact  with  a  very  large  surface  of  liquid, 
arid  the  absorption  is  consequently  far  more  perfect  than  if  effected  in  shallow 
vessels. 

When  gases  are  to  be  separated  ~by  the  absorption  of  one  or  more,  by  means 
of  various  substances,  the  same  apparatus  as  those  above  mentioned  should  be 
used.     Very  ingenious  apparatus  have  been  contrived  for  absorbing  gases  in 
accurate  experiments;  these  are  particularly  useful  when  the 
Fig.  43.          quantity  of  gas  absorbed  is  to  be  determined.     Their  forms  are 
various,  but  they  nearly  all  consist  of  several  glass  bulbs,  con- 
nected in.  various  positions  by  means  of  narrow  tubes,  and  nearly 
filled  with  the  absorbent.     The  gas,  if  not  completely  absorbed 
in  passing  into  the  first  bulb,  ascends,  or  is  forced  by  the  pres- 
sure of  gas  in  the  generator,  through  the  narrow  connecting  tube 
into  the  second  bulb,  and  so  on,  until  it  can  no  longer  escape 
absorption.     Liebiys  potassa-apparatus  (Fig.  43)  is  the  most 
important  and  useful  of  these. 

A  very  ingenious  method  is  resorted  to  for  the  separation  of 
mixtures  of  gases  in  eudiometrical  experiments,  by  absorption. 
A  small  ball  (about  as  large  as  a  pea)  of  the  substance  having  an  affinity  for 
the  gas  to  be  absorbed,  is  cast  or  moulded  (with  the  aid  of  a  little  water  or  gum, 
if  necessary),  round  the  extremity  of  a  piece  of  thin  flexible  iron  wire  of  con- 
siderable length.  This  ball  is  then  introduced  under  water  or  mercury  into  the 
gas  to  be  operated  upon,  which  is  contained  in  a  graduated  glass  tube,  the  wire 
being  pushed  upwards  into  the  tube  until  the  ball  protrudes  above  the  surface 
of  the  liquid.  When  absorption  has  ceased,  a  fresh  ball  may  be  introduced, 
and  every  trace  of  the  gas  to  be  absorbed  thus  removed  from  the  mixture.  A 
second  and  third  gas  may  be  then  absorbed  in  a  similar  manner,  by  means  of 
appropriate  balls. 

Sometimes  gases  are  absorbed  in  tubes  over  mercury  by  the  introduction  of 
liquids.     A  pipette,  the  long  end  of  which  is  bent  upwards  at  about  two  inches 
from  the  opening,  is  used  for  injecting  the  liquid  into  the  tube.     When 
Fig.  44.     charged  with  the  absorbent,  the  mouth  of  the  pipette  is  closed  with  the 
finger,  and  the  lower  opening  introduced  as  far  as  possible  into  the  tube, 
under  mercury ;  the  liquid  is  then  forced  up  into  the  tube  by  blowing 
cautiously  into  the  pipette.     Too  much  force  must  not  be  applied,  or 
the  liquid  will  be  at  once  forced  into  the  tube,  together  with  a  portion 
of  air  from  the  mouth.     A  small  portion  of  the  liquid  should  there- 
fore be  retained  in  the  pipette. 

§  37.  CONDENSATION  OF  GASES. — The  effect  of  powerful  pressure, 
assisted'  at  times  by  a  great  reduction  of  temperature,  has  been  most 
successfully  applied  by  Faraday,  to  the  condensation  of  many  gases  to 
the  liquid  and  solid  states.  The  method  employed  by  him  for  liquefy- 

Jing  gases  is  to  generate  them  in  a  confined  space  in  the  following  man- 
ner :  A  tube  of  strong,  tough  glass  (green  bottle-glass)  is  sealed  at  one 
end  and  bent  in  the  centre  at  an  angle  of  about  130  degrees.     The  mate- 
rials for  generating  the  gas  are  then  introduced,  so  as  to  occupy  a  portion  of  the 
closed  arm  of  the  tube,1  after  which  the  other  extremity  is  hermetically  sealed. 

1  If  the  gas  to  be  condensed  is  of  such  a  nature  as  not  to  be  evolved  by  the  action  of 
heat  upon  the  material  employed,  but  by  the  chemical  action  of  different  substances  on 


CONDENSATION   OP   GASES.  75 

The  gas  is  then  generated,  accumulating  in  the  confined  space ;  it  gradually 
exerts  a  very  great  degree  of  pressure,  whereby  a  portion  becomes  condensed  to 
a  liquid  in  the  extremity  of  the  tube  opposite  to  that  containing  the  materials. 
To  facilitate  the  condensation  of  the  gas,  this  extremity  of  the  tube  is  surrounded 
with  a  frigorific  mixture.  The  pressure  at  which  the  gas  condenses  is  ascertained 
by  a  slender  graduated  tube  or  gauge,  closed  at  one  end,  and  containing,  near 
the  open  extremity,  a  globule  of  mercury;  this  tube  is  introduced  into  the  con- 
densing tube,  together  with  the  materials  from  which  the  gas  is  generated.  In 
proportion  as  the  pressure  exerted  by  the  confined  gas  increases,  the  volume  of 
air  in  the  small  tube  decreases,  the  mercury  being  forced  towards  the  closed  end. 

By  this  method  alone,  Faraday  succeeded  in  liquefying  the  following  gases : 
sulphurous  acid,  carbonic  acid,  hydrochloric  acid,  hydrosulphuric  acid,  chlorine, 
cyanogen,  ammonia,  and  protoxide  of  nitrogen. 

Subsequently,  by  employing  very  stout  green  bottle-glass  tubes,  curved  so  as 
to  admit  of  their  immersion  in  frigorific  baths,  and  attached  to  powerful  con- 
densing syringes,  Faraday  obtained  the  following  results :  olefiant  gas,  the  fluor- 
ides of  boron  and  silicon,  and  phosphuretted  hydrogen,  were  liquefied;  hydro- 
bromic  and  hydriodic  acids  were  converted  into  crystalline  solids,  as  were  also,  of 
the  gases  previously  liquefied,  hydrosulphuric  and  sulphurous  acids.  The  follow- 
ing gases  exhibited  no  indications  of  liquefaction  when  cooled  down  to  — 166°  F. 
( — 74°. 4  C.)>  and  exposed  to  a  pressure  varying  from  27  to  28.5  atmospheres: 
carbonic  oxide,  coal  gas,  binoxide  of  nitrogen,  hydrogen,  and  oxygen. 

Thilorier  first  succeeded  in  applying  the  principle  of  Faraday's  gas  condensing- 
tube,  to  the  preparation,  of  liquid  carbonic  acid  upon  a  large  scale.  The  appa- 

Fig.  45. 


ratus  contrived  by  him  consists  of  two  very  stout  cylindrical  vessels  of  wrought 
iron  or  gun-metal,  one  of  which  acts  as  gas-generator,  the  other  as  receiver;  the 
latter  is  fixed  upon  a  flat  foot,  the  former  rests  by  trunnions  upon  an  iron  frame, 

each  other,  the  method  of  conducting  the  operation  varies  somewhat  from  the  above  brief 
description  ;  we  must  refer  for  further  particulars  to  large  works  on  Physics,  or  to  Fara- 
day's published  researches. 


76  CONDENSATION    OF   GASES. 

so  that  it  may  be  tilted  at  pleasure.  Both  vessels  are  provided  at  the  top  with 
very  accurate  stopcocks  or  valves  of  a  peculiar  description,  consisting  of  a  tube 
with  a  lateral  orifice,  and  containing  a  spherical  plug  of  lead  on  a  spindle,  which 
is  screwed  down  by  means  of  a  handle  into  a  brass  spherical  cavity,  having  at 
the  bottom  an  opening  into  the  cylinder. 

The  generating  cylinder  is  charged  with  2f  Ibs.  of  powdered  bicarbonate  of 
soda  and  Gj  Ibs.  of  water  at  100°  F.  (37°. 7  C-);  these  are  well  stirred  together, 
and  a  long,  narrow,  copper  tube  is  then  introduced,  containing  1  Ib.  3  oz.  of  oil 
of  vitriol ;  the  top  of  this  tube  must  be  carefully  rested  against  the  side  of  the 
cylinder,  so  that  none  of  the  acid  is  spilled.  The  stopcock  is  then  screwed  on 
very  firmly,1  and  the  cylinder  afterwards  turned  upon  its  trunnions  so  as  com- 
pletely to  invert  it ;  in  this  position  it  is  retained  a  short  time,  and  then  turned 
over  and  over  two  or  three  times,  by  which  means  the  acid  becomes  properly 
mixed  with  the  other  contents.  The  carbonic  acid  will  of  course  be  immediately 
generated,  and  collect  in  the  upper  part  of  the  vessel  with  considerable  elastic 
force.  When  the  generator  has  been  allowed  to  remain  at  rest  for  a  short  time, 
it  is  connected  with  the  other  cylinder  or  receiver,  by  means  of  a  stout  copper 
tube,  which  screws  on  to  the  lateral  opening  of  the  stopcocks.  The  receiver  has 
a  tube  passing  from  the  stopcock  nearly  to  the  bottom  of  the  cylinder,  and  is 
kept  surrounded  by  ice.  When  the  connection  is  perfect,  both  stopcocks  are 
opened,  whereupon  the  carbonic  acid  passes  over  and  liquefies  in  the  cooled 
receiver.  The  cocks  are  then  again  closed,  and  the  cylinders  separated ;  any 
portions  of  confined  gas  in  the  generator  are  allowed  to  escape,  the  sulphate  of 
soda  is  then  emptied,  and  a  fresh  charge  of  carbonate,  &c.  introduced,  as  before. 
The  operation  is  thus  repeated  five  or  six  times,  when  the  receiver  will  contain 
a  considerable  quantity  of  liquid  carbonic  acid.  The  greatest  care  is  required  in 
constructing  and  using  this  apparatus ;  under  any  circumstances,  the  operation  is 
a  dangerous  one,  several  severe  accidents  having  happened  at  different  periods, 
by  the  bursting  of  the  cylinders. 

When  the  stopcock  of  the  receiver  is  afterwards  opened,  some  of  the  liquid 
carbonic  acid  will  rush  out,  being  forced  up  through  the  long  tube  by  the  pres- 
sure of  the  atmosphere  of  gaseous  carbonic  acid  in  the  cylinder.  Being  a  highly 
volatile  liquid  (§  124),  a  portion  instantly  resumes  its  gaseous  form  upon  escaping 
from  the  stopcock,  whereby  the  remainder  becomes  cooled  down  to  so  low  a 
temperature  as  to  freeze,  bearing  a  great  resemblance  to  snow,  as  it  falls  from 
the  mouth  of  the  stopcock.  If  a  nozzle  be  screwed  on  to  the  opening  of  the 
stopcock,  and  the  liquid  be  allowed  to  escape  from  this  into  a  metal  box,  pro- 
vided with  hollow  wooden  handles,  the  portion  that  assumes  the  gaseous  state 
will  escape  through  the  latter,  while  the-box  will  soon  be  filled  with  solid  carbonic 
acid  (§  124).  The  latter,  being  a  bad  conductor  of  heat,  may  be  handled  with- 
out injury;  it  also  retains  its  solid  form  for  a  considerable  time.  If  mixed  with 
a  small  quantity  of  ether,  it  yields  a  semi-fluid  mass,  which  evaporates  very 
rapidly,  producing  thereby  the  most  intense  cold  •  large  masses  of  mercury  may 
be  frozen  by  these  means, -and  it  is  this  frigorific  mixture  that  Faraday  employed 
so  successfully  in  his  experiments  with  the  gases  just  now  alluded  to.  Several 
of  those  which  he  succeeded  in  condensing  by  the  application  of  a  comparatively 
moderate  pressure,  in  his  earlier  experiments,  were  afterwards  found  by  him  to 
condense  as  readily  by  exposure  to  the  frigorific  action  of  the  above  mixture. 

Another  kind  of  apparatus,  which  is  said  to  be  perfectly  safe,  has  been  con- 
structed by  Natterer,  for  the  liquefaction  of  carbonic  acid.  The  gas  is  forced, 
by  means  of  a  forcing-pump,  into  a  wrought-iron  cylinder  of  considerable  thick- 
ness, provided  at  the  top  with  a  valve  like  those  of  Thilorier's  cylinders,  and  at 

1  Washers,  or  collars  of  lead,  are  used  to  insure  the  perfect  tightness  of  the  apparatus 
under  the  enormous  pressure  exercised. 


DISTILLATION   AND    SUBLIMATION.  77 

the  bottom  with  a  spring-valve  opening  inwards.  The  gas  is  compressed  into 
the  cylinder  by  the  forcing-pump,  being  admitted  by  this  valve,  through  which 
none  can  again  make  its  escape,  since  the  spring  only  yields  to  external  pressure. 
The  cylinder  is  surrounded  by  another  vessel,  in  which  ice  is  placed. 


DISTILLATION    AND    SUBLIMATION. 

§  88.  These  very  important  operations  are  comparatively  simple  in  their  nature, 
requiring  almost  the  same  apparatus.  Their  object  is  the  separation  of  a  body 
from  extraneous  substances  by  its  conversion  into  vapor,  its  removal  in  that 
state,  and  its  subsequent  condensation.  The  operation  is  termed  sublimation,  if 
the  resulting  product  is  a  solid,  and  distillation  if  it  is  a  liquid. 

The  theory  of  the  process  of  sublimation  and  distillation  is  simple  enough, 
since  it  consists  merely  in  raising  the  substance  to  be  purified  to  a  temperature 
at  which  it  will  pass  over  into  the  gaseous  state,  and  conducting  the  resulting 
vapor  into  a  receiver,  the  temperature  of  which  is  sufficiently  low  to  cause  it  to 
return  to  the  liquid  or  solid  state.  Nevertheless,  the  very  different  temperatures 
at  which  bodies  vaporize,  and  at  which  they  may  be  condensed,  render  it  neces- 
sary that  the  apparatus  employed  should  be  modified  to  suit  the  various  condi- 
tions, and  that  many  precautions  should  be  minutely  attended  to.  We  will  first 
turn  our  attention  to  distillation,  and  consider  the  most  important  modifications 
of  apparatus  used  in  the  laboratory  for  distillation  at  different  temperatures. 

DISTILLATION    AT    HIGH    TEMPERATURES. 

Some  liquids  require  so  high  a  temperature  for  their  conversion  into  vapor, 
that  their  distillation  must  be  effected  over  furnaces.  Glass  vessels  cannot,  con- 
sequently, be  used  for  such  operations,  and  recourse  must  be  had  to  metallic 
vessels,  or  stills,  as  they  are  termed. 

These  consist,  generally  speaking,  of  a  boiler  to  contain  the  liquid,  to  which 
is  adapted  a  head,  terminating  in  a  beak,  which  fits  into  the  condensing  appa- 
ratus. 

A  cheap  and  very  serviceable  still  of  this  description  may  be  made  of  the 
common  culinary  digester,  by  removing  the  valve  at  the  top  of  the  lid  and  re- 
placing it  by  a  piece  of  iron  pipe,  bent  like  a  siphon,  at  an  angle  of  about  60°, 
the  long  arm  being  about  sixteen  inches,  and  the  short  arm  six  inches  in  length ; 
the  extremity  of  the  latter  is  firmly  screwed  into  the  lid  of  the  digester.  When 
the  boiler  of  the  still  has  been  charged  with  the  liquid  or  solid  to  be  distilled 
(the  operation  in  the  latter  case  is  called  dry  distillation),  the  head  is  fitted  on 
firmly.  If  the  modified  digester  above  described  is  used,  it  is  well  to  fill  the 
groove  of  the  lid,  into  which  the  lower  portion  fits,  with  white-lead,  which,  as 
the  former  is  hammered  on,  fills  up  all  interstices,  rendering  the  apparatus  per- 
fectly tight,  even  when  under  considerable  pressure. 

The  next  step  is  to  fit  the  beak  of  the  retort,  or  still,  into  the  condensing 
apparatus  or  refrigerator.  There  are  two  forms  of  condensers  in  general  use — 
the  worm,  and  the  Liebig's  condenser. 

THE  WORM  is  generally  used  in  larger  operations,  as  it  presents  a  much  greater 
condensing  surface  than  Liebig's  tube.  It  consists  of  a  spiral  pipe,  generally  of 
metal  (tin  being  in  most  cases  preferable),  inclosed  in  a  tub,  and  surrounded 
with  cold  water ;  the  lower  extremity  passing  out  at  the  side  of  the  tub  in  the 
form  of  a  spout.  The  upper  extremity,  which  likewise  protrudes  through  the 
side  of  the  tub,  is  generally  widened,  and  conical  in  form,  so  as  to  fit  upon  the 
beak  of  the  retort.  Should  the  latter  be  too  large  for  introduction  into  the 
worm,  it  is  necessary  to  fit  upon  it  a  conical  tube  of  metal  or  glass,  which  is 


rfO  DISTILLATION. 

termed  an  adapter,  the  thin  extremity  of  which  is  sufficiently  small  to  enter  the 
condenser.  It  is  advisable  to  lute  all  joints  in  an  apparatus  of  this  description 
with  white-lead,  as  the  temperature  of  the  portion  near  the  still-head  is  frequently 
so  high  as  to  char  corks  rapidly.  In  order  to  effect  perfect  condensation  of  the 
vapors  evolved,  it  is  necessary  to  allow  a  continual  supply  of  cold  water  to 
replace  that  in  the  tub,  as  it  becomes  warm  from  the  quantity  of  heat  commu- 
nicated to  it  by  the  condensed  vapor.  The  best  of  many  contrivances  to  effect 
this,  is  that  of  supplying  a  continuous  stream  of  cold  water  at  the  bottom  of  the 
tub,  and  removing  a  corresponding  quantity  from  the  top.  Great  care  must  be 
taken  that  at  least  two-thirds  of  the  condensing  tube  be  kept  perfectly  cold 
during  a  distillation. 

LIEBIG'S  CONDENSER. — When  the  distillation  to  be  performed  is  not  on  a 
very  large  scale,  or  the  volatilized  substance  is  condensed  with  comparative  ease, 

Fig.  46. 


the  Liebig's  condenser  may  be  nsed  with  advantage,  as  it  is  far  more  simple  in 
construction,  requires  much  less  water  to  effect  condensation  than  the  worm,  and 
is  more  easily  cleaned  than  the  latter.  It  consists  of  an  inner  tube  (of  glass  or 
metal),  surrounded  by  a  metal  tube  of  considerably  larger  dimensions ;  a  stream 
of  cold  water. is  kept  continually  passing  through  the  space  between  the  two 
tubes,  the  points  of  ingress  and  egress  of  the  water  being  similarly  situated  to 
those  in  the  worm-tubs. 

§  39.  RECEIVERS. — Various  forms  of  vessels  may  be  employed  as  receivers; 
the  principal  point  to  be  attended  to  is,  that  the  receiver  be  of  sufficient  capacity 
to  collect  the  products  of  the  distillation.  Large  wide-mouthed  bottles  or  flasks 
may  be  employed  as  receivers;  in  the  place  of  these,  other  forms  of  apparatus 
are  frequently  used,  consisting  of  glass  globes  of  various  sizes,  provided  with 
one  or  more  necks.  If  the  globe  is  furnished  with  several  openings,  one  of 
these  should  be  wider  than  the  others,  and  of  a  conical  form.  Such  vessels  are 
called  tubulated  receivers.  The  quilled  receiver  consists  of  a  globe  provided  with 
a  conical  opening  and  a  long  tube,  tapering  off  very  much  towards  the  end. 
This  receiver  may  be  fitted  into  a  bottle  by  means  of  this  tube  or  quill,  which 
is  made  to  pass  nearly  to  the  bottom,  and  allows  the  condensed  products  to  flow 
from  the  globe  into  the  bottle.  Should  globe-receivers  or  flasks  be  employed 
for  collecting  the  products  of  a  distillation,  they  should  be  very  loosely  fitted  on 
to  the  delivery-end  of  the  condenser  by  means  of  a  large  cork,  to  prevent  their 
falling  away  from  the  former;  they  may  also  be  placed  upon  rings  of  wood,  or 
iron,  covered  with  list,  which  are  very  useful  for  supporting  flasks  and  retorts 
upon  the  table. 


DISTILLATION.  79 

Distillations  at  high  temperatures,  or  dry  distillations,  are  frequently  accom- 
panied by  the  disengagement  of  gases,  which  it  is  sometimes  necessary  to  collect. 
In  such  cases,  the  receiver  must  be  fitted  air-tight  upon  the  mouth  of  the  con- 
denser, and  provided  with  a  tube  properly  bent,  to  serve  either  as  a  delivery- 
tube  or  connecting-tube,  to  which  any  purifying  apparatus  may  be  attached.  It 
frequently  happens  that  the  cooling  powers  of  the  condenser  employed  are  insuffi- 
cient to  effect  the  perfect  condensation  of  the  product,  in  consequence  either  of 
the  great  volatility  of  the  latter,  or  of  the  rapidity  with  which  the  vapors  are 
disengaged  in  the  retort.  In  such  cases,  the  lower  end  of  the  condenser  should 
enter  the  receiver  as  far  as  possible,  and  the  latter  should  be  surrounded  with 
cold  water ;  for  this  purpose,  it  is  placed  in  a  basin  of  sufficient  depth,  filled  with 
water ;  the  upper  surface,  which  cannot  be  immersed  in  the  water,  is  covered 
with  a  piece  of  coarse  blotting-paper  or  rag,  upon  which  cold  water  is  now  and 
then  poured. 

Should  a  still  lower  temperature  be  required  for  perfect  condensation,  the 
receiver  must  be  surrounded,  in  the  basin,  with  a  cooling  mixture.  If  ice  can 
be  procured,  it  should  be  pounded  up  in  a  mortar,  and  then  mixed  with  about 
half  its  bulk  of  salt.  The  receiver  is  then  surrounded  with  this  mixture,  and 
the  whole  covered  with  a  stout  piece  of  flannel  or  cloth,  to  prevent  the  access  of 
radiated  heat,  and  render  the  cooling  mixture  effectual  for  as  long  a  period  as 
possible.  If  ice  cannot  be  procured,  other  frigorific  mixtures  may  be  made  by 
mixing  together  various  salts  in  certain  proportions,  and  adding  water :  e.  g.  5 
parts  of  nitrate  of  potassa,  5  parts  of  chloride  of  ammonium,  and  1C  parts  of 
water. 

DISTILLATION   AT   LOWER   TEMPERATURES,   BUT   ABOVE   212°. 

§  40.  When  the  temperature  required  for  the  volatilization  of  a  substance  is 
not  very  high,  glass  vessels  are  used  for  the  generation  of  vapor ;  of  these  there 
are  two  kinds,  retorts  and  flasks. 

RETORTS. — For  simple  distillation,  the  form  of  the  retort  is  not  very  import- 
ant; it  is  desirable,  however,  that  the  neck  should  taper  off  gradually,  and  be 
tolerably  long. 

In  selecting  retorts,  it  should  be  observed  that  the  inner  concave  portion  of 
the  bend  be  not  sharp  or  in  folds,  and  that  the  opposite  convex  surface  be  round. 
Great  care  must  also  be  taken  that  the  bulb  or  body  of  the  retort  is  uniform, 
and  moderately  thin  in  substance,  and  as  free  from  air-bubbles  and  spots  as 
possible.  A  good  retort  should  be  fhinnest  at  the  bottom,  and  increase  gradually, 
but  slightly,  in  substance  towards  the  neck. 

Retorts  are  made  both  plain  and  tubulated.  The  former  are  more  likely  to 
stand  any  sudden  change  of  temperature,  on  account  of  their  greater  uniformity; 
but  the  latter  are  far  more  convenient,  as  the  operator  has  easy  access  to  the 
interior.  Tubulated  retorts  are  generally  fitted  with  glass  stoppers,  which,  if 
they  are  ground  in  accurately,  have  great  advantages  over  corks.  The  stopper 
should  be  slightly  conical,  and  when  moved  in  the  aperture  should  feel  per- 
fectly firm  and  steady. 

In  charging  a  plain  retort  with  a  liquid  or  solid,  a  few  precautions  must  be 
attended  to.  The  neck  of  the  retort  must  be  perfectly  clean  and  dry,  so  that  no 
particles  of  a  solid  will  adhere  to  it.  The  solid,  in  the  state  of  lumps  or  powder, 
is  introduced  by  means  of  a  card,  or  of  a  funnel  if  necessary,  so  as  to  fall  down 
one  side  of  the  neck,  the  latter  being  inclined  at  an  angle  of  about  40° ;  the  retort 
must  not  be  held  with  the  bottom  of  the  bulb  downwards,  but  inclined  upwards, 
to  prevent  any  lumps  from  falling  suddenly  upon  it.  A  conical  paper  tube  may 
also  be  used  for  the  introduction  of  the  substance.  Liquids  are  introduced  into 
plain  retorts  either  through  a  funnel-tube,  or  piece  of  wide  glass  tube,  sufficiently 


80  DISTILLATION. 

long  to  reach  the  bulb  of  the  retort  and  protrude  two  or  three  inches  at  the  other 
extremity  of  the  neck.  During  the  introduction  of  liquids,  the  bottom  of  the 
retort  should  be  inclined  downwards. 

Tubulated  retorts  are  charged  with  greater  ease  through  the  upper  aperture. 
Liquids  are  poured  in  through  funnels  sufficiently  long  to  pass  into  the  body  of 
the  retort  below  the  neck ;  solids  are  either  introduced  through  wide-necked  fun- 
nels (their  descent  being  aided  by  the  introduction  of  a  bit  of  wire  in  the  neck, 
which  is  moved  backwards  and  forwards),  or  if  in  the  state  of  coarse  powder  or 
lumps,  they  are  introduced  by  means  of  cards,  which  are  either  held  to  the  open- 
ing by  the  hand  and  slightly  agitated,  or  tied  round  the  outside  of  the  aperture, 
so  as  to  form  a  very  wide  funnel.  The  neck  of  the  retort  should  be  inclined 
upwards,  to  prevent  any  of  the  descending  solid  from  falling  into  and  soiling  it. 

FLASKS. — The  flasks  used  for  distillation  are  the  same  as  those  recommended 
for  the  generation  of  gases  (§  23).  When  there  is  any  great  risk  of  the  distil- 
lation terminating  in  the  fracture  of  the  vessel,  as  is  frequently  the  case  in  dry 
distillations,  Florence  flasks  are  generally  used  on  account  of  their  cheapness. 

These  and  other  flasks,  employed  as  retorts,  are  fitted  by  means  of  cork  and 
luting  with  a  wide- tube,  bent  at  a  somewhat  acute  angle,  the  longer  arm  of  which 
passes  into  the  condenser.  The  short  end  of  the  tube,  fitting  into  the  flask, 
should  not  be  above  two  inches  in  length. 

If  the  vapor  disengaged  in  the  operation  is  very  heavy,  or  easily  condensable, 
great  difficulty  will  be  experienced  in  making  it  pass  over  the  bend  of  the  tube 
into  the  condenser.  In  such  cases,  the  neck  of  the  flask  should  be  inclined  con- 
siderably, and  fitted  with  a  tube  as  above,  only  bent  at  an  obtuse  angle ;  by  this 
contrivance,  the  vapors  pass  over  more  easily. 

In  cases  where  the  vapor  condenses  readily,  before  it  passes  the  cork  of  the 
flask,  and  runs  back  into  the  latter,  it  is  advisable  that  the  bent  tube  should  be 
sufficiently  wide  at  the  short  end  to  admit  of  the  neck  of  the  flask  being  tightly 
fitted  into  it ;  the  longer  end  should  taper  off  gradually,  like  the  neck  of  a  retort ; 
in  fact,  the  neck  of  a  broken  retort,  properly  bent,  answers  very  well  for  this 
purpose. 

If  the  substance  to  be  distilled  be  fluid  or  semi-fluid,  or  if  it  is  likely  to  swell 
up  from  the  disengagement  of  a  gas,  or  ebullition,  the  retort  or  flask  used  should 
not  be  filled  more  than  one-half;  but  if  there  be  no  such  risk,  the  charge  may 
be  allowed  to  fill  two-thirds  of  the  body  of  the  vessel. 

For  the  condensation  of  volatile  liquids,  distilled  from  retorts  or  flasks,  the 
Liebig's  condenser  is  always  employed,  and  the  receiver  surrounded  with  a  cool- 
ing mixture,  if  necessary.  If  the  product  be  easily  condensable,  a  long,  wide 
glass-tube  may  be  substituted  for  the-  condenser,  and,  if  necessary,  wrapped 
round  with  strips  of  coarse  blotting-paper,  which  are  moistened  from  time  to 
time  with  cold  water. 

In  very  small  operations,  such  tubes  may  even  be  employed  for  rather  volatile 
liquids,  a  little  ether  being  substituted  for  the  water  with  which  the  paper  is 
moistened. 

If  the  neck  of  a  retort,  or  tube  of  a  distilling-flask,  is  sufficiently  small  in 
dimensions  in  comparison  to  the  wide  opening  of  the  condenser  or  adapter,  it 
may  be  fitted  into  the  latter  by  means  of  a  perforated  cork  and  luting.  In  many 
cases,  however,  the  neck  of  a  retort,  if  introduced  far  enough  into  the  condenser, 
will  fit  the  latter  too  closely  to  permit  the  interposition  of  luting  or  cork  between 
the  two. 

A  very  tight  joint  may  then  be  made,  by  wrapping  a  strip  of  bladder,  which  has 
been  softened  in  warm  water,  three  or  four  times  round  the  spot  where  the  retort- 
neck  or  tube  and  the  extremity  of  the  condenser  touch ;  the  apparatus  should 
be  steadied  with  the  left  hand,  and  the  bladder,  having  been  wrapped  once  round, 
pulled  slightly  with  the  other,  to  make  it  close  tightly  round  the  glass,  and  then 


DISTILLATION.  81 

wrapped  round  again.  Should  the  edges  of  the  bladder  not  close  upon  the  glass 
perfectly,  they  may  be  bound  down  to  it  by  means  of  two  very  narrow  slips  of 
bladder,  applied  in  the  same  manner,  or  may  be  tied  with  string.  A  joint  of 
this  description  is  very  firm  and  tight  when  dry,  as  the  bladder  then  contracts 
considerably.  It  is,  indeed,  always  advisable,  if  possible,  to  make  use  of  this 
description  of  joint  in  distillations,  as  in  many  operations,  the  cork,  and  even 
the  lute,  wiH  be  attacked  by  the  vapors  disengaged,  and  the  tightness  of  the 
joint  soon  destroyed;  the  products  of  the  distillation  will  also  frequently  become 
tinged,  by  dissolving  minute  portions  of  the  cork.  In  the  distillation  of  strong 
acids,  it  becomes  necessary,  however,  to  effect  the  junction  with  bladder  coated 
internally  with  plaster  of  Paris. 

In  distillations  of  very  small  quantities,  little  retorts,  blown  before  the  lamp 
out  of  moderately  wide  glass  tubes,  are  used;  these  may  also  be  replaced  by  short, 
wide  test-tubes,  provided  with  a  bent  tube.  Similar  tubes  may  then  also  be  con- 
veniently used  as  receivers,  since  they  may  be  surrounded  to  a  considerable  depth 
by  a  cooling  mixture. 

In  some  cases,  where  the  distillate  is  to  be  permitted  to  return  continually  to 
the  retort,  as  in  digestions,  or  operations  requiring  some  time  for  their  comple- 
tion, it  is  well  to  reverse  the  ordinary  direction  of  the  retort-neck  and  condenser, 
allowing  these  to  point  upwards,  so  that  the  condensed  vapors  may  flow  back 
again. 

§  41.  The  proper  application  of  heat  in  distillation  is  the  most  important 
point  upon  which  the  safety  and  success  of  the  operation  entirely  depends. 

The  retort  or  flask  is  placed  upon  a  sand-bath,  and  the  upper  portion  properly 
supported  by  the  ring  of  a  retort-stand,  or  some  other  support,  in  such  a  manner, 
however,  that  it  will  admit  of  being  slightly  moved  about. 

If  a  somewhat  higher  temperature  is  required  than  is  procurable  by  sand-heat, 
the  wire-gauze  support  may  be  substituted  for  the  sand-bath.  Before  heat  is 
applied,  great  care  must  be  taken  to  ascertain  that  the  outside  of  the  vessel,  and 
the  sand  employed,  are  perfectly  dry,  or  great  risk  will  be  incurred  of  the  flask 
or  retort  cracking  as  the  temperature  becomes  somewhat  high.  Heat  must  be 
applied  very  gradually  at  first,  and  slowly  increased  until  the  liquid  boils,  or  the 
distillation  has  fairly  commenced,  when  the  full  heat  requisite  for  the  operation 
may  be  applied. 

The  flame  of  the  lamp  employed  must  never  be  allowed  to  reach  any  portion 
of  the  glass  vessel  beyond  that  which  contains  the  substance  to  be  distilled,  lest 
it  be  cracked  by  coming  in  contact  with  the  cooler  liquid.  Great  care  must  be 
taken  to  keep  the  retort  and  the  lamp  out  of  the  reach  of  any  draught;  a  cur- 
rent of  cool  air,  on  approaching  a  hot  retort,  will  very  frequently  cause  its 
fracture,  and,  at  any  rate,  the  flame  of  the  lamp,  on  being  blown  about  by  a 
draught,  is  very  likely  to  touch  the  sides  of  the  vessel,  and  cause  fracture,  as 
above  stated ;  it  is  therefore  advisable  to  protect  the  body  of  the  retort  and  the 
lamp  by  means  of  a  screen. 

Much  waste  of  heat,  and  sometimes  also  of  material,  arises  from  the  partial 
condensation,  in  the  upper  part  of  the  retort,  of  the  vapors  disengaged  in  the 
lower  part,  owing  to  the  great  difference  of  the  tem- 
perature.   When  the  temperature  has  been  raised  to  Fig-  47. 
the  highest  pitch,  the  liquid  returning  to  the  bottom 
of  the  retort  will  frequently  undergo  decomposition. 
This  loss  may  be  avoided,  by  covering  the  upper  por- 
tion of  the  retort  with  a  hood  or  cone  of  thick  paper, 
cardboard,  flannel,  or  better,  of  tin-plate — a  con- 
trivance which  prevents  radiation,  and  saves  much 
heat.     When  a  distillation  is  finished,  the  lamp  is 
extinguished ;  but  the  retort  is  allowed  to  remain 
6 


82  DETERMINATION   OF   BOILING  POINTS. 

upon  the  hot  sand  or  gauze,  so  as  to  cool  down  very  gradually;  the  bottom 
should  not  be  exposed  to  the  air  until  it  is  nearly  cool.  The  retort  may  then  be 
disconnected  from  the  remaining  apparatus,  and  water  or  other,  solvents  intro- 
duced for  the  purpose  of  removing  any  residue. 

Much  difficulty  is  sometimes  met  with  in  the  distillation  of  various  liquids, 
such  as  dilute  alcohol,  alcoholic  extracts,  or  solutions  of  salts  and  oils  mixed 
with  water;  the  contents  of  the  retort  not  boiling  at  all  for  one  moment,  and, 
in  the  next,  bursting  into  vapor  suddenly,  and  sometimes  with  such  force  as  to 
eject  the  contents  of  the  retort,  and  even  to  break  the  latter.  This  may  be,  in 
most  cases  prevented,  or  considerably  diminished,  by  the  introduction  into  the 
retort  of  angular  fragments  of  glass  or  metal,  or  coils  of  metallic  wire  (platinum, 
copper,  or  silver  being  preferable).  If  two  liquids  are  to  be  distilled  together, 
such  as  oils  and  water,  which  are  not  miscible,  but  separate  into  two  layers,  long 
coils  of  wire,  or  pieces  of  wood,  extending  through  both  liquids,  should  be  intro- 
duced into  the  retort. 

These  promoters  of  regular  vaporization  must,  however,  never  be  introduced 
while  the  liquid  is  hot,  as  they  would,  in  most  cases,  occasion  such  an  instanta- 
neous and  powerful  disengagement  of  vapor  as  to  cause  great  loss  of  the  sub- 
stance, and  danger  to  the  apparatus  and  operator.1 

DISTILLATION   AT   TEMPERATURES   BELOW   212°. 

§  42.  The  form  of  apparatus  employed  for  distillations  at  low  temperatures  is 
precisely  the  same  as  that  already  described ;  the  only  difference  is  in  the  appli- 
cation of  heat  to  the  retort.  Instead  of  placing  the  latter  upon  a  sand-bath,  or 
wire  gauze,  it  is  placed  in  a  vessel  of  copper  or  tin-plate,  which  is  then  nearly 
filled  with  water,  a  proper  allowance  being  made  for  the  expansion  of  the  latter 
when  heated.  This  vessel  (which  is  termed  a  water-lath)  is  selected,  if  possi- 
ble, of  such  a  depth  as  to  admit  of  the  whole  .body  of  the  retort  or  flask  being 
immersed  in  water ;  a  small  ring  of  straw,  or  a  piece  of  rag  folded  three  or  four 
times,  is  placed  at  the  bottom  of  the  vessel,  so  as  to  interpose  between  it  and 
the  metal.  The  water  in  the  bath  is  then  gradually  heated  by  means  of  a  lamp 
to  the  temperature  required  for  the  distillation  of  the  substance,  and  its  original 
bulk  in  the  vessel  kept  up  by  the  addition  of  water,  until  the  operation  is  com- 
pleted. 

This  mode  of  distillation  affords  the  most  convenient  a$d  safest  means  of 
removing  alcohol  or  ether  from  extracts.3 

DETERMINATION   O^BOILING  POINTS. 

§  43.  The  boiling  points  of  many  liquids  afford  a  most  valuable  means  of 
testing  their  purity,  and  separating  them  from  each  other.  The  latter  object  is 
effected  by  simply  collecting  in  separate  receivers  the  products  that  are  observed 
to  pass  over  at  different  temperatures  during  an  operation. 

This  is  consequently  an  easy  method  of  separating  a  liquid  from  small  quan- 
tities of  impurities,  provided  they  differ  sufficiently  in  their  boiling  points.3 

1  It  may  be  proper  to  mention  that  the  distillation  of  oil  of  vitriol,  which  is  attended 
"with  great  danger  of  succussion,  is  effected  by  means  of  a  furnace  constructed  for  the 
purpose,  in  such  a  manner  that  the  heat  is  applied  to  the  surface  of  the  liquid,  the  bottom 
of  the  retort  projecting  below  the  grate.     The  introduction  of  small  pieces  of  quartz  into 
the  retort  has  also  been  recommended,  to  prevent  succussion  in  the  rectification  of  oil  of 
vitriol. 

2  If  an  uniform  temperature,  somewhat  above  212°  F.  (100°  C.),  be  required  for  a  dis- 
tillation, saline  solutions,  boiling   at   the   requisite  temperature,  may  be   conveniently 
employed.     Sometimes  even  an  oil  may  be  substituted. 

3  This  process  is  generally  known  as  fractional  distillation. 


DETERMINATION   OF   BOILING  POINTS.  83 

The  temperature  of  ebullition  of  a  liquid  may  be  ascertained  by  observing  the 
degree  at  which  it  constantly  boils,  and  repeating  the  observation  several  times 
with  the  product,  in  the  manner  to  be  presently  described.  In  order  to  deter- 
mine this  point,  it  is  necessary  to  have  a  thermometer  in  the  retort  during  the 
distillation. 

The  thermometers  employed  for  this  purpose  have  the  scale  marked  upon  the 
glass,  instead  of  being  provided  with  a  wooden  or  metal  scale;  they  are  round, 
and  the  mercury-bulb,  instead  of  being  globular,  is  elongated,  and  as  nearly  as 
possible  equal  in  diameter  to  the  stem.  A  good  cork,  fitting  accurately  into  the 
aperture  of  the  tubulated  retort  to  be  employed,  is  perforated  so  as  to  fit  tightly 
upon  the  stem  of  the  thermometer.  It  is  then  cut  through  on  one  side  with  a 
very  sharp  knife,  and  adjusted  upon  the  thermometer,  which  can  now  be  done 
with  ease  and  safety  in  such  a  manner  that  the  bulb  of  the  latter,  when  fixed  in 
the  retort,  reaches  to  within  a  quarter  of  an  inch  of  the  bottom.  The  retort 
having  been  charged  with  the  liquid  to  be  distilled,  which  must  not  occupy  more 
than  two-thirds  its  capacity,  a  small  coil  of  platinum-wire  is  introduced,  and  the 
thermometer  is  then  fitted  into  the  retort,  the  two  edges  of  the  cork  being  pressed 
firmly  together,  while  it  is  gradually  screwed  as  far  as  possible  into  the  aperture, 
care  being  taken  to  have  the  side  of  the  thermometer  on  which  the  scale  is 
marked  facing  the  operator.  The  degrees  are  more  easily  read  off  when  a  piece 
of  white  paper  is  held  behind  the  stem. 

In  determining  the  boiling  point  of  a  liquid,  or  for  separating  one  liquid  from 
another  by  their  boiling  points,  the  following  general  directions  will  be  found 
useful : — 

Great  care  should  be  taken  that  the  retort  and  condenser  or  adapter,  employed 
in  the  operation,  be  perfectly  clean  and  dry  before  they  are  connected.  Several 
stoppered  bottles,  or  other  vessels,  as  receivers,  perfectly  dry  and  clean,  should 
be  got  ready  before  the  operation,  each  provided  with  a  plain  label,  upon  which 
any  remark  may  be  written. 

The  first  portion  of  any  liquid  distilling  over  is  likely  to  contain  impurities; 
the  thermometer  will  therefore  be  observed  to  rise  gradually  until  these  have 
passed  over,  together  with  some  of  the  liquid.  As  soon  as  the  thermometer  has 
remained  stationary  for  about  half  a  minute,  the  first  receiver  is  changed  for  a 
fresh  one  (the  temperature  being  marked  upon  the  former,  between  which  the 
liquid  it  contains  passed  over) ;  the  distillation  is  then  proceeded  with  until  the 
temperature  again  rises ;  an  increase  of  five  degrees  is  allowed,  the  receiver  is 
then  replaced  by  a  third,  and  properly  labelled.  Should  the  thermometer  again 
become  stationary,  the  receiver  is  once  more  changed,  and  the  product  collected 
within  the  range  of  five  degrees,  as  before.  Towards  the  end  of  the  operation, 
the  temperature  generally  rises  rapidly,  and  the  product  is  frequently  colored, 
owing  to  the  decomposition  of  some  of  the  substance  in  the  retort.  Those  pro- 
ducts that  have  been  collected  at  a  definite  temperature  are  generally  rectified 
once  or  twice  more  in  the  same  manner,  the  first  and  last  portions  being 
collected  separately  from  that  which  again  passes  over  while  the  thermometer 
remains  stationary. 

In  each  successive  rectification,  the  range  of  temperature  will  be  observed  to 
decrease  considerably.  The  receiver  must  always  be  marked  with  the  tempera- 
tures between  which  the  liquid  they  contained  passed  over,  directly  they  are 
removed  from  the  apparatus,  in  order  to  avoid  errors. 

The  boiling  points  of  liquids  distilling  below  212°  are  taken  from  the  water- 
bath  in  the  manner  already  described. 

It  is  advisable,  before  submitting  a  liquid  to  an  operation  of  this  kind,  to 
allow  it  to  remain  for  some  time  in  contact  with  some  desiccating  agent,  and 
even  to  rectify  it  afterwards  over  a  fresh  portion  of  the  latter,  previously  to  its 
distillation  with  the  thermometer. 


84  DISINTEGRATION. 

When  the  quantity  of  liquid  to  be  distilled  with  the  thermometer  is  very  small, 
a  tube  retort  may  be  employed,  into  which  a  thermometer  is  fitted. 


SUBLIMATION. 

§  44.  The  apparatus  generally  employed  for  sublimation  are  retorts  or  flasks 
fitted  with  wide  bent-tubes,  flat  evaporating-dishes,  and  earthen  or  metal- pans. 

The  more  volatile  substances  may  be  sublimed  from  retorts  or  flasks  lead- 
ing into  proper  receivers.  The  process  is  conducted  like  that  of  distillation, 
with  this  exception,  that  any  cooling  arrangements  that  may  be  requisite  are 
applied  to  the  receiver,  into  which  the  retort-neck  or  tube  of  the  flask  is  inserted 
to  some  distance.  Should  the  substance  condense  in  the  neck  or  tube,  a  gentle 
heat  should  be  applied  to  the  latter,  by  moving  a  spirit-lamp  to  and  fro  along  it, 
until  the  product  volatilizes  again. 

Substances  requiring  a  higher  temperature  may  also  be  sublimed  from  Florence 
flasks,  by  placing  the  latter  in  a  deep  sand-bath,  and  imbedding  them  in  sand, 
which  may  be  gradually  raised  to  a  very  high  temperature  over  a  fire. 

Sublimation  may  be  performed  by  placing  the  substance  in  a  basin,  and  cover- 
ing it  with  another,  in  which  water  is  placed;  as  the  substance  passes  over  into 
vapor  from  the  heat  applied  to  the  lower  basin,  it  condenses  upon  the  cool  bottom 
of  the  upper  one. 

A  very  convenient  way  of  purifying  substances  by  sublimation  is  to  place  them 
in  a  pan  or  crucible,  the  mouth  of  which  is  afterwards  tied 
Fig.  48.  over  with  moderately  coarse  filtering-paper  perforated  with 

a  number  of  pin-holes.  A  cone  or  cylinder  of  stiff  paper, 
closed  at  one  end,  is  then  tied,  or  fixed  with  paste,  round 
the  edge  of  the  vessel,  to  which  heat  is  then  applied.  The 
vapors  are  purified  from  any  mechanical  impurities  as  they 
pass  through  the  filtering-paper,  and  condense  upon  the  inner 
surface  of  the  cone  or  cylinder,  from  whence  they  may  be 
removed  with  ease  after  the  operation  is  completed. 

In  separating  volatile  substances  by  sublimation  from  other 
matters,  it  is  advisable  to  powder  the  substance  finely,  and 
to  mix  it  with  from  one-third  to  one-half  its  bulk  of  sand, 
previously  to  its  being  heated.     The  same  precautions  should  be  taken  in  the 
application  of  heat  as  those  recommended  in  distillations. 


DISINTEGRATION. 

§  45.  It  is  frequently  necessary,  or  highly  advantageous,  to  reduce  solid  mat- 
ter to  a  minute  state  of  division  by  mechanical  means.  Various  processes  are 
resorted  to  for  this  purpose;  large  masses  are  reduced  to  smaller  lumps,  and  even 
to  a  coarse  powder,  by  the  hammer,  particularly  if  they  are  very  hard.  For 
this  purpose  the  mass  may,  in  some  cases,  be  held  lightly  in  the  left  hand,  and 
struck  smartly  with  the  hammer ;  or,  if  the  substance  be  very  hard,  or  in  smaller 
masses,  it  may  be  split  or  crushed  upon  the  anvil.  It  is  advisable,  at  times,  to 
wrap  the  mass  in  two  or  three  folds  of  cloth  or  thick  paper,  in  order  the  better 
to  retain  the  fragments.  The  blows  applied  should  be  smart,  and  their  force 
gradually  increased.  Tough  metals  and  alloys,  which^cannot  be  broken  by  mere 
hammering  upon  an  anvil  in  the  cold,  are  cut  with  nippers  or  a  knife,  if  suffi- 
ciently soft  and  thin,  or  heated  to  redness,  and  struck  in  that  state  until  they 
crack,  when  they  may  be  completely  separated  in  the  vice. 


DISINTEGRATION.  85 

If  the  metal  or  alloy  is  not  so  hard,  and  is  required  in  a  somewhat  fine  state 
of  division,  it  may  be  reduced  to  that  state  by  means  of  a  clean  hard  file.1 

Substances  are  most  frequently  reduced  from  large  to  smaller  lumps,  or  to 
powders  of  various  degrees  of  fineness,  by  means  of  the  mortar  and  pestle.  This 
instrument  is  made  of  various  dimensions  and  materials ;  the  most  common  of 
the  latter  are  iron,  Wedgwood,  and  Berlin  ware.  The  iron  mortars  are  used  for 
the  reduction  of  very  hard  substances;  those  of  stoneware  should  admit  of  the 
pulverization  of  most  substances  of  average  hardness,  and  the  preparation  of  solu- 
tions, acid  or  alkaline.  The  pestle  should,  if  possible,  be  of  one  piece ;  or  if  the 
handle  is  of  wood,  care  should  be  taken  that  it  is  well-seasoned,  close-grained, 
and  very  tightly  screwed  and  cemented  into  the  bottom.  The  handle  should  be 
of  a  proper  size  to  admit  of  its  being  firmly  grasped  by  the  hand ;  the  diameter 
of  the  lower  part  may  be  about  one-fourth  of  the  upper  diameter  of  the  mortar ; 
its  curve  should  be  somewhat  greater  than  that  of  the  mortar.  Small  pestles 
and  mortars  made  of  agate  are  employed  for  the  pulverization  of  very  hard  sub- 
stances or  small  portions  of  matter.  Very  hard  substances  may  also  be  conve- 
niently reduced  to  powder  by  means  of  a  crushing  mortar,  which  consists  of  a 
stout  steel  cylindrical  chamber,  into  which  fits  a  cylinder  sufficiently  small  to 
pass  with  ease  into  the  cavity.  The  substance  being  introduced  into  the  mortar, 
the  cylinder  is  placed  upon  it,  and  then  forced  down  by  repeated  blows  of  a  ham- 
mer ;  a  powder  may  thus  be  obtained  of  any  degree  of  fineness,  without  any 
risk  of  the  material  being  dispersed. 

In  breaking  a  substance  in  a  mortar  it  should  be  struck  with  sharp  and  rapid, 
but  not  too  powerful  blows  by  the  pestle.  If  the  substance  is  tough,  consider- 
able momentum  should  be  given  to  the  pestle ;  but  if  brittle,  it  should  be  held 
lightly  in  the  hand,  and  allowed  to  fall  with  little  more  than  its  own  force.  To 
prevent  any  fragments  from  flying  out  of  the  mortar  as  they  are  separated,  the 
latter  should  be  kept  covered  during  the  operation  with  a  flat  piece  of  mill-board, 
having  a  hole  in  the  centre  through  which  the  pestle  can  pass ;  or  a  cloth,  with 
a  hole  in  the  centre,  should  be  drawn  over  the  mouth  of  the  mortar,  and  held 
down  on  one  side  with  the  hand. 

§  46.  The  substance  having  been  broken  up  into  small  fragments  is  next  pul- 
verized. Instead  of  allowing  the  pestle  to  fall,  as  it  were,  upon  the  substance, 
it  is  forced  down  upon  it  by  being  made  to  press  it  from  the  side  of  the  mortar 
towards  the  centre.  The  stroke  should  be  continued  in  one  direction  while  the 
mortar  is  turned  slowly  with  the  left  hand ;  in  this  manner  the  whole  of  the 
substance  will  gradually  come  under  the  pestle. 

When  the  substance  is  reduced  to  a  coarse  powder,  the  comminution  is 
completed  by  trituration. 

The  quantity  of  substance  placed  in  the  mortar  at  one  time  should  not  be  too 
large,  so  that  coarse  particles  may  not  become  imbedded  in  the  fine  portion,  and 
thus  escape  trituration.  Thus,  when  a  lump  is  to  be  reduced  to  fine  powder,  it 
should  be  first  coarsely  pulverized,  and  then  a  small  portion  of  this  powder 
operated  upon  at  a  time,  in  order  to  reduce  it  to  a  proper  fineness.  Substances 
may  be  transferred  to  or  from  a  mortar,  or  loosened  from  its  sides,  by  means  of 
a  spatula. 

Bone  spatulas  (flat  paper-knives)  may  be  used  if  the  substance  is  not  likely 
to  affect  them.  Bright  steel  spatulas  are  also  convenient  at  times,  on  account 
of  their  greater  flexibility ;  they  must,  however,  always  be  cleaned  after  use, 
carefully,  or  they  will  soon  become  unfit  for  this  purpose.  Should  the  material 
operated  upon  attack  bone  or  steel,  a  spatula  of  platinum  or  palladium  must  be 

1  The  particles  of  steel  detached  from  the  file  in  this  operation  may  in  some  cases  be 
removed  by  a  magnet. 


86  SOLUTION. 

employed.  Pieces  of  card  or  thick  paper  may  also  be  substituted  for  the  spatula, 
if  the  powder  is  coarse,  or  if  the  material  is  soft  and  perfectly  dry. 

When  it  is  desired  to  obtain  a  powder  of  great  and  uniform  fineness,  the 
process  of  levigation  is  resorted  to.  This  consists  in  adding  water  to  the  substance 
in  the  mortar  when  it  has  been  rubbed  for  some  time,  mixing  the  powder  well 
up  in  it,  and  then  allowing  it  to  stand  for  a  short  time ;  the  coarse  particles  will 
descend  rapidly  to  the  bottom,  while  the  finer  remain  a  longer  time  suspended 
in  the  water,  which  is  then  poured  into  a  deep  basin  or  jar,  and  the  fine  powder 
allowed  to  subside,  the  heavier  portion  being  left  behind  in  the  mortar,  together 
with  a  little  water.  This  is  again  subjected  to  trituration  for  some  time,  and 
the  above  operation  repeated ;  the  disintegration  of  the  coarse  portion  is  pro- 
ceeded with  in  this  manner  until  nothing  is  left  in  the  mortar.  As  soon  as  the 
water  has  become  quite  clear,  it  may  be  poured  off,  and  the  powder  dried.  It 
is  sometimes  necessary  to  submit  the  powder  thus  obtained  to  a  second  set  of 
operations  similar  to  the  above,  to  obtain  the  requisite  fineness. 

Many  metals  which  are  required  in  small  fragments  may  be  reduced  to  the 
proper  state  of  division  by  granulation.  The  metal  is  melted  in  a  crucible,  and 
when  perfectly  liquid,  poured  from  a  height  of  three  or  four  feet  into  a  pail,  or 
other  deep  vessel,  filled  with  water. 

The  crucible  should  be  moved  about  while  the  metal  is  poured  out,  so  that 
the  granular  fragments  may  be  dispersed  over  the  bottom  of  the  vessel,  as  they 
would  otherwise  adhere,  forming  a  coherent  mass  of  granulation  which  is  more 
or  less  difficult  to  separate. 

Chemical  means  are  frequently  resorted  to  for  the  reduction  of  gold,  silver, 
copper,  platinum,  and  lead,  to  a  fine  state  of  division. 

Gold  may  be  obtained  in  a  pulverulent  state  by  boiling  its  terchloride  with  a 
solution  of  oxalic  acid,  or  by  mixing  it  with  a  solution  of  sulphate  of  iron ; 
silver,  by  the  introduction  of  a  plate  of  copper  into  a  solution  of  its  nitrate,  and 
brushing  the  metal  off  from  the  plate  as  it  is  deposited ;  lead,  by  the  introduc- 
tion of  a  plate  of  zinc  into  its  slightly  acid  solution ;  platinum,  by  heating  the 
ammonio-chloride  of  that  metal  to  redness  in  a  crucible;1  copper,  by  the  immer- 
sion of  a  piece  of  clean  iron  in  its  solution.  All  the  metallic  powders  thus 
obtained,  excepting  platinum,  require  to  be  purified  by  repeated  washings. 


SOLUTION,  INFUSION,  DIGESTION,   SATURATION, 

ETC. 

§  47.  SOLUTION  is  of  two  kinds ;  it  is  either  effected  by  liquids  which  exert 
no  chemical  influence  upon  the  substances  dissolved,  or  by  such  as  alter,  to  a 
greater  or  less  extent,  their  chemical  condition.  To  the  former  class  belong 
•water,  alcohol,  ether,  volatile  and  heavy  oils,  to  the  latter  the  principal  acids. 

The  most  important  solvent  is  water;  ,the  others  are  only  resorted  to  when  its 
application  is  ineffectual,  or  its  solvent  powers  insufficient. 

Various  means  may  be  resorted  to  for  ascertaining  the  solubility  of  a  body  ; 
the  most  simple  and  effectual  method  in  the  case  of  solids,  is  to  expose  a  small 
portion  of  the  substance  to  the  action  of  the  solvent,  with  the  aid  of  heat,  to 
separate  the  liquid  (two  or  three  drops  sufficing)  by  means  of  a  filter,  from  any 
portion  of  the  substance  that  is  not  acted  upon,  and  to  evaporate  it  slowly  and 
at  a  low  temperature  in  a  small  porcelain  or  platinum  vessel,  or  on  a  platinum 
spatula  or  piece  of  flat  foil;  should  any  residuum  be  obtained,  it  is  clear  that 
the  solvent  has  acted  upon  the  substance,  or  some  portion  of  it.  The  solubility 
of  a  liquid  may  be  indicated  by  agitating  a  small  portion  of  known  bulk  of  the 

1  The  finely-divided  platinum  thus  obtained  is  termed  spongy  platinum. 


SOLUTION.  87 

latter  together  with  the  solvent,  and  observing  whether,  after  the  liquids  have 
been  properly  mixed,  any  separation  takes  place,  or  whether  the  substance  to  be 
dissolved  has  decreased  in  bulk.  The  solubility  of  a  yas  may  be  ascertained  by 
observing  whether  the  bubbles  passing  through  the  solvent  diminish  in  size,  or 
whether,  on  agitating  a  portion  of  the  gas  in  a  closed  vessel  together  with  the 
solvent,  absorption  takes  place.  The  solvent  power  of  a  liquid,  at  ordinary 
temperatures,  is  generally  increased  more  or  less  by  the  application  of  heat. 

Numerous  kinds  of  vessels  are  employed  for  effecting  solution.  When  the 
application  of  heat  is  not  required,  the  substance  may  be  dissolved  in  stout  glass 
vessels  of  various  forms,  test-glasses  or  lipped  glasses,  and  jars  may  be  used; 
should  the  substance  require  the  aid  of  much  agitation  to  effect  its  solution,  it 
may  be  shaken  together  with  the  solvent  in  a  stoppered  or  corked  bottle  of  such 
dimensions  as  not  to  be  more  than  two-thirds  filled  by  the  liquid. 

The  apparatus  employed  in  the  solution  of  substances  by  the  aid  of  heat,  are 
dishes  and  capsules,  beakers,  flasks,  and  stirrers. 

DISHES. — These  are  made  of  various  materials;  those  of  earthen  and  Wedg- 
wood ware  will  answer  for  the  solution  of  many  substances  not  requiring  the 
application  of  a  very  high  temperature ;  great  care  must,  however,  be  taken  that 
they  are  compact  in  substance,  so  as  not  to  absorb  any  solution  that  may  be  in- 
troduced into  them.  They  should  not  become  stained  by  solutions  of  sulphate 
of  copper  or  of  indigo.  The  best  dishes  are  those  made  of  Berlin  or  Meissen 
porcelain,  since  they  are  very  compact,  and  thoroughly  glazed.  They  should  be 
lipped,  and  should  be  selected  as  thin  as  possible,  varying  from  one-eighth  to 
one-fourth  of  an  inch,  according  to  their  size.  WThen  employed  for  effecting 
solution,  these  dishes  should  be  chosen  as  deep  as  possible.  The  substance,  and 
particularly  the  glazing,  of  porcelain  and  earthenware  dishes,  is  attacked,  and 
sometimes  to  a  great  extent,  by  the  solutions  of  various  chemical  compounds; 
in  such  cases  it  is  necessary  to  have  recourse  to  dishes  of  silver,  or  even  small 
dishes  or  capsules  of  platinum.  These  should  be  provided  with  a  lip. 

BEAKERS. — These  glass  vessels  are  exceedingly  useful  for  effecting  solutions, 
since  they  are  generally  very  thin  and  uniform  in  substance,  and  made  of  well 
annealed  glass. 

They  are  also  very  tall  in  proportion  to  their  diameter,  which  is  likewise  a 
great  advantage.  They  may  be  had  of  various  sizes,  from  two  inches  to  ten  or 
twelve  inches  in  height,  and  of  proportionate  diameter.  Great  care  must  be 
taken  that  the  bottoms  be  not  thicker  in  substance  than  the  sides,  and  that  they 
are  without  the  knot  or  punty-mark  at  the  bottom.  A  flatter  kind  of  beaker, 
provided  with  a  lip,  is  also  imported  from  Germany,  and  is  very  convenient  for 
effecting  solutions. 

FLASKS. — The  cheapest  (and,  in  most  cases,  superior)  flasks  for  dissolving 
substances,  are  the  Florence  oil-flasks;  they  have  the  advantage  of  being  gener- 
ally very  thin  at  the  bottom.  When  larger  flasks  are  required,  they  should  be 
of  flint-glass ;  those  of  German  manufacture  are  generally  the  best,  on  account 
of  their  uniformity  of  substance,  and  the  goodness  of  the  glass.  It  is  more 
convenient  to  have  flat-bottomed  flasks  for  general  purposes;  the  bottom  should 
be  uniform  in  thickness  with  the  upper  part  of  the  flask,  if  not  thinner ;  the 
necks  should  be  rather  wide,  and  provided  with  a  projecting  ring  of  glass,  by 
which  they  may  be  securely  held.  If  the  flasks  are  round-bottomed,  they  may 
be  conveniently  supported  on  the  table  by  the  list-rings  already  referred  to. 

The  STIRRERS  employed  are  generally  made  of  solid  glass  rod,  from  one-sixth 
to  one-third  of  an  inch  in  diameter,  and  four  to  ten  inches  in  length.  Their 
extremities  should  be  carefully  rounded  off  by  fusion  before  the  blowpipe.  Some 
may  be  flattened,  and  others  provided  with  a  button  of  glass  at  the  extremities. 

§  48.  Solution  may  sometimes  be  effected  in  a  mortar,  by  following  the  direc- 
tions prescribed  for  levigation,  and  continuing  the  process  until  the  whole  of  the 


88  SOLUTION. 

soluble  substance  has  been  removed  from  the  mortar.  Solution  is  always  aided 
by  previous  mechanical  division  of  the  substance,  particularly  if  only  a  portion 
of  the  body  operated  upon  be  soluble,  the  surface  presented  to  the  solvent  being 
greatly  increased  thereby.  Heat  assists  solution  by  increasing  the  power  of  the 
solvent,  and  also  by  establishing  currents  in  the  liquid,  and  thus  continually  ex- 
posing the  substance  to  the  action  of  fresh  portions  of  the  solvent.  When  the 
application  of  heat  for  effecting  or  promoting  solution  has  to  be  continued  for 
some  time,  it  is  advisable  to  make  use  of  flasks  which  will  retain  more  com- 
pletely, and  partially  condense,  the  vapors  evolved.1 

Some  substances  require  continued  boiling,  or  treatment  at  lower  temperatures 
with  the  solvent,  in  order  to  effect  their  solution,  or  the  separation  of  soluble  from 
insoluble  portions.  In  the  latter  case,  the  process  is  called  digestion.  Dishes 
and  beakers  are  preferable  when  the  substance  requires  agitation  in  the  solvent 
by  means  of  stirrers,  or  when  portions  have  to  be  added  or  removed  during  the 
operation. 

The  vessel  in  which  the  solution  is  effected  should  be  heated  very  gradually ; 
it  is  always  safer  to  protect  it  from  the  flame  or  fire  by  the  sand-bath  or  sand- 
pot.  When  a  temperature  below  212°  is  required  for  solution  or  digestion,  the 
vessel  should  be  placed  upon  a  water-bath. 

All  the  precautions  recommended  in  heating  retorts  in  distillation  should  like- 
wise be  attended  to  in  effecting  solutions. 

The  addition  of  cold  liquid  to  the  hot  contents  of  a  basin  should  be  effected 
very  gradually  (the  latter  having  in  all  cases  been  previously  removed  from  the 
source  of  heat),  as,  in  descending  rapidly,  it  would  suddenly  change  the  tempera- 
ture of  the  bottom  of  the  dish,  and  thus  probably  crack  it. 

A  flask  or  dish  is  supported  over  the  flame  of  a  lamp  by  a  tripod,  or  the  ring 
of  a  retort-stand.  Should  the  ring  or  tripod  be  too  large,  a  triangle  of  strong 
iron  wire  may  be  placed  across  it,  and  the  vessel  firmly  supported  thereby. 
Should  the  contents  of  a  flask  be  in  danger  of  boiling  over,  the  flask  must  be 
lifted  away  from  the  flame  or  sand-bath,  the  portion  of  it  above  the  surface  of 
the  liquid  being  cooled  down  at  the  same  time  by  blowing  upon  it ;  the  vapor 
within  will  thus  be,  to  a  certain  extent,  condensed,  and  the  ebullition  diminished. 

Small  quantities  of  a  substance  may  be  dissolved  in  a  test-tube.  The  latter 
should  not  be  filled  above  two-thirds  with  liquid ;  it  should  then  be  held  in  an 
oblique  direction  in  the  upper  part  of  the  flame  of  a  lamp  ;  the  fingers  may  be 
protected  from  the  heat  either  by  wrapping  a  thick  piece  of  paper  or  cloth  round 
the  portion  of  the  tube  where  it  is  held,  and  twisting  the  end  together  so  as  to 
form  a  handle,  or  by  supporting  it  in  the  flame  by  means  of  a  small  metal  clasp, 
with  sliding  ring  and  wooden  handle,  which  is  termed  a  tube-holder.  In  boiling 
liquids  in  test-tubes,  the  evolution  of  vapor  is  often  very  irregular  and  sudden, 
particularly  when  any  dense  solid  is  operated  upon,  the  contents  of  the  tube,  or 
a  portion  of  them,  being  frequently  ejected  in  consequence;  a  slight  and  rapid 
agitation  of  the  tube  backwards  and  forwards  in  the  flame  will,  to  a  great  extent, 
prevent  this. 

When  solvents  boiling  at  low  temperatures  are  employed,  much  economy  of 
material  is  effected  by  partially  closing  the  upper  end  of  the  tube  with  the  fore- 
finger, the  vapor  being  thereby  prevented  from  escaping,  and  allowed  to  condense 
in  the  cooler  portion  of  the  tube.  The  tube  should  not,  in  such  cases,  be  filled 
more  than  about  one-third,  and  the  flame  of  the  lamp  need  only  be  applied  at 
intervals,  to  keep  up  ebullition. 

If  the  solution  of  a  substance  is  accompanied  by  effervescence,  it  should  be 

1  When  somewhat  volatile  or  precious  solvents  are  employed,  it  is  advisable  to  adapt  a 
long  wide  tube  to  the  mouth  of  the  flask,  in  order  that  the  condensed  vapor  may  return 
to  the  latter. 


SOLUTION. 


89 


effected  in  tall  jars,  or  in  flasks,  in  order  to  prevent  the  liquid  from  spirting  over 
the  sides  of  the  vessel ;  the  solvent  should  only  be  added  gradually,  that  the 
action  may  not  be  too  violent,  and  cause  the  liquid  to  froth  up  and  overflow. 

The  very  gradual  addition  of  the  proper  amount  of  solvent,  when  considerable 
accuracy  is  necessary,  may  be  effected  by  the  washing-bottle,  which  will  be  de- 
scribed under  the  head  of  edulcoration. 

Much  difficulty  is  frequently  experienced  in  pouring  solutions  from  a  flask, 
dish,  or  beaker,  to  another  vessel,  without  spilling  some  portion.  This  may  be 

Fig.  49. 


avoided  by  the  following  simple  means :  A  glass  rod,  first  wetted  with  the  solu- 
tion, is  applied,  in  an  almost  vertical  position,  to  the  edge  of  the  vessel  contain- 
ing the  liquid,  and  its  lower  extremity  allowed  to  dip  into  the  vessel  which  is  to 
receive  the  liquid;  the  full  vessel  is  then  gradually  inclined,  so  as  to  allow  the 
liquid  to  run  down  the  rod  in  a  steady  stream;  upon  restoring  the  vessel  to  its 
original  position,  when  the  requisite  quantity  has  been  decanted,  the  drop  of 
liquid  that  would  otherwise  run  down  the  side  of  the  vessel  from  the  edge,  is 
completely  withdrawn  by  the  rod.1 

Various  terms  are  applied  to  the  solution  of  organic  substances,  and  their 
extraction  from  vegetable  matters.  Infusion  is  effected  by  pouring  hot  water 
upon  the  substance,  and  straining  off  the  liquid;  decoction,  by  digesting  the  sub- 
stance for  some  time  with  the  solvent,  by  the  aid  of  heat;  and  maceration  by 
pouring  hot  or  cold  water  upon  the  substance,  and  allowing  it  to  digest  for  some 
time.  Soluble  constituents  may  be  conveniently  removed  from  porous  bodies  by 
lixiviation. 

The  substance  is  introduced,  in  the  state  of  a  coarse  powder,  into  a  large  fun- 
nel, closed,  at  first,  at  the  lower  end  of  the  neck,  with  a  cork,  and  at  the  upper 
* 

1  It  is  well,  in  addition,  to  grease  slightly  the  border  of  the  vessel  containing  the  liquid. 


90  FILTRATION. 

end  with  a  glass  plate.  Some  large  fragments  of  the  substance  to  be  dissolved, 
or  a  little  plug  of  asbestos,  or  tow,  are  placed  at  the  bottom  of  the  funnel ;  these 
serve  to  retain  the  finer  particles.  The  solvent  is  then  poured  upon  the  con- 
tents of  the  funnel,  so  as  to  cover  the  whole  mass ;  the  liquid,  as  it  penetrates 
the  particles,  gradually  takes  up  the  soluble  portions,  and  becoming  dense,  de- 
scends, making  room  for  fresh  portions  of  the  solvent.  After  a  time,  the  cork 
is  withdrawn  from  the  neck  of  the  funnel,  and  the  liquid  collected  as  it  drips 
through,  being  replaced  in  the  funnel  by  the  introduction  of  fresh  quantities  of 
the  solvent,  until  the  substance  is  exhausted.  The  use  of  the  cork  is  in  many 
cases  unnecessary,  when  the  soluble  portion  is  easily  extracted.  This  method  is 
very  convenient  for  the  removal  of  vegetable  principles  from  seeds  and  plants, 
and  various  forms  of  apparatus  are  in  use  for  effecting  extraction  in  this  manner, 
under  the  name  of  displacement-apparatus,  or  percolators,  the  principal  advan- 
tage of  which  over  the  simple  funnel  is  that  they  prevent  loss  of  the  solvent  by 
evaporation  during  the  process. 

§  49.  SATURATION.— A  liquid  is  saturated  with  a  solid  or  gas,  when  it  has 
been  charged  with  as  much  of  either  as  it  is  capable  of  dissolving.  The  method 
of  saturating  liquids  with  gases  has  been  described  under  the  head  of  solution  of 
gases  (§  36). 

SATURATION  OF  A  LIQUID  WITH  A  SOLID. — A  hot  saturated  solution  is  ob- 
tained by  dissolving  a  moderate  amount  of  the  solid  in  the  liquid,  heated  to  the 
proper  temperature,  and  then  adding  fresh  quantities  of  the  substance  to  the 
solution  at  intervals,  until  it  refuses  to  dissolve  any  more,  a  quantity  of  the 
substance,  consequently,  remaining  undissolved.  Liquids  generally  dissolve  a 
larger  quantity  of  a  solid,  with  the  aid  of  heat,  than  they  do  at  the  ordinary  tem- 
perature; the  most  expeditious  way,  therefore,  of  making  a  solution  saturated 
when  cold,  is  to  prepare  a  hot  saturated  solution,  to  allow  this  to  stand  until  per- 
fectly cool,  and  to  separate  the  portion  of  substance  that  has  remained  undis- 
solved, or  been  deposited  in  the  cooling  of  the  liquid. 

In  order  to  ascertain  whether  a  solution  is  saturated  while  hot,  a  drop  of  the 
liquid  is  transferred,  by  means  of  a  glass  rod,  to  a  cold  watch-glass,  or  piece  of 
glass- plate ;  the  deposition  of  crystals  of  a  solid  substance  indicates  the  saturation 
of  the  solution. 

This  deposition  may  be  promoted  by  stirring  or  agitation. 

With  some  substances  the  application  of  heat  is  not  admissible  in  the  prepara- 
tion of  a  saturated  solution  :  in  such  cases  the  solvent  is  placed  in  contact  with 
the  powdered  substance  in  the  cold,  in  a  stoppered  bottle,  or  vessel  in  which  it 
can  be  agitated.  Should  the  whole  of  the  substance  first  added  dissolve  after 
agitation,  a  fresh  portion  is  placed  in  contact  with  the  solution,  and  this  is  per- 
severed in,  either  until  there  is  no  perceptible  diminution  in  the  bulk  of  the  solid 
in  the  vessel,  or,  if  accuracy  is  required,  until  the  weight  of  a  certain  amount  of 
the  solid  is  not  diminished  by  being  left  some  time  in  contact  with  the  clear 
solution. 


FILTRATION,   E  DULC  OR  ATION,   DECANTATION, 
AND  SEPARATION   OF    LIQUIDS. 

§  50.  The  separation  of  solids  from  liquids  is  effected  by  filtration  or  decanta- 
tion.  The  apparatus  required  for  this  purpose  are  funnels  and  funnel-stands, 
tall  jars  or  beakers,  stirring-rods,  glass  plates,  and  filtering-paper. 

Filtrations  on  the  large  scale  are  performed  in  conical  bags  of  flannel,  or  in 
pieces  of  linen  cloth  of  moderate  fineness,  which  are  loosely  strained  over  wooden 
frames,  having  been  previously  well  soaked  in  water.  « 

The  form  of  glass  and  earthenware  funnels  should  vary  according  to  the  ope- 


EDULCORATION.  91 

ration  to  be  performed  with  them.  If  it  is  wished  to  filter  a  liquid  rapidly,  the 
funnels  should  be  ribbed;  or,  if  plain  funnels  are  used,  the  cone  and  neck  should 
not  join  at  a  sharp  angle.  When  the  substance  to  be  separated  from  a  solution 
is  in  a  state  of  very  minute  division,  it  is  necessary  that  the  cone  and  neck  of 
the  funnel  should  join  at  an  angle  of  about  130°,  and  the  former  should  taper 
gradually,  and  not  bulge  at  the  sides,  so  that  the  filter,  when  placed  in  it,  may 
touch  it  at  all  points. 

The  funnel  may  be  supported  by  the  ring  of  a  retort-stand,  by  tripod-stands, 
or  by  a  wooden  stand  consisting  of  a  flat  board  supported  on  four  feet,  about 
twelve  inches  high,  and  provided  with  round  holes  of  various  sizes.  The  lower 
extremities  of  the  feet  may  be  fixed  into  a  piece  of  board  corresponding  to  the 
top,  to  impart  firmness  to  the  stand. 

Various  kinds  of  filter  ing -paper  are  employed  by  chemists,  according  to  the 
nature  of  the  operation  required.  That  most  generally  used,  is  the  best  white 
blotting-paper.  When  greater  strength  is  required,  a  coarser,  and  much  thicker 
kind  of  blotting-paper  is  used.  All  ordinary  filtering-paper  is,  to  some  extent, 
contaminated  with  mineral  substances,  which  do  not,  however,  materially  inter- 
fere in  ordinary  operations.  At  times,  however,  particularly  in  quantitative 
analysis,  it  is  necessary  to  have  the  paper  as  nearly  chemically  pure  as  possible ; 
the  best  paper  of  this  description  is  imported  from  Sweden.  The  purity  of  filter- 
ing-paper is  indicated  by  the  quantity  of  ash  which  it  leaves  upon  being 
thoroughly  burnt.  It  is  very  convenient  to  keep  the  paper  ready  cut  into  cir- 
cular pieces  of  various  sizes.  By  folding  these  twice  in  opposite  directions,  the 
ordinary  filter  is  obtained. 

Rapid  filiations  are  effected  by  means  of  ribbed  filters.  If  the  filtering-paper 
employed  is  very  porous,  or  the  solid  operated  with  heavy,  or  difficult  to  separate 
from  the  liquid,  it  is  well  to  employ  double  filters. 

PRECAUTIONS  IN  FILTERING. — The  filter  should  in  no  case  protrude  beyond 
the  funnel;  its  edge  should  be  at  least  about  a  quarter  of  an  inch  below  that  of 
the  latter.  ( 

Before  throwing  any  substance  upon  a  filter,  the  paper  should  be  moistened 
with  water  (or  any  other  solvent  employed),  by  which  means  it  is  somewhat 
expanded,  and  the  small  pores  existing  in  it  thereby  considerably  contracted ;  if 
the  substance  is  poured  upon  the  filter  without  first  attending  to  this  precaution, 
a  portion  of  the  solid  will  frequently  pass  through  the  paper ;  and  small  particles 
are  more  liable  to  fill  up  the  pores  in  the  latter  to  such  an  extent  as  to  cause  the 
liquid  to  run  through  very  slowly.  The  filter  should  never  be  quite  filled  with 
liquid,  and  the  substance  to  be  filtered  should  be  poured  on  gradually  and  against 
the  sides  of  the  filter.  Should  the  first  portions  of  a  liquid  not  pass  through  the 
filter  quite  bright,  they  must  be  returned  thereto ;  and  this  must  be  repeated 
until  the  liquid  is  perfectly  bright,  when  it  is  collected  in  a  clean  receiver.  The 
spirting  occasioned  by  the  fall  of  the  liquid  as  it  drips  from  the  funnel  into  the 
receiver,  may  be  avoided  by  approaching  the  beak  of  the  funnel  to  the  side  of 
the  vessel,  when  the  liquid  will  trickle  down  as  it  filters  through.  It  is  neces- 
sary, at  times,  to  filter  solutions  rapidly  while  hot.  In  such  cases,  it  is  advisable 
to  fit  the  funnel  into  a  larger  one,  by  introducing  into  the  beak  of  the  latter  a 
perforated  cork,  adapted  to  hold  the  neck  of  the  smaller  funnel,  and  to  fill  up  the 
space  between  the  two  with  hot  water.  A  metal  case,  with  a  hollow  cylindrical 
arm  projecting  laterally,  and  closed  at  the  bottom,  is  frequently  substituted  for 
the  large  funnel,  and  is  very  convenient,  as  heat  may  be  applied  to  the  arm, 
which  is,  of  course,  filled  with  water,  and  the  latter  kept  at  the  boiling  point 
while  the  filtration  lasts. 

§  51.  Many  solids  are  purified  from  soluble  substances,  by  washing  them  with 
water  or  other  solvents,  either  by  filtration  or  decantation.  In  the  former  case, 
the  solution  is  allowed  to  drain  off  the  substance  as  much  as  possible  before 


92  DECANTATION. 

water  is  added;  the  filter  is  then  filled  up  with  pure  water,  hot  or  cold,  according 
to  circumstances;  and  fresh  quantities  are  added,  as  the  filter  becomes  empty, 
until  the  solid  is  sufficiently  washed.     It  is  advisable  in  washing  a  solid,  to 
bring  the  whole  of  the  substance  together  into  one  mass,  and 
Fig.  50.  not  to  allow  it  to  remain  as  a  coating  upon  the  sides  of  the 

filter.  This  may  be  conveniently  effected  by  forcing  a  jet 
of  water  against  the  sides  until  it  is  detached  and  carried 
down  by  the  stream.  The  apparatus  employed  for  obtain- 
ing this  jet  is  the  syringe,  or  wathing-botde.  There  are 
two  or  three  forms  of  washing-bottles;  the  most  convenient 
is  constructed  in  the  following  manner  :  a  narrow-mouthed 
bottle  or  flask  is  fitted  with  two  tubes,  the  one  bent  in  the 
form  of  a  siphon,  the  long  arm  of  which  passes  nearly  to 
the  bottom  of  the  bottle,  the  extremity  of  the  short  arm 
being  drawn  out  to  a  narrow  point  (so  as  to  deliver  a  fine 
stream  of  water) ;  the  other  tube  is  bent  at  an  angle  of 
about  100°,  its  two  arms  are  nearly  equal  (the  longest 
,  about  three  inches  in  length);  the  shorter  arm  is  fitted  into 
the  cork,  so  as  just  to  project  inside  the  bottle.  On  filling  the  latter  with  a 
liquid,  inserting  the  cork  and  tubes,  and  blowing  into  the  bottle  through  the 
short  tube,  the  liquid  is  forced  up  through  the  long  one,  and  passes  out  at  the 
short  arm  with  considerable  force,  in  a  small  stream.  By  inverting  the  bottle, 
the  air  will  enter  through  the  long  tube,  and  the  water  pour  out  of  the  smaller 
one,  the  opening  of  which  is  not  contracted;  some  force  may  be  imparted  to  the 
current  of  water  thus  obtained  by  blowing  into  the  bottle  through  the  narrow 
opening  of  the  long  tube.  By  throwing  a  jet  of  water  against  the  sides  of  the 
filter,  and  varying  its  direction  by  a  movement  of  the  hand  in  which  the  bottle 
is  held,  the  portion  of  solid  that  adheres  to  them  may  be  detached  and  washed 
down  towards  the  point  of  the  funnel.1 

Some  substances  adhere  so  obstinately  to  the  sides  of  the  filter  as  not  to  be 
easily  removed  by  the  washing-bottle ;  they  should,  in  that  case,  be  detached  by 
means  of  a  glass  rod  with  a  round  extremity,  great  care  being  taken  not  to 
damage  the  filter.  With  some  substances,  it  is  also  necessary  to  stir  up  the  mass 
upon  the  filter  with  a  glass  rod,  in  order  to  disturb  the  fissures  that  form  in  it, 
which  would  otherwise  allow  the  water  poured  upon  the  filter  to  pass  through 
them,  without  penetrating  the  greater  portion  of  the  substance. 

In  filtering  off  or  washing  a  substance,  it  is  advisable  to  keep  the  funnel 
covered  with  a  glass  plate,  which  serves  to  exclude  any  impurities  that  might 
otherwise  fall  into  the  funnel,  and  also  to  prevent  evaporation  if  the  liquid  fil- 
tered is  volatile  (particularly  in  hot  nitrations).  Large  crystals,  or  considerable 
masses  of  substance,  may  be  expeditiously  and  almost  completely  separated  from 
a  liquid,  by  throwing  them  upon  a  funnel,  into  the  neck  of  which  a  small  piece 
of  tow,  or  asbestos,  or  glass  rod  is  introduced,  allowing  the  liquid  to  drain  off. 

§  52.  DECANTATION. — Some  solids  may  be  separated  from  fluids,  or  purified 
by  a  process  termed  decantation.  This  consists  in  allowing  the  solid  to  subside 
to  the  bottom  of  the  vessel  (tall  jars  being  most  convenient),  and  removing  the 
clear  supernatant  liquid  either  by  pouring  it  off  slowly,  or  by  decanting  it  with 
a  siphon  or  pipette.  Glass  siphons  are  best  adapted  for  this  purpose ;  their 
size  and  bore  should  be  suited  to  the  quantity  of  material  operated  upon;  but 
little  need  be  said  with  regard  to  their  use.  The  mouth  of  the  short  arm  should 
not  be  allowed  to  approach  the  solid  too  closely,  lest  a  portion  of  it  should  be 

1  The  washing-bottle  is  also  very  useful  for  adding  small  quantities  of  water  or  other 
solvents  to  a  solid,  in  effecting  its  solution,  or  for  washing  it  down  to  the  bottom  of  any 
vessel  when  it  adheres  to  the  sides. 


DECANTATION. 


93 


Fig.  51. 


sucked  into  the  siphon  by  the  force  of  the  ascending  current.  For  small  opera- 
tions, where  the  liquid  is  to  be  decanted  to  a  great  nicety,  it  is  advisable  some- 
what to  contract  the  orifices  of  the  siphon,  in  order  to  reduce  the  size  of  the 
stream.  The  long  arm  should  be  held  by  one  hand,  near  the  extremity,  in  such 
a  manner  that  the  thumb  may  be  directly  opposite  its  mouth  when  it  is  neces- 
sary to  stop  the  current.  When  the  supernatant  liquid  has  been  decanted  from 
a  substance,  the  vessel  containing  the  latter  is  filled  up  with  water,  the  substance 
is  thoroughly  suspended  in  it  by  stirring  the  two  well  together  with  a  glass  rod, 
and  it  is  then  allowed  to  subside  perfectly,  and  the  water  decanted  when  clear; 
this  operation  being  repeated  until  the  substance  is  perfectly  washed. 

Small  quantities  of  liquid  may  be  decanted  from  solids  with  greater  safety  by 
means  of  the  pipette,  which  consists  of  a  narrow  glass  tube,  contracted  at  one 
extremity,  and  provided  with  a  large  bulb  at  about  three  inches  from  the  other 
end,  which  is  bent,  above  the  bulb,  at  an  angle  of  120°.  By 
immersing  the  constructed  extremity  in  the  liquid,  and  applying 
suction  to  the  other  end  with  the  mouth,  it  may  be  made  to 
ascend  into  the  bulb;  when  the  latter  is  filled,  the  tongue  is 
pressed  tightly  against  the  opening  of  the  bent  end,  the  pipette 
is  then  removed  from  the  vessel,  and  the  liquid  transferred  to  a 
receiver. 

Care  must  be  taken  not  to  allow  the  liquid  to  flow  back  when 
once  in  the  pipette,  as  this  would  occasion  a  disturbance  of  the 
particles  of  solid,  and  thus  prevent  for  a  time  the  removal  of 
the  liquid. 

This  tube  is  also  of  great  use  for  the  separation  of  two  im- 
miscible liquids.  The  operation  is  similar  to  that  just  described, 
the  pipette  being  introduced  into  the  upper  or  lower  liquid,  so 
that  its  extremity  reaches  nearly  to  the  bottom  of  the  layer.  It 
is  well,  in  separating  liquids  in  this  manner,  to  introduce  them 
first  into  long  narrow  glass  jars  or  tubes,  so  as  to  contract  the 
area  of  the  column  of  liquid  by  increasing  its  height,  and  thus 
rendering  the  separation  of  the  liquids  by  the  pipette  far  easier 
and  more  effectual.  This  operation  may  also  be  effected  in  va- 
rious other  ways.  Oils  may  be  separated  from  water,  in  which 
they  are  insoluble,  by  throwing  them  upon  a  wet  filter.  The 
water  will  pass  through,  and  the  oil  may  then  be  removed  by 
piercing  a  hole  in  the  bottom  of  the  filter.  Glass  funnels,  of 
which  the  stem  is  furnished  with  a  tightly-fitting  stopcock  (se- 
parating funnels'),  are  also  very  useful  for  separating  liquids. 
The  stopcock  being  closed,  the  liquids  are  poured  into  the  fun- 
nel, and  allowed  to  separate  perfectly.  By  then  opening  the 
cock,  the  lower  liquid  may  be  removed  from  the  upper,  care 
being  taken  to  allow  it  to  run  through  very  slowly  as  it  de- 
creases in  quantity,  and  to  close  the  cock  directly  the  upper 
liquid  approaches  it.  These  funnels  are  frequently  made  in  the 
form  of  globes,  provided  with  an  opening  at  the  top;  the  loss  of 
liquids  by  evaporation  is  much  decreased  by  their  use.  The  siphon  may  also 
be  used  for  the  separation  of  liquids. 


Fig.  52. 


94  EVAPORATION. 


EVAPORATION. 

§  53.  The  apparatus  necessary  for  evaporations  are  the  same  as  those  required 
for  solution,  with  the  addition  of  watch-glasses  and  small  slips  of  glass.  The 
dishes  employed  should,  however,  if  possible,  be  more  shallow  than  those  used 
for  making  solutions. 

Evaporation  takes  place  at  almost  any  temperature.  When  a  liquid  is  allowed 
to  evaporate  slowly  at  the  common  temperature,  it  is  said  to  undergo  spontaneous 
evaporation.  This  species  of  evaporation  is  had  recourse  to  principally  in  effect- 
ing crystallization,  and  in  the  desiccation  of  some  substances  to  be  presently 
mentioned.  The  vessel  containing  the  liquid  is  covered  with  filtering- paper,  to 
exclude  any  extraneous  impurities,  and  then  placed  in  a  dry  situation,  where 
there  is  a  continual  access  of  air  to  remove  the  vapor  as  it  gradually  forms. 
Spontaneous  evaporation  may  be  very  much  assisted  by  the  use  of  desiccators. 

The  method  most  generally  adopted  is  to  place 
the  vessel  containing  the  liquid  under  a  bell-jar, 
together  with  another  containing  sulphuric  acid, 
which  has  a  great  affinity  for  water ;  or  better 
still,  to  place  these  two  vessels  together  under 
the  receiver  of  an  air-pump. 

As  the  air  is  exhausted,  the  water  passes 
readily  into  vapor,  which  is  directly  absorbed  by 
the  sulphuric  acid,  thus  giving  place  to  a  fresh 
quantity  of  vapor,  which  is  in  turn  absorbed. 
The  vessel  containing  the  sulphuric  acid  should  present  a  much  larger  surface 
than  that  containing  the  liquid  to  be  evaporated,  and  they  should  be  so  placed 
that  the  latter  is  supported  by  the  former.  Other  substances  having  a  great 
affinity  for  water,  may  be  substituted  for  sulphuric  acid,  such  as  chloride  of  cal- 
cium, fused  potassa,  or  quicklime. 

When  the  evaporation  is  effected  by  the  aid  of  heat,  it  is  applied  in  the  man- 
ner directed  for  the  solution  .or  distillation  of  substances.  When  the  evapora- 
tion is  to  be  conducted  at  a  constant  temperature,  recourse  is  had  to  the  open 
water-bath  already  described,  or  to  a  similar  bath  filled  with  oil,  if  a  temperature 
above  212°  is  required,  a  thermometer  Jbeing  retained  in  the  bath  to  indicate 
the  temperature  during  the  operation. 

Evaporation  effected  below  ebullition  should  be  conducted  in  dishes  (which 
should  be  kept  covered  by  a  piece  of  filtering-paper  of  proper  size,  through  which 
a  glass  rod  has  been  passed  to  act  as  a  support)  :  any  crusts  which  may  form 
upon  the  surface  of  the  liquid  should  be  disturbed  from  time  to  time,  to  prevent 
their  retarding  vaporization. 

Evaporations  at  the  boiling  temperature  are  most  safely  conducted  in  flasks,  as 
the  liquid  is  thus  prevented  from  spirting  over  the  sides  of  the  vessel :  evapora- 
tion, when  thus  conducted,  proceeds  naturally  much  more  slowly,  as  the  vapor 
generated  cannot  escape  so  readily,  and  is  also  continually  condensed  to  some 
extent.  The  same  precautions  must  be  attended  to  in  the  application  of  heat  in 
evaporations  as  in  distillation  and  solution. 

In  evaporating  a  solution  to  dryness,  the  residual  mass  should  be  diligently 
stirred,  while  the  last  portion  of  water  is  passing  off;  this  considerably  promotes 
evaporation,  and  lessens  the  risk  of  loss  of  substance  from  spirting.  It  is 


EVAPORATION. 


95 


Fig.  54. 


generally  advisable  to  expose  the  residue  for  a  lengthened  period  to  a  com- 
paratively low  temperature,  in  order  to  expel  the  last  traces  of  moisture.1 

§  54.  The  expulsion  of  moisture  from  solid 
substances,  is  termed  desiccation.  This  is  ef- 
fected at  various  temperatures,  according  to 
the  nature  of  the  substance.  The  greater 
portion  of  moisture  may  be  removed  mecha- 
nically from  many  substances,  by  pressing 
them,  in  a  state  of  powder,  between  folds  of 
blotting-paper.  Some  bodies  require  perfect 
desiccation  at  the  ordinary  temperature;  these 
are  exposed  over  a  desiccating  agent,  in  vacuo, 
until  they  no  longer  part  with  any  moisture. 
Other  substances  are  desiccated  in  the  water- 
oven  ;  a  double  metal  box,  between  the  sides 
of  which  water  is  contained,  the  temperature 
being  maintained  at  212°  by  means  of  a  lamp 
placed  underneath  :  the  inner  box  is  provided 
with  apertures  through  which  a  current  of  air 
may  circulate.  For  desiccation  at  higher  tem- 
peratures we  employ  an  air-bath  (of  which  va- 
rious forms  exist),  also  provided  with  draught- 
holes  and  with  a  thermometer,  so  that  the  temperature  may  be  properly  regulated. 
Previously  to  desiccation,  the  substance  is  reduced  to  as  minute  a  state  of  division 
as  possible. 

A  crude  test  of  its  dryness  after  desiccation,  is  that  of  holding  a  cold  clean 
glass  plate  over  it  while  warm,  and  observing  whether  any  film  of  moisture  be 
deposited  thereon.  The  most  accurate  test  is,  however,  that  of  weighing  the 
substance  before  desiccation,  again  ascertaining  its  weight  after  it  has  been  ex- 
posed to  the  proper  temperature  for  about  an  hour,  and  repeating  the  weighings 
at  intervals  of  half  an  hour,  until  the  last  two  agree  with  each  other. 

Some  rather  volatile  substances  may  be  desiccated  by  maintaining  them  at  a 
moderate  temperature,  and  at  the  same  time  passing  a  current  of  air  over  them. 
The  substance  is  contained  in  a  bulb-tube,  one  end  of  which  is  connected  with  a 
long  chloride  of  calcium  drying-tube  (or  with  a  wash-bottle  containing  oil  of 
vitriol),  the  other  with  a  tube  leading  into  the  top  of  a  large  closed  vessel  filled 
with  water,  and  having  one  or  two  openings  at  the  top  for  the  reception  of  tubes 
(being  kept  closed  when  not  in  use),  and  a  cock  fitted  into  its  side,  near  to  the 
bottom.  Such  a  vessel  is  termed  an  aspirator.  Upon  turning  the  cock,  the 
water  will  run  out  of  the  vessel  and  become  replaced  by  air,  which  first  passes 
through  the  chloride  of  calcium  tube  (where  it  is  dried),  thence  over  the  heated 
substance  into  the  aspirator,  carrying  with  it  any  portions  of  moisture  that  may 
be  given  off  by  the  substance  operated  upon.  It  is  necessary  to  introduce  a 
second  drying- tube  between  the  aspirator  and  tube  containing  the  substance,  lest 
the  suspension  of  the  operation  should  allow  moist  air  to  pass  back  into  the  tube. 

When  a  substance  has  been  perfectly  dried,  it  should  be  at  once  transferred  to 
a  well-closed  bottle  or  tube,  in  which  it  is  preserved  until  required;  unless  this 
precaution  is  taken,  the  substance  will  absorb  moisture  to  a  greater  or  less  ex- 
tent in  almost  every  case;  some  bodies  absorb  moisture  rapidly  at  common  tem- 
peratures, i.  e.  are  deliquescent;  these  should  be  transferred  as  rapidly  as  possible 

1  It  is  often  found  convenient,  in  evaporating  to  dryness,  to  place  the  evaporating 
dish  upon  an  empty  tin  pot,  heated  over  a  flame,  the  application  of  heat  being  thus  ren- 
dered more  uniform  and  gradual.  Should  the  residue  adhere  firmly  to  the  basin  in  which 
it  has  been  evaporated,  it  is  most  easily  removed  by  means  of  a  spatula. 


96  CRYSTALLIZATION. 

while  warm.1  Crystals  and  precipitates  may  be  conveniently  and  expeditiously 
dried  by  spreading  them  upon  two  or  three  folds  of  blotting-paper,  and  then 
placing  the  latter  upon  a  porous  tile,  which  is  replaced  by  a  fresh  one  as  it  be- 
comes saturated  with  moisture.  In  many  cases  these  tiles  may  be  first  gently 
heated ;  they  then  effect  the  desiccation  of  the  substance  by  promoting  vaporiza- 
tion. 

CRYSTALLIZATION. 

§  55.  The  property  possessed  by  many  substances  of  assuming  definite  and 
peculiar  crystalline  forms,  frequently  serves  as  a  characteristic  by  which  they  may 
be  recognized  and  distinguished  from  one  another. 

Crystallization  also  affords  an  easy  and  effectual  method  of  purifying  chemical 
compounds;  it  is  generally  effected  by  means  of  solution,  fusion,  or  vaporization. 

CRYSTALLIZATION  BY  SOLUTION. — A  substance  is  crystallized  from  its  solvent 
in  one  of  two  ways ;  by  cooling  the  hot  saturated  solution,  or  by  spontaneous 
evaporation.  The  first  method  is  always  resorted  to  when  it  is  wished  to  effect 
rapid  crystallization,  the  size  and  forms  of  the  resulting  crystals  being  of  less 
importance  than  the  purification  of  the  substance.  Those  bodies  which  are  less 
soluble  in  hot  than  in  cold  solvents  are  crystallized  by  the  second  method,  which 
is  also  employed  for  procuring  good  crystals  by  gradual  deposition. 

A  hot  saturated  solution,  prepared  according  to  the  prescribed  method  (§  50), 
is  filtered,  if  necessary,  as  rapidly  as  possible  (a  hot- water  funnel  being  employed 
when  required),  and  allowed  to  cool  undisturbed  and  gradually.  If  the  solution 
is  very  concentrated,  or  has  been  agitated,  or  cooled  rapidly,  the  crystals  deposited 
are  small,  confused,  and  irregular  in  their  forms;  if  it  is  wished  to  obtain  regular 
crystals  from  a  hot  solution,  the  latter  should  not  be  too  strong,  and  the  above 
precautions  should  be  attended  to,  in  addition  to  which  it  is  advisable  to  cover 
the  opening  of  the  vessel  in  which  the  crystallization  is  effected,  to  prevent 
evaporation  on  the  surface  of  the  liquid,  and  the  consequent  formation  of  a  crust 
of  confused  crystals. 

When  the  crystallization  is  to  be  effected  by  spontaneous  evaporation,  a  satu- 
rated solution  of  the  substance  is  prepared  at  the  common  temperature,  and  placed 
in  a  moderately  shallow  evaporating  basin,  which  must  afterwards  be  carefully 
covered  with  blotting-paper,  unless  the  solution  can  be  preserved  in  some  place 
where  no  dust  or  impurity  ^can  reach  it.  Crystallization  by  spontaneous  evapora- 
tion may  be  much  assisted  by  placing  the  solution  under  a  bell-jar,  together  with 
some  rapid  absorbent  of  moisture;  or  by  introducing  it  under  the  receiver  of  an 
air-pump,  together  with  a  desiccating  agent,  and  exhausting  in  the  manner  de- 
scribed under  evaporation. 

If  crystallization  is  resorted  to  for  the  purification  of  a  substance,  the  crystals 
obtained  are  separated  from  the  solution  (or  mother-liquor}  when  perfectly  cool, 
by  gently  decanting  as  much  as  possible  from  the  crystals,  and  then  throwing 
them  upon  a  strainer  or  filter,  and  allowing  the  mother-liquor  to  drain  off.  A 
small  quantity  of  the  solvent  employed  is  then  poured  upon  them,  and  allowed 
to  drain  off,  so  as  to  remove  the  mother-liquor  still  retained  by  them.  If,  on 
applying  the  proper  tests  to  a  small  portion  of  the  substance,  it  is  now  found 
sufficiently  pure,  it  may  be  at  once  dried  for  use.  Should  it  require  further 
purification,  the  crystals  may  be  freed  still  more  perfectly  from  the  mother-liquor 
by  pressing  them  between  folds  of  blotting-paper,  and  then  recrystallizing.  This 
operation  may  be  repeated  until  the  resulting  crystals  are  sufficiently  pure. 

1  There  are  some  substances  which  lose  more  or  less  of  their  water  of  crystallization 
at  ordinary  temperatures,  i.  e.  are  efflorescent;  it  is,  however,  always  necessary,  when 
they  are  required  anhydrous,  to  submit  them  to  desiccation  by  one  of  the  above  methods. 


CRYSTALLIZATION.  97 

Substances  may  be  crystallized  from  weak  solutions  (or  mother-liquors)  either 
by  spontaneous  evaporation,  or  by  concentrating  the  solution  with  the  aid  of  heat, 
until  a  small  quantity  placed  upon  a  cold  surface  (a  glass  plate  or  watch-glass) 
deposits  crystals  upon  cooling :  it  may  then  be  set  aside  for  crystallization. 

The  method  generally  resorted  to  for  obtaining  perfect  and  large  crystals  of 
the  substance,  is  that  of  growing  or  feeding  a  crystal,  as  it  is  termed.  A  small 
and  perfect  crystal  is  selected  from  a  crop  obtained  by  one  of  the  above  methods, 
and  placed  in  a  vessel  of  moderate  depth,  containing  a  concentrated  solution  of 
the  same  substance,  in  the  cold.  The  vessel  is  then  covered  with  filtering-paper 
and  set  aside,  where  it  is  not  likely  to  be  disturbed.  After  the  lapse  of  about 
twelve  hours,  the  crystal  is  gently  turned  in  the  solution  so  as  to  rest  upon 
another  surface  ;  and  this  operation  is  repeated  regularly  twice  a  day  until  the 
crystal  has  attained  the  desired  size.  As  the  solution  becomes  weaker  it  must 
be  poured  off,  and  replaced  by  a  fresh  quantity  of  the  original  strength.  Great 
care  must  be  taken  that  the  solution  be  not  too  concentrated,  since  it  most 
probably  will  then  deposit  fresh  crystals,  and  very  frequently  upon  the  surfaces 
of  the  crystal  to  be  fed;  from  which  it  is  generally  found  difficult  to  detach  them 
without  injuring  the  surfaces  of  the  large  crystal. 

MEANS  OF  PROMOTING  CRYSTALLIZATION. — Two  or  three  methods  may  be 
resorted  to  for  promoting  crystallization  when  it  does  not  take  place  readily. 
The  solution  may  be  placed  in  a  stoppered  or  corked  bottle,  or  in  a  vessel  the 
mouth  of  which  may  be  closed  by  the  thumb  or  the  palm  of  the  hand,  and 
briskly  agitated  for  two  or  three  minutes;  or  the  solution  may  be  well  stirred, 
and  the  sides  of  the  vessel  rubbed,  with  a  smooth  glass  rod.  The  crystals 
obtained  in  both  cases  will  be  small,  and  generally  speaking  irregular;  many 
substances,  however,  which  would  not  be  deposited  from  their  solutions  until 
after  the  lapse  of  some  considerable  time,  may  be  made  to  crystallize  out  imme- 
diately by  the  above  methods.  The  latter  are,  therefore,  particularly  useful  in 
analysis,  when  it  is  wished  to  test  for  substances  of  this  nature  expeditiously. 

Solutions  which  have  remained  for  a  considerable  period  without  depositing 
crystals,  may  frequently  be  made  to  crystallize  by  the  introduction  into  the  solu- 
tion of  some  angular  fragment  (a  small  crystal  of  some  substance,  or  a  grain  of 
sand). 

§  56.  CRYSTALLIZATION  BY  FUSION. — Several  substances  may  be  crystallized 
very  beautifully  by  fusion.  This  is  particularly  the  case  with  several  metals, 
especially  bismuth,  and  also  sulphur,  spermaceti,  and  other  substances  fusing  at 
a  comparatively  low  temperature,  and  capable  of  assuming  crystalline  forms. 
To  effect  crystallization  by  this  method,  the  substance  is  melted  in  a  flat  ladle, 
and  then  placed  upon  a  warm  sandbath,  so  that  it  may  cool  very  gradually;  or 
the  body  may  be  first  melted  in  a  crucible,  and  then  poured  into  a  warmed  flat 
vessel,  and  allowed  to  cool.  When  a  tolerably  solid  crust  has  been  formed  on 
the  surface,  two  holes  should  be  pierced,  at  opposite  sides  of  the  edge,  by  means 
of  a  hot  rod  of  iron;  the  substance  that  has  not  yet  solidified  in  the  interior  is 
then  poured  out  as  rapidly  as  possible.  When  the  mass  in  the  flat  vessel  is 
cool,  it  is  removed  (which  involves  the  fracture  of  the  vessel,  unless  it  be  of 
iron),  and  very  carefully  cut  open.1  The  interior  will  be  found  crystallized. 
Fine  masses  of  crystals  cart  only  be  obtained  by  this  method  when  large  quan- 
tities of  the  substance  are  operated  upon. 

CRYSTALLIZATION  BY  VAPORIZATION. — The  principal  directions  for  obtaining 
crystals  by  vaporization  have  already  been  given  under  the  head  of  sublima- 

1  With  such  substances  as  sulphur  or  spermaceti,  this  is  readily  effected  by  means  of  a 
hot  knife.  Sulphur  must  not  be  heated  too  strongly,  as  otherwise  it  will  become  thick, 
and  adhere  to  the  vessel. 

7 


98  IGNITION. 

tion  (§  44).     We  have  but  to  add  that  the  more  gradual  the  application  of  heat, 
the  finer  are  the  crystals  obtained. 


IGNITION. 

§  57.  By  this  term  is  understood  the  exposure  of  a  solid  substance  to  a  high 
temperature,  for  the  purpose  of  altering  to  a  certain  extent  its  chemical  or  phy- 
sical constitution.  Some  substances,  ordinarily  acted  upon  by  solvents,  are 
rendered  insoluble  by  ignition ;  others  are  reduced  to  bodies  of  a  more  simple 
nature,  by  the  expulsion  of  certain  substances  which  are  either  volatile,  or  are 
converted  by  auxiliary  means  into  volatile  substances  at  elevated  temperatures. 

Some  substances  require,  in  their  ignition,  to  be  distributed  over  a  consider- 
able surface,  in  order  that  they  may  be  exposed,  as  far  as  possible,  to  the  action 
of  the  air.  Such  operations  are  generally  conducted  over  the  flame  of  a  gas- 
burner,  or  powerful  spirit-lamp,  in  thin  flat  dishes  or  capsules  of  porcelain,  pla- 
tinum, or  silver.  The  heat  should  at  first  be  applied  very  gradually  (the  dish 
or  capsule  being  supported  by  a  triangle  or  sand-bath),  and  care  should  be  taken 
that  the  substances  treated  in  this  manner  be  thoroughly  dried,  and  in  many 
cases  finely  powdered,  previously  to  ignition,  in  order  to  avoid  decrepitation  as 
much  as  possible.  When  it  is  desired  to  expose  the  substance  thoroughly  to  the 
action  of  the  air  during  ignition,  it  should  be  stirred  from  time  to  time  with  a 
piece  of  stout  platinum  wire,  a  platinum  or  steel  spatula,  or  a  glass  rod  (provided 
the  temperature  be  not  too  high).  Substances  which  require  ignition  in  contact 
with  air,  and  are  likely  to  decrepitate  or  suffer  loss  from  portions  being  carried 
away  by  the  vapors  evolved  during  the  operation,  should  be  heated  in  closed 
shallow  crucibles  (generally  of  porcelain  or  platinum),  the  lid  being  opened 
very  slightly,  to  admit  of  the  egress  of  vapor.  At  the  close  of  the  ignition,  the 
lid  may  be  partly  or  entirely  withdrawn,  and  the  access  of  air  to  the  crucible 
facilitated  by  slightly  tilting  the  latter,  and  holding  the  blade  of  a  spatula,  or 
the  lid  of  a  crucible,  edgewise  across  the  opening.  It  is  also  well,  towards  the 
close  of  the  operation,  to  raise  the  temperature  considerably  by  means  of  the 
blowpipe.  Substances  that  require  ignition  out  of  contact  of  air,  are  heated  in 
deep  covered  crucibles  (of  graphite  or  clay,  according  to  the  temperature  ap- 
plied). These  are  generally  heated  in  furnaces;  some  substances  of  a  peculiar 
nature  are  ignited  over  lamps,  or  by  the  blowpipe,  in  closed  platinum  or  silver 
crucibles.1  Before  placing  a  porcelain  crucible  in  a  fire,  or  exposing  it  to  the 
full  flame  of  a  lamp,  it  should  be  first  gradually  heated  to  some  extent,  to  avoid 
the  risk  of  its  fracture  by  the  sudden  change  of  temperature.  It  is  always  ad- 
visable to  commence  the  ignition  with  a  gentle  fire,  and  gradually  to  increase  the 
temperature.  A  flat  piece  of  fire-brick  or  tile  (or  an  inverted  crucible),  should 
be  placed  between  the  bars  of  the  furnace  and  the  bottom  of  the  crucible ;  the 
latter  is  then  surrounded  with  fuel,  it  being  generally  advisable  not  to  place  any 
above  the  cover.  In  removing  a  crucible  from  the  fire,  it  should  always  be  first 
placed  on  some  warm  spot  (e.  </.  the  top  of  the  furnace),  that  it  may  undergo  no 
very  sudden  change  of  temperature.  Iron  tongs,  of  various  forms  and  sizes, 
are  used  for  handling  crucibles.  It  is  always  advisable  slightly  to  incline  the 
crucible  in  seizing  and  lifting  it  with  the  tongs,  especially  when  its  weight  is 
considerable. 

In  qualitative  analysis,  small  quantities  of  substance  may  be  ignited  upon  a 

1  These  may  be  exposed  over  a  lamp  to  a  very  high  temperature,  by  placing  them  in  an 
iron  or  copper  jacket,  consisting  of  a  cone  open  at  both  ends,  provided  with  projecting 
slips  to  support  the  crucible,  and  a  second  similar  cone,  the  wide  opening  of  which  fits 
into  that  of  the  jacket.  A  silver  crucible  should  only  be  heated  over  a  spirit-lamp. 


FUSION.  99 

platinum  spatula  or  scrap  of  platinum  foil ;  when  it  is  necessary  to  examine  the 
matters  given  off  during  ignition,  small  portions  of  the  substance  may  be  heated 
in  hard  glass  tubes,  of  moderate  bore  and  about  four  inches  in  length,  open  at 
both  ends,  or  closed  at  one  extremity.  The  substance  is  placed  at  one  end, 
about  one  inch  from  the  opening  (if  an  open  tube  is  used),  and  then  heated  in 
the  flame  of  a  spirit  or  gas  lamp  (the  tube  being  held  more  or  less  obliquely, 
according  as  a  rapid  or  slow  current  of  air  is  required  to  pass  through  it). 


FUSION. 

§  58.  The  property  common  to  a  great  number  of  solid  bodies,  of  passing  over 
into  the  liquid  state  at  more  or  less  exalted  temperatures  (?'.  e.  their  fusibility), 
is  applied  by  the  chemist  for  effecting  certain  physical  or  chemical  changes  which 
cannot  well  be  brought  about  at  ordinary  temperatures. 

Many  compounds  which  obstinately  retain  water  of  crystallization,  or  con- 
stitutional water,  at  any  temperature  below  their  freezing-point,  may  be  rendered 
anhydrous  by  maintaining  them  in  a  state  of  fusion  for  some  time.  (It  should, 
however,  be  first  ascertained  that  such  bodies  undergo  no  further  decomposition 
at  their  fusing  temperature.)  When  substances  are  operated  upon  which  first 
fuse  in  their  water  of  crystallization  (undergo  an  aqueous  fusion),  the  applica- 
tion of  heat  must  be  persisted  in  until  the  substance  has  first  returned  to  the 
solid,  and  then  again  to  the  liquid  state.  Some  substances  are  rendered  more 
dense  and  compact  in  structure  by  fusion,  which  is  at  times  a  matter  of  great 
importance. 

The  mechanical  division  of  other  substances  (particularly  metals),  is  indirectly 
effected  by  fusion  (granulation,  see  §  46).  Fusion  is  likewise  very  frequently 
resorted  to  for  decomposing  or  altering,  to  a  certain  extent,  the  chemical  consti- 
tution of  substances. 

Frequently,  other  agents  besides  heat  are  called  into  action  to  effect  chemical 
changes  by  fusion.  Such  agents  are  substances  having  an  affinity  for  some  por- 
tion of  the  body  operated  upon,  converting  it  into  a  volatile  substance,  or  com- 
bining with  it  to  form  some  fusible  compound.  These  are  generally  employed 
either  when  it  is  wished  to  reduce  a  metallic  oxide  or  its  compound  to  the  state 
of  metal,  or  to  decompose  insoluble  compounds  in  such  a  manner  as  to  effect 
their  subsequent  solution.  Some  substances  are  employed  to  convert  certain 
metallic  oxides  into  oxides  of  a  higher  class.  These  reagents  (in  what  is  termed 
"  the  dry  way")  have  received  the  name  of  fluxes.  They  may  be  divided  into 
four  classes,  according  to  their  peculiar  action:  reducing,  oxidizing ,  double- 
decomposing,  and  simple  fluxes. 

The  most  important  reducing  fluxes  are,  carbonate  of  soda  or  potassa,  used 
together  with  charcoal,  and  in  some  cases  alone;  cyanide  of  potassium,  and 
Hack  flux. 

The  last  is  prepared  by  introducing  gradually,  in  small  quantities,  into  a  cru- 
cible heated  to  a  very  dull  redness,  a  mixture  of  two  parts  of  cream  of  tartar 
and  one  of  nitre.  The  resulting  flux  consists  of  a  very  intimate  mixture  of 
carbonate  of  potassa  and  charcoal,  the  latter  resulting  from  the  carbonization  of 
tartaric  acid. 

Charcoal  alone,  although  not  a  flux,  is  a  powerful  reducing  agent;  some 
oxides,  or  their  compounds,  fused  upon  or  together  with  charcoal,  are  reduced  to 
lower  oxides  or  entirely  deprived  of  oxygen. 

Black  flux  is  particularly  useful  in  bringing  the  charcoal  it  contains  into  inti- 
mate contact  with  the  substance  to  be  operated  upon. 

The  most  important  double-decomposition  fluxes  are,  a  mixture  of  three  parts 
of  carbonate  of  soda  with  four  of  carbonate  of  potassa;  and  hydrate  of  baryta. 


100  FUSION. 

The  nitrates  of  potassa  and  soda  are  the  oxidizing-fluxes. 

The  simple  fluxes  act  sometimes  merely  as  purifiers  or  protectors,  removing 
any  mechanical  impurity  contained  in  the  substance  operated  upon;  or,  by  being 
placed  upon  its  upper  surface,  preserving  it  from  .contamination  by  any  foreign 
matter  during  the  fusion. 

They  also  dissolve,  in  a  singular  manner,  a  number  of  metallic  oxides,  yield- 
ing with  them  slags  or  glasses  of  various  and  beautiful  colors.  The  principal 
of  these  simple  fluxes  are,  biborate  of  soda,  or  borax,  powdered  flint  or  green 
bottle-glass,  and  ammonio-phosphate  of  soda,  or  microcosmic  salt.1 

It  is  in  most  cases  essential  or  advantageous  that  these  fluxes  be  perfectly  dry 
and  finely  powdered  before  use.  The  simple  fluxes  may,  perhaps,  be  excepted 
from  this  rule. 

Fluxes  should  all  be  preserved  in  well-closed  bottles,  in  order  to  prevent  their 
absorbing  moisture,  or  becoming  impure. 

§  59.  CRUCIBLES. — Fusions  are  performed  in  crucibles  of  clay,  iron,  graphite, 
porcelain,  silver,  or  platinum. 

Those  of  hard  sandy  clay  (for  example,  the  Hessian  crucibles)  are  most  fre- 
quently employed.-  If  properly  made,  they  will  stand  a  high  red  heat,  and  are 
sufficiently  dense  to  retain  any  liquid  mass  for  some  time.  The  great  disad- 
vantage of  their  use  is  their  liability  to  be  attacked  by  the  fluxes  employed, 
the  substance  operated  upon  becoming  thus  contaminated  with  silica  or  alkalies; 
the  dissolving  action  of  the  flux  upon  the  crucible  is  sometimes  so  considerable 
as  to  destroy  its  power  of  retaining  the  substance. 

Iron  crucibles  may  be  sometimes  substituted  with  advantage;  these,  however, 
cannot  be  used  in  a  great  number  of  cases,  since  iron  is  also  very  easily  acted 
upon  by  most  fluxes.  When  the  fusion  has  to  be  effected  at  a  very  high  tem- 
perature, graphite  crucibles  are  employed ;  these  act  at  the  same  time  as  auxiliary 
reducing  agents  (in  consequence  of  the  carbon  which  they  contain). 

Crucibles  lined  with  charcoal  are  sometimes  used  in  effecting  reductions. 
Fine  charcoal-powder  is  mixed  up  with  thin  gum-water,  sufficient  only  to  moisten 
it,  without  causing  it  to  adhere.  The  crucible  is  lined  with  a  coating  of  about 
a  quarter  of  an  inch  in  thickness,  and  the  central  cavity  afterwards  made  as 
smooth  as  possible,  by  means  of  the  end  of  a  pestle.  The  reduction  and  fusion 
of  iron  is  effected  in  crucibles  prepared  in  this  manner. 

Fusions,  and  especially  reductions  on  the  small  scale,  are  effected  in  crucibles 
of  Berlin  or  Meissen  porcelain,  over  gas  or  spirit  lamps,  by  the  aid  of  the  blow- 
pipe. Platinum  crucibles  are  substituted  for  these  when  a  high  temperature  is 
required  for  the  decomposition  of  a  substance  by  fusion,  or  when  the  glazing  of 
the  crucible  is  likely  to  be  attacked  by  the  flux.  They  must,  however,  on  no 
account  be  employed  when  the  reduction  of  a  metal  is  likely  to  be  effected  by 
the  fusion,  as  in  such  cases  the  crucible  would  be  inevitably  destroyed,  or  very 
much  injured.  Caustic  alkalies,  or  phosphates,  and  silicates,  fused  in  the  pre- 
sence of  carbon,  likewise  attack  platinum ;  they  may,  however,  be  safely  fused 
in  silver  crucibles.3 

PRECAUTIONS  TO  BE  ATTENDED  TO  IN  FUSIONS. — A  fusion  is  an  operation 
requiring  great  care  and  constant  attention :  there  is,  indeed,  no  other  process 
in  chemistry  so  liable  to  casualties.  The  following  is  an  enumeration  of  the 
principal  precautions  that  should  always  be  strictly  attended  to. 

The  special  directions  given  with  regard  to  the  proportions  of  flux  and  sub- 

1  Bisulphate  of  potassa  is  a  powerfully  cleansing  flux,  on  account  of  the  free  acid  it 
contains,  and  it  is  particularly  useful  for  cleansing  platinum  vessels.     It  is  also  some- 
times employed  for  dissolving  minerals ;  e.  g.  chrome  iron-ore. 

2  Gold  crucibles,  alloyed  with  about  five  per  cent,  of  platinum,  are  said  to  be  much 
more  convenient  than  these  latter,  since  they  stand  a  far  higher  temperature. 


FUSION.  101 

stance  to  be  employed,  their  state  of  division,  &c.,  must  be  always  implicitly 
followed. 

The  charge  of  a  crucible,  and  its  size,  must  be  regulated  according  to  the 
nature  of  the  fusion.  Thus,  if  the  operation  is  accompanied  by  the  disengage- 
ment of  a  gas,  or  the  swelling  up  of  the  mass,  a  capacious  crucible  must  be 
used,  and  not  more  than  half  filled  with  the  mixture.  Substances  diminishing 
in  bulk  upon  fusion,  may  of  course  be  heated  in  smaller  crucibles,  or  in  larger 
quantities. 

The  crucible  must,  in  almost  every  case,  be  kept  covered,  but  in  such  a  manner 
that  the  lid  may  be  easily  removed  at  any  point  of  the  process,  as  it  is  necessary 
in  most  operations  to  examine  the  contents  of  the  crucible  from  time  to  time. 

The  heatiny  of  a  crucible  must  be  conducted  very  gradually  at  the  commence- 
ment, and  care  should  be  taken  to  have  the  source  of  heat  as  much  as  possible 
under  control,  so  that  the  temperature  may  be  lowered  at  any  time,  if  the  cruci- 
ble becomes  too  hot,  or  the  contents  evince  symptoms  of  boiling  over. 

If  the  operation  is  conducted  in  a  furnace,  it  is  frequently  necessary  to  with- 
draw the  crucible  rapidly  from  the  fire,  placing  it  upon  the  top  of  the  furnace, 
until  it  has  somewhat  cooled  down.  The  heat  should  always  be  raised  consider- 
ably towards  the  close  of  the  operation.  In  many  cases,  particularly  when 
reductions  have  been  effected  by  fusion,  it  is  advisable  to  sacrifice  the  crucible 
rather  than  to  disturb  the  mass  after  it  has  been  removed  from  the  fire.  In  that 
case,  the  crucible,  when  sufficiently  cooled  down,  is  laid  upon  an  anvil  or  stone 
slab,  and  smart  blows  are  then  applied  to  it,  by  means  of  a  hammer,  at  a  dis- 
tance of  about  half  an  inch  from  the  bottom.  The  fracture  of  the  crucible  is 
generally  effected  by  this  means  in  such  a  manner  that  the  bottom  separates 
from  the  sides,  and  any  button  of  metal  that  may  have  collected  there  is  then 
readily  removed  from  the  slag.  When  it  is  wished  to  preserve  the  crucible 
(those  of  porcelain,  clay,  &c.  being  referred  to),  the  fused  mass  must  not  be 
allowed  to  solidify  in  it,  even  though  capable  of  being  afterwards  removed  by  a 
solvent.  Many  fused  substances,  in  the  act  of  solidifying,  endanger  the  safety 
of  the  crucibles;  it  is  necessary,  therefore,  when  the  fusion  is  completed,  to  seize 
the  latter  firmly  with  the  tongs,  and  to  pour  out  the  fused  mass  upon  a  cold, 
clean,  and  perfectly  dry  stone  or  iron  surface;  the  crucible  may  then  be  placed 
in  some  warm  spot,  to  cool  gradually.  In  pouring  out  the  mass,  it  is  advisable 
to  move  the  crucible  about,  so  as  to  alter  the  direction  of  the  stream  issuing 
from  it,  thus  spreading  the  mass  over  a  larger  surface.  It  then  cools  down  more 
rapidly,  and  may  be  afterwards  operated  upon  more  conveniently  than  if  it  were 
in  a  thick  mass. 

In  fusing  any  substance  with  nitre,  when  the  oxidizing  action  of  the  latter 
is  so  violent  as  to  be  accompanied  by  deflagration,  as  in  the  oxidation  of  any 
organic  substance,  the  nitre  should  be  first  heated  alone  until  perfectly  fused, 
and  the  substance  then  gradually  introduced  by  means  of  a  spatula,  in  very  small 
quantities  at  a  time.  It  is  advisable  to  hold  the  crucible  cover  in  the  one  hand, 
by  means  of  the  tongs,  while  the  substance  is  being  introduced,  and  to  replace 
it  immediately  after  every  addition,  in  order  to  avoid  loss  by  spirting.  By  em- 
ploying a  mixture  of  nitre  and  chloride  of  sodium,  the  former  is  rendered  far 
more  manageable — its  action  being  thus  greatly  moderated. 

Cyanide  of  potassium  must  on  no  account  be  employed  as  a  flux  when  the 
substance  operated  upon  contains  any  nitrate  or  chlorate,  since  a  violent  ex- 
plosion would  invariably  result.  In  addition  to  the  above  directions,  those  given 
with  regard  to  ignition  should  also  be  applied  to  the  operation  of  fusion. 


102  SOURCES  or  HEAT  IN  THE  LABORATORY. 


SOURCES    OF    HEAT    IN    THE    LABORATORY. 

§  60.  "We  will  now  consider  some  of  the  most  important  means  employed  for 
beating  in  the  laboratory ;  since,  by  a  due  attention  to  these,  the  operator  may 
not  only  effect  a  considerable  reduction  in  expense,  but,  which  is  of  infinitely 
greater  importance,  may  considerably  economize  his  time,  and  may  attain  that 
neatness  in  his  processes  which  is  so  desirable  for  the  analytical  chemist. 

LAMPS. — The  simplest  of  all  our  sources  of  heat,  which  has  been  employed 
almost  from  time  immemorial,  is  the  common  spirit-lamp,  with  which  all  our 
readers  must  be  familiar;  we  should  recommend  them  to  be  made  of  glass,  with 
brass  mounting  for  the  wick;  the  plate  carrying  the  wick-tube  should  screw  into 
a  brass  socket  cemented  on  to  the  lamp;  a  glass  cap  for  spirit-lamps  is  to  be 
preferred  to  one  of  brass,  on  account  of  its  cleanliness.  In  extinguishing  the 
lamp,  the  flame  should  be  blown  out  before  the  cap  is  replaced,  or  the  air  within 
the  latter  is  of  ten  ~  rarefied  to  such  an  extent  that  considerable  exertion  is  required 
to  move  it.  Wood-naphtha*  in  Great  Britain,  is  the  cheapest  fuel  for  spirit- 
lamps;  its  flame  should  emit  very  little  light,  and  should  not  deposit  carbon 
upon  porcelain  dishes. 

The  heat  of  a  spirit-flame  may  be  much  increased  by  supplying  air  to  the 

interior;   this  is  effected  in   the  spirit-lamps  of 
Fig.  55.  Berzelius  and  Mitscherlich,  where  the  burner  is 

constructed  on  the  Argand  principle,  and  the 
naphtha,  or  alcohol,  supplied  from  a  reservoir 
connected  with  the  burner  by  a  long  narrow  tube ; 
these  lamps  produce  a  very  high  degree  of  heat, 
but  are  rather  difficult  to  trim,  and  somewhat 
liable  to  get  out  of  order ;  where  gas  cannot  be 
had,  however,  they  will  be  found  very  useful  sub- 
stitutes. 

The  roaring-lamp,  which  is  Described  in  the 
article  on  glassblowing,  cannot  be  used  in  opera- 
tions which  occupy  a  considerable  length  of  time; 
since  it  becomes  too  hot,  and  consumes  an  enor- 
mous quantity  of  fuel ;  but  for  rapid  fusions,  this 
instrument  is  very  useful. 

Oil-lamps  are  not  very  often  used  in  laborato- 
ries, where  their  grease  is  very  objectionable ;  the 
use  of  an  oil-flame  in  blowpipe  operations  will  be 
noticed  hereafter;  lamps  for  this  purpose  are 
usually  made  with  two  wicks,  a  round  one  for  a 
fine  blowpipe  flame,  and  a  flat  wick  for  a  large 

reducing  flame ;  these  should  be  very  smoothly  cut,  and  their  snuff  removed  from 
time  to  time. 

A  good  Argand  oil-lamp,  with  a  copper  chimney,  may  conveniently  replace 
gas  in  some  operations  on  sand-baths,  &c. 

GAS,  however,  is  far  preferable  to  any  other  source  of  heat  employed  in  the 
laboratory,  and  may  be  applied  in  a  great  many  different  ways;  we  shall  give  a 
brief  description  of  two  gas-burners  which  we  have  found  most  useful  in  prac- 
tice. The  most  pre-eminent  and  important  of  these  is  the  gauze-burner,  which 

1  Also  called  pyroxylic  spirit,  or  pyroligneous  ether.  In  the  United  States,  alcohol  is 
used  on  account  of  economy. 


FURNACES. 


103 


consists  of  a  cylindrical  metal  chimney  (Fig.  56,  Fig.  56. 

a),  about  five  inches  high,  and  two  inches  in  dia- 
meter, surmounted  by  a  screw-ring,  6,  in  which 
is  fitted  a  piece  of  rather  coarse  iron-wire  gauze; 
we  have  found  that  containing  nine  hundred 
meshes  to  the  square  inch  very  useful  for  this 
purpose.  The  burner  which  we  are  in  the  habit 
of  using  for  such  a  chimney  is  a  common  Argand 
of  I  inch  diameter,  carrying  twelve  holes,  and 
provided  with  four  arms  to  support  the  chimney; 
this  Argand  burner  is  screwed  on  to  a  plain  jet, 
so  that,  if  it  be  removed,  a  very  good  blowpipe 
flame  is  obtained ;  a  heavy  brass  foot  completes 
the  stand,  which  is  connected  by  means  of  a  vul- 
canized tube  with  the  gas-pipe,  so  that  it  may  be 
moved  to  any  part  of  the  table.  By  removing 
the  gauze  ring,  we  may  also  obtain  a  very  steady 
Argand  flame.1 

The  gauze-burner  acts  upon  exactly  the  same 
principle  as  the  safety-lamp  of  Sir  Humphry  Davy, 
viz  :  that  flame  cannot  be  communicated  through 
wire  gauze  of  a  certain  fineness ;  within  the  chim- 
ney of  the  burner,  the  gas  is  mixed  with  an 
amount  of  air  sufficient  to  burn  the  carbon  and 
hydrogen  simultaneously,  so  that  no  carbon  is 
separated  within  the  flame,  and  therefore  no  soot 
deposited ;  in  fact,  this  burner  not  only  equals 
the  spirit-lamp  in  this  respect,  but  also  possesses 
the  advantage  of  a  much  higher  range  of  temperature. 

The  common  ring  gas-burner  (Fig.  57,  a,  6),  with  sixteen  holes, 
will  also  be  found  useful  upon  the  working-table;  that  part  of 
the  latter  which  is  in  the  immediate  vicinity  of  the  burner  may 
be  covered  with  a  piece  of  sheet-iron,  to  protect  it  from  the  heat; 
an  iron  sand-bath  of  twelve  inches  in  diameter  may  be  very 
conveniently  heated  over  such  a  burner;  a  ready  support  for 
sand-baths  may  be  fashioned  out  of  an  inverted  flower-pot,  the 
bottom  of  which  is  removed,  and  square  notches  cut  with  a  saw 
in  the  edges  of  the  wide  chimney  thus  formed. 

§  61.  FURNACES. — It  scarcely  falls  within  our  province  to 
describe  the  various  furnaces  used  by  the  chemist,  but,  when  speaking  of  heating 
appliances,  we  cannot  pass  them  entirely  without  notice. 

A  very  good  general  furnace  may  be  builf  of  brick,  the  grate  being  arranged 
so  as  to  insure  a  thorough  draught,  and  so  placed  as  to  be  easy  of  access  to  the 
operator;  the  furnace  should  be  surmounted  by  a  sand-bath  of  pretty  large 
dimensions;  either  near  to,  or  in  connection  with  the  furnace,  there  should  be  a 
combustion-table,  covered  with  sheet-iron,  upon  which  operations  involving  the 
use  of  redhot  charcoal  may  be  conducted ;  or  this  combustion-table  may  be  con- 
structed of  brick,  and  a  grate  sunk  in  it  supplied  with  air  from  beneath,  and 
furnished  with  a  movable  conical  chimney  fop-increasing  the  draught ;  this  grate 
serves  to  supply  redhot  charcoal.  A  drying-dostt  for  filters,  &c.  may  be  conve- 
niently placed,  so  that  it  shall  be  heated  by  the  flue  of  the  furnace. 


Fig.  57. 


4  A  metallic  ring,  made  to  fit  exactly  over  the  wire-gauze,  and  with  a  hole  of  about  an 
inch  diameter  in  the  centre,  will  be  found  useful  to  furnish  a  small  flame  for  test-tubes,  &c. 


104  SOURCES   OF    HEAT   IN   THE   LABORATORY. 

One  of  the  best  portable  furnaces  is  that  known  as  Blactis  furnace,  which  is 
made  of  sheet-iron,  lined  with  fire-brick,  with  a  wide  iron  pipe  serving  as  a 
chimney,  which  may  be  conducted  into  the  main  chimney  of  the  laboratory;  this 
furnace  is  provided,  in  front,  with  two  fire-doors,  which  give  access  to  different 
parts  of  the  fire;  the  ash-pit  is  closed  by  sliding-doors,  which  permit  the  regu- 
lation of  the  draught ;  there  are  also  two  holes,  on  the  same  level,  at  opposite 
sides  of  the  furnace,  to  allow  of  the  passage  of  tubes.  A  sand-bath  is  placed 
at  the  top  of  the  furnace,  and  may  be  replaced  by  a  deep  sand-pot  for  operations 
with  retorts,  &c. ;  there  should  also  be  a  lid  with  which  the  furnace  may  be 
closed  for  crucible  operations. 

In  cases  where  small  crucibles  are  to  be  raised  to  a  very  high  uniform  temper- 
ature, a  piece  of  apparatus,  termed  a  muffle,  is  employed ;  this  is  a  nearly  semi- 
cylindrical  vessel  of  fire-clay,  closed  at  one  end,  and  furnished  with  long,  nar- 
row apertures  at  the  sides,  to  allow  of  the  radiation  of  heat  into  the  interior, 
and  of  the  passage  of  a  current  of  air;  this  muffle  is  placed  in  the  lower  aperture 
of  the  Black's  furnace  before  the  fire  is  lighted,  in  order  that  it  may  be  gradually 
heated  to  redness ;  the  crucibles,  &c.  are  placed  on  the  bottom  of  the  muffle. 

An  admirable  furnace  for  operations  where  glass  tubes  are  to  be  heated  to  red- 
ness, is  the  combustion-furnace  (Fig.  58),  employed  in  organic  analysis;  it  is  a 

trough  of  sheet-iron,  in  length  about  two  feet; 
-  68.  jn  width,  at  the  upper  part,  about  five  inches, 

at  the  lower,  three,  and  in  perpendicular 
depth,  about  three  inches ;  the  front  of  this 
furnace  is  closed  with  an  iron  plate,  perfo- 
rated with  a  hole  of  about  three-fourths  of 
an  inch  diameter  for  the  passage  of  tubes, 
but  the  hinder  end  of  the  trough,  a  b,  is  left 
open ;  the  bottom  is  provided  with  slits,  D  D,  made  transversely  at  somewhat  less 
than  an  inch  apart,  and  between  every  other  pair  of  slits,  is  placed  a  sheet-iron  sup- 
port for  the  tube.  This  furnace  should  also  be  furnished  with  several  movable 
screens  of  sheet-iron  (Fig.  59),  serving  to  divide  it  into  compartments, 
59.  aDcj  wjt}j  a  Cork-screen  to  hang  on  the  front,  in  order  to  protect  the 
corks  from  radiated  heat. 

When  in  use,  the  furnace  must  be  supported  over  the  combustion- 
table  upon  bricks,  which,  if  needful,  may  be  made  to  close  partially 
the  apertures  at  the  bottom,  in  order  to  moderate  the  draught.  The 
fuel  employed  is  always  charcoal,  which  should  be  of  such  quality  as  to  burn 
without  flame  or  much  scintillation,  and  to  remain  redhot  for  some  time  after  its 
removal  from  the  fire;  it  should  be  used  in  rather  large  fragments,  which  main- 
tain a  brighter  and  more  uniform  fire  than  the  small  coals;  the  intensity  of  the 
heat  may  be  increased,  if  necessary,  by  fanning  with  a  piece  of  mill-board.  The 
fire  may  be  gradually  enlarged  to  arcy  extent  by  moving  the  iron  screen  farther 
from  the  front,  which  is  very  convenient  in  heating  tubes  successively  throughout 
their  whole  length,  as  is  requisite  in  organic  analysis. 

A  portable  charcoal  chavfer  will  be  found  very  useful  for  supplying  redhot 
charcoal  in  such  operations  as  that  just  described,  as  well  as  for  affording  a  very 
uniform  and  manageable  source,  of  heat  in  various  operations  with  dasks  and 
retorts.  It  may  even  be  used  with  advantage  for  heating  porcelain  crucibles, 
where  a  good  gas-burner  is  not  at  tand. 

A  most  convenient  chauffer  is  a  nearly  cylindrical  iron  vessel,  about  seven 
inches  in  diameter  at  the  top  and  six  at  the  bottom,  which  is  fitted  with  a  grat- 
ing; the  sides  are  about  five  inches  high,  and  are  perforated  with  several  holes  of 
about  \  inch  in  diameter,  for  admission  of  air;  this  chauffer  should  be  supported 
on  three  legs,  and  provided  with  a  conical  chimney  of  sheet-iron,  about  eighteen 


THE   USE   OF   THE   BLOWPIPE. 


105 


inches  in  height,  which  may  be  placed  over  it  to  increase  the  draught ;  if  a  few 
redhot  coals  be  laid  at  the  bottom  of  the  chauffer,  then  covered  with  charcoal, 
and  the  chimney  placed  on,  a  very  brisk  fire  can  be  made  in  the  course  of  a  few 
minutes,  especially  if  the  draught  be  increased  by  the  use  of  a  pair  of  bellows. 
The  small  fire-clay  chauffers  now  imported  from  the  Continent  will  also  be  found 
very  useful. 

Little  other  furnace-fuel  is  used  in  the  laboratory,  besides  coke  and  charcoal; 
the  latter  is  only  used  in  the  combustion-trough  and  chauffer;  coke  being  decidedly 
the  best  fuel  for  ordinary  furnace-work.  Anthracite  is  now  much  used  for 
metallurgic  operations. 


THE    USE    OF   THE    BLOWPIPE. 

§  62.  THE  BLOWPIPE  consists  essentially  of  a  tube  of  convenient  size  and 
shape,  furnished  with  a  small  aperture  or  jet,  through  which  a  stream  of  air  may 
be  projected  into  the  flame. 

This  instrument  has  taken  a  great  many  forms;  the  simplest  of  these  is  the  com- 
mon soldering-pipe  (Fig.  60),  used  by  braziers,  which  is  a  conical  tube  of  brass  or 
tin,  of  about  one-third  of  an  inch  in  diameter 

at  the  larger  orifice,  from  which  it  tapers     Fig.  60.  Fig.  61. 

off  to  a  jet  of  the  required  size;  this  tube 
is  bent  at  a  somewhat  obtuse  angle.  Such 
a  blowpipe,  though  not  well  fitted  for 
analytical  investigations,  is  often  used  in 
the  laboratory  for  drawing  glass,  heating 
crucibles,  &c.,  since  its  orifice  is  rather 
large,  and  it  therefore  furnishes  a  broad 
flame.  The  great  defect  of  this  tube  con- 
sists in  the  want  of  a  contrivance  for  pre- 
venting the  projection  of  the  condensed 
moisture  from  the  mouth  into  the  blow- 
pipe flame.  This  imperfection  is  remedied 
in  Black's  blowpipe,  which  is  now  gene- 
rally used  in  analysis.  It  consists  of  a 

conical  tube  of  brass  or  japanned  tin,  the  small  orifice  of  which  has  a  diameter 
of  about  one-sixth  of  an  inch,  and  is  fitted  with  a  bone  mouth-piece ;  the  larger 
extremity  is  about  half  an  inch  in  diameter,  and  is  closed  by  a  brass  disk ;  at  a 
distance  of  about  half  an  inch  from  this  end  of  the  tube,  another,  but  much 
smaller  tube,  about  an  inch  and  a  quarter  long,  is  introduced  at  right  angles  to 
the  larger;  this  smaller  tube  is  fitted  with  a  perforated  conical  cap,  called  the 
jet,  which  may  be  removed  to  give  place  to  a  larger  or  smaller,  as  occasion  may 
require.  The  jets  are  sometimes  made  of  platinum,  but  more  commonly  of 
brass.1  It  will  be  seen  that  the  portion  of  the  blowpipe  between  the  smaller 
tube  and  the  closed  extremity,  forms  a  reservoir  to  contain  the  moisture  which 
condenses  in  the  tube,  and  thus  prevents  it  from  being  projected  into  the  flame. 
The  smaller  tube  is  sometimes  terminated  by  a  very  fine  aperture,  so  that  no 
cap  is  required  for  the  jet.  A  fine  jet  is  necessary  for  analytical  experiments, 
and  a  larger  one  for  glassblowing,  &c. 

There  are  many  other  forms  of  the  blowpipe,  but  the  above  is  one  of  the  least 
expensive,  and  is  sufficient  for  all  ordinary  purposes. 


Black's  Blowpipe. 


1  These  jets  are  somewhat  liable  to  be  stopped;  they  may  then  be  opened  with  a  fine 
platinum  wire,  not  with  any  sharp  instrument,  or  the  orifice  will  be  too  much  enlarged. 


106  APPARATUS  FOR  THE  BLOWPIPE. 

The  fame  which  is  best  adapted  to  the  use  of  the  blowpipe  in  the  laboratory 
is  that  of  coal-gas,  since  it  is  perfectly  free  from  dirt  and  grease,  and  admits  of 
being  regulated  with  great  nicety.  The  gas  should  issue  from  a  plain  cylindrical 
orifice,  of  one-quarter  to  one-fifth  of  an  inch  in  diameter;  if  the  walls  of  the  gas- 
jet  be  pretty  thick,  they  afford  a  convenient  rest  for  the  blowpipe,  for  which  a 
notch  may  be  made  in  the  margin  of  the  orifice.  When  gas  cannot  be  procured, 
a  good  oil-lamp,  with  a  pretty  thick,  smoothly-cut  wick,  will  answer  the  pur- 
pose; or  a  wax  candle  with  a  large  wick  may  be  substituted. 

The  principal  supports  used  for  the  test-specimens  in  experiments  with  the 
blowpipe,  are  charcoal,  platinum  wire  and  foil,  iron  spoons,  and  glass  reduction- 
tubes. 

The  charcoal  selected  for  the  purpose  should  be  compact,  free  from  cracks, 
and  its  fracture  should  be  smooth  and  shining;  it  should  not  readily  powder 
when  struck,  but  tend  rather  to  splinter;  this  charcoal  must  have  been  well  car- 
bonized, which  will  be  indicated  by  its  burning  without  flame  or  empyreumatic 
odor ;  it  must  not  be  "  barky,"  or  it  will  crepitate  and  scintillate  in  the  blow- 
pipe-flame, and  when  the  latter  is  directed  upon  its  surface,  it  should  leave  but 
little  white  ash ;  lastly,  it  should,  of  course,  be  perfectly  dry.  The  good  beech- 
charcoal  in  common  use  will  generally  be  found  to  answer  very  well  for  blow- 
pipe experiments ;  it  should  be  split  into  pieces  about  three  inches  long  and  one 
inch  in  diameter,  which  are  then  ground  flat  and  smooth  on  opposite  sides  by 
rubbing  upon  a  rough  stone. 

The  operator  should  be  provided  with  a  small  knife  to  cut  cavities  in  the 
charcoal,  and  with  a  spatula  for  lifting  the  fluxes,  &c. ;  a  small  pair  of  tweezers 
for  taking  up  metallic  globules  will  also  be  found  useful. 

In  some  experiments,  &  pestle  and  mortar  of  agate  are  necessary;  the  internal 
diameter  of  the  mortar  should  be  about  l£  inch,  and  its  depth  that  of  an  ordi- 
nary watch-glass. 

Two  sizes  of  platinum  wire  should  be  found  amongst  the  blowpipe  apparatus; 
the  thinner  kind  resembling  a  stout  horsehair,  the  other  having  the  thickness  of 
the  gut  used  for  fishing-lines ;  these  are  cut  into  pieces  of  three  and  four  inches 
in  length.1 

Platinum  foil  must  be  so  thick  that  a  piece  of  it,  two  inches  square,  will  not 
bend  with  its  own  weight ;  pieces  of  the  above  dimensions  are  suitable  for  most 
purposes. 

Iron  spoons  are  only  used  in  rough  experiments;  they  are  generally  rather 
thin  in  substance,  round,  shallow,  about  three-quarters  of  an  inch  in  diameter, 
and  provided  with  a  long  handle,  which  may  be  thrust  into  a  cork  to  protect  the 
hand. 

Glass  reduction-tubes  are  made  of  various  forms,  but  are  generally  either 
simply  closed  at  the  end,  or  expanded  into  a  bulb ;  the  method  of  making  these 
tubes  will  be  described  in  the  section  on  manipulation  of  glass ;  sumce  it  to  say 
here,  that  they  should  be  of  hard  German  glass,  in  order  better  to  resist  the 
high  temperature  to  which  they  are  often  exposed. 

§  63.    The  chief  reagents  employed  in  blowpipe  experiments  are  the  following  : 

Charcoal,  which  has  been  already  mentioned  as  a  support;  it  is  sometimes 
required  in  powder,  which  should  be  strongly  heated  in  a  closed  crucible,  to 
expel  volatile  matters,  previously  to  use.  Charcoal  is  the  chief  agent  employed 
for  abstracting  oxygen  in  operations  with  the  blowpipe. 

Carbonate  of  soda  (NaO.C02)  is  often  required  in  reduction-experiments, 
when  its  action  appears  to  depend  upon  the  momentary  isolation  of  a  portion  of 
its  sodium,  which  exercises  a  powerful  reducing  action  on  the  substance  operated 

1  These  wires  may  be  cleaned  after  use  by  boiling  in  cone,  hydrochloric  acid.  They 
should  be  kept  in  distilled  water. 


REAGENTS   FOR   THE   BLOWPIPE.  107 

upon.  It  acts  also  by  extracting  the  acid  from  salts,  and  thus  leaving  the  metal- 
lic oxide  more  exposed  to  the  action  of  reducing  agents,  and  sometimes  serves  to 
protect  the  surface  of  reduced  metals,  and  to  prevent  their  reoxidation. 

Carbonate  of  soda  employed  as  a  blowpipe  reagent,  should,  strictly  speaking, 
be  perfectly  pure ;  but  the  common  washing-soda  of  commerce,  after  one  or  two 
recrystallizations,  is  sufficiently  so  for  ordinary  purposes;  the  crystals  should  be 
thoroughly  dried  in  a  porcelain  dish  on  a  sand-bath,  and  afterwards  rather 
coarsely  powdered. 

Black  flux,  which  has  been  noticed  when  speaking  of  fusion,  is  also  sometimes 
employed  in  blowpipe  experiments. 

Cyanide  of  potassium  (KCy=KNCa,  prepared  by  Liebig's  process)  is  very 
valuable  as  a  reducing  agent ;  most  metallic  oxides,  when  fused  with  cyanide  of 
potassium,  part  with  their  oxygen  to  this  salt,  converting  it  into  cyanate  of 
potassa  (KO.CyO);  the  great  fusibility  of  the  cyanide,  however,  prevents  its 
application  in  many  cases.  This  reagent  should  be  used  in  the  form  of  a  coarse 
powder. 

A  rather  strong  solution  of  nitrate  of  cobalt  (CoO.N05)  is  sometimes  useful 
in  experiments  on  charcoal. 

Borax  (biborate  of  soda,  Na0.2B03-{-10Aq)  js  a  m0st  important  blowpipe 
reagent.  It  should  be  finely  powdered.  The  chief  value  of  borax  in  blowpipe 
analysis  depends  upon  its  property  of  dissolving  certain  metallic  oxides,  forming 
glasses  of  peculiar  colors.  When  heated  in  the  blowpipe-flame,  borax  first 
swells  up  (intumesces),  evolves  steam,  and  then  fuses  to  a  perfectly  colorless 
glass,  which  remains  transparent  on  cooling. 

Phosphorus- salt  (microcosmic  salt,  NaO.NH4O.HO.P05+8Aq)  is  sometimes 
used  instead  of  borax  for  producing  colored  glasses.  When  heated,  this  salt 
loses  its  ammonia  and  water,  and  is  converted  into  the  metaphosphate  of  soda 
(NaO.P05),  which  fuses  into  a  perfectly  clear  glass.  Phosphorus-salt  is  used  in 
small  crystals. 

Nitrate  of  potassa  (nitre,  KO.N05)  is  occasionally  employed  as  an  oxidizing 
agent ;  it  should  be  kept  in  powder. 

§  64.  It  may  be  useful,  in  this  place,  to  explain  a  few  terms  which  are  fre- 
quently used  in  describing  the  behavior  of  substances  under  the  blowpipe. 

INTUMESCENCE  is  the  swelling  up  of  the  fused  salt,  in  consequence  of  the 
rapid  expulsion  of  its  water  of  crystallization  j  borax  affords  a  very  good  example 
of  this  (§  63). 

DECREPITATION  has  been  already  defined  as  the  splitting  up  of  the  crystals 
of  a  salt,  by  the  expansion  of  the  mechanically-inclosed  water. 

DEFLAGRATION  is  the  vivid  combustion  observed  when  powerful  oxidizing 
agents  are  heated  in  contact  with  oxidizable  substances  (e.  </.  nitre  upon  char- 
coal), or  when  such  agents  are  exposed  to  the  inner  blowpipe-flame. 

DETONATION  takes  place  when  one  or  all  of  the  substances  acting  upon  each 
other  are  suddenly  converted  into  the  gaseous  form,  so  as  to  give  rise  to  a  sharp 
noise. 

INCANDESCENCE  is  the  production  of  a  bright  light,  when  solid  infusible  sub- 
stances are  introduced  into  the  hottest  part  of  the  blowpipe-flame. 

§  65.  Before  proceeding  to  describe  the  manipulations  with  the  blowpipe,  it 
will  not  be  out  of  place  to  say  a  few  words  with  regard  to  the  nature  of  the  blow- 
pipe-flame. 

In  a  coal-gas  flame  (which  is  quite  similar  to  the  flames  of  lamps  and  candles), 
the  carbon  and  hydrogen  which  constitute  the  fuel,  enter  into  combination  with 
oxygen  (forming  respectively  carbonic  acid  and  water),  but  not  simultaneously. 
The  affinity  of  hydrogen  being  greater  than  that  of  carbon,  for  oxygen,  under 
the  present  conditions,  the  former  undergoes  combustion  first,  leaving  the  carbon 
free  in  the  midst  of  the  flame,  by  the  heat  of  which  it  is  raised  to  so  high  a 


108 


THE   BLOWPIPE   FLAME. 


Fig.  62. 


, C 


-A 


Fig.  63. 


temperature,  that  it  emits  a  white  light;  this  carbon  afterwards  undergoes  com- 
bustion on  coming  in  contact  with  the  external  air. 

In  a  common  flame,  we  may  perceive  three  cones,  the  innermost  of  which  (Fig. 
62  A)  is  a  hollow  space,  filled  with  combustible  gas,  whilst  the  second 
or  luminous  cone,  B,  is  that  in  which  the  hydrogen  undergoes  com- 
bustion and  the  carbon  is  raised  to  a  white  heat,  to  be  subsequently 
burnt  in  the  cone,  c,  which  emits  very  little  light. 

In  examining  the  action  of  the  blowpipe  upon  such  a  flame,  it 
must  be  observed  that  the  air  projected  into  the  latter  does  not 
proceed  from  the  lungs,  but  is  simply  conveyed  through  the  pas- 
sages of  the  nose  into  the  mouth,  and  thence  ejected  by  a  muscular 
effort  of  the  cheeks,  so  that  a  stream  of  nearly  pure  atmospheric 
air  (oxygen  and  nitrogen)  is  forced  into  the  flame,  to  which  enough 
oxygen  is  thus  supplied  to  enable  the  carbon  and  hydrogen  to 
burn  simultaneously,  in  consequence  of  which  no  carbon  separates, 
and  the  flame  emits  no  white  light.     The  blowpipe-flame  (Fig.  63),  like  that  of  the 
ordinary  candle  or  gas-jet,  consists  of  three  parts;  the 
inner  hollow  cone,  where  the  cold  air  first  passes  into 
the  flame  ;  the  inner  cone  of  partial  combustion ;  and 
the   outermost  cone,  where  the  combustion  is  com- 
pleted.    In  that  part  of  the  inner  blue  cone  which 
is  nearest  to  the  blowpipe-jet,  there  must  be  an  excess 
of  oxygen,  and  in  this  place  the  combustion  is  perfect; 
beyond  this,  there  is  a  point  where  neither  the  oxygen 
nor  the  combustible  gas  is  in  excess,  and  this  is  con- 
sequently the  hottest  part  of  the  blowpipe-flame ;  this 
point  is  found  near  the  extremity  of  the  blue  flame ;  a 

little  within  the  point  of  the  blue  flame  (unless  a  very  considerable  amount  of 
air  be  forced  into  it  from  a  large  blowpipe-jet),  there  will  be  an  excess  of  com- 
bustible gas  (carbon  and  hydrogen),  which,  at  the  high  temperature  to  which  it 
is  here  raised,  is  capable  of  abstracting  oxygen  from  most  metallic  oxides,  thus 
reducing  them  either  to  metals  or  to  a  lower  state  of  oxidation.  This  part  of  the 
flame  is  termed  the  reducing  or  deoxidizing  flame. 

When  the  heated  gas  has  passed  the  point  of  the  blue  flame,  it  is  oxidized  at 
the  expense  of  the  surrounding  air,  and  gives  rise  to  the  very  slightly  luminous 
cone  of  complete  combustion.  Around  this  cone,  then,  there  is  an  excess  of 
oxygen,  and  if  any  substance  be  introduced  into  it  which  has  any  considerable 
affinity  for  this  element,  it  will  be  at  once  oxidized ;  hence  this  outer  tone  has 
been  named  the  oxidizing  flame.  The'  capabilities  of  the  different  blowpipe- 
flames  may  be  readily  tested  by  introducing  a  little  oxide  of  lead,  in  a  small  iron 
spoon,  into  the  inner  flame,  which  will  at  once  reduce  it  to  the  metallic  state, 
and  the  metal  thus  obtained  may  be  reoxidized  by  transferring  it  to  the  outer 
flame. 

In  order  to  obtain  a  well-defined  blowpipe-flame  with  the  gas-jet  above  de- 
scribed, the  aperture  of  the  blowpipe-jet  should  be  placed  just  within  the  flame, 
immediately  above  the  edge  of  the  aperture  from  which  the  gas  issues;  if  a 
reducing  flame  is  required,  a  blowpipe  with  a  small  jet  should  be  used,  a  larger 
orifice  being  better  suited  for  oxidation.  A  broad  scattered  flame,  which  is  very 
useful  for  heating  crucibles,  drawing  glass,  &c.,  is  obtained  when  the  blowpipe- 
jet  is  withdrawn  to  the  distance  of  -fa  or  -J-  inch  from  the  margin  of  the  gas- 
flame.  A  good  blowpipe-flame  should  be  free  from  white-light,  and  the  two  cones 
should  be  very  well  defined.  The  stream  of  air  must  not  be  intermitted,  the 
operator  acquiring,  by  continued  practice,  the  habit  of  breathing  through  the 
nose  without  relaxing  the  muscles  of  the  mouth  and  cheeks. 


BLOWPIPE   OPERATIONS.  109 

In  examining  the  action  of  the  blowpipe-flame  upon  test-specimens  placed  on 
charcoal  supports,  it  is  generally  desirable  to  ascertain  if  any  substance  is  re- 
duced to  the  metallic  state,  and  whether  the  surrounding  portion  of  charcoal  is 
covered  with  an  incrustation  of  oxide  resulting  from  the  reoxidation  of  the 
metallic  vapor  in  passing  through  the  outer  flame.  To  determine  these  points, 
a  piece  of  charcoal  having  been  selected  and  prepared  according  to  the  directions 
given  above,  a  small  shallow  cavity  (of  about  £  inch  in  diameter)  is  scooped  with 
a  penknife  at  one  end  of  the  smooth  surface,  within  about  half  an  inch  of  the 
edge,  and  in  this  the  test-specimen  is  placed,  and  covered  with  the  reagent  to  be 
employed;  the  charcoal  is  now  held  in  the  blowpipe-flame  in  such  a  manner  that 
the  reducing  (inner)  flame  may  be  directed  into  the  cavity,  and  the  oxidizing 
(outer)  flame  allowed  to  flow  over  the  surface  of  the  charcoal,  upon  which  it 
should  extend  itself  in  the  form  of  a  cone,  within  the  limits  of  which  we  after- 
wards look  for  the  incrustation;  the  stream  of  air  must  not  be  violent  at  first,  or 
the  substance  will  be  blown  away,1  but  should  be  increased  as  the  operation  pro- 
ceeds. The  specimen  to  be  examined  should  be  first  powdered. 

In  some  cases,  especially  in  the  analysis  of  minerals,  it  is  necessary  to  roast 
the  specimen,  by  exposing  it  for  some  time  to  the  outer  flame,  to  oxidize  and 
remove  sulphur,  &c.,  before  attempting  to  reduce  it;  this  should  always  J>e 
attended  to  in  the  case  of  metallic  sulphides,  the  carbonate  of  soda,  or  other 
reagent,  not  being  added  till  the  roasting  is  completed,  which  will  be  the  case 
when  the  odor  of  sulphurous  acid  is  no  longer  perceptible ;  the  test-specimen 
should  be  turned  about  once  or  twice  during  the  operation,  to  expose  fresh  sur- 
faces to  the  oxidizing  action. 

The  reduced  metal  is  generally  seen  either  in  one  pretty  large  globule  or  in  a 
multitude  of  smaller  particles,  which  may  generally  be  induced  to  unite  by  judi- 
ciously directing  the  blowpipe-flame  upon  them;  cyanide  of  potassium  is  very 
useful  in  favoring  the  union  of  such  globules,  since  it  becomes  very  liquid  at  a 
comparatively  low  temperature ;  the  globules  are  best  seen  when  the  mass  is  red- 
hot.  A  globule  having  been  obtained,  it  may  be  desirable  to  ascertain  whether 
it  is  malleable  or  brittle;  for  this  purpose,  it  is  allowed  to  cool  perfectly,  and 
carefully  removed  with  a  pair  of  tweezers;  having  been  placed  upon  the  bottom 
of  a  strong  inverted  mortar,  it  is  now  struck  sharply  with  the  pestle,  when,  if 
brittle,  it  of  course  falls  to  powder  (as  in  the  case  of  antimony),  if  semi-malleable, 
it  flattens  out,  at  the  same  time  breaking  into  several  pieces  (as  with  bismuth), 
and,  if  fully  malleable,  flattens  out  without  breaking  (like  lead). 

In  some  cases,  and  particularly  where  large  quantities  of  earthy  matters  are 
present,  small  portions  of  reduced  metal  are  disseminated  throughout  the  mass 
after  exposure  to  the  inner  blowpipe-flame,  but  will  not  join  into  globules;  to 
detect  these,  the  test-specimen,  together  with  the  surrounding  portions  of  char- 
coal, may  be  scraped  into  an  agate  mortar,  and  reduced  to  a  very  fine  powder ;  if 
this  is  submitted  to  repeated  levigation,  all  the  metallic  particles  will  be  left  behind. 
When  looking  for  an  incrustation  upon  the  surface  of  the  charcoal,  it  must  be 
remembered  that  the  latter  is  generally  covered  with  a  thin  film  of  bluish-white 
ash  after  having  been  exposed  to  the  oxidizing  flame. 

§  66.  A  few  metallic  oxides  are  recognized  by  the  color  of  their  compounds 
with  oxide  of  cobalt;  in  order  to  subject  them  to  this  test,  the  specimen  is  very 
strongly  heated,  on  charcoal,  in  the  hottest  part  of  the  blowpipe  flame ;  it  is 
then  removed  from  the  flame,  moistened  with  a  drop  or  two  of  the  solution  of 
nitrate  of  cobalt,  and  again  very  strongly  heated ;  the  color  of  the  resulting  com- 
pound should  be  observed  when  it  has  cooled,  and  by  daylight. 

The  formation  of  colored  glasses  by  dissolving  certain  metallic  oxides  in  fused 
borax  or  phosphorus-salt,  is  often  had  recourse  to  as  a  means  of  recognizing 

1  This  may  be  prevented  by  slightly  moistening  the  substance. 


110  GLASSBLOWING. 

them,  and  as  such  glasses  usually  present  different  appearances. in  both  flames, 
every  inference  obtained  in  this  way  is  supported  by  two  indications.  The  color- 
less glass  to  be  employed  must  first  be  prepared,  and  the  oxide  added  to  this  by 
degrees,  till  a  distinct  color  is  produced;  a  piece  of  the  thicker  variety  of  plati- 
num wire  above  mentioned  is  selected,  and  its  extremity  (previously  well  washed) 
bent  round  ia  the  form  of  a  loop,  which  should  be  somewhat  smaller  than  the 
section  of  the  reducing  flame;  this  loop  is  now  heated  to  redness  in  the  flame, 
and  plunged  into  the  flux  to  be  employed  (borax  or  phosphorus-salt),  when  a 
sufficient  quantity  will  adhere  to  it  to  form  a  small  bead  in  the  loop  when  fused 
in  the  blowpipe  flame;1  in  fusing  the  bead,  the  wire  must  be  dexterously  turned 
with  the  hand,  to  prevent  the  fused  flux  from  dropping  off,  and  the  fusion  is  dis- 
continued when  the  effervescence  and  boiling  have  ceased.  The  bead  thus 
obtained,  which  must  be  perfectly  transparent  and  colorless,  and  not  larger  than 
the  section  of  the  reducing- flame,  is  now  again  heated  to  redness,  and  a  very 
small  particle  of  the  substance  to  be  examined  made  to  adhere  to  it ;  the  glass 
is  fused  in  the  outer  flame  (near  the  point)  for  some  time,  the  bead  allowed  to 
cool,  in  order  that  its  color  may  be  observed,  a  fresh  quantity  of  the  substance 
added  as  before,  and  this  operation  repeated  (always  fusing  in  the  outer  flame) 
until  either  a  distinct  color  is  obtained,  or  a  considerable  amount  of  the  substance 
has  been  added  without  affecting  the  color  of  the  glass.  The  color  (by  trans- 
mitted daylight)  of  the  hot  and  cold  bead,  should  be  carefully  observed,  and  the 
latter  then  exposed  to  the  reducing  flame  for  some  seconds,  the  color  of  the  glass 
being  afterwards  again  noted.  It  is  obvious  that  the  smaller  the  bead,  consist- 
ently with  distinct  perception,  the  better;  and  that  very  little  of  the  coloring 
matter  should  be  added  at  once,  since  some  metallic  oxides  impart  such  intense 
colors  as,  when  in  considerable  quantity,  to  cause  the  bead  to  appear  black. 

Other  metallic  oxides  are  known  by  their  imparting  particular  tints  to  the  outer 
~blowpipe-flame,  in  consequence  of  the  reduction  and  volatilization  of  the  metal 
in  the  inner  flame,  and  its  subsequent  burning  with  the  color  in  question  on 
arriving  in  the  oxidizing  cone.  In  order  to  test  substances  in  this  manner,  a 
very  small  loop  is  made  at  the  extremity  of  the  thinner  platinum  wire,  and  well 
washed  with  distilled  water;  it  is  now  introduced  into  the  inner  flame,  and  if  it 
impart  any  tint  to  the  outer  flame,  it  is  removed,  after  a  few  seconds,  and  again 
washed ;  this  process  must  be  repeated  until  the  wire  ceases  to  tinge  the  flame  ;a 
the  loop  is  now  moistened  with  pure  water,  and  a  little  of  the  powder  under 
examination  is  taken  upon  it  and  introduced  into  the  point  of  the  inner  flame, 
where  it  should  be  held  for  two  or  three  minutes  before  we  conclude  that  it 
imparts  no  tint  to  the  outer  flame. 

When  substances  are  heated  on  platinum  foil,  in  iron  spoons,  or  glass  reduction- 
tubes,  it  is  usually  with  the  intention  of  raising  them  to  a  high  temperature 
without  subjecting  them  to  any  chemical  action  of  the  flame ;  a  broad-scattered 
blowpipe-flame  is  generally  used  for  this  purpose,  and  is  directed  on  to  the  bottom 
of  the  support. 

GLASSBLOWING. 

§  67.  It  is  an  important  qualification  of  the  practical  chemist  to  be  able  to 
fashion  the  simpler  kinds  of  apparatus  without  the  aid  of  the  glassblower,  since 

1  When  carbonate  of  soda  is  employed  as  a  flux,  the  loop  should  be  wetted,  in  order 
that  the  carbonate  may  adhere,  since  it  does  not  readily  attach  itself  to  the  redhot  wire. 
When  phosphorus-salt  is  used,  it  is  advisable  to  give  two  turns  to  the  wire  in  making  the 
loop,  and  to  allow  the  loops  thus  made  to  cross,  so  as  to  form  a  sort  of  grating  on  which 
the  very  fusible  glass  may  be  retained. 

2  This  (yellow)  tint  is  generally  imparted  to  the  flame  by  the  soda  derived  from  the 
fingers  of  the  operator,  who  should  not  touch  the  loop  when  once  cleansed. 


i 

I 


GLASSBLOWING.  Ill 

it  not  only  effects  a  considerable  saving  of  expense,  but  enables  him  to  give  to 
his  instruments  that  form  which  suits  his  own  taste ;  we  shall  here  give  a  few 
brief  directions,  which  may  be  useful  in  guiding  the  practice  of  the  novice  in  this 
department. 

Considerable  difficulty  is  experienced  in  drawing  and  blowing  glass  before  the 
mouth-blowpipe,  and  hence  certain  blowpipes  are  provided  especially  for  this 
purpose.  The  chief  of  these  are  known  as  the  table-blowpipe,  Herapath's  blow- 
pipe, and  the  spirit-blowpipe,  or,  as  it  is  commonly  termed  in  the  laboratory,  the 
roarer. 

The  table-blowpipe  is  simply  a  table  furnished  with  a  lamp  and  blowpipe-jet, 
to  which  air  is  supplied  from  a  pair  of  double-action  bellows,  worked  by  a  treadle 
and  weights  beneath  the  table ;  the  lamp  is  generally  supplied  with  oil,  and 
should  have  a  good  broad  wick,  which  is  kept  well  trimmed. 

The  Herapath's  blowpipe  consists  of  two  brass  tubes,  one  within  the  other,  so 
contrived  that  when  screwed  on  to  the  gas-pipe,  a  jet  of  gas  may  issue  from  the 
outer  tube,  and  a  stream  of  air  may  be  forced  from  the  mouth  through  a  tube  of 
vulcanized  Indian-rubber,  into  the  inner  brass  tube,  which  is  terminated  by  a 
blowpipe-jet ;  the  air  is  thus  projected  into  the  very  centre  of  the  gas-flame,  and, 
the  inner  tube  being  made  to  slide  up  and  down  in  the  outer,  the  jet  may  be 
approached  to,  or  withdrawn  from  the  flame,  so  as  to  furnish  a  blowpipe-flame  of 
any  dimensions. 

The  spir it-blowpipe-lamp  (Rose's  lamp)  is  a  sort  of  brass  pot  with  double  walls, 
into  the  interval  between  which  a  small  brass  tube  penetrates  nearly  to  the  top, 
and  enters  the  pot  at  the  bottom,  an  inch  above  which  it  terminates  in  a  pretty 
large  blowpipe-jet;  the  space  between  the  walls  is  about  three-parts  filled  (through 
an  aperture  made  for  the  purpose,  and  stopped  either  with  the  handle  of  the  pot 
or  with  a  good  cork)  with  wood-naphtha,  a  small  quantity  of  which  is  poured  into 
the  inside  of  the  pot,  so  as  to  reach  within  about  a  quarter  of  an  inch  of  the 
blowpipe  aperture;  if  this  be  kindled,  its  flame  heats  the  naphtha  between  the 
two  walls,  and  converts  it  into  vapor,  which  rushes  out  with  a  roaring  noise 
through  the  jet,  where  it  takes  fire,  thus  producing  a  broad  column  of  flame  very 
well  adapted  for  heating  crucibles,  drawing  thick  glass  tubes,  &c.  It  is  scarcely 
necessary  to  observe  that  the  naphtha  poured  into  the  space  between  the  walls 
must  be  perfectly  clear,  for  if  any  fragments  of  cork,  &c.  get  into  the  blowpipe- 
aperture,  the  lamp  may  burst  with  considerable  violence,  and  hence  the  danger- 
ous reputation  which  these  lamps  have  acquired;  with  a  little  care,  however, 
they  may  be  used  with  perfect  safety,  and  are  very  valuable  instruments,  espe- 
cially in  laboratories  where  gas  cannot  be  procured.  If  the  jet  of  vapor  should 
suddenly  cease,  the  lamp  must  be  immediately  extinguished  with  the  cover 
provided  for  this  purpose. 

The  ordinary  cases  of  working  in  glass  which  come  under  our  notice  in  the 
laboratory,  and  which  have  not  yet  been  referred  to,  are,  the  simple  closure  of 
tubes  so  as  to  preserve  a  uniform  thickness,  the  sealing  of  tubes  required  to 
stand  considerable  internal  pressure,  the  expansion  into  bulbs,  the  drawing  out 
of  tubes  to  a  long  open  point,  and  the  manufacture  of  the  combustion-tubes  used 
in  organic  analyses.1 

It  is  not  difficult  to  close  a  tube  so  as  to  preserve  a  uniform  thickness ;  a  piece 
of  tube  is  selected,  about  three  inches  longer  than  the  required  closed  tube,  and, 
having  been  first  heated  in  the  common  flame  (which  precaution  must  be  attended 

1  In  manipulating  with  glass  before  the  blowpipe,  it  should  be  observed,  that  the  Eng- 
lish glass  is  very  liable  to  blacken,  from  the  reduction  of  lead,  and  should  therefore  be 
heated  only  in  the  oxidizing  flame,  whilst  the  German  glass  may  be  exposed  to  the  hottest 
part  of  the  flame ;  in  fact,  for  most  purposes,  the  German  glass  is  much  superior  to  the 
English,  and  is  always  used  when  the  tubes  are  required  to  bear  a  high  temperature. 


112  GLASSBLOWING. 

to  in  all  glass-manipulations),  at  the  point  where  the  closing  is  to  be  effected,  it 
is  softened  at  about  a  quarter  of  an  inch  on  each  side  of  this  point,  by  means  of 
a  coarse  blowpipe  flame,  produced  by  the  mouth-blowpipe,  or  by  one  of  those 
especially  devoted  to  glassblowing.  The  glass  must  be  slowly  turned  round  in 
the  flame,  as  well  as  moved  from  side  to  side,  so  that  it  may  be  uniformly  heated; 
when  it  is  pretty  soft,  it  is  very  gently  drawn  out  in  the  flame  by  slowly  separat- 
ing the  hands,  the  tube  being  still  rotated,  until  the  end  is  drawn  off;  at  the  end 
of  the  tube  thus  formed,  there  will  be  a  little  knob  of  fused  glass,  termed  a  bleb, 
which  is  removed  by  means  of  a  piece  of  glass  rod,  first  gently  heated  in  the  flame, 
so  that  the  bleb  may  adhere  to  it.  Hitherto,  the  tube  has  been  held  in  the  left 
hand ;  it  is  now  shifted  to  the  right,  without  removing  it  from  the  flame,  and  so 
turned  that  the  whole  of  the  closed  extremity  may  be  uniformly  softened ;  when 
this  is  the  case,  the  tube  is  quickly  removed  from  the  flame,  and  blown  into  with 
a  steadily  increasing  pressure,  which  will  have  the  effect  of  ^regularly  expanding 
those  portions  of  the  glass  which  have  been  thickened  in  the  flame,  and  thus,  of 
equalizing  its  thickness.  If  great  pressure  be  suddenly  exerted  upon  the  soft 
glass,  it  will  be  blown  out  into  a  very  large  thin  bulb,  which  will  immediately 
burst. 

The  sealing  of  tubes  required  to  bear  considerable  pressure,  is  effected  much 
in  the  same  manner  as  the  simple  closure  just  described;  but,  in  drawing  off  the 
end,  it  is  retained  in  the  blowpipe  flame  until  it  has  acquired  the  necessary  thick- 
ness, and  no  attempt  need  be  made  to  take  off  the  bleb. 

In  the  manufacture  of  glass  bulbs,  the  latter  may  be  required  at  the  extremity 
of  the  tube  (as  in  thermometers),  or  in  the  middle  (as  in  the  tubes  employed  in 
reducing  metallic  oxides  by  hydrogen);  for  the  former  case,  a  piece  of  tube  of 
the  proper  thickness  having  been  selected  (of  course,  the  thicker  the  walls  of  the 
tube,  the  larger  the  bulb  may  be  made),  it  is  closed  at  one  end,  in  the  manner 
above  described,  and  the  bleb  removed ;  the  closed  extremity  is  then  well  and 
uniformly  softened  in  the  flame,  and  retained  there  until  the  glass  has  acquired 
a  thickness  proportionate  to  the  size  of  the  required  bulb;  the  tube  is  then 
rapidly  removed  from  the  flame,  and  a  steadily  increasing  pressure  applied  by 
the  mouth  till  the  bulb  is  of  the  proper  size;  if  this  is  not  the  case  after  a  first 
attempt,  the  bulb  must  be  uniformly  reheated  (which  will  cause  it  to  collapse), 
and  again  expanded. 

If  the  bulb  is  required  on  the  body  of  the  tube,  one  end  of  the  latter,  if  not 
closed,  must  be  stopped  by  a  cork,  the  tube  well  softened  regularly  for  about  an 
inch,  and  then  steadily  expanded,  as  in  the  other  cases;  if  the  tube  is  rather 
thin,  that  portion  upon  which  the  bulb  is  required  may  be  thickened,  by  gently 
pressing  the  tube,  as  it  were,  upon  itself,  when  soft. 

Tubes  of  moderate  width,  drawn  out  to  a  long  open  point,  are  often  required 
in  testing  for  arsenic.  These  are  made  by  well  softening  about  an  inch  and  a 
half  of  the  tube  (German  glass),  then  removing  it  from  the  flame,  and  rapidly 
but  steadily  drawing  the  ends  apart,  till  the  narrow  tube  thus  produced  is  of 
about  twice  the  required  length,  so  that  two  arsenic-tubes  may  be  obtained  by 
one  operation ;  they  are  then  separated  by  a  sharp  file. 

It  is  almost  impossible  to  describe  the  manipulation  requisite  in  drawing  out 
the  combustion-tubes  for  organic  analysis,  and  none  would  be  able  to  effect  it 
after  merely  reading  even  the  minutest  description.  The  tube  required  is  to  be 
(of  German  glass)  drawn  out  to  a  closed  broad  point,  forming  with  the  main 
tube  an  angle  of  about  45°,  in  such  a  manner  that  the  section  of  the  point  in 
any  part  may  be  perfectly  round,  not  flattened  or  elliptical;  this  is  the  result  of 
a  really  difficult  manipulation,  which  will  be  found  to  consist  in  forcibly  drawing 
out  the  softened  tube,  with  a  peculiar  turn  of  the  wrist,  which  at  once  gives  the 
proper  angle,  and  preserves  the  roundness  of  the  point. 


ELEMENTARY  CHEMISTRY. 


§  68.  AN  element  may  be  familiarly  defined  as  a  substance  which  cannot  be 
resolved  into  anything  further. 

Our  present  elements  are  only  the  boundaries  to  which  chemical  research  has 
hitherto  penetrated;  we  have  no  evidence  that  some  of  these  may  not  ultimately 
be  shown  to  be  compounds. 

The  number  of  elements  at  present  discovered  is  sixty-four,  of  which  only 
thirty-seven  are  ordinarily  met  with,  the  remainder  being  of  comparatively  rare 
occurrence,  and,  generally  speaking,  of  little  practical  importance. 

These  sixty-four  elements  are  divided  into  two  classes ;  the  metals  and  non- 
metallic  substances,  which  latter  are  often  improperly  termed  metalloids. 

The  distinctive  features  of  these  two  classes  are,  in  many  cases,  not  very 
decidedly  marked,  and  some  chemists  therefore  place  amongst  the  non-metallic 
bodies  certain  substances  which  others  rank  with  the  metals.  A  division  like 
this,  founded,  in  some  cases,  rather  upon  opinions  than  upon  facts,  may  be 
looked  upon  as  useful  in  affording  assistance  to  the  memory,  but  should  not  be 
considered  one  of  the  important  features  of  the  science. 

We  will  state  the  chief  points  upon  which  this  classification  of  the  elements 
depends. 

A  metal  usually  possesses  a  peculiar  power  of  reflecting  light,  which  is  denoted 
by  the  term  metallic  lustre,  and  it  is  a  better  conductor  of  heat  and  electricity 
than  are  non-metallic  substances. 

These  are  the  chief  physical  differences ;  but  it  is  in  their  chemical  relations 
that  the  difference  between  these  two  classes  of  elements  is  most  clearly  per- 
ceived. The  metals  possess,  generally,  a  great  afiinity  for  oxygen  and  the  salt- 
radicals  (chlorine,  bromine,  &c.),  with  which  they  combine  to  form,  respectively, 
bases  and  salts ;  in  fact,  this  property  of  forming  a  base  by  combination  with 
oxygen,  may  be  almost  regarded  as  a  sine  qud  non  in  the  definition  of  a  metal, 
for  there  are  few  metals  which  do  not  exhibit  it ;  whilst  none  of  the  non- 
metallic  bodies  are  capable  of  forming  basic  oxides,  and  these  latter  are  gene- 
rally characterized  by  a  tendency  to  form  powerful  acids  by  combination  with 
oxygen. 

It  may  then  be  generally  asserted  that  all  elements  which  possess  a  metallic 
lustre,  which  are  pretty  good  conductors  of  heat  and  electricity,  and  which  are 
capable  of  forming  basic  oxides,  are  metals,  and  that  those  elements  which  are 
not  thus  distinguished,  are  non-metallic  substances. 

The  metals  include  by  far  the  greater  number  of  the  elements,  the  non- 
metallic  bodies  numbering,  according  to  the  usual  division,  only  thirteen ;  but 
of  these  twelve  are  of  considerable  importance,  whilst  twenty-five  only  of  the 
metals  receive  any  application  worthy  of  notice  in  this  work. 

In  the  following  list,  the  elements  are  enumerated,  with  their  symbols  and 
equivalents. 
8 


114 


METALS. 


I.    NON-METALLIC    BODIES 

1.    Of  considerable  importance. 


BORON  . 

.    .     .    B 

_sa 

10. 

9 

IODINE  . 

I 

i 

127.1 

BROMINE   . 

.     .     .     Br 

-_ 

80 

NITROGEN  .     . 

.     .     N 

__ 

14 

CARBON 

.     .     .     C 

— 

6 

OXYGEN     ;T  v 

.     .     0 

= 

8 

CHLORINE  . 

.     .     .     Cl 

= 

35. 

5 

PHOSPHORUS  . 

.     .     P 

= 

32 

FLUORINE  . 

.     .     .     F 

= 

18. 

9 

SILICON      .    . 

.     .    Si 

ss 

21.3 

HYDROGEN 

.     .     .     H 

— 

1 

SULPHUR    .     . 

.     .     S 

8= 

16 

2.    Of  slight  importance. 
SELENIUM  Se  =  39.5 


II,    METALS. 

1.    Of  considerable  importance. 

ALUMINUM     . 

.     .    Al     «     13.7 

MAGNESIUM 

.     .     .     Mg    =     12.2 

ANTIMONY 

.     .     Sb     »  129 

MANGANESE 

.     .     Mn    =     27.6 

ARSENIC    .     . 

..    ;    As    =     75 

MERCURY 

.     .     .     Hg    =  100 

BARIUM     .V.^J 

.v  '.     Ba    =     68.5 

NICKEL      < 

.,     .     .     Ni     =     29.6 

BISMUTH  ."'^ 

'.!   ;    Bi    =  213 

PLATINUM 

.     .     .     Pt     =     98.7 

CADMIUM  .    . 

:;:  ;  ca  =  56 

POTASSIUM 

.    .     .     K      =     39.2 

CALCIUM   .     .' 

f    .'    Ca     =     20 

SILVER 

.     .     .     Ag    =  108.1 

CHROMIUM     . 

.     .     Cr     =     26.7 

SODIUM     ., 

.     .     .     Na     =     23 

COBALT      .    . 

.     .     Co     =     29.5 

STRONTIUM 

.     .     .     Sr     =     43.8 

COPPER 

.     .     Cu     =     31.7 

TIN       .     . 

...     Sn     —     59 

GOLD 

Au    =  197 

URANIUM 

.     .     .     U      =60 

IRON 

Fe     —     28 

ZINC      .     . 

.     .     .     Zn    —  32.6 

LEAD 

Pb    —  103  7 

2.    Of  slight  importance. 

CERIUM      .     . 

.     .     Ce     =     47 

PELOPIUM   . 

J    i    .    Pe 

DIDYMIUM 

.     .     D 

RHODIUM    . 

.     .     .     R     ==     52.2 

ERBIUM      .     . 

.     .     E 

RUTHENIUM 

.     .     .     Ru  =     52.2 

GLUCINUM 

.     .     Gl 

TANTALUM 

.     .     .     Ta   =  184 

ILMENIUM  .     . 

.     .     11 

TELLURIUM 

.     .     .     Te    =     64.2 

IRIDIUM      .    . 

.     .     Ir     =     99 

TERBIUM     . 

.     .     .     Tb 

LANTHANIUM  . 

.     .     La  ;  «• 

THORIUM    . 

.     .     .     Th  =     59.6 

LITHIUM     .    . 

.    .    Li    =       6.5 

TITANIUM  . 

.     .     .     Ti    =     25 

MOLYBDENUM  . 

.     .     Mo  =    46 

TUNGSTEN  . 

.     .     .     W1  =     95 

.     .     Nb 

VANADIUM  . 

.     .     .     y    =     68  6 

OSMIUM     *,  -.;._.* 

.     ,     Os   =     99.6 

YTTRIUM     . 

.     .     .     Y 

PALLADIUM 

.     .     Pd  =     53.3 

ZIRCONIUM 

.     .     .     Zr    =     22.4 

To  these  metals  we  must  now  add  DONARIUM,  which  was  discovered  in  the 
present  year  by  Bergemann,  in  certain  Norwegian  minerals. 

Another  new  metal,  NORIUM,  also  claims  a  place  in  the  list. 

Of  the  non-metallic  elements,  three,  oxygen,  hydrogen,  and  nitrogen,  are  per- 
manent gases;  and  four,  viz.,  chlorine,  bromine,  iodine,  and y?«on'?ze;  are  known 
as  the  elementary  salt-radicals. 

From  the  mineral  wolfram. 


OXYGEN. 


NON-METALLIC   BODIES 


OXYGEN.1 

Sym.  O.     Uq.  8.  8p.  Gr.  1.1057. 

§  69.  OXYGEN  was  discovered  by  Priestley,  in  August,  1774,  and  one  year 
later  by  Scheele,  who  was  then  unaware  of  Priestley's  discovery. 

Eighty-nine  per  cent,  (by  weight)  of  water  consists  of  oxygen ;  atmospheric 
air  also  contains  twenty-three  per  cent,  of  the  same  element,  which  likewise 
exists  in  combination  with  most  of  the  other  elements  in  various  proportions. 

Preparation. — The  most  important  methods  of  preparing  oxygen  are  : — 

I.  By  heating  binoxide  of  manganese  to  redness  in  an  iron  retort  (§  23) : — 

3MnOa=Mn304-f03. 

II.  By  heating  moderately  in  a  flask,  retort,  or  hard  glass  tube,  a  mixture  of 
powdered  chlorate  of  potassa  with  about  one-fifth  its  weight  of  binoxide  of  man- 
ganese.    (The  latter  is  not  altered  at  the  temperature  employed,  but  by  its  pre- 
sence considerably  promotes  the  decomposition  of  the  salt.     Sand  and  sesqui- 
oxide  of  iron  act  in  a  similar  manner,  but  with  less  energy.)     The  decomposition 
which  chlorate  of  potassa  undergoes,  is  shown  by  the  following  equation : — 

KO.C105=KC1+06.3 

The  oxygen  prepared  from  chlorate  of  potassa  and  binoxide  of  manganese, 
almost  always  contains  small  quantities  of  chlorine,  of  carbonic  acid,  and  of 
aqueous  vapor.  If  required  perfectly  pure,  it  may  be  passed,  first  through  a 
tube  containing  fragments  of  hydrate  of  potassa,  which  removes  the  two  former 
impurities,  and  afterwards  through  a  long  bent  tube  containing  pumice-stone, 
moistened  with  oil  of  vitriol,  to  remove  the  moisture  (§  28). 

III.  By  heating  the  red  oxide  of  mercury  : — 

HgO=Hg+0. 

IV.  By  heating  together  four  parts  of  strong  sulphuric  acid,  and  three  parts 
of  bichromate  of  potassa  :3 — 

K0.2Cr03+4(HO.S08)=KO.S03+Cra08.3S03+4HO-f08. 
§  70.  Properties. — Oxygen  is  a  colorless,  inodorous,  and  tasteless  gas,  which 

1  From  of  if?,  acid,  and  yvnitt,  1  produce. 

2  In  heating  chlorate  of  potassa  by  itself,  if  the  process  be  arrested  as  soon  as  the 
evolution  of  gas  begins  to  slacken,  the  salt  will  have  undergone  the  decomposition  repre- 
sented by  the  following  equation: — 

2KO.C105=KO.CL074.KC1+04. 

When  the  heat  is  again  continued,  the  evolution  is  renewed  with  increased  violence,  and 
the  whole  of  the  oxygen  is  evolved. 

3  Boussingault  has  recently  described  a  method  of  obtaining  oxygen  directly  from  the 
atmosphere,  by  passing  a  current  of  moist  air  over  heated  baryta  (BaO),  which  is  thus 
converted  into  binoxide  of  barium  (BaOg) ;  by  exposing  the  latter,  in  the  same  apparatus, 
to  an  elevated  temperature,  the  second  equivalent  of  oxygen  is  again  evolved,  and  may 
be  collected  as  usual.     This  process  has  the  advantage  of  being  continuous,  since  the 
same  amount  of  baryta  may  be  made  alternately  to  absorb  and  evolve  an  equivalent  of 
oxygen. 


116  OZONE. 

has  never  yet  been  condensed  to  the  solid  or  liquid  form.  It  is  very  sparingly 
soluble  in  water.  It  supports  combustion ;  any  substance  having  considerable 
affinity  for  oxygen,  on  being  introduced  into  it  while  undergoing  combustion, 
burns  with  greatly  increased  brilliancy  and  rapidity. 

If  a  piece  of  charcoal  be  attached  to  a  copper  wire,  heated  in  the  blowpipe- 
flame,  and  plunged  with  one  point  redhot  into  a  jar  of  oxygen,  it  burns  rapidly 
away,  being  converted  into  carbonic  acid.  Sulphur  and  phosphorus,  kindled, 
and  introduced  into  oxygen,  also  burn  with  great  brilliancy  (§  33). 

A  chip  of  wood  which  has  been  kindled  and  blown  out  so  as  to  leave  a  spark 
on  the  extremity,  immediately  bursts  out  into  flame  when  immersed  in  a  vessel 
of  oxygen,  thus  affording  a  rough  test  of  the  quality  of  the  gas. 

Some  substances  (e.  g.  steel  or  iron  wire),  which  only  undergo  gradual  oxida- 
tion when  exposed  to  the  air,  burn  rapidly  and  brilliantly  if  introduced  into 
oxygen,  while  in  contact  with  some  inflamed  substance  (§  33). 

Oxygen  is  indispensably  necessary  for  supporting  respiration;  animal  heat  and 
life  being  dependent  upon  a  gradual  combustion  (a  slow  combination  of  combus- 
tible substances  with  the  oxygen  inspired)  in  the  system.  This  combustion 
would,  however,  proceed  too  rapidly,  if  pure  oxygen  were  inhaled  (arterial  action 
being  increased  to  an  enormous  degree).  The  atmosphere  contains  this  element 
in  a  proper  state  of  dilution  for  respiration. 

Oxygen  combines  with  all  the  elements  (excepting  fluorine) ;  with  many  of 
them  it  unites  in  several  proportions.  Most  of  its  combinations  with  metals 
have  basic  properties :  those  which  it  forms  with  metalloids  are  termed  acids 

(§  10). 

Some  few  metallic  oxides,  consisting  of  three  equivalents  of  oxygen  to  one 
of  metal  (teroxides),  and  others  containing  still  more  oxygen,  possess  feeble  acid 
properties  (e.  g.  antimonious  and  antimonic  acids,  SbOs&  Sb05;  manganic  and 
permanganic  acids,  Mn03  &  MnflO7). 

The  name  of  oxygen  was  given  by  Lavoisier  to  this  element,  because  at  that 
time  all  known  acids  were  believed  to  contain  oxygen.  At  the  present  time  we 
are  well  acquainted  with  a  number  of  acids  that  contain  no  oxygen,  and  many 
circumstances  tend  to  favor  the  view  that  hydrogen  is  the  real  acidifying  prin- 
ciple.1 

§  71.  Uses  of  Oxygen. — Oxygen  is  sometimes  used  to  accelerate  combustion, 
thereby  much  augmenting  the  heat  and  light  of  certain  flames :  it  has  been  ap- 
plied to  this  purpose  in  the  Bude  light,  in  which  the  flame  of  the  Argand  lamp 
is  supplied  with  oxygen.  Substances  which  are  with  difficulty  oxidizable  are 
frequently  submitted  to  the  action  of  pure  oxygen  at  a  high  temperature ;  this 
is  especially  the  case  in  the  incineration  of  certain  organic  substances. 

§  72.  OzoNE.2 — This  remarkable  body  was  first  discovered  by  Schbnbein. 
He  detected  it  in  the  atmosphere  (by  means  of  tests  to  be  presently  described), 
and  found  it  to  be  formed  in  almost  every  instance  of  electric  discharge  into  the 
air;  also,  when  water  is  electrolyzed,  and  when  phosphorus  is  allowed  to  act 
upon  moist  air  at  ordinary  temperatures. 

Preparation. — Ozone  is  best  obtained  by  placing  a  piece  of  recently  scraped 
phosphorus,  about  half  an  inch  in  length,  into  a  clean  bottle  (of  about  two  quarts 
capacity),  in  the  bottom  of  which  is  as  much  water  as  will  half  cover  the  phos- 
phorus; the  mouth  should  then  be  closed  slightly  (to  prevent  any  mischief 
ensuing  if  inflammation  of  the  phosphorus  should  take  place),  and  the  bottle  set 
aside.  Ozone  is  almost  immediately  produced,  its  formation  being  indicated  by 
the  ascent  of  a  column  of  vapor  from  the  piece  of  phosphorus,  and  the  luminosity 

1  Some  interesting  experiments  recently  made  by  Faraday  have  shown  that  oxygen  i* 
possessed  of  decided  magnetic  properties. 

2  c£«iv,  to  smell. 


OZONE.  117 

of  the  latter  in  the  dark.  Ozone  may  be  detected  in  the  bottle  within  a  minute 
after  the  introduction  of  the  phosphorus ;  if  allowed  to  stand  for  six  or  eight 
hours,  the  air  in  the  bottle  will  be  abundantly  charged  with  it.  The  phospho- 
rus should  then  be  removed,  and  the  air  freed  from  phosphorous  acid  by  agitating 
some  water  in  the  bottle. 

Properties. — The  ozone  thus  obtained  (in  admixture  with  air)  has  the  follow- 
ing properties :  it  is  a  colorless  gas,  possessing  a  very  peculiar  odor,  which,  when 
concentrated,  much  resembles  that  of  chlorine,  but  when  diluted  is  precisely  the , 
odor  observed  when  an  electric  machine  is  in  action.  When  air  has  been 
powerfully  charged  with  ozone,  it  can  be  inspired  with  difficulty;  it  acts  power- 
fully on  the  mucous  membranes,  producing  very  disagreeable  sensations ;  small 
animals  immersed  in  it  soon  cease  to  exist.  Pure  ozone  must  therefore  be 
highly  poisonous. 

Ozone  is  insoluble  in  water;  it  possesses  powerful  bleaching  properties,  and  also 
acts  as  an  energetic  oxidizing  agent,  transforming  phosphorus  into  phosphoric 
acid,  and  powerfully  oxidizing  many  metals,  converting  them  and  their  lower 
oxides  into  the  highest  oxides  they  are  capable  of  forming.  Thus,  lead  and 
silver  are  converted  into  oxides,  antimony  and  arsenic  into  arsenic  acid  and 
antimonic  acid;  the  salts  of  the  protoxides  of  manganese,  cobalt,  nickel,  are 
decomposed  by  it,  the  acids  being  evolved  and  the  binoxides  formed.  It  also 
decomposes  many  hydrogen-acids  (e.  g.  hydrosulphuric  acid),  and  oxidizes 
organic  compounds.  It  combines  with  chlorine,  bromine,  and  iodine,  and  is  in 
many  respects  analogous  in  its  action  to  the  binoxide  of  hydrogen. 

Two  views  are  entertained  respecting  the  constitution  of  this  body;  the  one, 
that  it  is  oxygen  in  an  allotropic  condition — the  other,  that  it  is  a  compound  of 
oxygen  similar  to  binoxide  of  hydrogen.  The  former  is  the  view  which  possesses 
the  greater  number  of  supporters,  particularly  since  it  has  been  proved  that,  on 
passing  dry  ozonized  air  through  a  redhot  tube,  the  destruction  of  ozone  by  the 
heat  (it  being  only  capable  of  forming  at  ordinary  temperatures)  is  unaccompa- 
nied by  the  production  of  any  water.1  Many  organic  compounds,  such  as  ether 
and  turpentine,  when  exposed  to  the  action  of  air  and  light,  undergo  peculiar 
changes,  and  acquire  very  powerful  bleaching  and  oxidizing  properties,  appa- 
rently by  association  with  ozone. 

Tests  for  Ozone. — The  most  delicate  test  for  the  presence  of  ozone  is  prepared 
in  the  following  manner :  one  part  of  pure  iodide  of  potassium  and  ten  parts  of 
starch  are  boiled  together,  for  a  few  moments,  with  two  hundred  parts  of  water, 
and  white  filtering-paper  is  saturated  with  the  liquid  thus  obtained.  Such  paper 
is  immediately  turned  blue  when  introduced  moist  into  ozonized  air.  If  intro- 
duced dry  it  will  remain  colorless,  but  becomes  blue  immediately  upon  being 
moistened. 

Paper  prepared  with  a  solution  of  sulphate  of  manganese  is  also  a  good  test 
for  ozone,  becoming  rapidly  brown  from  formation  of  binoxide  when  introduced 
into  ozonized  air. 

1  By  very  recent  researches,  Baumert  believes  that  he  has  shown  the  ozone  obtained  in 
the  electrolysis  of  water  to  consist  of  a  teroxide  of  hydrogen.  He  passed  the  perfectly  dry 
ozone,  first  through  a  tube  containing  anhydrous  phosphoric  acid,  which  was  unaffected 
by  it,  then  through  a  tube  heated  to  redness,  and  lastly,  through  a  second  tube,  contain- 
ing phosphoric  acid,  which  indicated  the  presence  of  moisture  produced  in  the  decompo- 
sition of  the  ozone.  The  proportion  of  oxygen  was  determined  by  passing  the  ozone  into 
a  standard  solution  of  iodide  of  potassium. 


118  HYDROGEN. 


HYDROGEN.1 

St/m.  H.     Eq.  1.     Sp.  Gr.  0.0692. 

§  73.  HYDROGEN  was  discovered  by  Cavendish,  in  1766.  It  constitutes  11 
per  cent,  by  weight  of  water;  it  also  occupies  an  important  place  in  the  compo- 
sition of  nearly  all  organic  substances. 

Preparation. — Hydrogen  may  be  prepared  : — 

I.  By  passing  the  vapor  of  water  through  an  iron  tube  filled  with  iron  nails, 
and  heated  to  redness : — 

Fea  +  4HO=Fes04+H4. 

II.  By  adding  dilute  sulphuric  acid  (or  hydrochloric  acid)  to  granulated  zinc 
(or  fragments  of  iron),  covered  with  water,  in  a  Woulfe's  (or  common  wide- 
mouthed)  bottle  provided  with  a  funnel-tube  and  delivery-tube  (§  27)  : — 

Zn-fHO.S08=ZnO.S03+H. 

Fe-fHCl=FeCl+H. 
The  gas  may  be  collected  over  water  (§  29)  or  by  upward  displacement  (§  31)  : — 

III.  By  decomposing  water  with  potassium  or  sodium,  in  a  small  jar  filled 
with  mercury,  and  standing  over  the  mercurial  trough : — 

K+HO=KO+H. 

IY.  By  heating  zinc  or  iron  with  solution  of  potassa,  when  the  oxygen  of 
the  water  is  abstracted  by  the  metal. 

In  experiments  with  hydrogen,  the  operator  must  allow  the  gas  to  be  evolved 
for  two  or  three  minutes  without  attempting  to  collect  it,  so  that  all  the  atmo- 
spheric air  may  be  expelled  from  the  apparatus,  since  the  neglect  of  this  precau- 
tion may  be  attended  with  danger  from  the  formation  of  an  explosive  mixture. 

The  hydrogen  prepared  with  commercial  zinc  or  iron  is  never  pure.  It  has  a 
nauseous  odor  due  to  a  peculiar  compound  of  hydrogen  with  carbon  derived  from 
the  metal ;  small  quantities  of  sulphur  and  arsenic  are  also  obtained  from  the 
same  source,  and  pass  off  in  combination  with  hydrogen  (arsenic  is  also  some- 
times derived  from  the  oil  of  vitriol).  In  order  to  purify  this  gas,  it  should  be 
passed  first  through  solution  of  potassa;  secondly,  through  solution  of  nitrate  of 
silver,  and  lastly,  if  the  gas  be  required  free  from  aqueous  vapor,  through  a  bent 
tube  containing  pumice-stone  moistened  with  oil  of  vitriol,  or  through  a  wash 
bottle,  containing  this  liquid  (§  28).  It  is  difficult  to  dry  hydrogen  perfectly, 
on  account  of  its  high  diffusive  power  (§_22). 

§  74.  Properties. — Hydrogen  is  a  permanent  gas,  colorless,  and,  if  quite  pure, 
inodorous.  Its  solubility  in  water  is  somewhat  less  than  that  of  oxygen.  This 
gas  is  the  lightest  substance  known ;  its  lightness  may  be  readily  shown  by  pour- 
ing it  upwards  from  one  jar  into  another,  each  jar  being  afterwards  presented  to 
the  flame.  Hydrogen  is  a  very  inflammable  gas ;  if  a  lighted  taper  be  thrust 
up  into  an  inverted  jar  of  hydrogen,  the  taper  is  extinguished,  but  the  gas  takes 
fire  at  the  mouth  of  the  jar,  and  burns  with  a  pale  bluish  flame.  If  hydrogen, 
dried  by  means  of  chloride  of  calcium,  be  burnt  at  a  glass  jet  (§  32),  and  a  dry 
jar  held  over  the  flame,  the  water  which  is  produced  in  the  combustion  will  be 
observed  to  condense  upon  the  glass. 

The  flame  of  hydrogen,  though  very  faintly  luminous,  has  a  very  high  tempe- 
rature. 

If  a  jet  of  hydrogen  be  burnt  in  a  long  wide  glass  tube,  open  at  both  ends, 
the  vibrations,  caused  by  the  alternate  extinction  and  rekindling  of  the  flame, 
succeed  each  other  so  rapidly  as  to  produce  a  musical  tone. 

water,  yiwaw,  I  produce. 


OXIDES    OF    HYDROGEN.  119 

The  diffusive  power  (§  22)  of  hydrogen  is  exceedingly  high,  whence  it  can  be 
preserved  only  in  vessels  which  are  very  tightly  closed  with  stoppers. 


OXIDES  OF  HYDROGEN. 

Water HO. 

Binoxide  of  Hydrogen,  H02. 
WATER,  HO.     Eq.  9.     Sp.  Gr.  1. 

§  75.  A  mixture  of  two  volumes  of  hydrogen  and  one  volume  of  oxygen 
explodes,  when  brought  in  contact  with  flame,  when  suddenly  and  powerfully 
compressed,  or  when  an  electric  spark  is  passed  through  it,  producing  water, 
which,  in  the  state  of  vapor,  at  60°  F.  and  30  inches  bar.  would  occupy  two 
volumes. 

On  introducing  spongy  platinum  or  finely  divided  platinum  (platinum-black) 
into  a  mixture  of  the  gases,  it  is  instantly  exploded.  Or,  if  a  jet  of  hydrogen 
be  allowed  to  impinge  upon  a  ball  of  spongy  platinum  in  the  air,  the  metal  will 
become  redhot,  and  the  hydrogen  will  be  immediately  afterwards  ignited.  Fara- 
day has  shown  that  the  union  of  the  two  gases  may  be  even  effected  by  a  per- 
fectly clean  surface  of  rolled  platinum.  This  remarkable  property  of  platinum1 
led  Dobereiner  to  the  construction  of  his  beautiful  little  apparatus  for  the  pro- 
duction of  instantaneous  light.  Various  opinions  are  entertained  respecting  the 
manner  in  which  spongy  platinum  acts  in  effecting  the  combination  of  hydrogen 
with  oxygen.  Platinum,  in  a  finely  divided  state,  has  been  found  to  possess  the 
remarkable  property  of  condensing  in  its  pores  about  253  times  its  volume  of 
oxygen,  whereby  the  latter  must  be  rendered  even  denser  than  water.  It  has 
been  supposed  that  hydrogen,  coming  in  contact  with  oxygen  in  this  highly  con- 
densed state,  combines  with  it  immediately.  Another  view  taken  by  some 
chemists  of  this  phenomenon  is  based  upon  the  supposition  that  when  finely- 
divided  platinum  is  exposed  to  air  or  oxygen,  it  becomes  covered,  even  at 
the  common  temperature,  with  a  very  minute  coating  of  oxide,  which  is  reduced 
to  metal  again  by  hydrogen,  even  in  the  cold.  It  is  therefore  supposed  that, 
when  the  oxygen  of  the  air  and  a  jet  of  hydrogen  are  allowed  to  act  upon  spongy 
platinum,  a  series  of  continuous  oxidations  and  reductions  takes  place,  accom- 
panied by  a  rise  in  temperature  sufficient  to  heat  the  platinum  to  redness,  and 
thereby  to  set  fire  to  the  hydrogen. 

A  mixture  of  hydrogen  and  oxygen  in  proper  proportions  may  also.be  exploded 
in  an  eudiometer,  by  the  electric  spark  (§  32).  They  then  combine  with  a 
sudden  flash,  and  without  noise,  water  being  produced. 

The  combination  of  hydrogen  and  oxygen  is  accompanied  by  the  disengage- 
ment of  the  most  intense  heat  that  can  be  produced.  If  the  mixed  gases  are 
allowed  to  issue  under  some  pressure  from  a  narrow  jet,  and  inflamed,  the  heat 
disengaged  by  the  combustion  is  sufficiently  powerful  to  melt  platinum  and  pipe- 
clay, which  substances  resist  the  heat  of  all  furnaces.  The  flame  of  this  jet  of 
mixed  gases  (generally  termed  the  oxyliydrogen-blowpipe  jet)  is  very  pale,  but 
becomes  dazzling  the  moment  a  solid  infusible  substance  is  introduced  into  it. 
Thus,  if  the  flame  be  allowed  to  fall  upon  a  disk  of  lime,  a  star  of  most  intense 
light  is  obtained,  which  is  generally  known  by  the  name  of  the  Drummond  or 
lime-light.  This  phenomenon  is  owing  to  the  state  of  intense  incandescence  of 
the  particles  of  lime  when  exposed  to  the  heat  of  the  oxyhydrogen  flame.  Various 
forms  of  apparatus  have  been  contrived  to  supply  the  jet  with  the  mixed  gases. 

1  Other  substances  besides  platinum,  such  as  gold,  palladium,  and  even  some  stones 
and  glass,  possess  this  property  to  some  extent,  requiring,  however,  the  aid  of  heat  to 
effect  the  combination. 


120  OXIDES   OF   HYDROGEN. 

The  safest  are  those  in  which  the  gases  are  retained  in  separate  reservoirs,  and 
only  allowed  to  mix  in  small  quantities,  just  as  they  are  to  be  burnt,  that  por- 
tion of  the  apparatus  between  the  jet  and  the  chamber  in  which  the  mixture  is 
effected  being  stuffed  with  very  thin  brass  wires,  by  which  means,  owing  to  the 
conducting  power  of  the  metal,  the  temperature  is  so  far  reduced  that  all  danger 
of  explosion  is  avoided  (Hemminy 'sjef). 

§76.  THE  COMPOSITION  or  WATER  may  be  ascertained  in  various  ways. 

I.  By  Synthesis. — If  a  mixture  of  two  volumes  of  hydrogen  and  one  of  oxygen 
is  detonated  in  an  eudiometer,  as  just  now  mentioned,  the  gases  will  disappear 
entirely,  water  being  formed.     Again,  if  a  current  of  dry  and  pure  hydrogen  be 
passed  over  a  known  amount  of  pure  and  thoroughly-dried  black  oxide  of  copper 
in  a  bulb-tube,  to  which  a  gentle  heat  is  applied,  the  oxide  will  be  reduced  to 
the  metallic  state,  water  being  formed,  which  may  be  collected  by  attaching  a 
chloride  of  calcium  tube,  previously  weighed,  to  the  extremity  of  the  bulb-tube, 
the  latter  being  kept  hot,  in  order  to  prevent  the  condensation  of  the  water  until 
it  arrives  at  the  chloride  of  calcium  tube.     After  the  copper  is  perfectly  reduced, 
it  may  be  weighed;  the  loss  will  represent  the  oxygen  which  has  combined  with 
the  hydrogen ;  the  increase  of  weight  of  the  chloride  of  calcium  tube  will  give 
the  amount  of  water  produced  in  the  experiment. 

II.  By  Analysis. — The  decomposition  of  water  by  the  galvanic  current  may 
be  also  resorted  to  for  demonstrating  its  composition. 

If  the  current  is  allowed  to  pass  through  acidulated  water  contained  in  a  glass 
vessel,  the  poles  of  the  battery  being  terminated  by  platinum-plates,  which  are 
introduced  into  the  bottom  of  the  latter  in  such  a  manner  that  they  pass  up  a 
little  way  into  separate  graduated  tubes,  in  which  the  gas  is  collected  as  it  is 
generated  at  each  pole,  it  will  be  found  that  the  tube  over  the  negative  pole  is 
filled  with  gas,  while  that  over  the  positive  pole  is  only  half-filled  (the  dimen- 
sions of  the  tubes  being  alike);  upon  examination  of  the  gas,  that  evolved  at 
the  positive  pole  will  be  found  to  be  pure  oxygen,  while  that  collected  at  the 
negative  pole  is  hydrogen  (§  17). 

This  experiment  proves,  therefore,  that  water  consists  of  1  volume  of  oxygen 
to  2  of  hydrogen;  and  by  calculation  from  the  known  specific  gravities  of  these 
gases,  this  proportion  will  be  found  equal  to  1  by  weight  of  hydrogen,  and  8  of 
oxygen. 

§  77.  Properties  of  Water. — At  ordinary  temperatures  (of  warm  and  tempefate 
climates),  water  is,  when  pure,  a  colorless,  tasteless,  and  inodorous  liquid.  It 
solidifies  to  ice  or  snow  at  32°  F.  (0°  C.)  It  may,  however,  when  perfectly 
tranquil,  be  -cooled  down  to  a  temperature  far  below  the  freezing  point,  without 
solidifying,  but  if  then  agitated  in  the  slightest  degree,  it  will  instantly  become 
a  solid  mass,  the  temperature  simultaneously  rising  to  32°  F.  Ice  belongs  in 
form  to  the  hexagonal  system  of  crystals.  Snow  also  appears  in  regular  hexagonal 
tables,  and  in  groups  of  these,  more  or  less  elongated,  and  united  in  the  form  of 
a  star.  The  specific  gravity  of  ice  is  0.9184.  It  is  a  remarkable  circumstance 
that  water,  unlike  other  liquids,  contracts  when  cooled  beyond  a  certain  point, 
and  attains  its  maximum  density  at  39.2°  F.  (4°  C.)  If,  therefore,  a  mass  of 
water  is  exposed  to  air  having  the  temperature  of  its  freezing  point,  the  upper 
layer  will  sink  as  it  cools,  until  the  above  point  of  maximum  density  is  attained, 
after  which  contraction  will  no  longer  take  place,  and  consequently  the  surface 
will  be  covered  with  a  coating  of  ice,  which  protects  the  rest  of  the  liquid  from 
further  refrigeration;  and  herein  we  may  perceive  an  admirable  provision  of 
nature  for  the  preservation  of  the  inhabitants  of  the  waters  during  severe  win- 
ters, besides  the  many  other  most  important  results  arising  from  the  expansion 
of  the  freezing  water,  such,  for  instance,  as  the  disintegration  of  rocks,  &c. 

When  impure  water  freezes,  the  ice  which  separates  is  generally  free  from 
impurities;  thus,  when  sea- water  is  exposed  to  a  very  low  temperature,  crystals 


WATER.  121 

of  nearly  pure  ice  are  deposited,  the  salts  remaining  in  the  mother-liquor. 
Gases  dissolved  in  water  also  separate  when  the  latter  is  frozen,  and  remain  im- 
prisoned in  the  ice  in  the  form  of  minute  bubbles. 

Ice  is  transparent  and  colorless,  and  a  bad  conductor  of  heat.  At  tempera- 
tures above  32°  F.  (0°  C.)  it  melts  into  water;  the  latter  boils  at  212°  F. 
(100°  C.)1  being  converted  into  an  invisible  vapor  (steani).* 

The  specific  gravity  of  aqueous  vapor  is  0.622,  100  cubic  inches  weighing,  at 
212°  F.  (100°  C.)  14.96  grains.3 

In  the  state  of  vapor,  water  occupies  1700  times  the  space  which  it  does  at 
ordinary  temperatures  in  its  liquid  state.  Water  is  but  slightly  compressible. 
It  vaporizes  at  all  temperatures,  even  when  in  the  state  of  ice,  in  the  coldest 
climes;  hence  aqueous  vapor  is  continually  ascending  into  the  air  from  the  sur- 
face of  the  earth,  to  which  it  returns  when  condensed,  in  the  form  of  dew,  rain, 
hail,  snow,  or  rime  (hoar-frost). 

Water  is  a  perfectly  neutral  body;  yet  it  combines  with  a  great  number  of 
substances,  forming  what  are  termed  hydrates.  With  chlorine  and  bromine, 
and  with  these  elements  only,  it  forms  hydrates,  containing  10  atoms  of  water. 
It  also  combines  with  acids  and  with  bases,  forming  hydrates  which  correspond 
generally  in  their  composition  to  the  neutral  salts  of  these  substances;  it  there- 
fore occupies,  at. times,  the  place  of  a  base,  and  at  others  that  of  an  acid. 

With  neutral  salts,  water  enters  into  combination  in  two  different  conditions ; 
first,  as  water  of  crystallization,  which  is  easily  expelled  by  heat;  secondly,  as 
saline  or  constitutional  water,  which  is  more  difficult  to  separate  from  the  salt 
(§  21). 

Water  possesses  the  property  of  dissolving  the  greater  number  of  substances, 
acting  almost  invariably  as  a  simple  solvent.  By  this  means  solids  are  converted 
into  the  liquid  state;  this  property  of  water  is  of  the  highest  importance  to 
chemists,  enabling  them  to  effect  with  ease  chemical  changes  which  would  other- 
wise be  accomplished  with  difficulty. 

The  solvent  power  of  water  is  much  increased  by  an  elevation  of  temperature, 
as  we  have  already  noticed,  and  this  is  also  the  case  with  steam;  the  solvent 
action  of  water  at  high  temperatures  is  economically  applied,  in  the  apparatus 
known  as  Papin's  digester ;  to  the  extraction  of  nutritious  portions  of  animal 
food. 

§  78.  Water  cannot  occur  pure  in  nature,  on  account  of  its  solvent  property. 
Rain,  which  is  the  purest  kind  of  water,  always  contains  carbonate  and  nitrate 
of  ammonia.  Spring-waters  are  contaminated  to  a  greater  or  less  extent  with 
various  salts,  which  are  extracted  from  the  earth,  such  as  carbonate  of  lime 
(chalk),  sulphate  of  lime  (gypsum),  chloride  of  sodium,  and  other  alkaline  salts. 
Much  carbonate  of  lime  is  frequently  held  in  solution  in  water  by  free  carbonic 
acid,  which  forms  with  it  a  bicarbonate.  When  such  waters  are  boiled,  the  car- 
bonic acid  is  expelled,  and  the  carbonate  of  lime  precipitated  in  the  crystalline 
form,  together  with  a  certain  amount  of  sulphate  of  lime  and  sesquioxide  of  iron, 
forming  a  very  hard  incrustation  on  the  bottoms  of  steam-boilers,  the  safety  of 
which  is  often  thus  endangered. 

1  Grove  has  found  that  water  is  resolved  into  its  elements  at  very  high  temperatures. 
The  extremity  of  a  platinum  wire  was  fused  into  a  small  button,  afterwards  raised  to  a 
temperature  approaching  its  fusing  point  by  the  oxyhydrogen  blowpipe,  and  then  sud- 
denly plunged  into  water  ;  a  mixture  of  oxygen  and  hydrogen  was  immediately  evolved. 
Aqueous  vapor  was  also  decomposed  by  passing  it  through  a  platinum  tube  heated  to 
whiteness,  and  by  the  influence  of  electric  sparks  passing  from  pole  to  pole. 

2  The  white  clouds  of  steam  formed  when  aqueous  vapor  of  considerable  tension  escapes 
into  the  atmosphere,  should  be  distinguished  as  vesicular  vapor,  since  it  consists  of  a  num- 
ber of  vesicles  formed  by  minute  drops  of  water,  and  distended  by  true  aqueous  vapor. 

3  It  must  be  remembered  that  the  standard  with  which  the  specific  gravities  of  vapors 
are  compared  is  that  of  dry  atmospheric  air  at  60°  F.  (§  1.) 


122  OXIDES   OP   HYDROGEN. 

This  incrustation  may  be,  to  a  certain  extent,  prevented  by  various  means ; 
the  best  and  safest  chemical  process  is  that  proposed  by  Ilitterbrandt,  which  con- 
sists in  the  addition  of  chloride  of  ammonium  to  the  water  in  the  boiler.  The 
carbonic  acid  is  expelled  from  the  water  as  carbonate  of  ammonia,  while  the  lime 
is  held  in  solution  as  the  highly  soluble  chloride  of  calcium.  Chloride  of  tin  has 
lately  been  recommended  for  the  same  purpose.  Alkaline  carbonates  are  also 
found  to  prevent  the  incrustation  of  boilers. 

The  remarks  above  applied  to  spring-waters  will  suffice  for  those  of  rivers;  we 
have  only  to  add  that  the  latter,  in  the  neighborhood  of  large  towns,  are  often 
much  contaminated  with  organic  matters,  and  the  nitrates  and  salts  of  ammonia 
derived  therefrom. 

Waters  containing  much  earthy  impurity  are  termed  hard,  while  purer  waters 
are  called  soft.  The  former  are  more  agreeable  to  the  taste  than  the  latter,  but 
give  rise  to  the  production  of  insoluble  salts  (of  lime  and  magnesia),  with  the 
fatty  acid  of  the  soap,  and  are  hence  less  applicable  to  detergent  purposes.  Various 
methods  have  been  suggested  for  reducing  the  hardness  of  spring  and  river 
waters;  the  most  simple  and  efficacious  is  that  proposed  by  Clark,  which  consists 
in  adding  to  the  water  an  amount  of  solution  of  lime  sufficient  to  form  carbonate 
of  lime  with  the  free  carbonic  acid ;  the  carbonate  originally  held  in  solution  in 
the  water  is  thus  precipitated,  together  with  the  newly  formed  chalk.  (For  a 
mode  of  testing  the  hardness  of  water,  see  Quantitative  Analysis;  special 
methods.) 

Waters  containing  foreign  matters  in  solution,  to  such  an  extent  as  to  have  a 
peculiar  taste  or  smell,  or  to  acquire  medicinal  properties,  are  termed  mineral 
waters.  Of  these,  there  are  several  kinds;  saline  waters  are  such  as  contain  neu- 
tral salts  in  considerable  quantity,  such  as  sulphate  of  magnesia  (Epsom  salts), 
chloride  of  sodium,  &c.  The  waters  of  Cheltenham  afford  good  examples  of 
saline  waters.  Waters  containing  much  iron  are  termed  chalybeate.  (In  these 
the  iron  is  held  in  solution  as  carbonate  of  the  oxide  of  iron,  by  free  carbonic 
acid ;  upon  allowing  such  waters  to  stand,  or  on  boiling  them,  the  iron  is  depo- 
sited as  sesquioxide.)  Those  waters  containing  much  hydrosulphuric  acid  (sul- 
phuretted hydrogen),  or  free  carbonic  acid,  are  termed  sulphurous,  carbonated,  or 
acidulous  waters.  Examples  of  the  former  are  the  Harrowgate;  of  the  latter,  the 
Pyrmont  and  Seltzer  waters. 

Sea-water  is  peculiarly  rich  in  saline  constituents,  the  chief  of  which  are  chlo- 
rides of  sodium  and  magnesium,  sulphates  of  magnesia  and  lime,  and  traces  of 
bromides  and  iodides. 

Distillation  is  the  method  universally  employed  for  purifying  water  from  solid 
matter  (§  38). 

It  becomes  difficult  to  obtain  perfectly  pure  water  even  by  this  means,  since 
water  exercises  its  solvent  action  upon  most  metals,  and  even  upon  glass.  The 
following  special  precautions  should  be  attended  to  in  the  distillation  of  water. 
The  head  of  the  still  should  be  of  sufficient  height  to  preclude  the  possibility  of 
any  of  the  contents  splashing  into  the  worm,  which  should  not  be  made  of  lead 
or  iron,  but  rather  of  tin,  copper,  or  silver.  If  chloride  of  magnesium  exists  in 
the  water,  some  lime  should  be  added  previously  to  distillation,  since  that  salt  is 
decomposed  by  protracted  ebullition  with  water,  into  magnesia  and  hydrochloric 
acid,  which  latter  would  pass  over  into  the  distillate  if  the  above  precaution  were 
not  adopted. 

When  it  is  desired  to  have  water  perfectly  free  from  gases,  it  must  be  boiled 
for  some  time,  and  then  immediately  bottled  up  closely,  since  it  absorbs  air  by 
mere  exposure  in  open  vessels.  For  the  action  of  water  upon  lead,  see  the  his- 
tory of  lead. 


NITROGEN.  123 

BINOXIDE  OF  HYDROGEN,  OR  OXYGENATED  WATER. 
H0a.  Eq.  17. 

§  79.  This  compound,  which  was  discovered  by  Thenard,  in  1818,  is  formed 
when  certain  metallic  binoxides,  such  as  binoxide  of  barium  (which  is  always 
employed  for  this  purpose),  are  digested  with  dilute  acid  (e.  g.  hydrofluoric  acid) 
at  a  low  temperature,  when  the  change  will  be  represented  by  the  following  equa- 
tion : — 

BaO2-fHF=BaF+H03. 

This  substance  having  received  at  present  no  practical  application,  we  shall  not 
enter  more  minutely  into  detail  respecting  its  preparation,  which  requires  many 
precautions. 

Properties. — Binoxide  of  hydrogen  is  a  colorless,  transparent,  syrupy  liquid; 
its  taste  is  harsh,  bitter,  and  astringent,  something  like  that  of  tartar-emetic. 

It  does  not  freeze  at — 22°  F.  ( — 30°  C.),  and  evaporates  without  decomposition 
at  ordinary  temperatures;  it  does  not  redden  litmus,  but  gradually  bleaches  both 
turmeric  and  litmus ;  it  whitens  the  tongue,  and  also  the  cuticle  when  placed  on 
the  hand,  producing  violent  itching  after  a  time. 

Binoxide  of  hydrogen  retains  the  second  atom  of  oxygen  in  a  very  loose  state 
of  combination.  It  escapes  from  the  water  under  various  circumstances;  some- 
times so  rapidly  as  to  cause  violent  effervescence,  evolution  of  heat,  and  even 
explosion,  accompanied  at  times  by  a  flash  of  light.  The  decomposition  is  effected 
by  contact  of  the  binoxide  with  carbon,  binoxide  of  manganese,  and  various 
other  metallic  oxides,  by  several  metals,  and  also  by  heat.  Some  oxides,  in 
effecting  its  decomposition,  are  reduced  to  the  metallic  state,  or  to  a  lower  state 
of  oxidation  (oxides  of  gold,  silver,  mercury,  &c.,  and  the  red  and  brown  per- 
oxides of  lead).  No  reasonable  explanation  can  be  given  of  these  singular  re- 
actions. 

Binoxide  of  hydrogen  is  miscible  with  water  in  all  proportions,  and  also  com- 
bines with  the  hydrated  acids,  with  which  it  forms  compounds  in  which  it  is  less 
easily  decomposable  than  when  uncombined. 


NITROGEN1 

Sym-  N-     E(l-  14«  *•  Gr-  °-972- 

§  80.  Nitrogen  was  discovered  by  Rutherford,  in  1772. 

The  atmosphere  contains  about  77  per  cent,  by  weight,  or  79  per  cent,  by 
volume,  of  nitrogen.  This  element  is  also  an  important  constituent  of  animals 
and  vegetables.  It  occurs,  though  not  abundantly,  in  the  mineral  kingdom. 

Preparation. — I.  Nitrogen  may  be  obtained  by  abstracting  the  oxygen  from 
atmospheric  air;  this  is  effected  by  burning  some  phosphorus  or  sulphur  in  air, 
confined  over  water,  under  a  bell-jar ;  the  resulting  sulphurous  or  phosphoric  acid 
may  be  removed  by  washing  the  gas,  which  then  consists  of  pure  nitrogen.  (The 
washing  may  be  effected  by  cautiously  transferring  the  gas  from  one  jar  to  another, 
through  water.) 

Nitrogen  may  be  also  obtained, 

II.  By  passing  chlorine  into  a  solution  of  ammonia : — 

4NHa+Cla=3NH4Cl  +  N. 

III.  By  heating  a  strong  solution  of  nitrate  of  ammonia  with  granulated  zinc : — 

NH4O.N05-fZna=2ZnO+N2-f4HO. 

1  NtVfov,  nitre,  and  ytnaoa,  I  produce. 


124 


OXIDES   OF   NITROGEN. 


IV.  By  heating  a  mixture  of  nitrite  of  potassa  and  chloride  of  ammonium  : — 
KO.N03+NH4Cl=KCl  +  4HO-fN3. 

The  first  and  fourth  methods  only  are  in  general  use  in  the  laboratory. 

Properties. — Nitrogen  is  a  permanent  gas,  devoid  of  color,  taste,  and  smell, 
and  not  possessing  any  active  properties.  It  is  incombustible,  and  does  not  sup- 
port combustion;  it  consequently  will  not  support  respiration.  It  is,  however, 
not  poisonous  in  its  properties,  since,  when  mixed  with  oxygen,  it  may  be 
breathed  with  impunity ;  in  fact,  we  have  seen  above,  that  f  of  the  bulk  of  the 
atmosphere  consists  of  nitrogen. 

It  therefore  plays  an  important  part  in  diluting  oxygen  so  as  to  render  it  fit 
for  continuous  respiration.  This  gas  is  much  less  soluble  in  water  than  oxygen. 

Nitrogen  does  not  enter  into  direct  combination  with  any  elements  excepting 
oxygen,  with  which  it  may  be  made  to  unite  by  subjecting  the  mixture  of  the 
gases  to  a  succession  of  powerful  electric  sparks. 

It  may  be  obtained  in  combination  with  most  non-metallic  elements,  and  with 
a  few  metals.  Thus,  we  have  chloride,  iodide,  bromide,  and  carbide  of  nitrogen, 
and  nitrides  of  iron  and  copper.  The  most  important  compounds  of  nitrogen 
are  those  which  it  forms  with  hydrogen  and  oxygen.  It  combines  with  the  latter 
in  five  different  proportions,  forming  nitrous  oxide  (NO),  nitric  oxide  (N02), 
nitrous  acid  (N03),  peroxide  of  nitrogen  (N04),  and  nitric  acid  (N05). 

With  hydrogen,  it  produces  the  substance  ammonia  (NH3),  besides  which, 
three  other  compounds  of  nitrogen  and  hydrogen  are  assumed,  though  they  have 
not  yet  been  isolated — namely,  ammonium  NH4,  ainidogen  NHa,  and  imidogen 
NH. 


OXIDES  OF  NITROGEN. 


Protoxide  of  Nitrogen  .  .  NO 
Binoxide  of  Nitrogen  .  .  N0a 
Nitrous  acid  .  N0a 


Peroxide  of  Nitrogen 


NO, 


Nitric  acid N05 


PROTOXIDE  OP  NITROGEN,  NITROUS  OXIDE,  LAUGHING-GAS. 
NO.     Eq.  22.  Sp.  Gr.  1.524. 

Composition  by  Volume. — Two  volumes  of  this  gas  contain  two  volumes  of 
nitrogen  and  one  volume  of  oxygen. 

§  81.  Preparation. — Nitrous  oxide  is  prepared  by  heating  moderately  in  a 
glass  retort  the  nitrate  of  ammonia  (§  23,  et  seq). 

This  salt  is  decomposed  by  heat  into  nitrous  oxide  and  water : — 
NH4O.N05=2NO+4HO. 

The  application  of  heat  should  be  gradual,  and  the  temperature  not  raised  too 
high,  as  in  that  case  a  portion  of  the  salt  volatilizes  undecomposed,  and  a  vio- 
lent explosion  may  likewise  occur.  Care  must  be  taken  that  the  salt  be  free 
from  chloride  of  ammonium,  or  the  gas  obtained  will  be  contaminated  with  chlo- 
rine. 

The  protoxide  may  also  be  obtained  by  dissolving  zinc  in  very  dilute  nitric 
acid,  or  by  the  action  of  chloride  of  tin  upon  nitromuriatic  acid  :  the  best  method 
is  to  introduce,  gradually,  crystals  of  nitre,  or  small  cylinders  of  fused  nitre, 
into  a  strongly  acid  solution  of  chloride  of  tin,  heated  in  a  water-bath.  The 
most  convenient  apparatus  for  this  operation  is  a  wide-necked  generating-flask, 
fitted  with  an  upright  tube,  dipping  into  the  solution  of  tin;  and  sufficiently  wide 
to  admit  of  the  gradual  introduction  of  the  nitre.1 


1  It  has  been  lately  proposed  to  prepare  nitrous  oxide  by  heating  sal-ammoniac  with 
moderately  strong  nitric  acid. 


BINOXIDE   OF   NITROGEN.  125 

Protoxide  of  nitrogen  must  be  collected  over  mercury  or  warm  water,  being 
soluble  in  cold  water. 

Properties. — Nitrous  oxide  is  a  colorless  gas,  possessing  a  sweet  taste.  By 
exposure  to  a  pressure  of  about  50  atmospheres,  at  a  temperature  of  45°  F.  (7° 
C.),  it  is  converted  into  a  colorless  mobile  liquid,  producing  a  wound  like  a  burn 
when  placed  upon  the  hand.  This  liquid  may  be  solidified  by  exposure  to  the 
cold  of  a  carbonic-acid  bath  in  vacua  (about  — 150°  F.,  — 100°  C.),  a  white  mass 
being  obtained,  which  melts  in  the  hands,  and  evaporates  suddenly,  blistering 
the  skin.  The  gas  does  not  burn,  but  supports  combustion,  inflamed  substances 
burning  in  it  with  increased  energy.  Phosphorus,  when  fully  kindled,  and  plunged 
into  the  gas,  burns  in  it  with  great  brilliancy. 

It  does  not  affect  vegetable  colors,  being  an  indifferent  body.  It  may  be  in- 
haled for  a  short  time,  producing  very  singular  effects,  resembling  in  many  respects 
those  of  intoxication.  The  sensations  experienced  by  persons  inspiring  the  gas 
are  in  most  cases  of  an  agreeable  kind ;  the  effects  very  frequently  are,  increased 
muscular  action  and  an  irresistible  inclination  to  laugh.  Such  effects  only  last  for 
two  or  three  minutes,  and,  in  most  cases,  are  not  followed  by  depression  of  spirits 
or  exhaustion,  but  on  the  contrary,  by  increased  liveliness,  even  for  some  time 
after  the  gas  has  been  inhaled.  Sometimes,  however,  the  inhalation  of  the  gas 
is  followed  by  disagreeable  symptoms,  even  to  loss  of  consciousness.1  This  sin- 
gular property  of  nitrous  oxide  was  first  discovered  by  Sir  H.  Davy.  On  im- 
mersing animals  in  nitrous  oxide,  they  become  very  restless,  and  expire  after 
some  time. 

A  mixture  of  nitrous  oxide  with  an  equal  volume  of  hydrogen,  explodes 
when  inflamed,  water  being  formed,  and  nitrogen  liberated.  A  certain  quantity 
of  ammonia  is  also  produced.  Platinum-black  becomes  redhot  in  the  mixture, 
likewise  effecting  the  above  change. 

Nitrous  oxide  is  soluble  to  a  considerable  extent  in  cold  water,  one  volume  of 
the  latter  absorbs  about  0.7  or  0.8  of  the  gas,  which  is  evolved  again  upon 
boiling.  The  aqueous  solution  has  a  sweetish  taste. 

When  passed  through  a  redhot  porcelain  tube,  this  gas  is  decomposed,  yield- 
ing a  mixture  of  nitrogen,  oxygen,  and  binoxide  of  nitrogen. 

BINOXIDE  OP  NITROGEN,  NITRIC  OXIDE. 
N02.  fiq.W.  8p.Gr.lMlQ. 

Composition  by  Volume. — 1  volume  of  oxygen  to  1  volume  of  nitrogen  with- 
out condensation. 

§  82.  Preparation. — Nitric  oxide  is  prepared  by  dissolving  copper  in  mode- 
rately strong  nitric  acid  (spec.  grav.  1.2),  in  a  small  apparatus  similar  to  that 
employed  for  preparing  hydrogen  :— 

Cu3+4(HO.N05)=3(CuO.N05)-f4HO  +  N03. 

It  may  also  be  obtained  by  heating  mercury,  lead,  or  silver,  with  nitric 
acid. 

If  the  nitric  acid  is  employed  too  concentrated,  the  gas  is  frequently  con- 
taminated with  nitrogen.  It  may  be  collected  over  cold  water,  which  absorbs 
only  from  ^  to  JT  of  its  bulk  of  the  gas.2 

Properties. — Nitric  oxide  is  a  colorless  gas,  which  has  not  been  liquefied ;  the 
moment  it  comes  in  contact  with  air,  it  combines  with  oxygen,  forming  yellowish- 

1  The  best  apparatus  for  administering  laughing-gas  is  a  capacious  bladder,  provided 
with  a  wooden  mouthpiece,  having  a  lateral  opening,  which  may  be  closed  by  the  thumb 
of  the  operator  until  the  state  of  the  patient  renders  the  admission  of  air  necessary. 

2  Nitric  oxide  may  also,  like  the  protoxide  of  nitrogen,  be  prepared  by  the  action  of 
chloride  of  iron  upon  nitro-muriatic  acid,  or  upon  fragments  of  nitre,  in  the  presence  of 
free  hydrochloric  acid,  as  described  at  \  81. 


126  OXIDES   OF   NITROGEN. 

red  vapors  of  peroxide  of  nitrogen  (N04).  Its  smell  and  taste  cannot  therefore 
be  ascertained.  It  is  not  combustible,  and  supports  the  combustion  of  only  a 
few  substances  (e.  g.  burning  phosphorus).  It  can  only  be  resolved  into  its 
elements  at  a  very  high  temperature.  It  cannot  be  breathed  in  a  pure  state. 
It  does  not  affect  litmus,  being  a  neutral  body,  and  is  copiously  absorbed  by  a 
solution  of  protosulphate  of  iron,  producing-  a  brown  liquid,  from  which  the 
greater  portion  of  the  gas  may  be  expelled  again  by  continued  boiling. 

The  formation  of  hyponitric  acid  from  nitric  oxide,  by  contact  with  oxygen, 
forms  an  excellent  test  for  the  latter  gas  in  a  free  state. 

One  volume  of  sulphurous  acid,  when  mixed  with  two  of  nitric  oxide,  in  the 
presence  of  water,  is  slowly  converted  into  sulphuric  acid,  nitrous  oxide  being 
formed : — 

S03-fN03=S08+NO. 

A  mixture  of  equal  volumes  of  hydrogen  and  nitric  oxide,  when  inflamed  in 
the  air,  burns  with  a  greenish-white  flame,  yielding  hyponitric  acid  vapor,  the 
hydrogen  appearing  to  unite  with  oxygen  from  the  atmosphere  only. 

Iron,  and  a  few  other  easily  oxidizable  metals,  if  retained  in  contact  with 
nitric  oxide,  reduce  it  gradually  to  protoxide  of  nitrogen ;  but  if  the  gas  be 
passed  into  water  containing  the  binoxides  of  manganese  or  lead  in  suspension, 
the  nitrites  of  the  oxides  of  these  metals  are  formed  :  by  the  action  of  nitric  oxide 
under  similar  circumstances  upon  oxide  of  silver,  nitrite  of  silver  and  metallic 
silver  are  obtained. 

If  two  or  three  drops  of  bisulphide  of  carbon  be  poured  into  a  jar  of  nitric 
oxide,  well  agitated  therein,  and  afterwards  inflamed,  the  mixture  emits  a  bright 
blue  luminous  flash. 

TEROXIDE  OF  NITROGEN,  NITROUS  ACID,  HYPONITROUS  ACID. 
N03.^.  38, 

§  83.  Preparation. — This  compound  is  produced  when  nitric  oxide  is  brought 
in  contact  with  air,  in  the  presence  of  potassa  (or  another  strong  base),  the 
nitrite  of  potassa  being  formed. 

It  is  also  produced  by  passing  dry  nitric  oxide  through  anhydrous  hyponitric 
acid,  or  by  thoroughly  mixing  one  volume  of  oxygen  and  rather  more  than  four 
volumes  of  nitric  oxide,  and  cooling  the  mixed  gases  down  to — 4°  F.  (-20°  C.) 
The  best  method  of  producing  it,  is  to  heat  in  a  capacious  retort  one  part  of 
starch  with  eight  parts  of  nitric  acid,  of  spec.  grav.  1.25,  and  to  pass  the  gaseous 
product  through  a  long  chloride  of  calcium  tube,  and  then  through  an  U-tube, 
cooled  down  to  —4°  F.  (-20°  C.) 

Properties. — Nitrous  acid,  when  pure,  is  a  highly  volatile  liquid,  of  a  blue 
color,  which  boils  below  32°  F. ;  its  vapor  has  a  yellowish-red  color.  When  dis- 
tilled, it  undergoes  partial  decomposition,  being  reconverted  into  nitric  oxide  and 
hyponitric  acid : — 

2N03=N04+NOa. 

It  dissolves  in  water  at  32°  F.  (0°  C.)  without  decomposition,  yielding  a  light 
blue  solution,  which,  at  temperatures  above  32°  F.,  evolves  a  large  quantity  of 
nitric  oxide,  nitric  acid  remaining  in  solution  in  the  water : — 
3N03-fHO=2N03+HO.N05. 

Nitrous  acid  combines  with  many  bases,  forming  nitrites;  some  of  these  may 
be  obtained  by  heating  the  nitrates.  Thus,  when  nitrate  of  potassa  is  fused  and 
kept  for  some  time  at  a  red  heat,  it  parts  first  with  two  atoms  of  oxygen,  form- 
ing nitrite  of  potassa,  which,  by  continued  heating,  is  converted  into  caustic 
potassa. 

The  nitrate  operated  upon  should  therefore  be  heated  until  a  portion  dissolved 
in  water  gives  a  slight  alkaline  reaction,  and  affords,  with  nitrate  of  silver,  a 


NITRIC   ACID.  127 

pale-brown  precipitate,  which  consists  of  nitrate  of  silver  mixed  with  a  little  oxide, 
which  imparts  to  it  the  faint  brown  color. 

Nitrites  are  either  white  or  light  yellow,  and  most  of  them  may  be  crystallized. 

An  aqueous  solution  of  a  nitrite,  when  boiled  for  some  time,  is  converted  into 
nitrate,  nitric  oxide,  and  a  portion  of  the  base  being  liberated : — 

3(KO.N03)=2KO-fKO.N05+2N03. 

HYPONITRIC  ACID,  PEROXIDE  OF  NITROGEN,  NITROUS  ACID. 
N04.     Eq.  46. 

Composition  by  Volume. — 2  volumes  of  the  gas  contain  1  volume  of  nitrogen 
and  two  volumes  of  oxygen. 

Preparation. — This  acid  is  formed  when  nitric  oxide  is  mixed  with  oxygen 
or  atmospheric  air;  one  volume  of  dry  oxygen  is  mixed  with  nearly  two  volumes 
of  perfectly  dry  nitric  oxide,  and  passed  through  a  tube  cooled  down  to  — 4°  F. 
(_20°  C). 

Or  dry  nitrate  of  lead  is  submitted  to  distillation  in  a  retort  with  which  a 
cooled  reservoir  is  connected  (§  39) : — 

PbO.N05=PbO+0  +  N04. 

Properties. — Peroxide  of  nitrogen  is  obtained,  according  to  the  above  direc- 
tions, as  a  liquid,  which  is  colorless  at  — 4°  F.  ( — 20°  C),  but  on  the  temperature 
rising,  becomes  first  pale-yellow  and  afterwards  orange-yellow.  It  crystallizes  at 
about  — 4°  F.  in  colorless  prisms,  and  melts  again  at  15°. 8  F.  ( — 9°  C.)  It 
boils  at  about  82°  F.  (28°  C.),  yielding  a  dark  yellowish-red  vapor,  which 
becomes  apparently  nearly  black  when  further  heated. 

This  vapor  is  scarcely  condensable  when  mixed  with  air  or  other  gases ;  hence 
hyponitric  acid  was  formerly  believed  to  be  a  permanent  gas.  It  has  a  sweetish 
but  pungent  and  suffocating  odor,  and  an  acid  taste.  It  reddens  litmus,  and 
imparts  a  yellow  stain  to  animal  matters. 

Peroxide  of  nitrogen  is  decomposed  by  most  oxidizable  metals,  as  copper,  tin, 
mercury,  sodium,  and  potassium,  the  latter  taking  fire  in  it,  and  burning  with  a 
red  flame.  Water  decomposes  it,  nitric  acid  and  binoxide  of  nitrogen  being 
produced : — 

3N04-f2HO=NOa-f2(HO.N05). 

If  the  quantity  of  water  present  is  small,  the  products  of  decomposition  are  ni- 
trous acid  and  nitric  acid : — 

2N04+HO=N03+HO.N05. 

The  peroxide  of  nitrogen  was  formerly  termed  nitrous  acid,  but  it  is  decom- 
posed by  the  alkaline  bases,  giving  rise  to  nitrates  and  nitrites. 


NITRIC  ACID. 

N05  (anhydrous)  or  hydratcd  acid,  HO.N05.     Eq.  54. 

§  85.  Nitric  acid  occurs  in  nature,  in  combination  with  potassa,  soda,  lime, 
and  magnesia  (particularly  with  the  two  first  named,  with  which  it  forms  nitre 
and  cubic  nitre).  In  some  hot  climates,  such  as  those  of  India  and  Peru,  these 
salts  form  incrustations  of  considerable  thickness  on  the  surface  of  the  soil. 
Nitric  acid  is  also  found  in  the  water  of  some  springs  and  rivers  in  the  neigh- 
borhood of  populous  towns,  in  rain  water  after  thunderstorms,  and  in  some 
plants,  which  absorb  it  from  the  soil. 

ANHYDROUS  NITRIC  ACID,  N05,  has  been  recently  discovered  by  Deville,  who 
succeeded  in  obtaining  it  by  passing  a  very  slow  current  of  chlorine,  first  over 
chloride  of  calcium  and  sulphuric  acid,  and  afterwards  over  well-dried  nitrate  of 


128  OXIDES   OF   NITROGEN. 

silver,  previously  heated  to  203°  F.  (95°  C.),  and  then  maintained  at  a  tempera- 
ture of  136°  to  150°. 8  F.  (56°  to  66°  C.)  The  products  are  passed  into  a 
U-tube,  cooled  down  to  5°. 8  F.  ( — 21°  C.)  Oxygen  escapes,  and  crystals  of 
nitric  acid  are  obtained,  besides  a  volatile  liquid,  probably  nitrous  acid. 

Properties. — Deville  describes  anhydrous  nitric  acid  as  a  substance  crystallizing 
in  brilliant  colorless  rhombic  prisms,  which  fuse  at  84°.2  to  86°  F.  (29°  to  30°  C.) 
It  boils  at  113°  to  122°  F.  (45°  to  50°  C.),  and  is  decomposed  at  about  that 
temperature.  When  brought  into  contact  with  water,  it  dissolves  with  con- 
siderable evolution  of  heat,  hydrated  nitric  acid  being  formed. 

HYDRATED  NITRIC  ACID,  HO.N05. 

§  86.  Nitric  acid  is  formed  in  nitre-heaps,  by  the  spontaneous  decomposition 
of  nitrogenous  animal  matter  in  the  presence  of  bases.  Ammonia  is  first  disen- 
gaged, and  this  appears  to  be  gradually  converted  by  the  oxygen  of  the  air  and 
contact  with  porous  bodies,  into  nitric  acid  and  water,  the  former  combining  with 
the  base  to  form  a  nitrate  : — 

NH3+08=3HO+N05. 

Nitric  acid  is  likewise  formed  by  the  action  of  the  electric  spark  upon  a  mix- 
ture of  nitrogen  and  oxygen,  in  the  presence  of  water,  and  is  most  probably  pro- 
duced in  this  manner  during  thunderstorms.  Ammonia  also  yields  nitric  acid 
when  exposed  to  the  action  of  oxidizing  agents  under  certain  circumstances. 

Preparation. — Hydrated  nitric  acid  is  prepared  by  distilling  a  mixture  of 
equal  parts  by  weight  of  hydrated  sulphuric  acid  (oil  of  vitriol)  and  nitrate  of 
potassa.  The  distillation  is  conducted  in  a  glass  retort,  the  neck  of  which  should 
be  rather  long,  and  is  passed  at  once  into  the  cooled  receiver.  No  cork  or  lute 
may  be  used  (§  40).  Since  the  nitre  of  commerce  generally  contains  some 
chloride  of  potassium  or  sodium,1  the  first  portion  of  acid  that  passes  over  con- 
tains chlorine,  and  should  therefore  be  rejected. 

The  above  proportions  correspond  nearly  to  one  equivalent  of  nitre  and  two  of 
hydrated  sulphuric  acid  (1  equivalent  of  nitre=101,  2  equivalents  of  sulphuric 
acid=98;  a  slight  excess  of  acid  is  advantageous).  The  decomposition  which 
the  nitre  undergoes  is  represented  by  the  following  equation : — 

KO.N05+2(HO.S03)=KO.H0.2S03-fHO.N05. 

Nitric  acid  is  also  obtained  if  one  equivalent  only  of  sulphuric  acid  is  employed. 
A  much  higher  temperature  is,  however,  then  required,  by  which  a  portion  of 
the  nitric  acid  is  decomposed,  being  converted  into  oxygen  and  peroxide  of  nitro- 
gen. The  latter  is  absorbed  by  the  nitric^ acid,  imparting  to  it  a  brownish  color.2 
The  bisulphate  of  potassa  is  also  far  more  readily  removed  from  the  retort  than 
the  neutral  sulphate  produced  in  the  latter  case,  on  account  of  its  greater  fusi- 
bility and  solubility. 

Nitrate  of  soda  is  sometimes  used  instead  of  nitrate  of  potassa,  and  is  generally 
employed  for  the  manufacture  of  this  acid  on  the  large  scale  (one  equivalent  of  the 
gait  being  used,  to  one  of  hydrated  sulphuric  acid). 

The  distillation  of  nitric  acid  on  the  large  scale  is  effected  in  horizontal  cast-iron 
cylinders.  In  order  to  insure  the  purity  of  nitric  acid  (which,  if  the  first  portion 
be  collected  separately,  will  be  nearly  free  from  chlorine,  but  may  contain  sulphuric 
acid  and  small  quantities  of  fixed  salts),  it  should  be  redistilled  with  the  addition 
of  a  small  quantity  of  nitre.  (Tests  for  the  purity  of  nitric  acid,  see  Analysis, 
Reagents.)  To  obtain  nitric  acid  perfectly  free  from  chlorine,  it  may  be  mixed 

1  A  very  simple  method  of  expelling  the  chlorine  from  nitre  consists  in  stirring  it  at  a 
gentle  heat,  with  a  few  drops  of  nitric  acid,  till  a  specimen  dissolved  in  water  no  longer 
gives  a  turbidity  with  nitrate  of  silver. 

2  If  the  acid  be  required  colorless,  it  may  be  rendered  so  by  gently  heating  it  until  all 
peroxide  of  nitrogen  is  expelled. 


NITRIC   ACID.  129 

with  an  excess  of  nitrate  of  silver  and  redistilled.  The  best  method  of  obtaining 
very  concentrated  nitric  acid,  is  to  distil  the  ordinary  acid  with  two  parts  of  ou 
of  vitriol,  at  a  temperature  not  exceeding  284°  to  302°  F.  (140°  to  150°  C.) 

Properties. — Hydrated  nitric  acid  is  a  colorless  liquid  when  pure,  giving  off 
dense  grayish-white  fumes  on  exposure  to  damp  air,  in  consequence  of  the  forma- 
tion of  a  less  volatile  hydrate.  The  strongest  acid  has  a  specific  gravity  of  1 .522  ; 
it  freezes  at  a  temperature  between — 40°  and  — 65°.2  F.  (—40°  and  —  54°  C.), 
yielding  a  mass  like  butter.  Hydrated  acid  of  the  highest  specific  gravity  begins 
to  boil  at  about  108°  F.  (42°  0.),  the  boiling-point  gradually  rising  as  the  acid 
becomes  weaker  (a  portion  being  decomposed  into  peroxide  of  nitrogen  and  oxy- 
gen), until  the  temperature  has  reached  248°  F.  (120°  C.),  when  an  acid  of  the 
spec.  grav.  1.42"  (having  the  formula  HO.N05-f  3HO,  and  containing  60  per  cent, 
of  N03),  is  obtained.  If,  on  the  other  hand,  an  acid  weaker  than  this  last  be 
distilled,  the  boiling-point  gradually  rises  to  248°  (water,  with  a  little  acid,  passing 
over),  and  the  acid  of  spec.  grav.  1.42  then  distils  over,  so  that  this  acid  is  the 
constant  product  of  the  distillation  of  hydrated  nitric  acid  of  any  strength. 

Hydrated  nitric  acid  has  a  pungent  characteristic  odor,  and  is  very  acid  and 
corrosive,  destroying  organic  matter  or  staining  it  yellow.  It  possesses  a  con- 
siderable affinity  for  water,  which  it  attracts  from  the  atmosphere ;  when  the 
strong  acid  is  mixed  with  water  much  heat  is  evolved.  Snow,  when  mixed  with 
moderately  strong  nitric  acid  (sp.  gr.  1.4),  liquefies  instantly,  intense  cold  being 
produced. 

Hydrated  nitric  acid  undergoes  decomposition  with  considerable  facility.  When, 
its  vapor  is  passed  through  a  redhot  porcelain  tube,  it  is  decomposed  into  nitrogen 
and  oxygen,  or  peroxide  of  nitrogen  and  oxygen,  according  to  the  temperature 
employed.  It  undergoes  decomposition  by  mere  exposure  to  the  light,  becoming 
yellow.  In  consequence  of  the  feeble  manner  in  which  nitric  acid  retains  a  por- 
tion of  its  oxygen,  it  is  a  most  powerful  oxidizing  agent,  acting  upon  all  oxidizable 
substances  with  more  or  less  violence.  These  oxidations  are  generally  attended 
by  evolution  of  heat,  which  in  some  instances  is  so  great  as  to  inflame  the  sub- 
stance acted  upon.  Thus,  phosphorus  thrown  into  the  strongest  nitric  acid  inflames, 
and  is  converted  into  phosphoric  acid ;  oil  of  turpentine,  and  some  other  essential 
oils,  are  also  inflamed  when  mixed  with  the  strongest  nitric  acid.  Small  pieces 
of  redhot  charcoal,  thrown  into  strong  nitric  acid,  continue  to  glow  with  increased 
brilliancy. 

Lower  oxides  are  converted  into  higher  by  nitric  acid,  and  most  metals  are  first 
oxidized  and  then  dissolved.  The  very  strongest  nitric  acid  has  no  action  upon 
many  metals,  such  as  iron  and  lead,  but  when  slightly  diluted  it  oxidizes  them 
powerfully.  When  metals  are  exposed  to  the  oxidizing  action  of -nitric  acid,  the 
latter  loses  one,  three,  and  sometimes  five  equivalents  of  oxygen ;  and  in  the  case 
of  those  metals  which  decompose  water  in  the  presence  of  acids  (as  tin  and  zinc), 
ammonia  is  also  formed. 

Nitric  acid  combines  with  basic  oxides  to  form  nitrates,  most  of  which  are  neu- 
tral, their  composition  being  represented  by  the  formula  MO.N05.  There  are 
also  some  basic  nitrates  containing  a  larger  proportion  of  base  to  the  acid  than 
that  above  given. 

Nitrates  are  decomposed  by  heat;  in  some  cases  oxygen  is  at  first  liberated,  the 
nitrites  being  formed,  which  are  decomposed  by  continued  application  of  heat;  in 
other  cases  the  acid  is  decomposed  into  peroxide  of  nitrogen  and  oxygen. 

Nitrates  are  also  decomposed  by  sulphuric  acid,  and  mostly  deflagrate  when 
thrown  upon  ignited  charcoal. 

The  action  of  nitric  acid  upon  organic  substances  consists  either  in  a  simple 
conversion  of  the  substance  into  products  of  oxidation,  or  merely  in  the  oxidation 
of  one  or  more  equivalents  of  hydrogen,  which  are  replaced  by  an  equivalent 
9 


130  ATMOSPHERIC   AIR. 

quantity  of  peroxide  of  nitrogen  (N04).     An  example  of  the  first  kind  of  action 
is  the  conversion  of  oxalic  acid  into  carbonic  acid : — 

C203-f  0(from  nitric  aciJ)=2C03. 

The  second  kind  of  action  is  illustrated  by  the  production  of  nitrdbenzol,  and 
dinitrobenzol  from  benzol,  which  is  represented  in  the  following  equations  : — 

CMH6+HO.N05=C1S 


Benzol  Nitrobenzol 

C13H6+ 2(^0^0,)=:^  |  §fo4+4HO. 

Benzol  Dinitrobenzol 

FUMING  NITRIC  ACID  is,  properly  speaking,  a  mixture  of  very  strong  nitric 
acid  with  peroxide  of  nitrogen.  It  is  a  red  liquid,  evolving  yellowish  red  fumes 
on  exposure  to  the  ajr.  Fuming  nitric  acid  is  turned  green  by  addition  of  a 
small  quantity  of  water,  nitric  oxide  being  evolved ;  a  large  quantity  of  water 
destroys  the  color. 

Uses  of  Nitric  Acid.1 — The  oxidizing  and  solvent  powers  of  nitric  acid  render 
it  a  highly  valuable  agent  in  the  hands  of  the  chemist.  * 

In  combination  with  potassa,  it  is  largely  used  in  the  manufacture  of  gunpow- 
der and  also  in  fireworks.  It  is  also  used  in  dyeing,  for  the  production  of  yellow 
patterns  upon  a  colored  ground.  The  dilute  acid  is  employed  in  lithography. 
Nitric  acid  is  occasionally  used  in  medicine,  and  also  as  a  fumigating  agent,  its 
fumes  being  less  irritating  than  those  of  chlorine.  For  this  purpose  pounded 
nitre  and  sulphuric  acid  are  heated  together  in  an  open  vessel.  Certain  vegeta- 
ble substances  when  acted  upon  by  this  acid,  yield  highly  explosive  compounds. 
This  property  has  of  late  been  applied  to  the  manufacture  of  gun-cotton,  gun- 
paper,  &c. 

ATMOSPHERIC    AIK. 

Sp.  Gr.  1.    100  cubic  inches  weigh  31.0117  grs. 

.§  87.  The  air  which  constitutes  our  atmosphere  consists  of  a  mechanical 
mixture  of  oxygen  and  nitrogen,  containing  small  and  variable  quantities  of 
aqueous  vapor,  carbonic  acid,  and  traces  of  a  few  other  substances  both  inorganic 
and  organic.  The  property  possessed  by  gases  of  becoming  intimately  and  tho- 
roughly mixed,  however  much  they  may  differ  in  their  density,  or,  in  other 
words,  the  diffusion  of  gases,  accounts  for  the  great  uniformity  of  this  mechanical 
mixture  in  different  parts  of  the  atmosphere. 

Oxygen  and  nitrogen  are  present  in  the  atmosphere  in  the  proportion  of  about 
two  equivalents  of  the  latter  to  one  of  the  former;  100  volumes  of  air  contain 
79.19  nitrogen,  and  20.81  oxygen.  By  weight,  the  proportions  are  77  nitrogen, 
and  23  oxygen. 

Numerous  methods  have  been  resorted  to  for  determining  the  proportions  of 
oxygen  and  nitrogen  in  atmospheric  air.  The  branch  of  chemistry  to  which  such 
operations  belong  is  termed  eudiometry,  and  has  already  been  referred  to,  and 
the  apparatus  employed  therein  described  (§  32).  Volta's  method  is  that  most 

1  The  impure  nitric  acid  of  commerce  is  known  by  the  name  of  aqua  fortis  :  its  spec, 
grav.  ranges  from  1.4  to  1.5,  and  it  generally  contains  hydrochloric  and  sulphuric  acids 
as  impurities. 

The  nitrous  acid  of  commerce  consists  of  nitric  acid  containing  N04,  and  is  usually  pre- 
pared by  distilling  nitrate  of  potassa  with  half  its  weight  of  sulphuric  acid. 


ATMOSPHERIC  AIR.  131 

generally  adopted  for  determining  the  amount  of  oxygen.  A  certain  volume  of 
air  is  confined  in  an  eudiometer  over  water  or  mercury,  and  mixed  with  about 
half  its  bulk  of  pure  hydrogen  ;  a  second  measurement  is  then  made,  and  the 
mixture  afterwards  exploded  by  the  electric  spark  (§  32).  The  gaseous  residue 
in  the  tube,  after  detonation,  consists  of  nitrogen  and  the  excess  of  hydrogen ; 
this  is  measured,  and  the  amount  deducted  from  the  volume  before  the  explosion; 
the  result  divided  by  three,  gives  the  amount  of  oxygen  contained  in  the  air, 
since  the  whole  of  that  element  will  have  combined  with  the  hydrogen  to  form 
water,  and  the  latter  consists  of  one  volume  of  oxygen  to  two  of  hydrogen.  The 
oxygen  is  sometimes  determined  by  introducing  a  stick  or  ball  of  phosphorus, 
attached  to  a  fine  iron  wire,  into  a  measured  portion  of  air  confined  over  water. 

If  this  arrangement  be  allowed  to  remain  for  about  twenty-four  hours  in  a 
warm  place,  the  phosphorus  undergoes  slow  combustion,  being  converted  into 
phosphorous  acid,  which  is  absorbed  by  the  water,  while  nitrogen  only  remains 
in  the  tube.  Oxygen  may  also  be  estimated  in  a  variety  of  ways  by  means  of 
substances,  principally  in  the  liquid  state,  having  a  powerful  affinity  for  oxygen, 
which  they  abstract  from  air  at  ordinary  temperatures.  Thus,  Sir  H.  Davy  re- 
commended for  this  purpose,  a  solution  of  sulphate  of  iron  saturated  with  nitric 
oxide ;  a  solution  of  a  salt  of  the  suboxide  of  copper  in  ammonia  is  also  frequently 
used,  and  Liebig  has  not  long  since  discovered  that  an  alkaline  solution  of  pyro- 
gallic  acid  absorbs  oxygen  rapidly  from  the  air,  and  is  the  most  convenient  reagent 
for  effecting  its  analysis.  Another  most  accurate  method  of  analyzing  air,  is  to 
allow  a  quantity  to  flow  into  an  exhausted  glass  globe  (of  known  weight),  first 
passing  through  a  series  of  tubes  containing,  respectively,  potassaand  concentrated 
sulphuric  acid,  and  then  through  a  weighed  tube  filled  with  bright  copper  turn- 
ings, and  heated  to  redness  in  a  charcoal  fire.  The  increase  in  the  weight  of  the 
latter  tube,  owing  to  the  oxidation  of  the  copper,  gives  the  amount  of  oxygen 
corresponding  to  the  nitrogen  weighed  in  the  globe. 

§  88.  The  following  is  a  short  account  of  the  foreign  matters  existing  in  the 
atmosphere. 

Aqueous  Vapor. — The  quantity  of  aqueous  vapor  existing  in  air  is  very  variable, 
depending  much  on  the  temperature ;  its  presence  is  highly  essential  to  animal 
and  vegetable  life ;  perfectly  dry  air  would  soon  prove  fatal  both  to  plants  and 
animals.  The  presence  of  water  in  the  atmosphere  is  easily  demonstrated,  by 
exposing  some  deliquescent  substance  (such  as  fused  chloride  of  calcium)  to  the 
air ;  the  moisture  will  soon  be  attracted,  and  after  a  time  the  chloride  will  become 
quite  liquid. 

Various  instruments  have  been  constructed  for  the  determination  of  moisture 
present  in  the  atmosphere,  which  are  termed  hygrometers. 

That  most  generally  approved  of  has  been  contrived  by  Daniell  (usually  known 
as  the  wet-bulb  hygrometer).  Another  method  of  determining  the  water  is  that 
of  Brunner,  which  consists  in  drawing  a  measured  quantity  of  air,  by  means  of 
an  aspirator,  through  a  weighed  tube  containing  asbestos  moistened  with  strong 
sulphuric  acid,  and  ascertaining  the  increase  in  the  weight  of  the  tube. 

Carbonic  Acid. — This  gas  is  always  present  to  a  small  extent  in  air  (according 
to  Marchand,  3.1  in  1000),  being  derived  from  the  processes  of  combustion  and 
respiration.  The  carbonic  acid  thus  constantly  produced,  is  to  a  great  extent 
removed  from  the  air  by  plants,  to  the  existence  of  which  it  is  essential,  since 
they  assimilate  its  carbon,  and  restore  the  oxygen  to  the  air. 

The  amount  of  this  gas  present  in  air  may  be  ascertained  by  drawing  air  as 
above  directed,  first  through  a  drying  tube,  and  then  through  another  tube  with 
two  divisions,  containing  hydrate  of  potassa  in  the  first,  and  some  asbestos  moist- 
ened with  sulphuric  acid  in  the  second  division  (to  absorb  any  moisture  carried 
away  from  the  hydrate  of  potassa).  The  increase  in  weight  of  this  tube  will  give 
the  amount  of  carbonic  acid. 


132  NITROGEN  AND  HYDROGEN. 

Ammonia. — This  impurity  in  the  atmosphere  is  generated  by  the  putrefaction 
of  nitrogenized  organic  substances ;  though  it  may  be  distinctly  detected  in  air, 
and  particularly  in  rain  water  (by  which  it  is  absorbed  from  the  atmosphere),  its 
quantity  is  very  inconsiderable.  It  is  absorbed  in  a  remarkable  manner  by  some 
substances  when  exposed  to  the  air.  Thus,  sesquioxide  of  iron,  or  white  clay, 
previously  ignited,  will  be  found  when  heated  after  protracted  exposure  to  the 
air,  to  evolve  considerable  quantities  of  ammonia. 

Besides  the  above  impurities,  a  few  others  are  at  times  to  be  detected  in  the 
air  or  in  rain-water,  particularly  in  the  neighborhood  of  large  towns ;  the  chief 
of  these  is  hydrosulphuric  acid.  Certain  organic  matters  are  also  contained  in 
the  air.  It  is  supposed  that  the  contagious  matter  of  several  epidemic  diseases 
exists  in  the  form  of  an  organic  poison  disseminated  through  the  atmosphere, 
and  to  which  the  name  of  miasma  has  been  given.  Marsh-gas  is  also  an  impu- 
rity found  in  the  air  in  the  neighborhood  of  stagnant  waters,  or  in  coal-mines, 
where  it  forms  the  highly  dangerous  fire-damp. 

The  average  composition  of  the  air  is  always  the  same,  since  a  most  simple 
and  beautiful  balance  is  kept  up  in  nature  between  animal  and  vegetable  respira- 
tion. As  already  stated,  the  oxygen  consumed  in  the  production  of  carbonic 
acid  by  combustion  in  air  or  respiration  of  animals,  is  continually  restored  to  the 
atmosphere  by  the  plants,  which  retain  for  their  own  nourishment  the  carbon,  to 
serve  again  as  support  for  animal  life. 

The  constitution  of  atmospheric  air  was  for  a  long  time  matter  of  dispute ;  it 
is  now,  however,  generally  believed  to  be  a  mechanical  mixture  of  oxygen  and 
nitrogen,  the  constant  composition  of  which  may  be  accounted  for  by  reference 
to  the  law  of  diffusion,  and  by  a  consideration  of  the  slight  difference  in  the 
specific  gravities  of  its  component  gases. 

The  following  arguments  may  be  cited  in  support  of  this  view : — 

1.  The  composition  by  volume  of  atmospheric  air  would  be  anomalous,  if  it 
were  a  combination  of  nitrogen  and  oxygen. 

2.  The  properties  of  air  are  such  as  would  be  predicted  of  a  mere  mechanical 
mixture  of  the  two  gases. 

3.  A  mixture  of  nitrogen  and  oxygen  in  proper  proportions  exhibits  all  the 
properties  of  atmospheric  air,  without  our  perceiving  any  of  the  phenomena 
usually  attendant  upon  chemical  combination. 

4.  Water,  exposed  to  air;  absorbs  each  gas  in  the  same  proportion  as  if  it  were 
ia  a  perfectly  free  state. 

NITKOGEN  ANB-HYDROGEN. 

(Imidogen)      ....     NH  Ammonia       ....     NH3 

(Amidogen)     ....     NH2  (Ammonium)      .     .     .     NH4 

Those  inclosed  in  brackets  are  hypothetical. 

AMIDOGEN,  NHa=Ad.  Eq.  16. 

§  89.  "We  are  not  acquainted  with  this  body  in  a  separate  state ;  we  have, 
however,  very  good  reasons  for  assuming  its  existence  in  many  compounds. 

When  potassium  and  sodium  are  heated  in  ammoniacal  gas,  it  will  be  found 
that  one-third  of  the  hydrogen  escapes ;  the  residue  has  the  composition  KNH3, 
or  NaNH2  :— 

NH3+K=KNH3+H. 

This  compound  is  termed  amidide,  or  amide  of  potassium. 

When  certain  metallic  chlorides  are  mixed  with  aqueous  ammonia^  compound 
amides  are  also  produced : — 

2HgCl+2NH3=HgNH3.HgCl+NH4Cl. 


AMMONIA.  133 

A  far  larger  number  of  amides  exist  in  organic  chemistry,  consisting  of  ami- 
dogen  in  combination  with  some  other  complex  atoms.  When  brought  into 
contact  with  water  in  the  presence  of  acids  or  alkalies,  they  are  resolved  into 
ammonia  and  oxidized  products. 

AMMONIA. 
NH2.     Eq.  17.     Sp.  Gr.  0.590.2. 

Composition  by  Volume. — 1  volume  of  nitrogen  and  3  volumes  of  hydrogen 
combine  to  form  2  volumes  of  ammonia. 

§  90.  Ammonia  occurs  in  the  air  as  carbonate  of  ammonia;  in  some  rivers, 
springs,  and  mineral  waters,  as  chloride  of  ammonium,  or  some  other  salt.  The 
rock-salt  of  the  Tyrol  contains  chloride  of  ammonium  (sal-ammoniac);  sesquioxide 
of  iron  and  aluminous  or  ferruginous  rocks,  after  exposure  to  air,  yield  ammonia 
when  heated;  some  plants  contain  salts  of  ammonia;  it  is  also  found  in  one  or 
two  minerals  of  recent  formation,  and  in  animal  secretions. 

When  a  mixture  of  2  volumes  of  nitric  oxide  and  5  volumes  of  hydrogen  is 
passed  over  spongy  platinum,  or  other  porous  substances  (heated  to  redness), 
ammonia  and  water  are  produced.  The  quantity  formed  by  exposing  a  mixture 
of  nitrogen  and  hydrogen  gases  to  the  action  of  an  electric  current  is  very  minute; 
but  if  hydrogen,  at  the  moment  of  its  liberation,  meet  under  certain  circumstances 
with  nitrogen,  ammonia  will  be  produced.  In  the  rusting  (oxidation)  of  iron  by 
water  containing  atmospheric  air,  ammonia  is  formed  in  this  manner.  Most 
nitrogenized  organic  substances  yield  ammonia,  either  by  dry  distillation,  or  by 
heating  with  an  alkali.  Animal  secretions  yield  ammonia  in  abundance,  when 
allowed  to  undergo  fermentation  or  putrefaction.  Thus,  in  urine,  the  urea 
(cyanate  of  ammonia)  gradually  passes  over  into  carbonate  of  ammonia  : — 

NH4O.C3NO+4HO=2(NII4O.COa) 

urea  carbonate  of  ammonia. 

Large  quantities  of  ammonia  are  also  obtained  in  the  distillation  of  coal  (for 
the  preparation  of  gas)  and  of  bones ;  and  from  these  sources  most  of  the  am- 
monia of  commerce  is  at  present  obtained. 

Carbonate  of  ammonia  was  first  extensively  prepared  from  camels'  dung,  in 
Egypt. 

Preparation. — The  best  mode  of  preparing  dry  ammonia  in  the  laboratory,  is 
to  heat  gradually  in  a  retort  or  flask,  a  mixture  of  1  part  of  chloride  of  ammo- 
nium, and  2  parts  of  hydrate  of  lime,  allowing  the  gas  to  pass  first  into  a  small 
bottle  with  a  safety-tube,  in  which  any  moisture  may  be  to  a  great  extent  con- 
densed, and  afterwards  through  a  tube  filled  with  fragments  of  quicklime,  to 
complete  the  desiccation  of  the  gas,  which  must  either  be  collected  over  mercury, 
or  by  upward  displacement  in  inverted  vessels,  it  being  considerably  lighter  than 
air.  The  production  of  ammonia  in  this  process  is  thus  represented : — 

NH4Cl+CaO.HO=CaCl-fNHa+2HO. 

Properties. — Ammonia  is  a  colorless  gas,  of  a  peculiar  and  exceedingly  pun- 
gent odor;  it  does  not  support  combustion,  but  a  jet  of  the  gas  burns  with  a 
yellow  flame  in  an  atmosphere  of  oxygen.  When  inspired  pure,  it  is  fatal  to 
animals.  It  is  converted  by  a  pressure  of  six  and  a  half  atmospheres  at  50°  F. 
(10°  C.)  into  a  colorless,  mobile  liquid,  the  spec.  grav.  of  which  is  0.76; 
gaseous  ammonia  is  likewise  transformed  at  a  very  low  temperature,  into  a  color- 
less, translucent,  crystalline  solid,  which  melts  at — 113°  F.  ( — 75°  C.)  Liquid 
ammonia  may  be  obtained  by  heating  some  chloride  of  silver  saturated  with 
gaseous  ammonia,  in  one  arm  of  a  sealed  tube  of  tough  glass  (such  as  recom- 
mended by  Faraday  for  the  liquefaction  of  gases),  and  surrounding  the  other 
arm  with  ice ;  the  ammonia  will  be  evolved,  and  condensed  by  its  own  pressure 


134  NITROGEN   AND   HYDROGEN. 

in  the  cold  extremity  of  the  tube.  On  allowing  the  chloride  to  cool,  the  ammo- 
nia is  again  absorbed  by  it;  the  heat  evolved  by  this  recombination  raises  the 
temperature  of  the  chloride  of  silver  to  100°.4  F.  (38°  C.);  while  the  other 
end  of  the  tube  in  which  the  ammonia  was  condensed,  becomes  very  cold. 

Ammonia  is  powerfully  alkaline ;  when  brought  into  contact  with  hydrogen- 
acids,  or  with  hydrated  oxygen-acids,  it  produces  ammoniacal  salts;  and  hence 
volatile  acids,  such  as  hydrochloric,  nitric,  and  acetic,  are  often  used  as  a  test 
for  gaseous  ammonia,  with  which  the  vapors  of  these  acids  produce  white  clouds. 

If  a  flask  filled  with  ammoniacal  gas  be  opened  under  water,  the  latter  rushes 
in  with  great  rapidity,  in  consequence  of  the  absorption  which  takes  place. 

SOLUTION  OF  AMMONIA,  LIQUOR  AMMONIA. 

Water  absorbs  nearly  half  its  weight  (or  about  670  times  its  volume)  of  am- 
moniacal gas.  A  solution  of  this  description  constitutes  the  aqua  ammonias 
forfissima  of  commerce. 

It  is  prepared  by  connecting  a  glass  or  earthenware  vessel,  charged  with  the 
above  mentioned  mixture  for  the  preparation  of  ammonia  (slightly  moistened 
with  water),  with  three  Woulfe's  bottles,  fitted  with  safety-tubes;  the  first  con- 
taining but  little  water,  the  second,  an  amount  about  equal  to  the  weight  of 
chloride  of  ammonium  employed,  and  the  third,  a  smaller  quantity. 

The  gas  is  washed  in  the  first  bottle  (the  first  portion  being  also  absorbed), 
the  water  in  the  second  bottle  then  becomes  gradually  saturated  with  pure  am- 
moniacal gas;  that  in  the  third  retains  any  ammonia  that  may  escape  absorption 
in  the  second  bottle.  These  bottles  should  be  kept  cool  by  being  surrounded 
with  cold  water. 

Properties. — The  solution  of  ammonia  is  colourless.  It  varies  in  spec.  grav. 
from  nearly  1.000  to  0.850,  according  to  its  strength.  (The  strongest  ammonia 
of  commerce  has  a  spec.  grav.  of  about  0.87).  It  does  not  freeze  until  between 
—36°  and  —42°  F.  (—38°  —41°  C.)  It  possesses  the  peculiar  odor  of  the 
gas,  and  a  sharp  burning  taste.  The  greater  portion  of  ammonia  is  expelled 
from  its  solution  below  212°  F.  (100°  C.) 

Solution  of  ammonia  is  most  extensively  used  by  chemists,  being  a  highly 
important  reagent.  It  is  also  employed  medicinally,  for  which  purpose  it  is 
diluted  to  the  spec.  grav.  0.96. 

Dry  ammoniacal  gas,  when  submitted  to  the  electric  spark,  is  resolved  into  3 
volumes  of  hydrogen  and  1  of  nitrogen;  ammonia  may  be  also  decomposed  by 
contact  with  highly  heated  platinum,  copper  or  iron,1  and  by  detonation  with 
oxygen.  Chlorine  gas  decomposes  it  rapidly  at  ordinary  temperatures,  yielding 
nitrogen  gas  and  hydrochloric  acid;  the  latter,  combining  with  another  portion 
of  ammonia,  forms  chloride  of  ammonium;  an  excess  of  chlorine  produces 
chloride  of  nitrogen  (§  97). 

4NH3-fCl3=3(NH4Cl)-fN. 

This  action  is  at  times  accompanied  by  the  production  of  a  flash  of  light. 
Ammoniacal  gas  is  also  decomposed  under  various  circumstances,  and  with  more 
or  less  rapidity,  by  some  of  the  oxides  of  nitrogen  (particularly  hyponitric  acid), 
by  some  metallic  oxides,  &c. 

AMMONIUM,  NH4.     Eq.  18. 
§  91.  This  compound  has  never  yet  been  isolated;  numerous  observations, 

1  It  has  been  very  recently  shown  that  ammonia  is  resolved  into  its  elements  at  a  tem- 
perature far  below  redness,  when  passed  through  tubes  containing  heated  quicklime.  It 
has  even  been  proposed  to  employ  this  method  for  the  preparation  of  hydrogen  free  from 
arsenic,  &c.,  when  the  presence  of  nitrogen  is  not  objectionable. 


AMMONIUM.  135 

however,  have  led  chemists  to  believe  that  it  exists,  and  is  in  its  properties  simi- 
lar to  a  metal. 

If  a  galvanic  current  is  allowed  to  act  upon  a  solution  of  an  ammoniacal  salt, 
the  end  of  the  negative  pole  dipping  into  mercury,  the  latter  is  observed  to  in- 
crease gradually  in  bulk  to  a  considerable  extent,  becoming  of  the  consistency 
of  butter,  and  at  the  same  time  retaining  its  metallic  lustre.  By  placing  aii 
amalgam  of  potassium  or  sodium  on  a  piece  of  moistened  chloride  of  ammonium, 
or  in  a  solution  of  the  latter,  the  same  compound  is  produced.  This  is  regarded 
as  the  amalgam  of  mercury  with  the  substance  ammonium,  NII4.  When  it  is 
placed  in  water,  the  mercury  returns  to  its  original  state,  hydrogen  and  ammonia 
being  evolved.  The  increase  in  weight  which  the  mercury  exhibits  when  con- 
verted into  the  amalgam,  is  very  trifling.  The  decomposition  of  potassium- 
amalgam  by  chloride  of  ammonium  is  represented  as  follows : — 
HgK  -f  NH4C1 = KC1 + HgNHv 

The  assumption  of  the  existence  of  the  compound  metal,  ammonium,  based 
upon  this  and  other  experiments,  furnishes  us  with  a  very  simple  view  respecting 
the  constitution  of  the  ammoniacal  salts. 

Ammonia  was  formerly  believed  to  combine  directly  with  hydrogen-acids  and 
also  with  oxygen-acids.  The  composition  of  the  hydracid  salts  is  in  accordance 
with  this  view,  since  they  may  be  represented  by  the  general  formula,  NHg.HR;1 
it  is  most  probable,  however,  that  if  an  oxygen-acid  unites  (as  it  sometimes  does) 
directly  with  NH3,  it  does  not  form  a  true  salt,  but  that  the  presence  of  an  equi- 
valent of  water  is  indispensably  necessary  to  the  production  of  a  salt  of  ammonia 
with  an  oxygen-acid.  This  difference  in  the  behavior  of  ammonia  with  the  two 
classes  of  acids  is  not  easily  explained,  unless  we  adopt  the  view  of  Berzelius  in 
assuming  the  existence  of  the  substance  ammonium,  NH4. 

Ammonia -fl  eq.  of  water,  NH8+HO,  must  then  be  viewed  as  NH40=AmO, 
the  oxide  of  ammonium,  analogous  to  KO,  the  oxide  of  potassium  or  potassa; 
this  oxide  then  unites  with  oxygen-acids  to  form  salts  of  the  oxide  of  ammonium, 
such  as  NH4O.S03  or  AmO.S03;  NH3.HC1,  the  hydrochlorate  of  ammonia, 
must  in  this  case  be  viewed  as  NH4C1,  or  AmCl,  chloride  of  ammonium,  analo- 
gous to  chloride  of  potassium.  An  analogy  between  the  salts  of  ammonia,  and 
those  of  the  alkalies  to  which  they  are,  in  many  respects,  so  similar,  cannot  be 
traced  by  the  first  mode  of  viewing  their  composition ;  but  as  soon  as  we  assume 
the  existence  of  ammonium,  the  most  striking  analogy  is,  as  we  have  shown, 
exhibited  between  the  composition  of  the  salts  of  ammonia  and  of  potassa  or 
soda;  the  main  difference  consisting  in  the  point,  that  Am(NH4)  is  a  compound, 
while  K  and  Na  are  elements;  several  analogous  cases  are,  however,  to  be  found 
in  chemistry,  in  which  a  compound  body,  the  chemical  or  physical  properties  of 
which  are  indeed  perfectly  well  known,  comports  itself  towards  other  bodies 
exactly  like  certain  elements;  and,  indeed,  most  chemists  are  far  from  maintain- 
ing the  impossibility  of  a  future  discovery  that  some  of  the  present  elements  are 
compound  bodies  (§  101). 

Various  objections  have  been  raised  to  the  ammonium-theory  of  Berzelius,  and 
Other  theories  have  also  been  advanced;  the  above  is,  however,  the  most  simple, 
and  hence  is  most  generally  adopted  by  chemists. 

1  R  representing  the  radical  of  the  hydrogen-acid. 


136  CHLORINE. 


CHLORINE.1 

Sym.  Cl.     Eq.  35.50.     Sp.Gr.  2.44. 

§  93.  Scheele  discovered  chlorine  in  1774.  Gay-Lussac  and  The'nard  were, 
"however,  the  first  to  class  it  among  the  simple  bodies  in  1809.  Its  elementary 
character  was  afterwards  fully  established  by  Davy. 

Chlorine  occurs  in  combination  in  many  mineral  substances,  such  as  rock-salt 
(chloride  of  sodium),  also  in  sea-water  and  marine  plants,  as  chlorides  of  sodium 
and  potassium. 

Preparation.  —  Chlorine  is  obtained  :  — 

I.  By  gently  heating  in  a  flask,  binoxide  of  manganese  with  strong  hydro- 
chloric acid  :  — 

MnOa+2HCl=MnCl+2HO+Cl. 

II.  By  heating  a  mixture  of  binoxide  of  manganese,  chloride  of  sodium,  and 
moderately  dilute  sulphuric  acid  :  — 

Mn03+NaCl+2(HO.S03)=MnO.S08+NaO.S03+2HO  +  Cl. 

When  chlorine  is  required  perfectly  dry,  it  should  be  passed  through  concen- 
trated sulphuric  acid. 

The  gas  may  be  collected  either  by  downward  displacement  (§  31),  or  if  re- 
quired perfectly  free  from  atmospheric  air,  over  water,  the  delivery-tube  being 
passed  to  the  top  of  the  gas-jars.1 

Properties.  —  Chlorine  is  a  yellowish-green  gas,  of  a  pungent  suffocating  odour; 
it  is  incombustible,  and  supports  the  combustion  of  a  few  bodies  for  which  it  has 
an  affinity.  Some  elements,  such  as  antimony  and  phosphorus,  inflame  sponta- 
neously in  chlorine,  as  also  certain  compounds  rich  in  hydrogen,  such  as  ammo- 
nia and  oil  of  turpentine;  a  wax  taper  continues  to  burn  for  some  time  in  this 
gas,  with  deposition  of  carbon,  the  hydrogen  of  the  wax  combining  with  the 
chlorine,  which  has  a  most  powerful  affinity  for  that  element.  Chlorine  is  in- 
capable of  supporting  respiration,  causing  instantaneous  death  when  inhaled  pure; 
when  breathed  in  small  quantities,  it  excites  cough  and  sneezing,  accompanied 
by  an  oppressive  and  choking  sensation  in  the  chest,  sometimes  followed  by  spit- 
ting of  blood.  When  highly  diluted,  it  may,  however,  be  administered,  to  alle- 
viate symptoms  of  phthisis. 

It  may  be  condensed  by  a  pressure  of  about  four  atmospheres  to  a  yellow 
limpid  liquid,  of  spec.  grav.  1.33. 

Chlorine,  especially  when  moist,  discharges'  vegetable  colors.  It  also  possesses 
the  remarkable  property  of  destroying  organic  odors  and  infectious  matters. 

Two  views  are  taken  of  this  property  of  chlorine.  In  cases  when  dry  chlo- 
rine is  employed,  it  appears  to  abstract  hydrogen  directly  from  the  substance, 
thereby  converting  the  latter  into  some  colorless  or  inodorous  body  ;  but  if  water 
is  present  (and  moist  chlorine  bleaches  much  more  rapidly  than  the  dry  gas),  its 
hydrogen  is  most  probably  abstracted  by  the  chlorine,  and  the  liberated  oxygen 
acts  upon  the  organic  matter,  either  destroying  it  entirely,  or  converting  it  into 
some  colorless  or  inodorous  product. 

Water  dissolves  about  twice  its  volume  of  chlorine  gas  at  ordinary  tempera- 
tures. (The  solution  may  be  prepared  by  passing  a  slow  current  of  chlorine 


fo?,  yellowish-green. 

Maumene  has  recommended  another  process  for  the  preparation  of  chlorine,  when 
the  admixture  of  nitrogen  would  not  be  objectionable.  75  parts  of  dry  nitrate  of  ammo- 
nia, 25  of  dry  chloride  of  ammonium,  and  400  of  sand,  are  mixed,  and  heated  in  a  capa- 
cious flask  or  retort. 


HYPOCHLOROTJS   ACID. 


137 


through  water,  until  the  latter  is  saturated.)  It  has  the  color,  odor,  and  bleach- 
ing properties  of  the  gas,  arid  must  be  preserved  in  the  dark  in  small  bottles, 
perfectly  filled  and  well  stoppered,  as  it  is  liable  to  decompose  on  exposure  to 
light  (into  hydrochloric  acid  and  oxygen).1 

Chlorine  has  extremely  powerful  affinities  for  some  metalloids,  and  for  most 
metals.  In  combination  with  nitrogen,  it  forms  a  highly  explosive  liquid,  chlo- 
ride of  nitrogen ;  it  combines  with  hydrogen  to  form  hydrochloric  acid.  Oxygen 
unites  with  it  in  several  proportions  (though  not  directly,  under  any  circum- 
stances), producing  hypochlorous  acid  (CIO),  chlorous  acid  (C103),  peroxide  of 
chlorine  (C104),  chloric  acid  (C105),  perchloric  acid  (C107). 

Chlorine  also  forms  one  or  two  compounds  with  carbon.  It  combines  with 
most  metals,  forming  chlorides  of  various  compositions,  corresponding  in  most 
cases  with  their  oxides. 

Uses  of  Chlorine. — Immense  advantage  has  been  derived  from  the  use  of  chlo- 
rine as  a  bleaching  agent.  In  bleaching  by  {he  old  process,  by  exposure  to  the 
sun  and  air,  a  large  surface  of  ground  was  required,  and  long  exposure  was 
necessary,  from  which  considerable  damage  to  the  fabrics  resulted. 

The  chief  modes  of  applying  chlorine  as  a  bleaching  agent  are :  the  retort- 
lleachingj  in  which  the  moist  gas  is  employed,  and  the  use  of  bleaching-powder 
(chloride  of  lime),  of  which  more  will  be  said  hereafter.  The  latter  substance 
is  also  generally  used  as  a  source  of  chlorine  when  this  gas  is  employed  as  a 
disinfectant ;  if  the  chloride  of  lime  be  mixed  into  a  paste  with  water,  and  sul- 
phuric acid  added  from  time  to  time,  a  regular  evolution  of  chlorine  is  main- 
tained. 


CHLORINE   AND   OXYGEN. 


Hypochlorous  acid     .     .   CIO 
Chlorous  acid   ....    C103 
Peroxide  of  Chlorine      .    C104 


Chloric  acid 
Perchloric  acid 


C105 
C107 


HYPOCHLOROUS  ACID,  CIO.    Eg.  43.5. 


Composition  by  Volume. — 2  volumes  of  chlorine  and  1  volume  of  oxygen  form 
2  volumes  of  hypochlorous  acid. 

§  94.  Preparation. — This  acid  is  produced  by  diffusing  finely-divided  red 
oxide  of  mercury  through  about  twelve  times  its  weight  of  water,  which  is  intro- 
duced into  a  bottle  containing  chlorine  gas,  and  agitated  therein  till  the  latter 
is  absorbed.  A  solution  of  hypochlorous  acid  is  thus  obtained,  together  with  an 
oxychloride  of  mercury : — 3 

2HgO+Cla=HgO.HgCl  +  C10. 

The  oxychloride  of  mercury  is  removed  by  subsidence,  and  the  weak  solution 
obtained,  introduced  into  a  small  flask,  which  is  then  heated  in  the  water-bath, 
and  the  evolved  gas  conducted  into  a  smaller  portion  of  water,  when  a  pure  solu- 
tion of  CIO  is  obtained;  afterwards,  the  gas  may  be  evolved  from  this  solution 
by  introducing  a  few  fragments  of  some  highly  deliquescent  salt,  such  as  chloride 
of  calcium,  or  nitrate  of  lime;  but  the  experiment  is  attended  with  considerable 
danger.  The  gas  may  be  obtained  in  the  anhydrous  state  by  passing  dry  chlo- 
rine over  red  oxide  of  mercury  in  a  tube  surrounded  with  a  freezing  mixture. 
The  gas  disengaged  is  collected  over  mercury  in  bottles  provided  with  tight  and 

1  When  cooled  nearly  to  the  freezing  point,  the  solution  of  chlorine  deposits  yellow 
crystals  of  hydrate  of  chlorine,  Cl-j-lOHO,  which  Faraday  employed  in  order  to  obtain  the 
gas  in  a  liquid  state. 

2  The  solution  of  hypochlorous   acid  thus   obtained   generally  contains   chloride  of 
mercury. 


138  CHLORINE  AND  OXYGEN. 

greased  stoppers.     Hypochlorous  acid  must  not  be  allowed  to  remain  long  in 
contact  with  mercury,  since  the  latter  gradually  decomposes  it. 

Properties. — Hypochlorous  acid  is  a  deep  yellow  gas,  possessing  a  very  power- 
ful penetrating  odor.  It  may  be  liquefied  by  passing  the  dry  gas  into  a  U-tube, 
cooled  down  to  a  temperature  of  — 4°  F.  ( — 20°  C.)  When  exposed  to  a  gentle 
heat,  or  brought  into  contact  with  some  combustible  bodies  (white  unsized  paper, 
for  example),  it  explodes,  yielding  two  volumes  of  chlorine  and  one  volume  of 
oxygen.  It  rapidly  decomposes  many  organic  substances.  It  is  easily  absorbed 
by  water,  the  latter  taking  up  about  100  times  its  own  volume.  The  solution 
has  a  pale  yellow  color,  and  possesses  powerful  bleaching  properties,  and  the 
peculiar  odor  of  the  gas.  It  is  not  acid  to  test-papers,  and  is  easily  decomposed 
by  light,  and  by  organic  substances  having  affinities  for  chlorine  or  oxygen. 

The  combinations  of  this  acid  with  bases  are  termed  hypoclilorites.  The  so- 
called  chlorides  of  the  alkalies,  or  alkaline  earths  (the  bleaching  salts),  consist 
of  a  mixture  of  chloride  of  the  mStal  with  the  hypochlorite  of  the  base.  They 
are  prepared  by  passing  chlorine  into  water  containing  the  bases,  or  their  car- 
bonates, dissolved  or  in  suspension;  the  temperature  being  kept  low  during  the 
operation.  The  decomposition  may  be  expressed  as  follows : — 
2CaO  -f  Cl3=CaCl  +  CaO.ClO. 

It  is  to  be  observed  that  this  decomposition  only  takes  place  when  cold  dilute 
solutions  of  the  bases  are  employed;  if  these  be  hot  or  concentrated,  no  hypo- 
chlorite is  formed,  but  instead,  a  chlorate  and  chloride : — 

6KO+C16=KO.C105+5KC1. 

Hypochlorites  may  be  distinguished  from  the  bleaching  salts  by  their  com- 
portment with  acids.  The  former  yield  hypochlorous  acid,  the  latter  chlorine, 
when  treated  with  an  acid : — 

MO.C10+HO.S08=MO.S08+HO+C10. 

(MO.C10+MCl)+2(HO.S03)=2(MO.S03)2HO+Cla. 

The  hypochlorites  have  a  peculiar  astringent  taste ;  they  consist  of  1  eq.  of 
base  to  1  eq.  of  acid. 

Their  solutions,  as  well  as  those  of  the  bleaching  salts,  undergo  gradual  de- 
composition at  ordinary  temperatures.  When  boiled,  they  are  converted  into 
chlorates  and  chlorides : — 

3(MO.C1O)=MO.C105+2MC1. 

The  hypochlorites  possess  bleaching  properties,  but  the  most  powerful  action 
is  produced  by  adding  an  acid  to  the  chlorides  of  lime,  &c.,  since,  as  we  have 
just  seen,  chlorine  is  evolved.  Hypochlorites  have  the  power  of  converting 
low  metallic  oxides,  such  as  the  oxides  of  lead  and  manganese,  into  higher 
oxides. 

The  chlorides  of  soda  and  lime  are  used  most  extensively,  as  bleaching  and 
disinfecting  agents,  in  the  manner  above  described.  Their  oxidizing  action  upon 
certain  organic  substances  is  also  accompanied  by  the  production  of  beautiful 
though  transient  colors,  which  afford  the  chemist  suitable  means  for  testing  for 
such  compounds. 

EUCHLORINE. — This  gas  was  first  described  by  Sir  H.  Davy,  in  1811.  It  is 
evolved  when  1  part  of  chlorate  of  potassa  is  heated  with  two  parts  of  hydro- 
chloric acid  and  2  of  water.  It  has  a  bright  yellow  color,  a  smell  similar  in 
some  respects  to  chlorine,  though  peculiarly  sweet,  and  possesses  bleaching  pro- 
perties. It  contains  chlorine  and  oxygen  in  the  proportion  of  their  equivalents, 
like  hypochlorous  acid,  but  has  been  pretty  clearly  proved  to  be  a  mixture  of 
chlorine  and  peroxide  of  chlorine.  The  most  remarkable  circumstance  connected 
with  the  formation  of  this  gas,  is,  that  it  always  consists  of  the  same  proportions 


CHLOROUS   ACID.  139 

of  its  elements.     The  following  equation  may  explain  the  decomposition  of  chlo- 
rate of  potassa  by  hydrochloric  acid : — 

4(KO.C105)+12HCl=4KCl+C19+3C10f+12HO 

CHLOROUS  ACID,  C108.     Eg.  59.5.     Sp.  Gr.  2.646. 

§  95.  This  acid  is  produced  by  heating  a  mixture  of  chlorate  of  potassa  and 
nitric  acid  with  some  deoxidizing  agent  (such  as  arsenious  acid).  Its  formation 
seems  to  be  the  result  of  the  action  of  nitrous  acid,  produced  by  the  deoxidation 
of  nitric  acid,  upon  the  chloric  acid  : — 

N08+C105=N05+C103. 

Properties. — Chlorous  acid  is  a  dark  greenish -yellow  gas,  possessing  a  pungent 
odor  and  bleaching  properties.  It  may  be  condensed  to  a  red  liquid  by  exposure 
to  intense  cold. 

When  heated  to  135°  F.  (57°  C.)  it  explodes,  being  resolved  into  chlorine 
and  oxygen.  Contact  with  combustible  substances  likewise  causes  it  to  explode. 

Water  dissolves  about  six  times  its  volume  of  the  gas ;  the  color  of  the  solu- 
tion varies  from  green  to  yellow  according  to  its  degree  of  saturation.  It  pos- 
sesses bleaching  properties,  and  exerts  an  oxidizing  action  on  many  of  the  lower 
metallic  oxides.  Chlorous  acid  combines  with  bases  to  form  chlorites,  some  of 
which  are  crystallizable.  It  is  expelled  from  its  combinations  by  carbonic  acid. 

PEROXIDE  OP  CHLORINE,  HYPOCHLORIC  ACID,  CIO,.     JZq.  67.5. 
'Sp.  Gr.  2.338. 

Preparation. — Finely  powdered  chlorate  of  potassa  is  very  gradually  mixed 
into  a  paste  with  strong  sulphuric  acid,  and  gently  heated  in  a  bath  containing  a 
mixture  of  alcohol  and  water.  A  yellow  gas  is  disengaged,  which  must  be  cau- 
tiously collected  by  downward  displacement,  or  over  mercury,  upon  which,  how- 
ever, it  acts  considerably.  The  greatest  care  must  be  taken  not  to  raise  the 
temperature  too  high,  or  explosion  will  immediately  ensue ;  it  is,  indeed,  advi- 
sable for  the  operator  to  wear  an  iron  wire  mask.  The  chlorate  of  potassa 
employed  should  be  as  pure  and  dry  as  possible,  since  the  presence  of  water  or 
chloride  of  potassium  greatly  increases  the  risk  of  explosion.  The  decomposition 
is  expressed  by  the  following  equation : — 

3(KO.C105)-f2(HO.S03)=2(KO.S03)+KO.C107-f-2C104+2HO. 

Properties. — Peroxide  of  chlorine  is  a  yellow  gas,  of  rather  brighter  color  than 
chlorine,  and  a  somewhat  aromatic  smell.  It  destroys  the  color  of  moist  litmus 
paper.  The  gas  may  be  converted  by  pressure  at  0°  F.  ( — 18°  C.)  into  a  deep 
yellow,  mobile,  transparent  fluid,  which  evaporates  rapidly  on  exposure  to  air, 
and  is  highly  explosive.  Peroxide  of  chlorine  is  easily  decomposed,  either  by 
exposure  to  light,  by  heat,  or  by  the  electric  spark.  It  also  explodes  violently 
if  brought  into  contact  with  sulphur  or  phosphorus.  It  is  somewhat  soluble  in 
water;  the  solution  is  rapidly  decomposed  on  exposure  to  sunlight.  Water  also 
forms  a  solid  hydrate  when  poured  upon  the  liquid  peroxide  of  chlorine  at  32° 
F.  (0°  C.) 

When  brought  into  contact  with  an  alkali,  peroxide  of  chlorine  appears  to  be 
converted  into  chloric  and  chlorous  acids: — 

2KO  +  '2C104=KO.C105+KO.C103, 

and  hence  the  existence  of  this  substance  as  an  independent  acid  is  much 
doubted. 

CHLORIC  ACID,  C105  (anhydrous).     Eq.  75.5. 
This  acid  is  produced  by  boiling  the  solution  of  a  hypochlorite;  or  by  passing 


140 


CHLORINE  AND   OXYGEN. 


chlorine  into  a  hot  concentrated  solution  of  an  alkali.     Hypoehlorous  acid  is  first 
produced : — 

6KO  +  C16=3(KO.C10)  +  3KC1, 

which  is  subsequently  decomposed  as  follows  : — 

3(KO.C10)+3KC1=KO.C105+5KC1. 

Properties. — Chloric  acid  has  not  been  obtained  in  the  anhydrous  state;  its 
concentrated  solution  (obtained  by  adding  an  equivalent  proportion  of  sulphuric 
acid  to  chlorate  of  baryta,  and  submitting  the  decanted  liquid  to  spontaneous 
evaporation  in  vacua)  is  colorless,  and  has  highly  acid  properties;  it  has  an  oily 
appearance  and  a  pungent  smell ;  paper  dropped  into  it  takes  fire ;  it  is  decom- 
posed at  temperatures  above  104°  F.  (40°  C.);  when  boiled  it  is  converted  into 
perchloric  acid,  chlorine,  and  oxygen  : — 

2C105=C107+C1+03. 

Chloric  acid  is  not  decomposed  by  light;  its  oxidizing  properties  are  very 
powerful. 

The  compounds  of  chloric  acid  with  bases,  called  chlorates,  are  decomposed  by 
heat ;  in  most  cases  the  oxygen  contained  in  the  salt  is  evolved,  metallic  chlorides 
remaining  behind.  , 

When  mixed  with  combustible  substances,  such  as  phosphorus,  sulphur,  sugar, 
antimony,  arsenic,  &c.  chlorates  explode,  frequently  with  great  violence,  either 
by  friction,  or  by  the  application  of  heat;  in  these  cases  the  combustible  sub- 
stances extract  the  oxygen,  which  is  in  a  state  of  but  feeble  combination  with  the 
chlorine.  Chlorates  are  decomposed  by  concentrated  sulphuric  acid,  the  chloric 
acid  being  converted  into  perchloric  and  hypochloric  acids,  with  disengagement 
of  chlorine  and  oxygen.  The  decomposition  is  attended  by  decrepitation  and 
the  disengagement  of  heat,  frequently  so  considerable  as  to  produce  detonation 
and  flashes  of  light.  A  mixture  of  chlorate  of  potassa  with  an  equal  bulk  of 
sugar  inflames  when  brought  into  contact  with  a  small  quantity  of  oil  of  vitriol. 

Chlorates  are  also  decomposed  by  nitric  acid,  the  chloric  acid  being  converted 
into  peroxide  of  chlorine,  chlorine,  and  oxygen.  Hydrochloric  acid,  when  added 
to  a  chlorate,  evolves,  as  just  now  stated,  a  yellow  gas  known  by  the  name  of 
euchlorine. 

The  chlorates  are  soluble  in  water;  some  of  them  to  such  an  extent  as  to  be 
deliquescent.  Their  solutions  have  no  action  on  vegetable  colors,  unless  mixed 
with  a  free  acid,  when  a  bleaching  property  is  imparted  to  them  by  the  decom- 
position of  the  salt. 

Uses  of  Chlorates  — Chloric  acid  in  the  free  state  has  met  with  no  application, 
on  account  of  the  difficulties  attending  its  preparation  in  any  considerable  quan- 
tity ;  the  explosive  property  of  chlorates  when  mixed  with  combustible  substances 
has  been  turned  to  considerable  advantage  in  the  preparation  of  detonating  mix- 
tures, chlorate  of  potassa  being  the  salt  most  generally  employed.  This  salt, 
mixed  with  phosphorus,  sulphur,  &c.  forms  the  principal  mixture  for  the  prepa- 
ration of  lucifer  matches. 

CHLOROCHLORIC  ACID.     C13013=2C10S.C103. 

Millon  has  found  that  by  passing  euchlorine  through  several  U-tubes  surrounded 
by  freezing  mixtures,  a  red  liquid  was  condensed,  resembling  liquid  peroxide  of 
chlorine;  it  is  soluble  in  water,  boils  at  about  89.6°  F.  (32°  C.),  and  does  not 
explode  below  a  temperature  of  158°  F.  (70°  C.)  Like  peroxide  of  chlorine,  it 
yields  a  chlorate  and  a  chlorite  when  treated  with  potassa ;  the  proportions  of  the 
salts  formed  are,  however,  2  eqs.  of  chlorate  to  1  of  chlorite.  Hence,  he  assigns 
to  this  acid  the  above  composition. 


CHLOROPERCHLORIC  ACID.  141 

PERCHLORIC  ACID,  C107.     Eq.  91.5. 

Preparation. — This  acid  is  produced  when  chloric  acid  is  distilled ;  and  when 
chlorate  of  potassa  is  acted  upon  by  oil  of  vitriol  at  a  gentle  heat,  peroxide  of 
chlorine  being  simultaneously  produced,  as  has  been  already  shown.  It  is  also 
formed  when  peroxide  of  chlorine  is  acted  upon  by  the  galvanic  current.  The 
most  convenient  mode  of  obtaining  it,  however,  is  by  heating  chlorate  of  potassa 
until  one-third  of  its  oxygen  is  expelled, 

2  (KO.C105)=KO.C107-f  KCl-f  04, 

purifying  the  perchlorate  from  the  chloride  by  crystallization  (the  former  being 
far  more  insoluble  than  the  latter),  and  distilling  the  perchlorate  with  an  equal 
weight  of  sulphuric  acid,  first  diluted  with  half  its  weight  of  water.  The  aqueous 
perchloric  acid  thus  obtained  is  freed  from  sulphuric  acid  by  treatment  with 
baryta- water,  and  from  chlorine  by  digestion  with  oxide  of  silver ;  the  dilute  acid 
is  concentrated  by  gentle  evaporation. 

Properties. — Perchloric  acid,  when  concentrated,  fumes  slightly  on  exposure 
to  air;  it  is  colorless,  has  an  oily  appearance,  and  boils  at  392°  F.  (200°  C.) 

Unlike  the  other  compounds  of  chlorine  with  oxygen,  this  acid  does  not  possess 
bleaching  properties.  It  is  the  most  stable  of  the  oxides  of  chlorine,  and  its 
affinity  for  bases  is  considerable. 

The  perchlorates  are  generally  formed  from  the  potassa  or  baryta  salts  (ob- 
tained as  above  from  the  chlorates)  by  mixing  their  solutions  with  the  silicofluo- 
rides  or  sulphates.  They  are  all  soluble,  and  mostly  deliquescent,  and  are  decom- 
posed by  heat,  like  the  chlorates,  though  with  less  facility.  They  explode  when 
thrown  on  ignited  charcoal,  but  are  less  powerful  in  their  action  than  the  chlo- 
rates. 

CHLOROPERCHLORIC  ACID.     C13017=2C107.C103. 

This  acid  is  formed  by  the  action  of  light  upon  chlorous  acid.  By  exposing 
this  gas  (perfectly  dry)  to  sunlight  or  diffused  daylight,  it  is  decomposed  into 
perchloric  acid,  oxygen,  and  chlorine.  If,  however,  the  bottle  is  immersed  in 
water,  and  thus  submitted  to  the  action  of  light,  at  a  temperature  of  68°  F.  (20° 
C.),  a  reddish  liquid  is  produced,  which  forms  dense  fumes  when  exposed  to 
moist  air,  and  is  decomposed  by  heat.  When  treated  with  potassa,  it  yields  2 
equivalents  of  perchlorate  and  1  equivalent  of  chlorite  of  potassa ;  this  shows  it 
to  have  the  above-mentioned  formula. 

Of  the  above  compounds  of  chlorine  with  oxygen,  five  are  very  similar  to  each 
other,  namely,  CIO,  C103,  C104,  C13013,  and  C13O17;  it  is,  therefore,  not  easy  to 
distinguish  them  perfectly  one  from  another.  Much  attention  has  been  paid  of 
late  to  the  oxygen  compounds  of  chlorine  by  several  chemists.  Millon  adopts  a 
view  regarding  the  constitution  of  these  compounds,  by  which  an  easy  explana- 
tion of  the  conversion  of  chloric  into  perchloric  acid,  and  some  other  phenomena 
exhibited  by  these  oxygen  compounds  of  chlorine,  is  afforded.  The  following 
table  exhibits  the  formulae  of  these  acids,  and  Millon's  view  regarding  their  con- 
stitution : — 

Hypochlorous  acid  .  CIO 

Chlorous  acid      .     .  C103 

Hypochloric  acid     .  C104=Cl4016=3C103-f  C107 

Chloric  acid  .     .     .  C105=ClaOM=  C103+  C107 

Chlorochloric  acid    .  C13013  =2C103-f  C107 

Chloroperchloric  acid  C130I7  =  C103+2C107 

Perchloric  acid  .     .  C107 


142  CHLORINE  AND  HYDROGEN. 


CHLORINE   AND   HYDROGEN. 

HYDROCHLORIC  ACID,  MURIATIC  ACID. 
HC1.    Eq.  36.5.    Sp.  Gr.  1.284. 

Composition  l>y  Volume. — 2  volumes  of  chlorine  and  2  volumes  of  hydrogen 
combine  to  form  4  volumes  of  this  acid. 

§  96.  Hydrochloric  acid  has  been  discovered,  in  the  uncombined  state,  in  a 
thermal  spring  in  New  Grenada  (S.  America). 

Chlorine  and  hydrogen,  when  mixed  in  equal  volumes,  may  be  made  to  com- 
bine by  exposure  to  sunlight,  to  flame,  to  the  electric  spark,  or  to  the  action  of 
spongy  platinum,  and  of  diffused  daylight;  and  also  when  passed  through  a  red- 
hot  tube.  In  the  four  first  cases,  the  combination  is  attended  by  explosion. 

The  affinity  of  chlorine  for  hydrogen  is  so  great  as  to  cause  the  decomposition 
of  most  hydrogen  compounds.  Many  organic  substances  are  decomposed  by 
chlorine  at  ordinary  temperatures  (oil  of  turpentine,  for  example),  hydrochloric 
acid  being  formed.  Others  require  a  high  temperature  or  contact  with  flame 
(olefiant  or  coal-gas,  for  instance). 

Preparation. — The  usual  method  of  preparing  hydrochloric  acid  gas  is,  to  heat 
a  mixture  of  fused  chloride  of  sodium  and  concentrated  sulphuric  acid ;  the  gas 
being  dried  by  passing  it  through  oil  of  vitriol. 

The  decomposition  is  expressed  by  the  equation  : — 

NaCl  +  HO.S08=NaO.SO,+HCl. 

(The  gas  being  soluble  in  water,  must  be  collected  over  mercury,  or  even  by  dis- 
placement.) 

Properties. — Hydrochloric  acid  is  a  colorless  gas,  of  a  peculiar,  suffocating, 
pungent  odor;  it  does  not  support  respiration  or  combustion,  neither  is  it 
combustible.  It  reddens  vegetable  blues,  but  possesses  no  bleaching  properties. 
It  may  be  liquefied  by  exposure  to  a  pressure  of  about  40  atmospheres,  at 
50°  F.  (45°. 3  C.)  It  forms  a  colorless  liquid,  of  lower  refractive  power  than 
•water. 

Hydrochloric  acid  gas  forms  dense  fumes  when  exposed  to  damp  air,  in  conse- 
quence of  its  condensing  the  aqueous  vapor;  water  absorbs  it,  with  a  considerable 
rise  of  temperature,  taking  up,  at  ordinary  temperatures,  nearly  its  own  weight, 
or  480  times  its  volume.  If  a  flask  filled  with  the  gas  be  opened  under  water, 
the  latter  rushes  in  with  great  violence. 

SOLUTION  OF  HYDROCHLORIC  ACID  (formerly  called  spirit  of  salt)  is  best  pre- 
pared by  heating  a  mixture  of  6  parts  of  chloride  of  sodium  and  10  of  concen- 
trated sulphuric  acid,  previously  diluted  with  4  parts  of  water,  in  a  capacious 
glass  retort  or  flask,  connected  with  a  set  of  Woulfe's  bottles,  arranged  similarly 
to  those  employed  for  the  preparation  of  solution  of  ammonia.  The  bulk  of  the 
water  employed  for  the  absorption  of  the  gas  increases  considerably;  the  hydro- 
chloric acid  obtained  in  the  second  bottle  is  perfectly  colorless  and  pure,  having 
a  spec.  grav.  of  about  1.21.  The  water  in  the  third  bottle  serves  to  retain  any 
portion  of  acid  that  may  escape  through  the  second. 

The  hydrochloric  acid  of  commerce,  common  muriatic  acid,  is  prepared  by 
heating  a  mixture  of  equal  equivalents  of  salt  and  oil  of  vitriol  in  capacious  hori- 
zontal cast-iron  cylinders,  and  conducting  the  gas  evolved  into  bottles  containing 
water  as  above. 

This  acid  generally  contains  several  impurities,  the  chief  of  which  are  sulphuric 
and  sulphurous  acids,  and  chlorine,  and  at  times,  also,  chloride  of  arsenic,  tin,  or 


HYDROCHLORIC  ACID.  143 

iron  (the  two  former  from  the  commercial  oil  of  vitriol).1  For  modes  of  testing 
for  impurities  in  hydrochloric  acid,  see  Analysis,  Reagents. 

Properties. — Solution  of  hydrochloric  acid,  when  pure,  is  colorless,  and  has  a 
pungent  but  pure  acid  odor;  when  concentrated,  it  evolves  dense  fume's  on  expo- 
sure to  air;  its  spec,  grav.,  when  in  the  most  concentrated  state,  is  1.2109;  it 
then  contains  hydrochloric  acid  in  the  proportion  of  1  to  6  of  water.  When 
boiled,  it  evolves  hydrochloric  acid  gas,  and  the  boiling-point,  which  is  at  first 
considerably  below  212°,  rises  as  the  aqueous  acid  becomes  weaker;  at  a  tem- 
perature rather  higher  than  212°  F.  (100°  C.)  the  acid  distils  over  unchanged; 
its  spec.  grav.  is  then  about  1.1. 

When  metallic  oxides  are  treated  with  hydrochloric  acid,  the  corresponding 
chlorides  are  produced,  water  being  simultaneously  formed  by  the  combination  of 
the  hydrogen  in  the  acid  with  the  oxygen  of  the  base ;  the  following  general 
formula  represents  the  action  of  this  acid  : — 

MO+HCl=MCl-fHO. 

When  solution  of  hydrochloric  acid  is  exposed  for  some  time  to  the  solar  rays, 
chlorine  is  liberated  (Fischer). 

Uses  of  Hydrochloric  Acid. — This  acid  is  much  used  in  the  manufacture  of 
bleaching-powder,  and  of  glue.  It  is  also  employed  for  dissolving  metals,  and  for 
preparing  the  chlorides. 

NITRO-HYDROCHLORIC,  OR  NiTRO-MuRiATic  ACID.  Aqua  regia. — When  1 
part  of  nitric  acid  is  mixed  with  2  or  3  parts  of  hydrochloric  acid,  they  decom- 
pose each  other,  yielding  a  yellow  fuming  liquid  of  highly  corrosive  nature,  pos- 
sessing the  power  of  dissolving  gold  and  platinum,  which  are  not  acted  upon  by 
either  of  the  acids  separately. 

When  a  metal  is  acted  upon  by  this  liquid,  it  is  converted  into  a  chloride,  an 
inferior  oxide  of  nitrogen  being  evolved. 

Various  opinions  have  been  entertained  respecting  the  true  constitution  of 
nitro-muriatic  acid.  E.  Davy  believes  the  liquid  to  contain  a  compound  of  equal 
volumes  of  chlorine  and  nitric  oxide,  to  which  he  has  given  the  name  of  chloro- 
nitrous  acid  (N03C13).  Baudrimont  obtained  from  a  mixture  of  2  parts  of  nitric 
acid  and  3.  of  hydrochloric  acid,  a  red  gas,  condensing  at  a  low  temperature,  and 
rapidly  absorbed  by  water;  he  calls  this  compound  chloronitric  acid,  considers  it 
to  have  the  composition  N03C13,  and  explains  its  formation  by  the  following 
equation : — 

N05-f2HCl=N03Cl2-f-2HO. 

Gay-Lussac  obtained,  by  submitting  the  gases  evolved  by  boiling  nitro-hydro- 
chloric  acid  to  a  freezing  mixture,  a  lemon-yellow  liquid,  to  which  he  has  assigned 
the  formula  NOaCla,  and  the  name  hypochloronitric  acid,  since  he  views  it  as 
hyponitric  acid,  in  which  two  atoms  of  chlorine  replace  two  of  oxygen. 

Its  formation  would  be  explained  thus  : — 

N05+3HC1=N02C13+3HO  +01. 

By  the  latter  explanation,  the  evolution  of  chlorine  is  accounted  for,  which  is 
always  observed  in  the  preparation  of  nitro-muriatic  acid. 

The  action  appears,  however,  to  be  of  a  more  complicated  nature,  since  Gay- 
Lussac  also  found  the  above  condensed  product  to  contain  a  compound  of  1  of 
chlorine  to  1  of  nitric  oxide,  N03C1,  to  which  he  gave  the  name  of  chloronitrous 
acid.  According  to  this  chemist,  when  a  metal,  such  as  gold,  is  acted  upon  by 
aqua  reyia,  the  chlorine  evolved  from  the  latter  combines  with  the  metal,  and 
chloronitric  acid  is  evolved ;  hence,  he  believes  the  action  of  nitro-muriatic  acid 
upon  gold  to  be  due  to  the  chlorine  liberated  in  the  decomposition  of  the  two  acids. 

1  The  Bellow  color  of  the  hydrochloric  acid  of  commerce  is  owing  to  the  presence  of 
sesquioxide  of  iron,  or  of  free  chlorine. 


144  CHLORIDES   OF   THE   METALS. 


CHLORINE    AND    NITROGEN. 

CHLORIDE  or  NITROGEN. 
according  to  Davy  (NC14)  156.]    Sp.  Gr.  1.653. 

§  97.  This  compound  is  obtained  by  passing  chlorine  gas  through  a  solution 
of  chloride  of  ammonium,  or  by  inverting  a  jar  of  chlorine  over  a  solution  of  that 
salt  at  a  temperature  of  80.6°  F.  (32°  C.)  : — 

NH4Cl+Cli=NCl4+4HCL 

As  the  gas  is  slowly  absorbed  by  the  solution,  an  oily  liquid  is  formed  on  the 
surface  of  the  latter,  falling,  after  a  time,  in  drops  to  the  bottom  of  the  vessel. 
These  should  be  carefully  collected  by  means  of  a  syringe,  and  transferred  to  a 
perfectly  clean  thick  cup  of  lead.  The  greatest  care  is  necessary  in  the  prepa- 
ration of  this  liquid,  and  it  is  prudent  for  the  operator  to  protect  himself,  as  far 
as  possible,  from  injury  arising  from  probable  explosion,  by  means  of  gloves  and 
an  iron  mask. 

Properties. — Chloride  of  nitrogen  is  an  oily  liquid  of  a  light  yellow  color,  which 
volatilizes  rapidly  in  air;  it  does  not  freeze  at  — 40°  F.  ( — 40°  C.),  and  distils 
below  160°  F.  (71°  C.)  Its  odor  is  pungent,  and  its  vapor  attacks  the  eyes. 
It  possesses  the  remarkable  property  of  exploding  when  brought  into  contact  with 
phosphorus,  arsenic,  fats,  essential  and  fatty  oils,  &c.,  or  even  spontaneously,  at 
times.  It  is  more  gradually  decomposed  by  some  acids,  alkalies,  and  saline  solu- 
tions. In  the  former  cases,  the  products  of  decomposition  are  chlorine  and  nitrogen 
gases;  in  cases  of  more  gradual  decomposition,  the  resulting  products  vary.  Ma- 
nipulations with  this  liquid  have  been  frequently  attended  with  disastrous  conse- 
quences. Dulong,"the  discoverer,  lost  an  eye  and  several  fingers;  Davy  was  also 
deprived  of  the  sight  of  an  eye  through  experimenting  with  it.  The  quantity 
operated  upon  in  any  case  should  therefore  be  very  small,  the  vessels  employed 
must  be  perfectly  clean,  and  the  operator  should  be  properly  protected,  as  recom- 
mended above. 

Several  views  may  be  taken  of  the  composition  of  chloride  of  nitrogen.  It  is 
not  even  certain  that  it  contains  no  hydrogen ;  its  peculiar  nature  renders  it 
exceedingly  difficult  to  establish  its  formula  with  any  degree  of  certainty. 

CHLORIDES   OF  THE   METALS. 

Chlorine  combines  with  the  metals  in  various  proportions,  the  chlorides  of  a 
metal  usually  corresponding  to  its  oxides.  These  compounds  are  either  produced 
by  direct  combination  of  chlorine  with  the  metals,  or  by  solution  of  the  oxides  in 
hydrochloric  acid,  as  above  stated. 

Chlorine  also  decomposes  many  metallic  oxides  forming  the  corresponding 
chlorides,  oxygen  being  evolved,  or  a  chlorate,  or  hypochlorite,  simultaneously 
formed.  Some  metals,  such  as  zinc  and  iron,  exert  a  decomposing  action  on 
hydrochloric  acid,  chlorides  being  formed,  and  hydrogen  liberated.  Some  chlo- 
rides are  also  produced  when  chlorine  is  allowed  to  act  upon  the  oxides  in  the 
presence  of  a  reducing  agent  (charcoal).  Thus,  though  chlorine  will  not  act  on 
sesquioxide  of  chromium  alone,  a  mixture  of  this  oxide  with  charcoal,  exposed 
to  the  action  of  chlorine  at  a  high  temperature,  furnishes  sesquichloride  of  chro- 
mium, the  oxygen  forming  carbonic  oxide  with  the  charcoal : — 
Cr303+Cl3+C3=CrflCl3+3CO. 

Some  chlorides  of  the  metals  are  liquid  at  ordinary  temperatures  (for  example, 


BROMINE.  145 

the  bichloride  of  tin,  and  the  pentachloride  of  antimony);  others  are  solid.  Many 
metallic  chlorides  are  volatile.  They  are  all  soluble  in  water  with  the  exception 
of  chloride  of  silver,  subchloride  of  mercury,  subchloride  of  copper,  and  the  pro- 
tochlorides  of  gold  and  platinum.  Many  of  the  soluble  salts  crystallize,  from 
their  aqueous  solutions,  either  as  anhydrous  or  hydrated  chlorides  (e.  g.  chloride 
of  barium,  BaCl-f  2HO,  and  chloride  of  calcium,  CaCl-f  6HO),  most  of  which 
part  with  their  water  of  crystallization  when  heated,  while  one  or  two  yield 
hydrochloric  acid,  metallic  oxides  remaining  behind.  Some  chlorides  in  the 
anhydrous  state  have  a  very  powerful  affinity  for  water,  deliquescing  rapidly  when 
exposed  to  damp  air.  These  are  frequently  used  as  desiccators  or  dehydrators 
(e.  g.  the  chlorides  of  zinc  and  calcium). 

Oxychlorides  form  a  peculiar  class  of  salts,  produced  by  the  combination  of 
the  metallic  chlorides  with  oxides  of  the  same  metals  (for  example,  oxychloride 
of  lead,  PbCl.SPbO,  and  oxychloride  of  antimony,  SbCl3.5Sb03). 


BROMINE.1 

Sym.  Br.     Eq.  80.     Sp.  Gr.  2.966. 

§  98.  Bromine  was  discovered  by  Balard,  in  1826.  It  is  found  in  minute 
quantities  in  sea-water  (as  bromide  of  magnesium,  or  of  an  alkaline  metal) ;  it 
occurs  in  rather  large  quantities  in  many  mineral  springs  (for  instance,  those  of 
Kreutznach  and  Cheltenham),  and  exists  also  in  many  marine  plants  and  ani- 
mals. Minute  quantities  of  bromine  have  also  been  detected  in  coal. 

Preparation. — The  solution  of  alkaline  bromides,  obtained  from  evaporated 
sea  or  spring-waters,  or  from  the  ashes  of  marine  plants,  is  submitted  to  a  cur- 
rent of  chlorine  until  the  yellow  color  produced  no  longer  increases  in  depth. 
The  bromine  is  thus  liberated  (being  replaced  in  its  combinations  by  chlorine); 
the  liquid  is  then  shaken  with  ether,  by  which  the  bromine  is  extracted. 

The  ethereal  solution  of  bromine  which  rises  to  the  surface,  is  separated  from 
the  saline  solution,  and  agitated  with  a  strong  solution  of  potassa,  by  which  the 
bromine  is  converted  into  bromate  of  potassa,  and  bromide  of  potassium  : — 
6KO+Br6=5KBr-fKO.Br05. 

The  alkaline  solution  is  then  separated  from  the  ether,  and  evaporated  to  dry- 
ness,  the  residue  fused  (whereby  the  bromate  of  potassa  is  converted  into  bromide 
of  potassium),  and  afterwards  distilled  with  binoxide  of  manganese  and  sulphuric 
acid,  diluted  with  half  its  weight  of  water  : — 

KBr  +  Mn02+2(HO.S03)=KO.S03+MnO.S03+2HO+Br. 

The  bromine  thus  obtained  is  freed  from  water  by  rectification  over  fused  chlo- 
ride of  calcium.  Commercial  bromine  generally  contains  bjomide  of  carbon. 

Properties. — Bromine  is  a  heavy,  mobile  liquid,  appearing  dark  brownish-red 
by  reflected  light,  and  hyacinth-red  by  transmitted  light.  It  solidifies  at  about 
— 7°. 2  F.  •( — 22°  C.)  to  a  yellowish-brown,  brittle,  crystalline  mass,  volatilizes 
very  rapidly  when  exposed  to  the  air,  and  boils  at  about  145°  F.  (63°  C.)  Its 
vapor  (sp.  gr.  5.3933)  resembles  peroxide  of  nitrogen  in  color,  and  has  a  very 
disagreeable  pungent  smell.  It  is  poisonous  (though  not  quite  so  powerful  in  its 
action  as  chlorine),  giving  rise  when  inhaled  to  cough,  and  increased  secretion  of 
the  mucous  membrane,  accompanied  at  times  with  giddiness  and  other  unpleasant 
effects.  A  drop  placed  on  the  hand  immediately  destroys  the  cuticle,  producing 
a  sore.  Bromine  has  a  close  analogy  to  chlorine  in  its  chemical  relations;  the 

1  From  fyZftoti  a  stench. 
10 


146  BROMINE  AND  HYDROGEN. 

latter  being,  however,  the  more  powerful  in  its  affinities.  Bromine,  nevertheless, 
combines  with  great  energy  with  most  other  elements.  Thus,  phosphorus  and 
antimony  take  fire  spontaneously,  when  introduced  into  bromine  vapor.  Like 
chlorine,  also,  it  bleaches  organic  coloring  matters,  and  for  a  similar  reason. 

One  part  of  bromine  is  soluble  in  33.3  parts  of  water  at  59°  F.  (15°  C.) 
The  solution  has  a  yellowish-red  color,  and  gradually  decomposes  when  kept, 
especially  on  exposure  to  light,  hydrobromic  acid  being  formed.1  Bromine  gives 
a  yellowish-red  color  with  starch. 

Its  principal  compound  with  oxygen  is  bromic  acid,  Br05;  with  hydrogen  it 
forms  hydrobromic  acid,  HBr.  Bromine  is  also  known  in  combination  with 
carbon,  chlorine,  and  iodine,  and  forms  bromides  with  many  metals,  quite  analo- 
gous to  the  corresponding  chlorides. 


BROMINE    AND    OXYGEN., 

§  99.  When  bromine  is  added  to  a  cold  dilute  solution  of  fixed  alkali,  either 
in  the  caustic  state,  or  as  carbonate,  a  solution  is  obtained  possessing  bleaching 
properties;  the  analogy  which  bromine  exhibits  to  chlorine  in  so  many  instances, 
renders  it  probable  that  in  this  case  a  compound  of  bromine  and  oxygen  similar 
to  hypochlorous  acid,  namely,  hypobromous  acid,  BrO,  is  formed,  producing 
bleaching  compounds  when  united  to  ba'ses.  Comparatively  little  is  known, 
however,  with  regard  to  the  true  nature  of  the  above  reaction. 

BROMIC  ACID,  Br05.     Eq.  120. 

This  acid  is  produced  when  bromine-water  is  mixed  with  an  excess  of  solution 
of  potassa  (see  Preparation  of  Bromine),  or  heated  with  hypochlorous  acid, 
chlorine  being  disengaged;  it  is  also  formed  when  pentachloride  of  bromine  is 
acted  upon  by  potassa : — 

BrCl5+6KO=5KCl+KO.Br05. 

Preparation. — Bromic  acid  is  best  obtained  by  decomposing  a  solution  of 
bromate  of  baryta  with  an  equivalent  quantity  of  sulphuric  acid,  separating  the 
sulphate  of  baryta  formed,  and  concentrating  the  clear  liquid  by  gentle  evapora- 
tion. 

Properties. — Bromic  acid  has  not  been  obtained  in  an  anhydrous  state.  In 
combination  with  water  it  forms  a  colorless  liquid,  reddening  litmus,  and  bleach- 
ing it  after  a  little  time. 

It  volatilizes  when  heated,  being  partially  decomposed  into  bromine  and 
oxygen.  In  most  of  its  properties  it  is  analogous  to  chloric  acid. 

Bromates  are  mostly  soluble  in  water.  When  heated  to  redness,  they  are 
decomposed,  bromides  being  in  some  cases  formed,  and  oxygen  evolved;  in  other 
cases  the  oxides  are  obtained  with  simultaneous  evolution  of  oxygen  and  bromine- 
vapor.  They  possess  explosive  properties  similar  to  those  of  the  chlorates. 


BROMINE    AND    HYDROGEN. 

HYDROBROMIC  ACID. 
HBr.     Eq.  81.     Sp.  Gr.  2.73. 

Composition  by  Volume. — 2  volumes  of  hydrogen  and  2  volumes  of  bromine 
form  4  volumes  of  the  gaseous  acid. 

1  When  a  solution  of  bromine  is  cooled  to  nearly  the  freezing-point  of  water,  crystal- 
line scales  are  obtained  of  a  hydrate  of  bromine,  having  the  formula  Br  -f-  10HO. 


METALLIC   BROMIDES.  147 

Bromine  and  hydrogen  may  be  made  to  combine  directly,  by  passing  them 
through  a  heated  tube,  especially  if  it  contain  platinum-sponge.  Hydrobromic 
acid  is  gradually  produced  by  exposure  of  bromine,  together  with  water,  to  the 
sun's  rays ;  but  is  most  readily  formed  when  those  two  bodies  are  brought  in 
contact  with  some  substance  having  a  powerful  affinity  for  oxygen  (some  de- 
oxidizing agent)  such  as  phosphorous,  sulphurous,  and  arsenious  acids,  metals, 
&c.  It  is  also  produced  with  ease  by  bringing  bromine  in  contact  with  most 
hydrogen  compounds,  such  as  hydrosulphuric  acid,  phosphide  of  hydrogen, 
hydriodic  acid,  or  ammonia.  Alcohol,  ether,  and  many  organic  substances, 
likewise  convert  bromine  into  hydrobromic  acid. 

Preparation. — This  acid  is  obtained  by  gently  heating,  in  a  small  retort, 
phosphorus  and  bromine,  together  with  a  very  little  water,  and  collecting  the 
gas  over  mercury.  Its  formation  is  represented  by  the  following  equation : — 

P+Br3+3HO=P03-f3HBr. 

It  may  also  be  prepared  by  moistening  6  parts  of  crystallized  sulphite  of  soda 
with  1  part  of  water,  adding  3  parts  of  bromine,  and  applying  heat. 

An  aqueous  solution  of  hydrobromic  acid  is  best  obtained  by  passing  hydro- 
sulphuric  acid  gas  through  water  containing  a  little  bromine,  and  adding  fresh 
quantities  of  the  latter  as  it  disappears  by  the  action  of  the  gas : — 

Br-f-HS=HBr+S. 

Some  sub-bromide  of  sulphur  is  formed  in  the  process,  which  is  decomposed 
by  water  into  hydrobromic  acid  and  sulphurous  acid : — 
2HO+2SaBr=2HBr+S02+S3. 

The  solution  of  hydrobromic  acid  thus  obtained  is  heated  rather  below  ebulli- 
tion, until  the  excess  of  hydrosulphuric  acid  is  expelled,  and  afterwards  sepa- 
rated by  filtration  from  the  sulphur. 

Properties. — Hydrobromic  acid  is  a  colorless  transparent  gas,  of  a  pungent 
odor  and  acid  taste.  It  reddens  litmus  powerfully,  and  fumes  on  exposure  to 
damp  air.  It  liquefies  at  —92°  F.  (— 68°.8  C.),  and  solidifies  at  —100°  F. 
( — 73°. 1  C.)  It  is  rapidly  absorbed  by  water,  with  evolution  of  heat;  the 
strongest  solution  of  hydrobromic  acid  has  a  spec.  grav.  of  1.29,  and  fumes  on 
exposure  to  air;  it  boils  at  a  temperature  below  212°  F.,  being  rendered  weaker; 
more  dilute  acid  boils  at  a  higher  temperature,  and  becomes  stronger  by  boiling. 
When  chlorine  is  mixed  with  hydrobromic  acid,  hydrochloric  acid  is  formed,  and 
bromine  liberated,  chloride  of  bromine  being  formed  if  the  chlorine  is  in  excess. 
Some  metals,  when  brought  into  contact  with  hydrobromic  acid,  decompose  it, 
forming  metallic  bromides  with  evolution  of  hydrogen;  the  oxides  of  metals 
also  decompose  hydrobromic  acid,  yielding  bromides  and  water.  The  properties 
of  metallic  bromides  will  be  presently  described. 

BROMINE  AND  CHLORINE. — When  chlorine  is  passed  through  bromine,  and 
the  vapors  evolved  condensed  by  a  freezing  mixture,  a  very  volatile  reddish-yel- 
low liquid,  the  chloride  of  bromine,  is  obtained.  It  emits  yellow  fumes,  of  a 
very  pungent  odor,  exciting  a  flow  of  tears.  If  water  is  present  in  the  bromine, 
bright  yellow  crystals  of  chloride  of  bromine  are  obtained. 

METALLIC  BROMIDES. — These  are  formed  either,  as  just  now  stated,  by  the 
action  of  hydrobromic  acid  on  some  metals,  or  on  metallic  oxides,  or  by  the  direct 
combination  of  bromine  with  the  metals. 

They  are  solid  at  ordinary  temperatures,  fuse  when  moderately  heated,  and 
are  volatile  at  high  temperatures.  In  most  of  their  properties  they  are  very 
analogous  to  chlorides ;  they  are  decomposed  by  the  action  of  chlorine,  the  latter 
replacing  the  bromine  in  its  combination  with  a  metal ;  they  are  also  decomposed 
by  hydrochloric  acid,  the  products  being  hydrobromic  acid  and  metallic  chlorides. 
Most  bromides  are  soluble  in  water.  They  sometimes  combine  with  their  corre- 
sponding oxides,  forming  oxybromides,  analogous  to  oxychlorides. 


148  IODINE. 


IODINE.1 

.     Eq.  127.1.     Sp.  Gr.  4.948. 

§  100.  Iodine  was  first  discovered  by  Courtois,  in  1812,  and  was  subsequently 
submitted  to  examination  by  Gay-Lussac  (in  1813-14). 

Iodine  is  found  in  many  saline  springs  and  mineral  waters  (existing  in  them 
as  iodides  of  sodium,  calcium,  or  magnesium).  It  also  occurs  in  very  minute 
quantities  in  sea- water,  but  more  abundantly  in  marine  plants  and  animals 
(sponge).  Iodine  likewise  exists  in  a  few  minerals.  Small  quantities  of  iodine 
have  recently  been  obtained  from  coal. 

Preparation. — Various  methods  are  employed  for  obtaining  iodine  from  the 
ashes  of  marine  plants,  &c.  That  most  generally  in  use  is  to  evaporate  the  aque- 
ous extract  until  most  of  the  other  salts  have  crystallized  out,  and  then  to  preci- 
pitate the  mother-liquor  with  a  mixture  of  two  and  a  half  parts  of  sulphate  of 
iron,  and  one  part  of  sulphate  of  copper.  The  subiodide  of  copper  is  thus  ob- 
tained, the  reaction  being  represented  by  the  following  equation  : — 

2(FeO.S03)+2(CuO.S03)-fKI=Cu3I+re203.3S034-KO.S03. 

Precipitate 

The  subiodide  of  copper,  when  heated  with  binoxide  of  manganese  and  sulphuric 
acid,  yields  iodine,  which  is  disengaged  in  violet  vapors,  condensing  to  black  crys- 
tals as  they  cool. 

A  method  of  preparing  iodine  from  the  mother-waters  has  lately  been  pro- 
posed, in  which  the  iodine  is  liberated  by  a  mixture  of  sulphuric  and  nitric  acids, 
and  separated  by  filtering  through  lampblack,  which  takes  up  the  iodine,  and 
yields  it  again  to  potassa.  The  alkaline  solution  is  then  evaporated  to  dryness, 
the  residue  ignited,  and  afterwards  distilled  with  binoxide  of  manganese  and 
sulphuric  acid. 

Properties. — Iodine  is  a  grayish-black  substance,  possessing  metallic  lustre, 
and  somewhat  resembling  plumbago  in  appearance.  Its  crystalline  forms  belong 
to  the  right  prismatic  system  (the  primary  form  being  the  acute  rhombic  octo- 
hedron).  It  is  soft  and  brittle,  fuses  at  224°. 6  NF.  (107°  C.)  solidifying  to  a 
laminated  mass  on  cooling.  It  boils  at  347°  F.  (175°  C.)  passing  over  into 
violet  vapors,3  which  condense  upon  cooling  into  crystals.  Iodine  resembles 
chlorine  somewhat  in  its  odor;  it  may  be  said  to  have  a  marine  smell ;  its  taste 
is  very  acrid  and  astringent.  Water  dissolves  iodine  very  sparingly  (one  part 
being  soluble  in  7000  of  water) ;  the  solution  has  a  brown  color.  It  is  far  more 
soluble  in  alcohol  and  ether,  forming  deep  brown-red  solutions;  and  is  also  solu- 
ble to  a  considerable  extent  in  solutions  of  hydriodic  acid  and  iodide  of  potassium. 
Iodine  is  destitute  of  bleaching  properties. 

Free  iodine  yields  a  deep  blue  color  with  starch,  and  imparts  a  transient  yel- 
low stain  to  the  skin,  and  other  organic  matters. 

This  element  combines  with  hydrogen,  oxygen,  phosphorus,  and  the  metals, 
like  chlorine  and  bromine ;  it  also  unites  with  the  two  latter  substances. 

Iodine  is  poisonous  when  taken  internally ;  small  quantities  may,  however,  be 
administered  medicinally. 

The  chief  Uses  of  Iodine  depend  upon  its  medicinal  properties.  It  is  employed 
principally  to  reduce  glandular  swellings,  and  in  scrofulous  diseases.  This  appli- 
cation of  iodine  arose  from  its  discovery  in  the  ashes  of  sponge,  for  a  long  period 
used  as  a  medicinal  agent. 

1  From  Ixht,  violet-colored.  2  The  vapor-density  of  iodine  is  8.716. 


IODIC   ACID.  149 

Iodine  is  also  employed  in  various  forms  (sometimes  in  conjunction  with  bro- 
mine), for  photographic  purposes.  The  iodine  of  commerce  is  sometimes  adul- 
terated with  plumbago  or  sulphide  of  antimony,  &c.,  which  will  be  left  behind 
when  the  iodine  is  volatilized  by  a  gentle  heat.1 


IODINE    AND    OXYGEN. 

lodic  acid I05. 

Periodic  acid I0r 

§  101.  The  existence  of  two  other  compounds  of  iodine  and  oxygen  has  been 
asserted  by  several  chemists,  although  nothing  definite  has  been  arrived  at  with 
regard  to  their  real  nature — namely,  iodic  oxide,  and  iodous  or  hypo-iodous  acid. 

Salts  have  been  obtained,  the  composition  of  which  is  expressed  by  the  formula, 
MO. 10;  the  acid  they  contain,  however,  has  never  been  satisfactorily  isolated; 
the  ease  with  which  these  salts  decompose  into  iodates  and  iodides,  renders  it 
even  possible  that  they  are  mixtures  of  those  salts. 

IODIC  ACID,  I05.     ^  167.1. 

When  iodine  is  left  in  contact  with  excess  of  chlorine,  together  with  a  quan- 
tity of  water,  hydrochloric  and  iodic  acids  are  formed;  or,  in  the  presence  of 
potassa,  the  chloride  of  potassium  and  iodate  of  potassa : — 

I-fCl5-f5HO=5HCl-fI05. 
I-fCl5+6KO=5KCl+KO.I05. 

When  iodine  is  dissolved  in  an  aqueous  solution  of  potassa,  iodate  of  potassa  is 
formed,  together  with  iodide  of  potassium : — 

I6+6KO=5KI+KO.I05. 

Preparation. — The  best  method  of  obtaining  iodic  acid,  consists  in  boiling 
iodine  with  the  strongest  nitric  acid,  in  a  capacious  and  long-necked  flask,  until 
it  is  perfectly  oxidized,  and  then  expelling  the  excess  of  nitric  acid  by  evapora- 
tion of  the  liquid  to  dryness,  resolution  in  water,  and  repeated  evaporation.  It 
may  also  be  prepared  from  the  iodate  of  baryta,  by  boiling  nine  parts  of  this  salt 
with  two  parts  of  diluted  sulphuric  acid,  filtering  off  the  precipitated  sulphate  of 
baryta,  and  evaporating  the  clear  solution. 

Properties. — Iodic  acid  crystallizes  from  its  solution  (previously  concentrated 
to  the  consistency  of  syrup)  in  six-sided  tables.  These  crystals  are  white  and 
translucent;  they  are  very  soluble  in  water,  and  but  slightly  so  in  alcohol. 
They  contain  one  atom  of  water,  which  is  expelled  at  338°  F. (170°  C.);  the 
anhydrous  acid  thus  obtained  again  yields  the  hydrate  when  in  contact  with 
water. 

Iodic  acid,  when  heated  to  fusion,  is  decomposed  into  oxygen  and  iodine  vapor. 
It  parts  with  its  oxygen  when  heated  with  combustible  substances;  the  decom- 
position is  not  accompanied  with  detonation.  It  is  also  decomposed  by  hydro- 
bromic,  hydrochloric,  hydrosulphuric,  and  sulphurous  acids,  the  iodine  being 
liberated.  This  reaction  is  taken  advantage  of  in  testing  for  sulphurous  acid, 
with  a  mixture  of  iodic  acid  and  starch. 

Metallic  oxides  combine  with  iodic  acid  in  three  different  proportions,  some 
iodates  containing  one,  some  two,  and  others  three  atoms  of  acid  to  one  of  base. 
Iodates  are  but  slightly  or  not  at  all  soluble  in  water ;  they  detonate  and  defla- 
grate when  heated  with  combustible  substances,  like  chlorates,  though  not  so 
powerfully.  They  are  converted  by  heat  into  metallic  iodides,  oxygen  being 

1  Iodide  of  cyanogen  has  also  been  found  in  iodine  of  commerce. 


150  IODINE   AND    HYDROGEN. 

alone  liberated ;  or  some  evolve  oxygen  and  iodine,  the  metallic  oxides  being 
obtained. 

PERIODIC  ACID,  I07.     Eq.  183.1. 

Preparation. — This  acid  is  formed  by  passing  chlorine  through  a  warm  mix- 
ture of  iodate  of  soda  and  caustic  soda;  periodate  of  soda  is  obtained,  being 
deposited  as  a  powder  upon  concentration  of  the  liquid.  The  free  acid  is  pre- 
pared by  precipitating  a  solution  of  the  periodate  in  cold  dilute  nitric  acid,  with 
nitrate  of  lead,  boiling  the  precipitate  (periodate  of  lead)  with  dilute  sulphuric 
acid,  filtering  off  the  sulphate  of  lead,  and  evaporating  the  clear  solution,  from 
which  the  acid  is  then  deposited  in  hydrated  crystals,  which  lose  their  water  at 
320°  F.  (160°  C.). 

Properties. — Periodic  acid  crystallizes  in  transparent  colorless  prisms,  having 
the  composition  I05.5HO.  They  deliquesce  in  air,  fuse  at  266°  F.  (130°  C.), 
and,  at  about  400°  F.  (204°. 5  C.)  are  converted  into  anhydrous  iodic  acid. 
Periodic  acid  is  but  slightly  soluble  in  alcohol,  and  less  so  in  ether.  It  yields  with 
nitrate  of  silver  a  precipitate  insoluble  in  nitric  acid.  The  acid  is  decomposed 
by  sulphurous  acid,-  hydrochloric  acid,  and  sulphuretted  hydrogen,  iodine  being 
liberated. 

The  periodates  generally  are  sparingly  soluble.  In  these  salts,  the  five 
equivalents  of  water  of  the  hydrated  acid  are  replaced,  in  part,  by  base.  There 
are  two  soda-salts,  having  respectively  the  composition,  2NaO.I07.3HO  and 
NaO.I07.4HO.  The  potassa-salt  has  the  formula  KO.IOr  The  baryta-salt, 
2BaO.I07.3HO.  The  lead-salt  3Pb0.2HO.I07.  They  are  decomposed  by  heat. 


IODINE    AND    HYDROGEN. 

HYDRIODOUS  ACID,  HI3. — This  acid  is  said  to  be  formed  by  exposing  a  solu- 
tion of  hydriodic  acid  to  the  air,  or  by  its  contact  with  excess  of  iodine. 

It  has  not  been  obtained  in  the  anhydrous  state;  its  solution  is  dark-brown, 
and  smells  of  iodine,  which  it  gradually  deposits  in  crystals  on  protracted  ex- 
posure to  air. 

HYDRIODIC  ACID,  HI.     Eq.  128.1.     Sp.  Gr.  4.43. 

Composition  by  Volume. — 2  volumes  of  iodine  and  2  volumes  of  hydrogen 
produce  4  volumes  of  hydriodic  acid. 

This  acid  is  produced  when  a  mixture  of  iodine-vapor  and  hydrogen  is  passed 
through  a  redhot  tube.  It  is  formed  in  far  larger  quantity  when  hydrogen  is 
passed,  together  with  iodine- vapor,  through  a  tube  containing  spongy  platinum 
gently  heated.  In  the  presence  of  some  substance  having  a  strong  affinity  for 
oxygen  (e.  g.  phosphorus),  iodine  decomposes  water  with  formation  of  hydriodic 
acid. 

Iodine  also  abstracts  the  hydrogen  from  phosphide  of  hydrogen,  hydrosulphuric 
acid,  ammonia,  and  some  organic  compounds. 

Preparation. — To  obtain  the  gaseous  acid,  one  part  of  phosphorus,  and  six- 
teen parts  of  iodine,  are  carefully  placed  in  alternate  layers  with  coarsely  pow- 
dered glass,  and  the  whole  covered  with  a  layer  of  the  glass  powder  (Fig.  64) ;  the 
mixture  is  heated  very  cautiously,  a  little  water  afterwards  added  to  decompose 
the  iodide  of  phosphorus,  and  the  gas  collected  over  mercury,  or  better,  by  dis- 
placement; a  safer  method  is  to  dissolve  fourteen  parts  of  iodide  of  potassium  in 
a  small  quantity  of  water,  to  add  one  part  of  phosphorus  and  twenty  of  iodine, 
and  heat  gently;  a  third  method  consists  in  heating  three  parts  of  iodine  with 
six  of  sulphite  of  soda  and  one  of  water.  Liquid  hydriodic  acid  is  obtained  by 


IODIDE   OF   NITROGEN.  151 

introducing  together,  in  a  sealed  bent  tube,  one  Fig.  64. 

part  of  iodine  and  two  of  persulphide  of  hydrogen, 
a  small  quantity  of  water  being  present  in  the 
tube  at  the  bend.  Upon  bringing  the  mixture 
(which  forms  a  yellowish-brown  liquid)  in  contact 
with  water,  sulphur  is  immediately  separated,  and 
hydriodic  acid  produced,  the  greater  part  of  which 
condenses,  in  the  opposite  extremity  of  the  tube, 
to  a  yellow  liquid.  By  exposure  to  a  temperature 
of  — 590.8  F.  (—51°  C.)  it  solidifies  to  a  trans- 
parent colorless  mass. 

Properties. — The  gaseous  acid  is  colorless  and 
transparent,  possessing  an  acid  taste  and  suffocat- 
ing odor,  similar  to  that  of  hydrochloric  acid ;  it 
fumes  on  exposure  to  air,  is  incombustible,  and 
does  not  support  combustion.  Hydriodic  acid  is 
absorbed  by  water  to  about  the  same  extent  as  hydrochloric  acid. 

An  aqueous  solution  is  best  obtained  by  passing  hydrosulphuric  acid  gas 
through  water,  in  which  finely-divided  iodine  is  suspended,  until  the  brown 
color  of  the  liquid  disappears ;  the  latter  is  then  separated  from  the  precipitated 
sulphur  by  filtration,  and  maintained  at  a  temperature  of  somewhat  above  ebul- 
lition until  the  excess  of  hydrosulphuric  acid  is  expelled.  The  production  of 
hydriodic  acid  is  shown  by  the  following  equation  : — 

I-fHS=HI  +  S. 

It  is  advisable  to  add  the  iodine  gradually  in  small  quantities,  as  the  solution 
becomes  colorless,  agitating  the  latter  repeatedly. 

A  solution  of  hydriodic  acid  may  also  be  obtained  by  decomposing  a  solution 
of  iodide  of  barium  by  an  equivalent  proportion  of  sulphuric  acid,  and  filtering 
the  liquid. 

The  most  concentrated  solution  boils  between  257°  and  262°  F.  (125°  and 
128°  C.)  It  fumes  on  exposure  to  air,  and  gradually  decomposes  if  kept,  oxy- 
gen being  absorbed  and  iodine  separated.  It  dissolves  a  considerable  quantity 
of  iodine,  forming  a  brown-red  solution. 

Hydriodic  acid  is  decomposed  when  passed  with  oxygen  through  a  redhot  tube, 
the  products  being  iodine  and  water.  It  is  also  decomposed  by  chlorine  and 
bromine,  with  the  formation  of  hydrochloric  or  hydrobromic  acid ;  by  several 
metals  (metallic  iodides  resulting) ;  and  by  some  few  acids  (nitric,  cone,  sulphuric, 
hypochlorous,  &c.). 

Metallic  oxides,  when  acted  upon  by  hydriodic  acid,  are  converted  into  iodides 
with  formation  of  water. 

IODIDE  OF  NITROGEN. — When  powdered  iodine,  or  chloride  of  iodine,  is 
treated  with  solution  of  ammonia,  a  black  powder  is  formed,  to  which  the  name 
of  iodide  of  nitrogen  is  given, 

Its  composition  is  not  accurately  known;  it  is  probably  either  NI  or  NI3.  It 
possesses  highly  explosive  properties;  even  when  allowed  to  dry  by  exposure  to 
air  at  ordinary  temperatures,  it  frequently  explodes  spontaneously,  being  resolved 
into  its  elements. 

When  any  quantity  is  prepared,  therefore,  it  should  be  divided  into  several 
portions  while  moist,  so  as  to  diminish  the  danger,  or  risk  of  total  loss,  by  spon- 
taneous explosion.  Friction,  a  slight  blow,  or  slight  'elevation  of  temperature, 
causes  instantaneous  explosion. 

Iodide  of  nitrogen  decomposes  under  water,  nitrogen  gas  being  evolved,  and 


152  IODINE. 

iodate  of  ammonia  or  iodide  of  ammonium  formed,  iodine  being  likewise  sepa- 
rated.1 

IODINE  AND  CHLORINE. — These  elements  combine  to  form  two  compounds  : — 

1.  The  Chloride  of  Iodine,  IC1,  is  produced  by  passing  dry  chlorine  over  dry 
iodine  until  a  perfectly  liquid  substance  is  formed,  or  by  distilling  one  part  of 
iodide  of  potassium  with  four  parts  of  chlorate  of  potassa.     This  compound  is 
also  produced  when  iodine  is  dissolved  in  aqua  regia.    It  is  a  reddish  oily  liquid, 
of  a  pungent  odor,  attacking  the  eyes  powerfully,  and  staining  the  skin.     It  is 
very  soluble  in  water,  and  is  also  soluble  in  alcohol ;  it  decolorizes  indigo  and 
litmus  solutions.     It  is  decomposed  by  heat  into  terchloride  of  iodine,  and  free 
iodine.     Ammonia  decomposes  it  into  chloride  of  ammonium  and  iodide  of 
nitrogen. 

2.  Terchloride  of  Iodine,  IC13. — This  compound  is  obtained  by  treating  iodine 
with  an  excess  of  chlorine,  or  iodic  acid  with  hydrochloric  acid.     It  is  an  orange- 
yellow  solid,  crystallizing  in  long  needles;  it  melts  at  between  68°  and  77°  F. 
(20°  and  25°  C.),  and  evolves  chlorine,  which  it  again  absorbs  as  it  cools.     It  is 
decomposed  by  water,  in  which  it  is  not  so  soluble  as  the  chloride. 

IODINE  AND  BROMINE. — Two  compounds  are  also  formed  by  iodine  and  bro- 
mine; the  one  by  bringing  iodine  in  contact  with  a  small  amount  of  bromine; 
this  is  termed  the  sub-bromide  of  iodine  ;  it  is  a  solid,  passing  over  into  reddish- 
brown  vapor  when  heated.  The  other  compound,  the  penta-bromide  of  iodine,  is 
produced  by  the  action  of  excess  of  bromine  upon  iodine.  It  is  a  dark-brown 
liquid,  pretty  soluble  in  water.  Both  these  compounds  yield,  on  treatment  with 
alkalies,  a  bromide  and  an  iodate. 

METALLIC  IODIDES. — These  are  produced  either  by  the  action  of  iodine  on 
metals,  or  of  hydriodic  acid  on  some  metals  or  metallic  oxides.  Some  are  exceed- 
ingly soluble  in  water  (alkaline  iodides)  crystallizing  like  the  chlorides;  most 
iodides  are  somewhat  soluble  in  water,  and  a  few  are  decomposed  by  it  into  the 
metallic  oxides  (which  are  precipitated),  and  into  hydriodic  acid.  Many  metal- 
lic iodides  possess  beautiful  colors.  When  heated  with  access  of  air,  the  greater 
number  are  decomposed,  iodine  being  evolved,  and  the  metallic  oxides  formed ; 
their  solutions  are  decomposed  by  chlorine  or  bromine  (or  solutions  of  these  ele- 
ments); they  are  likewise  decomposed  by  nitric  and  sulphuric  acids.  Some 
iodides  also  combine  with  the  corresponding  oxides,  forming  oxyiodides. 

Chlorine,  bromine,  and  iodine  sometimes  exert  a  remarkable  and  interesting 
action  upon  organic  substances,  consisting  in  the  removal  of  one  or  more  equiva- 
lents of  hydrogen,  and  its  replacement  by  an  equivalent  quantity  of  one,  or  even 
two,  of  the  salt- radicals,  thus  giving  rise  to  a  very  important  class  of  substitution- 
products. 

We  may  take  this  opportunity  of  directing  attention  to  the  interesting  specu- 
lations of  Dumas  with  regard  to  the  remarkable  relation  observed  between  the 
atomic  weights  of  certain  elements. 

This  eminent  chemist  has  pointed  out  the  circumstance  that  there  are  certain 
groups  or  triads  of  elements,  resembling  each  other  in  their  most  important  pro- 
perties, the  equivalents  of  which  are  in  such  a  ratio  that  the  sum  of  the  extremes 
is  equal  to  twice  the  mean.  Thus,  if  the  sum  of  the  atomic  weights  of  chlorine 
and  iodine  (35. 5-f  127.1=162.6)  be  divided  by  2,  the  quotient  is  nearly  the 
atomic  weight  of  bromine  (80).  Again,  half  the  sum  of  the  equivalents  of 
barium  (68.5)  and  calcium  (20)  is  nearly  the  equivalent  of  strontium  (43.8). 
Another  triad  comprehends  potassium,  sodium,  and  lithium.  These  highly 

1  Bunsen  has  recently  investigated  this  subject.  He  found  that  the  compound  obtained 
by  the  action  of  ammonia  upon  an  alcoholic  solution  of  iodine  had  the  formula  NI3.NH3, 
while  that  precipitated  by  ammonia  from  a  dilute  solution  of  iodine  in  aqua  regia  was 
4NI3.NH3. 


FLUORINE  AND  HYDROGEN.  153 

interesting  facts,  taken  in  conjunction  with  the  circumstance  that  the  members 
of  the  same  triad  are  often  found  in  association,  appear  to  render  it  not  altogether 
improbable  that  the  compound  nature  of  the  middle  term,  at  least,  of  each  triad 
may  hereafter  be  demonstrated. 


FLUORINE.1 

Sym.  F.     Eq.  19. 

§  102.  The  process  of  etching  on  glass  by  means  of  fluor-spar  was  known  as 
far  back  as  1670.  Scheele,  in  1771,  declared  fluor-spar  to  be  a  compound  of 
lime  with  a  peculiar  acid,  which  was  regarded  by  him  and  several  other  chemists 
who  subsequently  investigated  the  subject,  to  be  an  oxygen  compound  of  an  un- 
known element.  In  1810,  Ampere  first  considered  the  acid  to  be  a  compound 
of  hydrogen  and  fluorine. 

Fluorine  is  found,  though  not  very  abundantly,  in  the  mineral  kingdom,  in 
combination  with  various  metals  (as  in  apatite,  fluor-spar,  topaz,  &c.);  it  also 
occurs  in  minute  quantities  in  human  urine,  in  bones,  teeth,  and  also  in  the 
ashes  of  some  plants,  and  in  sea-water.  It  is  also  said  to  exist  in  small  quantity 
in  blood  and  milk. 

Nothing  can  be  said  with  regard  to  the  nature  of  fluorine  itself,  since  repeated 
attempts  made  by  various  eminent  chemists  to  isolate  it  have  not  been  attended 
with  any  satisfactory  result.  Its  powerful  affinities,  which  appear  to  surpass 
even  those  of  oxygen,  cause  it  to  unite  with  other  substances  at  the  instant  of 
its  liberation ;  its  properties  in  the  uncombined  state  are  hence  quite  unknown ; 
it  appears  probable,  however,  from  the  nature  of  its  compounds,  that  it  is  a 
gaseous  element,  much  resembling  chlorine. 

Those  investigators  who  have  believed  that  they  obtained  it  in  the  separate 
state,  describe  it,  for  the  most  part,  as  a  gas  similar  to  chlorine. 

Fluorine  combines  with  most  of-  the  metals,  and  also  with  hydrogen,  boron, 
silicon,  sulphur,  selenium,  and  phosphorus;  its  compounds  are  analogous  in 
their  properties  to  those  of  chlorine,  bromine,  and  iodine,  with  which  elements, 
as  with  oxygen,  it  evinces  no  tendency  to  unite. 


FLUORINE    AND    HYDROGEN. 

HYDROFLUORIC  ACID. 
HF.     Eq.  20.     Sp.  Gr.  1.0609. 

Preparation. — This  acid  is  obtained  by  heating  together  one  part  of  finely 
powdered  fluor-spar  (free  from  any  silica)  and  two  parts  of  oil  of  vitriol,  in  a 
leaden  retort,  in  which  no  solderings  must  be  used.  The  product  is  collected  in 
a  receiver  of  lead,  loosely  adapted  to  the  neck  of  the  retort,  and  surrounded  by 
a  freezing  mixture.  The  formation  of  hydrofluoric  acid  is  explained  by  the  fol- 
lowing equation : — 

CaF+HO.S03=CaO.S03-fHF. 

The  acid  must  be  preserved  in  bottles  of  lead  or  gutta  percha  (vessels  of  gold 
or  platinum  might  also  be  employed  for  its  preparation  and  preservation). 

Properties. — Hydrofluoric  acid  is  a  colorless,  very  volatile  liquid,  boiling  not 

1  From  fluo,  to  flow,  on  account  of  its  solvent  properties. 


154  SULPHUR. 

much  above  59°  F.  (15  C.)1  It  fumes  when  in  contact  with  air,  has  a  pungent 
odor,  powerfully  attacks  the  respiratory  organs,  and  is  highly  corrosive;  if  dropped 
upon  the  skin  it  immediately  produces  a  very  painful  sore,  even  its  vapor  pro- 
duces pains  under  the  nails.  Hydrofluoric  acid  decomposes  all  compounds  of 
silicon  on  account  of  the  powerful  affinity  of  fluorine  for  that  element;  hence  it 
immediately  corrodes  glass  and  porcelain,  and  cannot,  therefore,  be  prepared  or 
preserved  in  vessels  of  those  materials. 

Hydrofluoric  acid  is  decomposed  by  the  galvanic  current;  many  metals  also 
decompose  it,  fluorides  being  produced,  and  hydrogen  disengaged. 

Most  metallic  oxides  decompose  it,  forming  fluorides  and  water.  A  solution 
of  hydrofluoric  acid  is  best  obtained  by  placing  in  the  leaden  or  platinum  re- 
ceiver of  the  apparatus  described  above,  a  quantity  of  water  just  sufficient  to 
cover  the  mouth  of  the  retort  neck. 

The  hydrated  acid  is  a  thin  colorless  liquid,  fuming  when  concentrated.3  It 
is  in  the  state  of  aqueous  solution  that  hydrofluoric  acid  is  found  in  commerce. 
It  must  be  preserved  in  vessels  of  lead  or  of  gutta  percha. 

Metallic  fluorides  may  be  obtained  as  above  stated,  by  the  action  of  some 
metals,  and  of  metallic  oxides,  upon  hydrofluoric  acid;  volatile  metallic  fluorides 
may  be  formed  by  heating  a  mixture  of  fluor-spar,  the  metallic  oxide,  and  oil  of 
vitriol.  The  fluorides  of  the  metals  resemble  the  metallic  chlorides  in  most 
respects.  Many  of  them  are  soluble  in  water,  the  solutions  act  upon  glass. 
Some  of  them,  when  heated  in  a  flame  containing  aqueous  vapor,  are  decomposed 
into  metallic  oxides  and  hydrofluoric  acid.  They  are  also  decomposed  by  chlorine 
in  presence  of  water,  and  by  several  powerful  acids,  such  as  sulphuric  and  nitric 
acids,  the  sulphates  or  nitrates  being  produced,  and  hydrofluoric  acid  disengaged. 

Several  metallic  fluorides  combine  with  an  equivalent  of  hydrofluoric  acid, 
forming  compounds  soluble  in  water  and  reddening  litmus.  Their  composition 
is  expressed  by  the  formula  MF.HF. 

Hydrofluoric  acid  is  extensively  employed  for  etching  glass. 


SULPHUR. 

Sym.  S.     Eq.  16.     Sp.  Gr.  2.087. 

§  103.  Sulphur  occurs  in  an  uncombined  state  in  volcanic  districts,  and  also 
in  masses  of  sulphate  of  strontia.  It  is  found  in  combination  with  bases  as  sul- 
phuric acid,  occurs  combined  directly  with  metals  (as  sulphides),  and  exists  also 
in  many  organic  substances. 

Preparation. — In  Sicily,  the  volcanic  sulphur  is  separated  by  distillation  from 
earthy  matters.  Sulphur  is  also  prepared  in  England  and  Germany  by  roasting 
or  distilling  iron-pyrites  (bisulphide  of  iron). 

Sulphur  exists  in  commerce  in  three  forms,  to  which  the  names  of  roll  sulphur, 
flowers  of  sulphur,  and  milk  of  sulphur,  have  been  given. 

The  flowers  of  sulphur  are  obtained  by  conducting  the  vapor  of  sulphur  into 
capacious  chambers,  the  sides  of  which  are  kept  cool ;  the  sulphur  condenses  in 
the  form  of  a  fine  crystalline  pale  yellow  powder.  When  the  sides  of  the  cham- 

1  The  liquid  acid  is  stated  by  Louyet  to  be  a  hydrate.     He  found  that,  when  passed 
over  anhydrous  phosphoric  acid,  the  latter  deliquesced,  and  no  liquid  was  condensed  in 
the  cooled  receiver.     This  chemist  arrived  at  the  conclusion  that  hydrofluoric  acid  is  a 
gas  at  — 12°  C.  (10°.5  F.),  under  ordinary  pressure,  and  does  not  exert  a  sensible  action 
upon  glass. 

2  The  specific  gravity  of  the  strongest  liquid  acid  (1.06)  is  increased  to  1.25  by  the 
addition  of  a  certain  amount  of  water. 


SULPHUR.  155 

ber  become  hot,  the  sulphur  fuses,  and,  trickling  down,  collects  at  the  bottom, 
and  is  run  into  cylindrical  moulds ;  in  this  state  it  is  called  roll-sulphur. 

Milk  of  sulphur  is  prepared  by  adding  a  slight  excess  of  acid  to  a  solution  of 
sulphur  prepared  by  boiling  flowers  of  sulphur  with  milk  of  lime  or  potassa;  the 
sulphur  is  precipitated  as  a  fine,  nearly  white  powder,  which  is  collected,  washed, 
and  dried.  It  .appears  yellowish-gray  when  dry,  and  is  considered  by  some 
chemists  to  be  a  compound  of  sulphur  and  water.  (For  the  preparation  of  milk 
of  sulphur  see  §  161). 

Properties. — Sulphur  is  a  pale  yellow  solid,  devoid  of  taste  or  smell.  It  is 
dimorphous;  when  native,  or  crystallized  from  its  solution  in  bisulphide  of  car- 
bon, or  chloride  of  sulphur,  its  form  is  that  of  the  acute  rhombic  octahedron; 
when  crystallized  by  fusion,  it  is  obtained  in  long  thin  rhombic  prisms. 

The  two  varieties  of  crystals  of  sulphur  appear  to  be  mutually  convertible, 
their  form  depending  upon  the  temperature  to  which  they  are  exposed ;  thus,  if 
a  rhombic  octohedron  of  sulphur  be  gently  warmed  in  the  hand,  it  becomes 
opaque,  and  finally  splits,  which  is  apparently  due  to  its  change  into  an  aggrega- 
tion of  crystals  belonging  to  the  oblique  prismatic  system. 

In  the  amorphous  state,  sulphur  is  opaque.  When  heated,  it  exhibits  a  singular 
instance  of  aUotropy.1  It  melts  at  226°  F.  (107°. 8  C.)  to  a  brownish-yellow,  trans- 
parent, thin,  oily  fluid ;  at  about  320°  F.  (160°  C.)  it  begins  to  become  red  and  vis- 
cid; as  the  temperature  rises,  it  gradually  becomes  so  thick  that  it  will  scarcely  run 
out  of  an  inverted  vessel.  Beyond  a  certain  temperature  (about  482°  F.,  250°  C.) 
it  again  becomes  more  fluid,  though  not  so  much  so  as  at  240°  to  248°  F.  (116° 
to  120°  C.),  and  retains  a  brownish-red  color.  If  it  is  then  allowed  to  cool 
gradually,  it  first  returns  to  the  viscid  state,  then,  on  cooling  still  further,  once 
more  becomes  quite  liquid.  When  cooled  rapidly,  it  does  not  pass  through  the 
intermediate  viscid  state.  If  allowed  to  drop  into  water  when  it  is  in  its  most 
fluid  state,  it  solidifies  directly  to  a  brittle  mass  of  the  ordinary  light-yellow 
color;  but  if  immersed  in  water  when  near  its  boiling  point,  i-t  is  converted  into 
a  soft  reddish-brown  transparent  mass,  capable  of  being  kneaded  or  drawn  out 
into  threads  with  the  fingers;  sulphur  in  this  state  is  frequently  used  for  taking 
impressions,  as  it  again  becomes  (after  the  lapse  of  a  few  days)  hard,  yellow,  and 
crystalline. 

Sulphur  boils  at  about  800°  F.  (315°  C.),  being  converted  into  an  orange- 
colored  vapor,  which  possesses  a  peculiar  though  not  powerful  odor,  and  condenses 
to  small  drops  upon  a  cool  surface.  The  density  of  sulphur-vapor  is  6.617. 

When  heated  in  air  to  above  560°  F.  (293°. 3  C.),  sulphur  takes  fire,  burning 
with  a  pale  blue  flame.  The  resulting  vapors  are  very  suffocating,  and  consist 
of  sulphurous  acid,  which  is  the  only  compound  produced  to  any  extent  by  the 
direct  combination  of  sulphur  and  oxygen.  In  presence  of  moisture,  a  trace  of 
sulphuric  acid  is  also  formed. 

Sulphur  is  a  very  bad  conductor  of  heat  and  electricity,  becoming  highly  elec- 
tric by  friction. 

It  is  insoluble  in  water,  but  soluble,  though  sparingly,  in  alcohol  and  ether, 
more  soluble  in  the  oils,  in  subchloride  of  sulphur,  and  bisulphide  of  carbon.3 

1  The  term  allotropy  is  now  frequently  used  to  denote  a  property  possessed  by  several 
substances,  of  existing  in  different  states  without  undergoing  any  important  modification 
of  their  chemical  nature.     No  satisfactory  explanation  can  as  yet  be  given  of  this  re- 
markable property;  it  appears  probable,  however,  that  the  bodies  in  question  are  induced 
by  certain  circumstances  to  undergo  a  peculiar  alteration  in  their  physical  structure  (or 
the  arrangement  of  their  atoms),  and  thus  become  endowed  with  properties  so  different 
from  those  they  originally  possess,  that  they  would  at  once  pass  for  distinct  substances  if 
their  identity  were  not  proved  by  their  chemical  character. 

2  It  has  been  observed  that  sulphur,  in  some  forms,  is  insoluble  in  alcohol,  ether,  and 
bisulphide  of  carbon.     This  is  the  case  with  a  portion  of  the  sulphur  precipitated  by  the 
action  of  water  upon  the  chloride  of  sulphur,  by  the  action  of  hydrochloric  acid  upon 


156 


SULPHUR  AND    OXYGEN. 


When  boiled  with  strong  nitric  acid,  it  is  converted  into  sulphuric  acid.  It  is 
endowed  with  powerful  affinities.  It  forms  several  compounds  with  oxygen. 

With  hydrogen  it  forms  pentasulphide  of  hydrogen  (HS5)  and  hydrosulphuric 
acid  (HS).  It  also  combines  in  several  proportions  with  carbon  (the  principal 
compound  being  bisulphide  of  carbon,  CS2),  and  forms  compounds  with  chlorine, 
phosphorus,  and  boron.  It  unites  with  metals,  forming  sulphides,  analogous  in 
most  instances  in  their  composition  to  the  oxides. 

Uses  of  Sulphur. — This  substance  is  extensively  used  in  the  manufacture  of 
gunpowder  and  of  lucifer  matches;  it  is  also  employed  as  a  source  of  sulphurous 
acid  for  bleaching  purposes,  and  for  the  preparation  of  sulphuric  acid.  Of  late 
years,  the  application  of  sulphur  in  the  manufacture  of  what  is  called  vulcanized 
Indian-rubber  has  acquired  considerable  importance.  It  is  also  frequently  applied 
as  a  remedial  agent  in  cutaneous  diseases. 


SULPHUR  AND  OXYGEN. 


Hyposulphurcrus  acid 
Sulphurous  acid 
Hyposulphuric  acid 
Trithionic  acid  . 


Tetrathionic  acid  .  .  .  S4  0 
Pentathionic  acid  .  .  .  S5  O 
Sulphuric  acid  .  .  .  ..SO 


HYPOSULPHUROUS  ACID,  S203.     Eq.  48. 

§  104.  This  acid  is  produced  in  various  ways  in  combination  with  bases,  but 
cannot  be  obtained  in  a  separate  state.  It  may  be  produced  by  boiling  an 
aqueous  solution  of  an  alkaline  sulphite  with  sulphur: — 

KO.S02+S=KO.S202; 

or  by  fusing  a  mixture  of  sulphur  and  an  alkaline  hydrate  at  a  moderate  heat, 
an  alkaline  pentasulphide  is  simultaneously  produced: — 

3KO  +  S12=2KS5+KO.S203. 

It  is  also  produced  by  the  exposure  of  the  hydrosulphate  of  an  alkaline  sul- 
phide to  the  air. 

Properties. — It  has  already  been  stated  that  hyposulphurous  acid  cannot  be 
isolated,  for,  when  separated  from  its  salts,  it  immediately  resolves  itself  into 
sulphurous  acid  and  sulphur.  Its  combinations  with  bases  are  termed  hyposul- 
phites '}  these  last  generally  consist  of  one  equivalent  of  acid  to  one  of  base.  The 
hyposulphites  of  the  alkalies  and  alkaline  earths  are  soluble  in  water.  When 
heated  out  of  contact  with  air,  they  are  decomposed,  water,  sulphur,  and  hydro- 
sulphuric  acid  being  evolved,  and  a  mixture  of  sulphite  and  sulphate  of  the  base 
remaining  behind. 

The  aqueous  solution  of  an  alkaline  hyposulphite  does  not  alter  on  exposure  to 
air,  unless  excess  of  the  alkali  be  present,  in  which  case  it  gradually  becomes 
oxidized  until  a  sulphate  is  formed. 

These  salts  are  decomposed  by  stronger  acids,  the  solution  remaining  clear  at 
first,  but  gradually  becoming  milky  (especially  when  heated)  from  deposition  of 
sulphur,  and  evolving  sulphurous  acid. 

Bromide,  iodide,  and  chloride  of  silver  (the  latter  when  freshly  precipitated), 
are  soluble  in  an  alkaline  hyposulphite.  This  property  has  led  to  the  extensive 

solutions  of  hyposulphites,  and  with  that  formed  when  hydrosulphuric  acid  acts  upon  sul- 
phurous acid  in  the  presence  of  water.  This  modification  of  sulphur  has  been  found  to 
fuse  at  a  higher  temperature  than  ordinary  sulphur,  but  if  maintained  between  220°  and 
248°  F.  for  some  time,  it  is  gradually  changed,  enters  into  fusion,  and  is  afterwards  found 
to  be  perfectly  soluble  in  bisulphide  of  carbon. 


SULPHUROUS   ACID.  157 

use  of  hyposulphite  of  soda  in  photography,  for  removing  from  the  picture,  after 
its  exposure  to  light,  the  sensitive  coating  of  iodide  of  silver. 

SULPHUROUS  ACID. 
S0a.     Eq.  32.     Sp.  Gr.  2.234. 

Composition  by  Volume.  —  1  volume  of  sulphur-vapor  and  6  volumes  of 
oxygen  form  6  volumes  of  sulphurous  acid. 

Sulphurous  acid  occurs  in  volcanic  districts,  in  the  gaseous  state,  and  in  solu- 
tion in  various  springs. 

It  is  produced  by  the  combustion  of  sulphur  in  oxygen,  by  heating  sulphur 
with  many  metallic  oxides,  by  the  deoxidation  of  sulphuric  acid,  and  by  the 
decomposition  of  subchloride  of  sulphur  by  water. 

Preparation. — Concentrated  sulphuric  acid  is  heated  with  copper-clippings,  in 
a  flask  furnished  with  a  funnel-tube  and  evolution-tube,  and  the  gas  disengaged 
passed  through  a  small  quantity  of  water,  to  detain  any  sulphuric  acid  that  may 
be  carried  over.  Another  method  is  to  heat  charcoal  in  a  coarse  powder,  with 
sufficient  sulphuric  acid  to  wet  it  thoroughly ;  a  mixture  of  carbonic  and  sul- 
phurous acids  is  thus  obtained.  ^ 

The  following  equation  shows  the  formation  of  the  gas  by  the  first-named 
process : — 

Cu+2(HO.S03)=CuO.S03+S03+2HO; 
while  the  second  method  is  thus  represented  : — 

C+2(HO.SO,)=COa+2SOfl+2HO. 

The  latter  process  can  only  be  applied  when  the  presence  of  carbonic  acid  is 
of  no  consequence.  A  good  method  of  obtaining  the  pure  gas  is,  to  heat  in  a 
long  tube  a  mixture  of  one  part  of  sulphur  with  three  of  black  oxide  of  copper, 
covered  with  a  layer  of  the  latter,  which  is  first  heated : — 

2CuO+S3=CuaS  +  S03. 

If  the  gas  is  required  dry,  it  must  be  passed  through  a  tube  containing  fragments 
of  chloride  of  calcium.  Being  soluble  in  water,  it  must  be  collected  over  mercury, 
or  by  downward  displacement. 

Properties. — Sulphurous  acid  is  a  colorless  gas,  incombustible,  and  a  non- 
supporter  of  combustion,  possessing  a  suffocating  smell  and  peculiar  taste;  it  is 
highly  injurious  in  its  effects  when  respired,  and  generally  produces  a  hard  cough, 
which  lasts  for  some  time.  Sulphurous  acid  possesses  bleaching  properties;  this 
is  probably  the  result  of  its  great  affinity  for  oxygen;  it  does  not,  however,  per- 
manently destroy  vegetable  colors,  like  chlorine,  since  they  are  restored  by  the 
addition  of  stronger  acids,  probably  because  a  colorless  compound  of  sulphurous 
acid  with  the  coloring  matter  is  formed,  which  is  decomposed  by  the  stronger  acid. 

This  gas  may  be  liquefied  by  pumping  it  into  a  tube  previously  exhausted  and 
cooled,  until  the  pressure  obtained  amounts  to  4  or  5  atmospheres;  or  by  passing 
the  gas,  perfectly  dried,  as  above,  into  a  bottle  surrounded  with  a  freezing  mix- 
ture of  equal  weights  of  ice  and  salt,  and  provided  with  an  exit-tube.  The  liquid 
obtained  by  these  methods  must  be  preserved  in  sealed  tubes.  It  is  transparent 
and  colorless ;  its  sp.  gr.  is  1.45  ;  it  boils  at  14°  F.  ( — 10°  C.) 

The  cold  produced  by  its  reconversion  into  the  gaseous  state  is  very  intense  ; 
if  poured  upon  water,  the  latter  freezes  immediately,  even  in  a  redhot  crucible. 

By  exposure  of  this  liquid  to  the  intense  cold  produced  by  a  mixture  of  ether 
and  solid  carbonic  acid,  or  by  allowing  it  to  evaporate  very  rapidly,  it  is  converted 
into  white  flakes. 

If  moist  sulphurous  acid  gas  is  passed  through  a  redhot  tube,  it  is  decomposed 
into  sulphur  and  sulphuric  acid;  if  the  gas  is  mixed  with  hydrogen,  the  products 
are  water  and  sulphur ;  if  the  redhot  tube  contains  charcoal,  carbonic  oxide  and 


158  HYPOSULPHURIC  ACID. 

sulphur  are  obtained.  Some  metals,  on  being  heated  in  sulphurous  acid  gas, 
are  converted  into  sulphides  and  oxides.  Sulphurous  acid  is  converted  by  nitric 
acid  into  sulphuric  acid ;  and  it  acts  as  a  powerful  deoxidizer,  on  account  of  its 
great  affinity  for  oxygen. 

Water  dissolves  a  considerable  quantity  of  sulphurous  acid;  the  solution  has 
a  peculiar  acid  taste,  and  the  odor  of  burning  sulphur.  On  exposing  it  to  the 
air,  some  of  the  gas  escapes,  while  a  portion  is  converted  into  sulphuric  acid. 
By  subjecting  moist  gaseous  sulphurous  acid  to  a  temperature  of  about  17°. 6  F. 
( — 8°  C.),  a  crystallized  hydrate  of  this  acid  is  obtained,  the  composition  of  which 
appears  to  be  SOa+9HO.  The  crystals  remain  solid  until  heated  to  about 
39°. 2  F.  (4°  C.),  when  they  fuse,  evolving  sulphurous  acid. 

The  salts  of  sulphurous  acid,  or  sulphites,  are  obtained  by  passing  a  current  of 
the  gas  into  water  containing  the  bases,  or  their  carbonates,  suspended  in  it. 
They  are  inodorous,  and  have  a  sharp  taste,  similar  to  that  of  the  acid. 

The  sulphites  of  the  alkalies  are  soluble  in  water,  as  are  also  all  acid  sulphites; 
many  others  which  are  insoluble  may  be  dissolved  in  a  solution  of  sulphurous 
acid.  They  are  decomposed  by  stronger  acids,  with  evolution  of  sulphurous  acid. 
Some  sulphites  evolve  their  acid  when  heated;  others  are  resolved  into  sulphate 
and  sulphide,  thus: — 

4(MO.S03)=3(MO.S03)+MS. 

The  sulphites  of  most  heavy  metals,  when  heated  with  a  substance  having  an 
affinity  for  oxygen,  such  as  charcoal,  are  reduced  to  sulphides.  They  undergo 
gradual  oxidation  on  exposure  to  air,  particularly  in  the  presence  of  moisture, 
sulphates  being  produced. 

Uses  of  Sulphurous  Acid. — Sulphurous  acid  and  alkaline  sulphites  are  fre- 
quently used  as  reducing  or  deoxidizing  agents ;  many  oxides  are  at  once  reduced 
to  the  metallic  state  (gold,  silver,  mercury,  &c.),  by  its  action,  while  others  part 
with  a  portion  of  their  oxygen.  Sulphurous  acid  is  likewise  extensively  used  for 
bleaching  silken  and  woollen  goods  and  straw  plait,  and  also  for  disinfecting 
clothes. 

Bisulphite  of  lime  has  been  recently  applied  in  the  process  of  refining  sugar. 
The  property  which  sulphurous  acid  possesses  of  destroying  organic  ferments  is 
made  use  of  in  order  to  purify  the  interior  of  casks  used  for  wines,  &c.,  in  which 
a  little  sulphur  is  generally  burnt  previously  to  using  them  a  second  time. 

HYPOSULPHURIC  ACID  (also  DITHIONIC  ACID). 
Sa05   Eq.  72. 

"When  finely  powdered  binoxide  of  manganese  is  diffused  through  water,  and 
a  current  of  sulphurous  acid  passed  into  the  latter,  an  elevation  of  temperature 
ensues,  and  a  solution  of  hyposulphate  of  manganese,  containing  a  little  sulphate, 
is  obtained: — 

2SOa+MnOa=MnO.S305. 

The  temperature  of  the  liquid  should  be  kept  low  during  the  operation,  since  the 
amount  of  sulphate  of  manganese  formed  appears  proportionate  to  the  increase 
of  temperature.  The  solution  obtained  is  decomposed  by  baryta-water,  which 
removes  the  sulphuric  acid  and  protoxide  of  manganese,  the  former  as  sulphate 
of  baryta,  and  the  latter  as  hydrated  oxide.  By  adding  to  the  filtered  solution 
of  hyposulphate  of  baryta  sufficient  dilute  sulphuric  acid  to  precipitate  the  baryta, 
and  filtering  off  the  sulphate,  a  solution  of  hyposulphuric  acid  is  obtained. 

Properties. — Hyposulphuric  acid  does  not  exist  in  the  anhydrous  state;  when 
the  solution  is  concentrated  in  vacuo,  it  yields  a  heavy,  transparent,  inodorous, 
and  strongly  acid  liquid. 


SULPHURIC   ACID.  159 

If  heated  to  212°  F.  (100°  C.),  it  is  decomposed  into  sulphurous  and  sulphuric 
acids  :  — 


On  exposure  to  air,  it  is  gradually  converted  into  sulphuric  acid. 

The  hyposulphates  are  soluble  in  water,  and  crystallize  with  facility.     When 
heated,  they  evolve  sulphurous  acid,  and  are  converted  into  sulphates  :  — 
MO.Sa05=MO.S03+S03. 

They  are  decomposed  by  strong  acids,  and  if  heat  be  applied,  the  sulphates 
are  produced,  and  sulphurous  acid  evolved  (which  is  oxidized  if  nitric  acid  be 
employed). 

Hyposulphuric  acid  is  said  to  be  formed  from  sulphurous  acid,  by  imperfect 
exposure  to  air  for  a  long  period. 

SULPHURIC    ACID. 

S03.     Eq.  40. 

§  105.  This  acid  occurs  in  large  quantities  in  the  vegetable  and  mineral  king- 
doms, in  combination  with  various  bases  (such  as  the  alkalies,  alkaline  earths, 
the  oxides  of  iron,  copper,  lead,  zinc,  alumina,  &C.).1 

Sulphuric  acid  is  produced  by  the  action  of  1  volume  of  oxygen  upon  2  vo- 
lumes of  sulphurous  acid,  in  the  presence  of  water,  and  by  the  introduction  of 
redhot  platinum  into  the  mixture.  It  is  also  formed  by  the  oxidation,  in  various 
ways,  of  the  lower  oxides  of  sulphur. 

It  has  recently  been  shown  by  Wbhler  that  sulphuric  acid  is  formed  in  large 
quantity,  when  a  dry  mixture  of  2  volumes  of  sulphurous  acid  and  1  volume  of 
oxygen  is  passed  over  certain  metallic  oxides  heated  to  dull  redness  in  a  glass 
tube.  The  formation  of  sulphuric  acid  was  observed  to  take  place  with  very 
great  facility  under  the  influence  of  a  mixture  of  oxide  of  copper  and  sesquioxide 
of  chromium,  prepared  by  precipitation.  The  same  amount  of  oxide  appeared 
capable  of  producing  an  unlimited  quantity  of  sulphuric  acid. 

ANHYDROUS  SULPHURIC  ACID. 

S03. 

Preparation,  —  This  compound  is  obtained  by  distilling,  at  a  gentle  tempera- 
ture, the  most  concentrated  liquid  sulphuric  acid,  commonly  known  as  fuming, 
or  Nordhauien  sulphuric  acid,  in  a  small  retort,  to  the  neck  of  which  is  properly 
fitted  a  dry  receiver,  surrounded  with  ice.  The  corrosive  property  of  the  acid 
renders  impossible  the  employment  of  cork  or  luting  in  the  construction  of  the 
apparatus. 

The  first  portion  of  the  acid  which  passes  over  is  anhydrous,  and  will  condense 
to  a  white  crystalline  solid. 

The  anhydrous  acid  may  also  be  obtained  by  distilling  hydrated  sulphuric 
acid  with  anhydrous  phosphoric  acid,  the  affinity  of  the  latter  for  water  being 
considerably  more  powerful  than  that  of  anhydrous  sulphuric  acid. 

Properties.  —  This  substance  crystallizes  in  groups  of  long  thin  needles,  which 
are  opaque  and  white.  Its  spec.  grav.  is  1.97.  When  gently  heated,  it  fuses, 
yielding  a  liquid  generally  possessing  a  brownish  tint,  owing,  probably,  to  a 
trace  of  organic  matter  which  the  acid  decomposes.  It  boils  at  between  125°.  6 
and  132°.  8  F.  (52°  and  56°  C.);  its  vapors  are  colorless  in  the  absence  of 
moisture.  Its  affinity  for  water  is  so  powerful  that,  when  brought  together  with 

1  Sulphuric  acid  has  been  discovered,  in  the  uncombined  state,  in  a  thermal  spring  in 
New  Granada  (S.  America). 


OP  THE 


160  SULPHURIC   ACID. 

the  latter,  it  makes  a  violent  hissing  noise,  and  evolves  a  considerable  amount  of 
heat.  The  perfectly  dry  acid  is  said  not  to  redden  litmus-paper ;  it  chars  many 
organic  substances  at  the  ordinary  temperature.  When  exposed  to  moist  air,  it 
evolves  dense  white  fumes,  and  becomes  gradually  converted  into  hydrated  sul- 
phuric acid,  or  oil  of  vitriol. 

FUMING,  OR  NORDHAUSEN  SULPHURIC  ACID,  2S03.HO,  is  obtained  by  the 
distillation  of  basic  sulphate  of  sesquioxide  of  iron,  which  is  prepared  by  heating 
crystals  of  green  vitriol  (FeO.S03  + 7HO),  when  water  is  at  first  disengaged, 
and  latterly  sulphurous  acid,  the  decomposition  being  represented  by  the  following 
equation  : — 

2(FeO.S03)=S03+Fe303.S03. 

If  this  basic  sulphate  of  sesquioxide  of  iron,  which  still  retains  a  little  water,  be 
exposed  to  a  high  temperature,  the  Nordhausen  acid  distils  over.  It  is  a  some- 
what viscid  liquid,  generally  of  a  light-brown  color  (owing  to  organic  matter),  of 
the  spec.  grav.  1.896. 

When  cooled  down  to  a  little  below  32°  F.  (0°  C.),  it  solidifies  to  a  crystal- 
line mass.  It  fumes  on  exposure  to  air,  owing  to  its  powerful  affinity  for  water  ] 
when  subjected  ta  distillation,  the  first  portion  that  passes  over  consists  of  anhy- 
drous sulphuric  acid,  which  solidifies  in  the  receiver ;  the  quantity  of  the  latter 
obtained  in  this  way  frequently  amounts  to  25  per  cent,  of  the  fuming  acid. 
The  residue  in  the  retort,  after  this  has  passed  over,  is  oil  of  vitriol,  or  ordinary 
sulphuric  acid.  This  fuming  acid  evolves  much  heat,  and  frequently  hisses, 
when  thrown  into  water. 

CONCENTRATED  SULPHURIC  ACID — (OiL  or  VITRIOL).     IIO.S03. 

This  acid,  which  is  generally  considered  to  be  the  mono  or  protohydrate  of 
sulphuric  acid,  is  prepared  in  spacious  leaden  chambers,  the  floors  of  which  are 
covered  with  water,  and  into  which  are  simultaneously  passed  sulphurous  acid 
and  nitrous,  or  nitric  acid  vapors,  atmospheric  air,  and  jets  of  steam.  The  sul- 
phurous acid  is  now  generally  prepared  for  this  purpose  by  burning  sulphur  in  a 
small  furnace,  built  against  the  wall  of  the  chamber ;  the  nitrous,  or  nitric  acid 
vapors,  are  obtained  by  heating  a  mixture  of  nitre  and  oil  of  vitriol,  which  is  usually 

Fig.  65. 


contained  in  a  vessel,  &,  heated  by  the  flame  of  the  burning  sulphur.  A  small 
boiler,  a,  erected  on  one  side  of  the  chamber  furnishes  the  jets  of  steam,  and 
valves  are  provided  for  the  due  admission  of  air.  After  the  water  at  the  bottom 
of  the  chamber  has  attained  a  certain  specific  gravity  (1.35  to  1.50)  from  the 
absorption  of  sulphuric  acid,  it  is  drawn  off,  and  a  fresh  quantity  introduced, 
which  in  turn  acts  upon  fresh  portions  of  sulphurous  acid,  so  that  a  small  quan- 
tity of  nitrous  vapor  operates  as  a  continuous  vehicle  for  conducting  oxygen  from 
the  air  to  the  sulphurous  acid. 

The  presence  of  aqueous  vapor  is  indispensable  to  the  production  of  sulphuric 
acid ;  if  sulphurous  acid  and  peroxide  of  nitrogen  gases  are  mixed  when  per- 
fectly dry,  they  have  no  action  upon  each  other;  when  a  small  quantity  of  moist- 
ure is  present,  however,  they  form  a  white  crystalline  substance,  which  is  imme- 
diately decomposed  into  sulphuric  acid  and  binoxide  of  nitrogen  upon  the 
introduction  of  more  aqueous  vapor.  This  experiment  may  be  conveniently 


SULPHURIC   ACID.  161 

made  in  a  glass  globe  on  a  small  scale.  If  the  supply  of  aqueous  vapor  be 
therefore  but  small  in  comparison  to  that  of  the  mixed  gases,  the  sides  of  the 
vessel  become  coated  with  the  above  crystalline  compound,  which  disappears  upon 
the  introduction  of  a  fresh  supply  of  steam.  When  the  dilute  sulphuric  acid  at 
the  bottom  of  the  chamber  has  attained  a  certain  specific  gravity,  it  is  drawn  off, 
and  is  concentrated  by  evaporation  in  shallow  leaden  vessels  till  it  attains  a  spec, 
grav.  of  1.70,  when  it  is  transferred  into  vessels  of  glass  or  platinum  (stills  of  the 
latter  material  being  generally  used),  and  boiled  down  until  its  spec.  grav.  is 
1.84,  when  it  constitutes  the  oil  of  vitriol  of  commerce. 

The  theory  of  the  formation  of  sulphuric  acid  cannot  be  said  to  be  thoroughly 
understood ;  the  following  appear  to  be  the  most  important  reactions  that  take 
place  in  the  leaden  chamber.  The  peroxide  of  nitrogen  (N04),  or  nitric  acid 
vapors,  being  made  to  mix,  in  the  presence  of  water,  with  sulphurous  acid,  con- 
vert the  latter  into  sulphuric  acid  by  parting  with  a  portion  of  their  oxygen  ;  the 
binoxide  of  nitrogen  resulting  from  this  action,  absorbing  fresh  oxygen  from  the 
air  introduced  into  the  chamber,  becomes  again  converted  into  hyponitric  acid. 
It  would  appear  that  the  formation  of  the  crystalline  compound  is  accidental,  and 
must  be  attributed  to  a  deficient  supply  of  water. 

Various  other  methods  have  been  suggested  for  the  preparation  of  sulphuric 
acid,  though  the  above  is  the  only  one  employed  on  a  large  scale.  One  of  these 
methods  consists  in  passing  a  mixture  of  sulphurous  acid  and  moist  air  through 
a  tube  containing  platinum-sponge,  or  balls  of  very  fine  platinum  wire,  or  even 
pumice-stone.  Sulphurous  acid,  when  mixed  with  moist  oxygen  or  air,  in  con- 
tact with  finely  divided  platinum,  becomes  immediately  converted  into  sulphuric 
acid. 

Commercial  oil  of  vitriol  generally  contains  various  impurities,  especially  if 
iron  or  copper  pyrites  be  substituted  for  sulphur  as  sources  of  sulphurous  acid. 
The  most  common  are  sulphate  of  lead,  derived  from  the  leaden  chamber  or 
evaporating-pan ;  the  oxides  of  nitrogen,  and  sometimes  also  arsenic  and  selenium, 
may  be  detected  in  it  (the  latter  impurities  arising  from  the  sulphur). 

The  pure  monohydrated  sulphuric  acid  is  obtained  by  rectifying  oil  of  vitriol, 
free  from  arsenic  and  oxides  of  nitrogen,1  or  by  distilling  Nordhausen  or  fuming 
sulphuric  acid ;  the  anhydrous  acid  is  first  obtained  from  the  latter,  and  the  last 
portion  that  distils  over  is  pure  oil  of  vitriol. 

PROPERTIES  OF  THE  MONOHYDRATED  ACID. — It  is  an  oily  colorless  liquid, 
of  specific  gravity  1.848  ;  it  freezes  at  —29°  F.  (—34°  C.),  and  boils  at  590°.(> 
F.  (310°  C.),  its  vapors  being  colorless  and  very  suffocating:  they  form  dense 
fumes  on  exposure  to  air.  It  possesses  a  powerful  affinity  for  water,  evolving 
much  heat  when  diluted.  This  is  partly  owing  to  the  condensation  of  volume, 
since  a  mixture  of  sulphuric  acid  and  water  will  be  found  to  occupy  much  less 
space  than  did  the  two  liquids  before  mixture. 

The  avidity  with  which  sulphuric  acid  absorbs  water  (from  air  or  gases  for 
example)  renders  this  substance  a  valuable  dehydrating  or  desiccating  agent  in 
the  hands  of  the  chemist.  In  consequence  of  this  powerful  affinity  of  sulphuric 
acid  for  water,  organic  substances  are  charred  when  immersed  in  it;  the  acid  as- 
suming a  brown  tinge,  due  to  the  separation  of  carbon,  part  of  the  hydrogen  and 
oxygen  having  been  converted  into  water,  and  removed  by  the  sulphuric  acid. 

When  the  vapor  of  sulphuric  acid  is  passed  through  a  porcelain  tube  at  a  high 
red  heat,  it  is  decomposed  into  sulphurous  acid  and  oxygen.  Charcoal  decom- 

1  The  distillation  of  sulphuric  acid  must  be  conducted  with  great  care,  on  account  of 
the  succussions  that  generally  take  place  when  it  is  boiled,  owing  to  the  irregular  disen- 
gagement of  vapor;  the  precautions  mentioned  at  g  41  should  be  attended  to,  since  the 
violence  of  the  succussions  is  thereby  considerably  decreased ;  Berzelius  recommends, 
however,  in  addition,  that  the  retort  be  heated  at  the  sides  only,  and  never  at  the  bottom. 
11 


162  SULPHURIC   ACID. 

poses  sulphuric  acid  when  heated  with  it,  the  products  being  sulphurous  and  car- 
bonic acids.  Many  metals  also  decompose  sulphuric  acid  with  the  aid  of  heat, 
sulphurous  acid  being  evolved,  and  sulphates  of  the  metallic  oxides  produced. 

BIHYDRATED  SULPHURIC  ACID,  2HO.S08,  produced  by  the  combination  of 
one  equivalent  of  sulphuric  acid  and  two  of  water,  is  a  liquid  having  the  specific 
gravity  1.78;  it  solidifies  to  transparent  colorless  six-sided  prisms,  at  about  39°. 2 
F.  (4°  0.);  when  it  is  heated  to  between  401°  and  410°  F.  (205°  and  210°  C.), 
one  equivalent  of  water  is  expelled  together  with  some  sulphuric  acid;  and  oil  of 
vitriol  is  obtained. 

TERHYDRATED  SULPHURIC  ACID,  3HO.S03. — This  hydrate  of  sulphuric  acid 
has  a  spec.  grav.  of  1.632;  it  boils  at  between  379°.4  and  390°.2  F.  (193°  and 
199°  C.),  no  acid  being  volatilized  at  that  temperature.  When  dilute  sulphuric 
acid  is  evaporated  in  vacuo  over  oil  of  vitriol,  this  hydrate  is  left. 

COMBINATIONS  OF  SULPHURIC  ACID  WITH  METALLIC  OXIDES. — Sulphuric 
acid  may  be  considered  as  the  most  powerful  acid,  sirjce,  under  ordinary  circum- 
stances, it  expels  all  others  from  their  combinations.  There  are  two  classes  of 
sulphates;  the  neutral  salts,  represented  by  the  general  formula,  MO.S03,  and 
the  bisulphates,  MO.S03,  HO.S03,  or  MO.H0.2S03.  Many  of  the  neutral 
sulphates  are  soluble  with  difficulty,  or  wholly  insoluble  in  water.  The  acid 
sulphates  of  the  alkalies,  and  some  other  oxides,  are  far  more  soluble  than  the 
corresponding  neutral  salts. 

Sulphates  are  decomposed  by  ignition  with  charcoal;  in  some  cases  the  metallic 
sulphides  are  obtained,  carbonic  oxide  and  carbonic  acid  being  disengaged;  in 
others,  the  metals  are  reduced,  and  carbonic  oxide,  sulphurous  and  carbonic  acids 
evolved.  Many  sulphates  are  decomposed  by  a  current  of  hydrogen  at  a  red 
heat,  water,  and  the  metallic  sulphides  being  produced.  Alkaline  sulphates 
existing  in  somewhat  dilute  aqueous  solutions  (for  example,  in  mineral  waters) 
undergo  gradual  decomposition  when  allowed  to  remain  in  contact  with  organic 
matter ;  the  sulphur  parts  with  its  oxygen,  which  oxidizes  the  organic  matters, 
and  metallic  sulphides,  or  hydrosulphuric  acid,  are  produced.1  A  particle  of  cork 
allowed  to  fall  accidentally  into  the  water,  is  sufficient  to  induce  this  decomposition. 

Uses  of  Sulphuric  Acid. — The  great  facility  and  cheapness  with  which  sul- 
phuric acid  may  be  manufactured  on  a  large  scale,  has  rendered  it  by  far  the  most 
valuable  chemical  agent  in  the  manufactures  and  arts.  The  important  functions 
which  it  exercises  in  the  manufacture  of  soda  need  merely  be  adverted  to. 

As  a  chemical  agent,  sulphuric  acid  is  also  one  of  the  highest  importance.  In 
consequence  of  its  powerful  affinities  for  bases,  it  may  be  employed  to  separate 
most  other  acids  from  their  combinations;  its  affinity  for  water  is  also  turned  to 
advantage  by  the  chemist,  as  already  mentioned.  One  of  the  most  recent  uses 
to  which  sulphuric  acid  has  been  applied  as  a  reagent,  is  met  with  in  the  process 
of  silver-refining,  when  auriferous  silver  is  boiled  with  oil  of  vitriol,  which  dis- 
solves the  silver  in  the  form  of  sulphate,  without  acting  upon  the  gold.  (The 
silver  is  precipitated  from  the  solution  by  means  of  slips  of  copper.)  The  Nord- 
hausen  sulphuric  acid  possesses  the  property  of  dissolving  indigo,  yielding  a 
solution  much  used  by  dyers. 

§  106.  We  have  written  the  formula  of  hydrated  sulphuric  acid  (HO.S03), 
consistently  with  the  older  view,  which  regards  it  as  a  compound  of  water  with 
the  anhydrous  acid,  S03.  The  circumstance,  however,  that  S03  is  not  capable 
of  entering  into  combination  with  bases,  and  does  not  appear  to  possess  the  pro- 
perties of  an  acid,  until  it  has  been  brought  in  contact  with  water,  has  led  many 

1  It  has  been  observed  that  well-water,  containing  much  sulphate  of  lime,  which  had 
been  shaken  with  an  ethereal  oil  and  allowed  to  stand  in  a  close  vessel  for  some  weeks, 
became  charged  with  hydrosulphuric  acid,  while  the  oil  diminished  in  bulk,  and  carbonate 
of  lime  separated  from  the  water. 


BINARY  THEORY  OF  ACIDS.  163 

chemists  to  believe  that  the  so-called  hydrated  acid  is  really  the  hydrogen-acid 


of  a  radical  S04;  for 


HO.S03=H.S04, 


and  sulphuric  acid  then  becomes  analogous  to  hydrochloric  acid,  containing  the 
compound  radical  S04  in  place  of  chlorine. 

Upon  this  hypothesis  many  of  the  reactions  of  sulphuric  acid  could  be  explained 
in  a  far  simpler  manner  than  upon  the  older  view ;  compare,  for  example,  its 
action  upon  zinc : — 

Older  view:  Zn+HO.S03=ZnO.S03+H. 

New  view:    Zn-f  HS04=ZnS04+H. 

The  latter  equation  is  quite  similar  to  that  which  represents  the  action  of  hydro- 
chloric acid  upon  zinc : — 

Zn  +  HCl=ZnCl+H. 

Upon  this  theory,  the  sulphates  would  no  longer  be  regarded  as  compounds  of 
sulphuric  acid  with  the  metallic  oxides,  but  as  haloid  salts,  composed  of  metals 
combined  with  the  radical  S04.  According  to  the  older  view  of  the  constitution 
of  sulphuric  acid,  sulphates  are  formed  by  the  substitution  of  an  equivalent  of 
base  for  the  equivalent  of  water  in  the  hydrated  acid,  whereas  the  new  theory 
regards  them  as  produced  by  the  replacement  of  the  hydrogen  by  a  metal,  the 
oxygen  of  the  oxide  combining  with  the  displaced  hydrogen  to  produce  water;  the 
following  equations  exhibit  the  formation  of  sulphate  of  copper  upon  both  views : — 

Older  view:  CuO+HO.S03=CuO.S03+HO. 
New  view:  CuO-f  HS04=CuS04+HO. 

It  will  be  seen  that,  in  the  latter  case,  the  formation  of  a  sulphate  is  analogous  to 
that  of  a  chloride,  by  the  action  of  hydrochloric  acid  upon  a  metallic  oxide  : — 

CuO+HCl==CuCl+HO. 

This  binary  theory,  as  it  is  generally  termed,  has  been  applied  to  other  acids 
and  salts,  the  formulae  of  some  of  which  are  given  in  the  subjoined  list,  in  juxta- 
position with  those  which  they  would  have  according  to  the  new  view  : — 

Old  view.  New  riew. 

Nitric  acid HO.N05  HN08. 

Nitrates M0.1N05  MN06 

Metaphosphoric  acid       .     .     .  HO.P05  HP06 

Metaphosphates MO.P05  MP06 

Pyrophosphoric  acid       .     .     .  2HO.P05  H2P07 

Pyrophosphates 2MO.P05  M2P07 

Tribasic  phosphoric  acid      .     .  3HO.P05  H3P08 

Tribasic  phosphates    ....  3MO.P05  M3P08 

One  great  objection  to  this  theory  is,  that  the  new  radicals  are  hypothetical; 
neither  S04,  N06,  P06,  P07,  nor  P0?,  has  been  obtained  in  the  separate  state. 
This,  however,  would  not  form  an  insuperable  bar  to  its  adoption,  since  the 
chemist  does  not  refrain,  in  other  cases,  from  assuming  the  existence  of  a  radical 
when  the  behavior  of  a  series  of  compounds  appears  to  justify  such  an  assump- 
tion. 

LESS  IMPORTANT  OXIDES  OP  SULPHUR. 

§  107.  TRITHIONIC  ACID,  S305.  Eq.  88. — This  acid  is  prepared  by  boiling 
a  saturated  solution  of  bisulphite  of  potassa,  for  some  days,  with  flowers  of  sul- 
phur (until  the  yellow  color  at  first  observed  disappears),  and  filtering  while 
hot.  Trithionate  of  potassa  crystallizes  out,  and  is  separated  from  excess  of  sul- 

1  MO  representing  any  basic  protoxide. 


164  ACIDS   OF   SULPHUR. 

phur  by  solution  in  a  small  quantity  of  tepid  water.  The  potassa-salt  is  after- 
wards decomposed  by  means  of  tartaric  or  perchloric  acid;  an  aqueous  solution  of 
the  acid  is  thus  obtained,  which  may  be  concentrated  by  gentle  evaporation. 

Properties. — The  aqueous  solution  of  this  acid  is  colorless,  transparent,  and 
inodorous;  it  is  not  a  very  powerful  acid.  It  easily  decomposes,  even  at  ordinary 
temperatures,  being  resolved  into  sulphur,  sulphurous,  and  sulphuric  acids: — 

S305=S03+S03+S. 

Heat  accelerates  the  decomposition.  It  is  also  decomposed  by  nitric  acid  into 
sulphuric  acid  and  sulphur. 

The  trithionates  have  not  been  much  studied;  the  potassa  salt  is  the  best 
known.  It  is  easily  decomposed  by  heat,  or  by  more  powerful  acids,  sulphur 
being  precipitated,  and  sulphurous  acid  frequently  evolved. 

TETRATHIONIC  ACID,  S405.  Eg_.  104. — On  dissolving  iodine  in  hyposulphate 
of  baryta,  iodide  of  barium  and  tetrathionate  of  baryta  are  formed,  as  is  shown 
by  the  following  equation : — 

2(BaO.S303)  +  I=BaI  +  BaO.S405- 

The  tetrathionate  of  baryta  is  insoluble  in  strong  alcohol,  and  may  therefore, 
by  digestion  in  the  latter,  be  separated  from  the  admixture  of  iodine  and  iodide 
of  barium.  An  aqueous  solution  of  the  acid  may  be  obtained  by  carefully  de- 
composing the  baryta-salt  with  sulphuric  acid. 

Properties. — The  solution  of  tetrathionic  acid  is  transparent  and  colorless;  it 
is  decomposed  by  heat  into  sulphur,  sulphurous  and  sulphuric  acids : — 

s.o.-so.+so.-t-si,. 

Nitric  acid  decomposes  it,  but  hydrochloric  and  sulphuric  acids  do  not.  When 
in  contact  with  a  strong  base,  this  acid  sometimes  decomposes  into  trithionic  acid 
and  sulphur. 

The  salts  of  tetrathionic  acid  may  be  best  obtained  in  the  crystalline  state  by 
mixing  their  aqueous  solutions  with  alcohol.  They  are  decomposed  by  heat,  like 
the  trithionates. 

PENTATHIONIC  ACID,  S505.  Eq.  120. — This  acid  is  produced  by  the  action  of 
hydrosulphuric  and  sulphurous  acids  upon  each  other;  water  being  simultaneously 
formed,  and  sulphur  deposited  : — 

5HS +5S03=S5054-  5HO  +  S5. 

An  aqueous  solution  is  obtained  by  passing  excess  of  hydrosulphuric  acid  into 
a  saturated  solution  of  sulphurous  acie^  digesting  the  filtered  solution  with  slips 
of  copper  until  it  is  perfectly  clear,  separating  the  dissolved  copper  from  the 
solution  by  hydrosulphuric  acid,  and  expelling  the  excess  of  the  latter  by  heat. 

Properties. — The  solution  of  pentathionic  acid  is  colorless  and  inodorous ;  it 
does  not  decompose  at  ordinary  temperatures,  and  a  weak  solution  may  be  con- 
centrated by  the  aid  of  heat,  without  decomposition,  until  it  attains  a  specific 
gravity  of  1-37,  when  it  is  decomposed,  hyposulphurous,  sulphurous,  and  sul- 
phuric acids  being  formed,  and  sulphur  deposited.  Oxidizing  agents  convert  it 
into  sulphuric  acid. 

But  little  is  known  respecting  the  pentathionates ;  they  are  very  unstable,  the 
fifth  equivalent  of  sulphur  existing,  apparently,  but  very  loosely  combined  in  the 
acid ;  frequently,  strong  solutions  of  pentathionates  resolve  themselves  into  the 
more  stable  tetrathionates,  with  deposition  of  sulphur;  it  is,  therefore,  very  dif- 
ficult to  obtain  the  pentathionates  in  a  solid  form,  even  by  evaporation  of  their 
solutions  in  vacuo. 


HYDROSULPHURIC   ACID.  165 


SULPHUR    AND    HYDROGEN. 

PENTASULPHIDE  OF  HYDROGEN,  OR  HYDROSULPHUROUS  ACID. 

HS5.     Eq.  81. 

§  108.  Preparation. — When  solutions  of  alkalies  or  alkaline  earths  are  boiled 
with  excess  of  sulphur,  the  metallic  pentasulphides  are  obtained,  together  with 
the  hyposulphites.  Upon  gradually  adding  a  clear  solution  of  a  pentasulphide 
thus  prepared  (which  is  of  a  deep  orange  color)  to  a  great  excess  of  moderately 
strong  hydrochloric  acid  (one  of  concentrated  acid  to  two  of  water),  and  rapidly 
stirring,  a  viscid,  almost  transparent,  light  yellow  liquid  separates,  collecting  at 
the  bottom  of  the  vessel.  This  liquid,  which  is  the  pentasulphide  of  hydrogen, 
generally  contains  an  excess  of  sulphur,  which  is  liberated  by  the  decomposition 
of  the  hyposulphite  by  the  acid. 

Properties. — Pentasulphide  of  hydrogen  is  a  light  yellow,  transparent,  oily 
liquid,  possessing  a  peculiar  acrid,  somewhat  sulphurous  odor,  and  a  taste  both 
sweet  and  bitter.  It  dissolves  sulphur  to  a  considerable  extent,  becoming  viscid; 
its  true  composition  has  therefore  never  been  quite  satisfactorily  established.  It 
undergoes  spontaneous  decomposition  when  kept,  being  resolved  into  hydrosul- 
phuric  acid  and  sulphur;  hence  it  gradually  becomes  viscid,  and  finally  solid, 
when  preserved;  and  if  the  decomposition  is  allowed  to  take  place  in  sealed 
tubes,  the  hydrosulphuric  acid  is  liquefied  by  its  own  pressure.  Elevation  of 
temperature  accelerates  this  decomposition;  it  is  however  prevented,  or  consid- 
erably retarded,  by  the  presence  of  acids.  Several  metals  and  metallic  oxides, 
some  sulphides,  powdered  charcoal,  and  several  other  substances,  promote  the 
decomposition  of  pentasulphide  of  hydrogen,  which,  in  this  respect,  is  very  simi- 
lar to  the  binoxide  of  hydrogen.  It  is  inflammable,  burning  with  a  blue  flame, 
and  yielding  sulphurous  acid  and  water. 

HYDROSULPHURIC  ACID,  SULPHURETTED  HYDROGEN. 
HS.     Eq.  17.     Sp.  Gr.  1.1912. 

Composition  by  Volume. — 1  volume  of  sulphur- vapor  and  6  volumes  of  hydro- 
gen form  6  volumes  of  the  gas. 

Sulphuretted  hydrogen  occurs  in  nature  in  a  great  number  of  mineral  and 
sulphurous  springs;  also  in  marshy  districts,  as  a  product  of  vegetable  decom- 
position. It  is  always  formed  in  the  putrefactive  decomposition  of  organic  mat- 
ters containing  sulphur. 

Preparation. — This  acid  is  prepared  by  introducing  some  fragments  of  sulph- 
ide of  iron  (of  the  size  of  a  small  nut)  into  the  generating  vessel  of  a  hydrogen- 
apparatus,  provided  with  a  washing-bottle  (see  §  27)  containing  a  little  water; 
the  generating-bottle  is  half  filled  with  wafer,  and  concentrated  sulphuric  acid 
gradually  added,  the  bottle  being  slightly  agitated  after  each  fresh  addition,  so  as 
to  insure  immediate  mixture  of  the  acid  with  the  water.  The  production  of  the 
gas  is  as  follows : — 

FeS  +  HO.S03=FeO.S03  +  HS. 

The  gas  must  be  collected  over  a  strong  solution  of  salt,  or  hot  water,  or  even 
over  mercury,  although  the  latter  is  slightly  acted  upon.  When  obtained  in  this 
manner,  it  frequently  contains  a  little  free  hydrogen,  carburetted  hydrogen,  &c.; 
a  purer  gas  may  be  obtained,  although  in  much  smaller  quantity,  by  heating 
powdered  tersulphide  of  antimony  with  concentrated  hydrochloric  acid : — 

SbS3+3HCl=SbCl3-f3HS. 

This  gas  must  be  dried,  if  necessary,  by  means  of  chloride  of  calcium,  since  it 
decomposes  oil  of  vitriol. 


166  NITROSULPHURIO  ACID. 

Properties. — Sulphuretted  hydrogen  is  a  colorless  gas,  possessing  a  peculiar 
odor  (that  of  rotten  eggs);  it  is  highly  poisonous,  producing  fainting  and  syn- 
cope when  diluted  with  air,  and  acting  as  a  narcotic  poison  when  inhaled  pure. 
It  does  not  support  combustion,  but  burns  with  a  pale  blue  flame,  the  products 
being  sulphurous  acid  and  water : — 

HS+03=HO+SOa. 
A  little  sulphuric  acid  is  generally  produced  at  the  same  time. 

It  reddens  litmus-paper,  but  this  reddening  disappears  on  exposing  the  paper 
to  the  air.  Sulphuretted  hydrogen  may  be  converted  by  a  pressure  of  17  at- 
mospheres, into  a  transparent  colorless  liquid,  which  is  far  more  mobile  than 
ether,  has  the  specific  gravity  0.9,  and  dissolves  sulphur  with  the  aid  of  heat, 
depositing  it  again  on  cooling.  At  a  temperature  of  — 122°  F.  ( — 85°. 7  C.) 
sulphuretted  hydrogen  solidities  to  a  white  crystalline  translucent  substance. 

If  sulphuretted  hydrogen  be  passed  through  a  redhot  tube,  it  is  decomposed, 
hydrogen  escaping,  and  sulphur  being  deposited.  A  mixture  of  sulphuretted 
hydrogen  and  oxygen  explodes  upon  the  approach  of  flame,  the  products  being 
water  and  sulphur,  or  sulphurous  acid,  according  to  the  proportion  of  oxygen 
employed. 

Sulphuretted  hydrogen  is  oxidized  with  great  facility  by  some  acids  and  by  a 
few  high  metallic  oxides,  these  becoming  converted  into  lower  oxides.  Thus, 
chromic  acid  is  converted  into  sesquioxide  of  chromium,  and  sesquioxide  of  iron 
into  oxide,  by  treatment  with  sulphuretted  hydrogen,  water  being  formed,  and 
sulphur  precipitated,  oxides  of  sulphur  being  also  sometimes  produced. 

When  hydrosulphuric  acid  is  passed  into  moderately  strong  nitric  acid,  its 
hydrogen  is  oxidized,  and  the  greater  portion  of  the  sulphur  separated  in  a  pecu- 
liar viscid  state.  A  little  sulphate  of  ammonia  is  formed  at  the  same  time. 

When  passed  through  concentrated  sulphuric  acid,  this  gas  is  also  decomposed, 
water  and  sulphurous  acid  being  formed,  and  sulphur  deposited.  Chlorine, 
bromine,  and  iodine  decompose  sulphuretted  hydrogen,  the  results  being  hydro- 
chloric, hydrobromic,  and  hydriodic  acids  respectively,  and  sulphur.  A  few 
metals  also  decompose  this  gas  when  heated  in  it,  the  sulphides  being  produced 
and  hydrogen  evolved. 

Sulphuretted  hydrogen  is  soluble  to  a  considerable  extent  in  water,  which 
absorbs  about  2£  times  its  own  volume  at  ordinary  temperatures;  the  solution 
possesses  properties  similar  to  those  of  the  gas;  it  undergoes  gradual  decomposi- 
tion on  exposure  to  air  and  light,  sulphur  being  deposited;  it  should,  therefore, 
be  kept  in  closely  stoppered  bottles,  quite  full.  A  hydrate  of  the  acid  may  also 
be  formed,  existing  only  at  low  temperatures. 

Sulphuretted  hydrogen  acts  upon  metallic  oxides  in  solution,  converting  them 
into  sulphides  with  formation  of  water.  These  compounds  will  be  presently  re- 
verted to. 

§  109.  SULPHUR  AND  NITRQGEN. — By  the  action  of  water  upon  a  substance 
produced  by  the  combination  of  chloride  of  sulphur  (SCI)  with  ammonia,  a  light 
green  solid  is  produced,  which  is  a  combination  of  sulphur  with  nitrogen,  having 
the  formula  NSg,1  and  which  is  decomposed  by  water  into  hyposulphurous  acid 
and  ammonia. 

NITROSULPHURIC  ACID. — A  compound  of  sulphurous  acid  and  binoxide  of 
nitrogen  called  sulphite  of  nitric  oxide,  or  nitrosulphuric  acid,  having  the  formula 
N02.SOa,  exists  in  combination  with  the  alkaline  bases,  but  cannot  be  obtained 
in  the  separate  state. 

The  nitrosulphates  are  prepared  by  treating  alkaline  sulphites  with  nitric 
oxide.  They  are  crystalline  and  colorless,  their  composition  is  represented  by 
the  formula,  MO.N03.S02. 

1  Or,  according  to  Fordos  and  Gelis,  NS2. 


CHLORIDES   OF   SULPHUR.  167 

SULPHATE  OF  NITRIC  OXIDE. — This  substance  is  formed  when  dry  binoxide 
of  nitrogen  is  passed  over  anhydrous  sulphuric  acid  as  long  as  it  is  absorbed,  or 
when  liquid  sulphurous  and  hyponitric  acids  are  agitated  together  in  a  sealed 
tube.  It  is  also  formed  by  allowing  dry  sulphurous  acid,  binoxide  of  nitrogen 
and  air  to  mix  in  a  glass  globe. 

Properties. — This  peculiar  compound  crystallizes  in  rectangular  prisms,  or  in 
masses  of  white  silky  needles.  Its  spec.  gray,  is  2.14.  It  begins  to  fuse  at 
422°. 6  F.  (217°  C.),  and  becomes  quite  fluid  at  446°  F.  (230°  C.);  its  boiling- 
point  is  nearly  that  of  mercury;  it  distils  without  decomposition.  It  is  rapidly 
decomposed  by  contact  with  water,  nitric  oxide  being  evolved,  and  hydrated  sul- 
phuric acid  formed.  This  compound,  or  one  very  similar  to  it,  has  already  been 
referred  to,  as  obtained  in  the  preparation  of  sulphuric  acid  in  the  absence  of  a 
sufficient  amount  of  moisture;  when  exposed  to  the  air,  it  deliquesces,  forming 
a  colorless  liquid,  which,  however,  gradually  evolves  red  fumes,  in  consequence 
of  the  action  of  atmospheric  moisture. 

SULPHUR  AND  CHLORINE. 

§  110.  SUBCHLORIDE  OP  SULPHUR. — SaCl.  Eq.  67.5.  Sp.  Gr.  1.687.  Pre- 
paration.— Dry  chlorine  gas  is  passed  into  a  retort  containing  dried  flowers  of 
sulphur,  until  nearly  the  whole  of  the  latter  is  converted ;  the  subchloride  is 
then  distilled  off  from  the  excess  of  sulphur  at  a  gentle  heat. 

Properties. — Subchloride  of  sulphur  is  a  reddish-brown  oily  liquid,  of  a  peculiar 
sweet  but  disagreeable  and  suffocating  odor;  it  boils  at  about  280°.4  F.  (138°  C.); 
the  spec.  grav.  of  its  vapor  is  4.70.  It  is  gradually  decomposed  by  water,  yield- 
ing hyposulphurous  and  hydrochloric  acids  and  sulphur  (perhaps  also  a  small 
quantity  of  sulphuric  acid) : — 

2S3Cl+2HO=2HCl+S3Oa+S3. 

The  hyposulphurous  acid  is  soon  decomposed  into  sulphur  and  sulphurous  acid. 
Subchloride  of  sulphur  dissolves  sulphur  in  considerable  quantities,  depositing 
it  in  the  crystalline  form,  if  allowed  to  evaporate  spontaneously.     This  compound 
is  employed  in  one  of  the  processes  for  vulcanizing  caoutchouc. 

CHLORIDE  OF  SULPHUR,  SCI.    Eq.  51.5.     Sp.Gr.  1.62. 

Preparation. — Dry  chlorine  is  passed  in  excess  through  sulphur,  or  the  pre- 
ceding compound;  the  resulting  liquid  is  repeatedly  distilled  at  a  temperature 
of  about  140°  F.  (60°  C.)  in  a  current  of  chlorine  gas,  which  is  passed  into  the 
liquid  during  the  distillation. 

Properties. — Chloride  of  sulphur  is  a  dark  red-brown  somewhat  mobile  liquid, 
of  a  similar  odor  to  the  preceding  substance,  and  fuming  on  exposure  to  air;  its 
boiling  point  is  147°. 2  F.  (64°  C.),  and  the  spec.  grav.  of  its  vapor  is  3.7.  It 
is  decomposed  by  water  into  hydrochloric  and  hyposulphurous  acids : — 

2SC1+2HO=2HC1+S303. 

A  small  quantity  of  sulphuric  acid  is,  however,  simultaneously  produced.1    Chlo- 
ride of  sulphur  is  capable  of  dissolving  phosphorus. 

Two  other  chlorides  of  sulphur,  the  bichloride  and  terchloride^  appear  also  to 
exist;  there  is,  however,  but  little  known  respecting  their  nature.  The  terchlo- 
ride  forms  two  or  three  compounds  with  different  proportions  of  sulphuric  acid.3 

1  From  recent  experiments,  it  appears  that  some  of  the  polythionic  acids  are  also  pro- 
duced when  the  chlorides  of  sulphur  are  decomposed  by  water. 

2  Two  .compounds  of  ammonia  with  chloride  of  sulphur  have  been  obtained,  containing 
respectively,  1  and  2  eqs.  of  ammonia.     When  the  former  compound  is  exposed  for  some 
hours  to  a  temperature  of  212°  in  a  sealed  tube,  it  is  converted  into  chloride  of  ammonium 
and  a  yellow  solid  of  the  formula  NS4C1,  which  is  termed  chlorosulphide  of  nitrogen. 


168  METALLIC   SULPHIDES. 

SULPHUR  AND  BROMINE. — Bromine  dissolves  sulphur,  yielding  an  oily 
brownish-red  liquid,  rather  darker  than  the  preceding  compounds ;  the  amount 
of  sulphur  taken  up  by  bromine  at  ordinary  temperatures  appears  to  be  in  the 
proportion  of  two  equivalents  to  one  equivalent  of  the  latter ;  no  really  definite 
compounds  have,  however,  been  obtained.  The  bromides  of  sulphur  appear  to 
be  analogous  to  the  chlorides. 

SULPHUR  AND  IODINE. — When  sulphur  and  iodine  are  gently  heated  together, 
in  the  proportion  of  1  part  of  sulphur  to  7.9  parts  of  iodine,  single  equivalents, 
they  combine  and  liquefy ;  the  brown  liquid  solidifies  on  cooling  to  a  blackish- 
gray  crystalline  mass  of  iodide  of  sulphur,  SI;  it  is  insoluble  in  water,  and  is 
decomposed  on  exposure  to  air.  It  has  met  with  medicinal  application  in  cuta- 
neous diseases. 

METALLIC  SULPHIDES. — The  compounds  of  sulphur  with  metals  are  produced 
in  various  ways ;  they  are  sometimes  formed  by  bringing  the  metals  in  contact 
with  sulphur  at  ordinary  or  elevated  temperatures.  Some  metals  combine  with 
sulphur  when  heated  in  its  vapor,  undergoing  combustion  analogous  to  their 
combustion  in  oxygen. 

They  may  also,  be  produced  by  exposing  compounds  of  metallic  oxides  with 
the  acids  of  sulphur  to  the  action  of  reducing  agents  (e.  g.  hydrogen  or  charcoal) 
with  the  aid  of  heat ;  by  igniting  metallic  oxides  with  sulphur,  or  exposing  them 
to  the  vapor  of  bisulphide  of  carbon  at  a  red  heat ;  by  decomposing  metallic 
oxides  or  their  salts  by  means  of  sulphuretted  hydrogen  or  an  alkaline  sulphide. 
Many  sulphides,  particularly  those  containing  large  proportions  of  sulphur, 
occur  in  the  mineral  kingdom. 

Metallic  sulphides  are  solid,  and  generally  crystalline ;  they  present  a  greater 
variety  of  color  and  appearance  than  any  other  class  of  compounds;  many  possess 
a  metallic  lustre. 

The  sulphides  of  most  heavy  metals  are  insoluble  in  water;  those  of  the  metals 
of  the  alkalies  and  alkaline  earths  are,  however,  soluble  ;  their  solutions  undergo 
gradual  oxidation  on  exposure  to  air.  Some  sulphides  part  with  their  sulphur 
at  a  moderate  heat ;  others  require  a  high  temperature  for  their  decomposition, 
but  are  converted  into  oxides  or  metals,  with  evolution  of  sulphurous  acid,  by 
the  action  of  air  or  oxygen  with  the  aid  of  heat.  Most  sulphides  are  decomposed 
by  the  stronger  acids  (hydrochloric  or  sulphuric  acid),  sulphuretted  hydrogen 
being  evolved,  and  the  metallic  chlorides  or  sulphates  formed.  Chlorine  decom- 
poses many  sulphides,  yielding  chlorides  of  sulphur  and  of  the  metals ;  nitric 
and  nitro-hydrochloric  acids  convert  them  into  oxides  and  sulphuric  acid,  a  portion 
of  sulphur  being  sometimes  liberated.  The  sulphides  obtained  by  precipitation 
with  sulphuretted  hydrogen,  or  alkaline  sulphides,  are  generally  hydrates,  and 
frequently  differ  very  considerably  in  color  from  the  corresponding  anhydrous 
sulphides ;  they  lose  their  water  when  heated  out  of  contact  with  air,  and  are 
easily  oxidized  at  ordinary  temperatures  by  the  latter. 

Some  few  metallic  sulphides  (containing  large  proportions  of  sulphur)  may  be 
considered  to  possess  acid  properties,  inasmuch  as  they  are  capable  of  combining 
with  certain  so-called  sulphur-bases  (e.g.  KS,  NaS,  &c.)  to  form  double  sulphides, 
or  sulphur-salts;  some  sulphides  also  combine  with  metallic  oxides,  forming  the 
so-called  oxysulphides. 


SELENIUM   AND   OXYGEN.  169 


SELENIUM.1 

Sym.  Se.     Eq.  39.5.     Sp.  Gr.  4.3. 

§  111.  This  element  was  discovered  by  Berzelius,  in  1817.  It  exists  in  small 
quantities  in  a  great  variety  of  minerals,  especially  in  combination  with  lead, 
silver,  copper,  and  mercury,  and  also  with  sulphur;  it  is  found  in  small  quanti- 
ties in  some  varieties  of  iron  pyrites,  which  yield  on  distillation  seleniferous  sul- 
phur. In  the  use  of  sulphur  obtained  from  these  sources,  for  the  preparation  of 
sulphuric  acid,  a  seleniferous  deposit  is  formed  on  the  floor  of  the  leaden  chamber. 

Preparation. — Various  methods  are  employed  for  obtaining  selenium  from  its 
ores,  or  from  the  seleniferous  deposit ;  these  consist  in  the  conversion  of  the  sele- 
nium into  selenious  or  selenic  acid  by  oxidation  with  nitre  or  nitric  acid;  and 
their  subsequent  reduction  by  sulphurous  acid. 

Properties. — Selenium  is  obtained,  by  precipitation,  as  a  red  powder,  which 
becomes  semi-fluid  at  about  212°  F.  (100°  C.),  fusing  perfectly  at  a  somewhat 
higher  temperature;  it  boils  at  about  1326°  F.  (700°  C.);  its  vapor  is  yellow, 
somewhat  darker  in  color  than  chlorine ;  it  condenses  to  small  dark  drops  of 
metallic  lustre,  or  to  a  red  crystalline  powder  (flowers  of  selenium),  which  is 
very  inflammable,  being  converted  into  selenious  acid. 

On  cooling  after  fusion,  selenium  remains  soft  for  some  time,  so  that  it  may 
be  moulded  into  any  form;  after  solidification,  it  appears  as  a  brittle,  nearly  black, 
or  leaden-gray  mass,  possessing  considerable  metallic  lustre,  and  transmitting  red 
light  through  very  thin  scales.  When  rapidly  cooled,  its  surface  appears  red 
brown  ;  its  fracture  is  conchoidal.  It  may  be  crystallized  in  four-sided  prisms.3 
Selenium  is  insoluble  in  water ;  it  dissolves  in  concentrated  sulphuric  acid,  im^ 
parting  a  green  color  to  the  liquid;  water  reprecipitates  it  from  this  solution. 
When  heated  in  air,  it  produces  a  colorless  gas,  which  possesses  a  very  powerful 
odor,  similar  to  that  of  horseradish;3  this  compound  is  oxide  of  selenium,  SeO. 
Oxygen  also  combines  with  this  element  to  form  selenious  acid,  Se03,  and  selenic 
acid,  Se03.  With  hydrogen,  it  forms  hydroselenic  acid,  HSe;  it  also  unites 
with  sulphur,  phosphorus,  chlorine,  bromine,  and  with  the  metals,  yielding  sele- 
nides,  which  correspond  to  sulphides. 

The  relations  of  selenium  to  solvents  are  similar  to  those  of  sulphur,  to  which 
it  is  very  analogous  in  most  of  its  chemical  characters. 


SELENIUM  AND  OXYGEN. 

Oxide  of  selenium SeO 

Selenious  acid SeOa 

Selenic  acid .     Se03 

OXIDE  OF  SELENIUM,  SeO.     Eq.  47.5. 

This  oxide  is  formed,  as  already  stated,  by  the  combustion  of  selenium  in  air 
or  oxygen  (some  selenious  acid  being  simultaneously  produced). 

It  is  a  colorless  gas,  possessing  a  peculiar  odor,  similar  to  that  of  horseradish; 


1  From  o-eXijvu,  the  moon. 

2  The  analogy  between  sulphur  and  selenium,  as  regards  their  allotropic  modifications, 
has  been  rendered  evident  by  the  recent  experiments  of  Hittorf. 

3  According  to  Sacc,  this  odor  is  due  to  the  formation  of  a  minute  quantity  of  hydro- 
selenic acid;  upon  heating  selenium  in  perfectly  dry  air,  no  odor  whatever  was  observable. 


170  SELENIC   ACID. 

it  has  no  acid  properties,  and  is  but  slightly  soluble  in  water,  to  which  it  imparts 
its  characteristic  odor. 

SELENIOUS  ACID,  Se03.     Eq.  55.5. 

Preparation. — When  selenium  is  burnt  in  air  or  oxygen,  selenious  acid  is 
produced,  besides  the  above  oxide.  It  is  generally  obtained  by  dissolving  sele- 
nium in  warm  nitric  or  nitromuriatic  acid,  and  distilling  the  solution  ;  the  nitric 
and  hydrochloric  acids  pass  over  first,  and  the  selenious  acid  is  left,  subliming 
upon  continued  application  of  heat. 

Properties. — Selenious  acid  is  a  solid,  white,  translucent  substance,  which  may 
be  obtained  by  sublimation  in  white  four-sided  needles,  possessing  a  peculiar  lustre. 

Its  vapor  is  yellow,  somewhat  resembling  chlorine.  It  has  an  acid  taste,  and 
the  vapor  possesses  a  pungent  odor.  It  is  very  soluble  in  cold  water,  and  still 
more  so  in  hot.  Its  concentrated  hot  aqueous  solution  deposits  crystals  of  a 
hydrate,  which  in  their  appearance  much  resemble  nitre. 

Selenious  acid  and  its  salts  are  deoxidized  by  sulphurous  acid,  selenium  being 
precipitated  in  dark  red  flakes  : —  - 

SeOa+2(HO.S02)=Se+2(HO.S03). 

The  decomposition  is  much  accelerated  by  heat.  A  solution  of  selenious  acid, 
containing  an  admixture  of  some  powerful  mineral  acid  (hydrochloric  or  sulphuric 
acid),  is  decomposed  on  the  introduction  of  iron,  zinc,  silver,  and  several  other 
metals,  the  selenium  being  deposited  in  the  form  of  a  red-brown  film.  Selenious 
acid  is  also  decomposed  by  hydrosulphuric  acid,  with  formation  of  bisulphide  of 
selenium  and  water  : — 

SeOa+2HS=SeS2  +  2HO. 

Selenious  acid  possesses  considerable  affinity  for  bases,  with  which  it  forms 
selenites. 

SELENIC  ACID,  HO.Se03.    Eq.  72.5. 

Preparation. — This  acid  is  formed  by  fusing  selenium,  or  metallic  selenides, 
with  nitre;  seleniate  of  potassa  is  thus  obtained;  this  is  dissolved  in  water,  and 
a  solution  of  nitrate  of  lead  added ;  seleniate  of  lead  is  precipitated,  which  is  well 
washed,  then  suspended  in  water,  and  decomposed  by  hydrosulphuric  acid.  The 
solution  of  selenic  acid  is  separated  by  filtration  from  the  sulphide  of  lead,  and 
concentrated  by  gentle  evaporation,  until  its  specific  gravity  is  about  2.6.  In  this 
state  it  has  nearly  the  composition  of  monohydrated  selenic  acid,  HO.Se03.  If 
evaporated  further,  it  undergoes  decomposition. 

Properties. — Selenic  acid  cannot  exist  in  the  anhydrous  state.  The  concen- 
trated solution  is  transparent  and  colorless ;  it  bears  great  resemblance  to  sul- 
phuric acid. 

When  heated  above  545°  F.  (285°  C.)  it  decomposes  into  selenious  acid  and 
oxygen.  Hydrochloric  acid  also  decomposes  it,  with  the  aid  of  heat ;  chlorine  is 
evolved  and  selenious  acid  produced. 

Upon  mixing  concentrated  selenic  acid  with  water,  nearly  as  much  heat  is 
evolved  as  in  the  dilution  of  oil  of  vitriol. 

The  affinity  of  selenic  acid  for  bases  is  nearly  equal  to  that  of  sulphuric  acid. 

The  seleniates  correspond  to  and  are  isomorphous  with  the  sulphates.  The 
neutral  salts  are  all  soluble  in  water,  excepting  those  of  oxide  of  lead,  baryta, 
and  strontia.  When  thrown  upon  redhot  charcoal,  seleniates  deflagrate,  selenides 
being  generally  produced.  They  are  reduced  by  hydrogen  to  selenides.  When 
treated  with  hydrochloric  acid,  they  are  converted  into  selenites,  chlorine  being 
evolved. 


COMPOUNDS   OF   SELENIUM.  171 


SELENIUM    AND    HYDROGEN. 

HYDROSELENIC  ACID,  SELENIURETTED  HYDROGEN. 
HSe.     ^.40.5.     S/>.  GV.  3.42. 

§  112.  Preparation. — Upon  adding  hydrochloric  acid  or  dilute  sulphuric  acid 
to  selenide  of  potassium  or  of  iron,  hydroselenic  acid  is  disengaged : — 
HCl-fFeSe=HSe+FeCl. 

It  must  be  collected  over  mercury. 

Properties. — Seleniuretted  hydrogen  is  a  colorless  gas,  possessing  an  odor  very 
like  that  of  sulphuretted  hydrogen ;  it  is  even  more  poisonous  than  the  latter ; 
it  produces  a  very  painful  sensation  and  irritation  in  the  mucous  membrane  of 
the  nose  and  eyes ;  it  destroys  the  sense  of  smell  for  some  time,  and  frequently 
brings  on  a  bad  cough,  lasting  for  some  days.  It  is  inflammable,  burning  with  a 
blue  flame,  oxide  of  selenium  and  selenious  acid  being  produced,  and  selenium 
deposited. 

Hydroselenic  acid  is  absorbed  by  water  even  more  plentifully  than  hydro- 
sulphuric  acid  ]  the  solution  is  colorless,  and  has  a  faint  odor.  It  is  gradually 
decomposed,  like  hydrosulphuric  acid,  in  contact  with  air ;  selenium  being  de- 
posited in  dark-red  flakes. 

When  a  solution  of  seleniuretted  hydrogen  is  added  to  (or  the  gas  passed 
through)  solutions  of  most  of  the  heavy  metals,  selenides  are  precipitated ',  most 
of  them  are  either  dark  brown  or  black ;  the  salts  of  cerium,  manganese,  and 
zinc,  however,  give  flesh- colored  precipitates. 

SELENIUM  AND  CHLORINE. — The  action  of  chlorine  on  selenium  gives  rise  to 
the  production  of  two  compounds ;  when  chlorine  is  passed  over  selenium,  the 
latter  melts,  considerable  heat  being  disengaged,  and  a  brown  liquid  formed ;  if 
the  action  of  chlorine  be  continued,  this  liquid  is  converted  into  a  white  solid. 

The  first  of  these  products  is  the  subchloride  of  selenium,  Se3Cl.  It  is  an  oily, 
transparent,  brown,  volatile  liquid,  heavier  than  water,  whicn  decomposes  it 
gradually  into  hydrochloric  and  selenious  acids,  and  selenium. 

Bichloride  of  Selenium,  SeCla,  is  the  white  substance  above  referred  to,  pro- 
duced by  the  action  of  excess  of  chlorine  upon  the  subchloride.  It  is  more 
volatile  than  the  latter,  and  sublimes  in  white  crystals.  When  it  is  brought  in 
contact  with  water,  a  slight  effervescence  ensues,  accompanied  by  disengagement 
of  heat  and  its  conversion  into  selenious  and  hydrochloric  acids.  By  treating  the 
bichloride  with  a  fresh  quantity  of  selenium,  it  is  reconverted  into  the  subchloride. 

SELENIUM  AND  BROMINE. — There  appear  to  be  several  compounds  of  selenium 
and  bromine ;  but  that  in  which  these  elements  are  found  in  the  proportion  of 
five  of  the  latter  to  one  of  the  former,  appears  to  be  the  most  stable. 

SELENIUM  AND  SULPHUR. — These  two  substances  may  be  made  to  mix  in  all 
proportions  by  fusing  them  together.  Two  definite  combinations  of  selenium  and 
sulphur  have,  however,  been  obtained ;  the  bisulphide  and  the  tersulphide  of 
selenium. 

Bisulphide  of  Selenium,  SeS2,  is  produced  by  passing  hydrosulphuric  acid  into 
a  solution  of  hydroselenic  acid ;  a  yellow  precipitate  is  formed,  which  collects  to 
a  red  mass  when  the  liquid  is  heated. 

The  Tersulphide  of  Selenium,  SeS3,  is  formed  when  three  equivalents  of  sul- 
phur and  one  of  selenium  are  fused  together. 

METALLIC  SELENIDES  are  prepared  artificially  by  methods  similar  to  those 
which  furnish  the  sulphides,  to  which  they  are  analogous  in  their  properties. 
The  selenides  of  the  alkaline  metals  are  red,  or  red-brown;  those  of  the  other 


172 


PHOSPHORUS. 


metals  (with  the  exceptions  before  mentioned)  are  dark-colored,  and  possess  a 
certain  metallic  lustre.  When  heated  in  air  they  are  decomposed,  though  not  so 
rapidly  as  the  sulphides ;  the  selenium  burns  away  with  a  reddish-blue  flame. 
Some  selenides,  like  the  sulphides,  exist  in  combination  with  water.  The  alkaline 
selenides  are  soluble  in  water;  they  generally  possess  a  reddish  tinge,  owing 
doubtless  to  excess  of  selenium,  as  they  soon  decompose  on  exposure  to  air  ; 
when  mixed  with  acids  they  evolve  hydroselenic  acid. 


PHOSPHORUS.1 

Sym.  P.     Eq.  32.3     Sp.  Gr.  1.77. 

§  113.  This  element  was  discovered  by  Brandt,  in  1669,  who  obtained  it  by 
distilling  the  residue  of  urine;  the  first  method  of  preparing  it  was  published  by 
Kiinckel. 

Phosphorus  occurs,  in  combination  with  oxygen  and  metallic  oxides,  in  the 
bones  of  animals,  in  urinary  and  other  excrements,  and  in  many  portions  of  the 
vegetable  creation.  It  exists  in  fibrin  and  albumen,  both  animal  and  vegetable. 
In  the  mineral  kingdom  it  occurs  as  phosphoric  acid,  in  combination  with  lime 
(as  apatite),  alumina  (wavellite),  lead,  copper,  &c.,  and  also  in  meteoric  iron. 
It  likewise  is  found  occasionally  in  marshy  districts,  as  phosphuretted  hydrogen 
(resulting  from  vegetable  or  animal  decay).3 

Preparation. — In  order  to  obtain  phosphorus,  bones,  which  consist  almost 
entirely  of  gelatin  and  phosphate  of  lime,  are  calcined  in  open  vessels  until  the 
former  is  entirely  burnt  away.  The  bone  ash  thus  obtained  is  then  reduced  to 
powder;  3  parts  of  this  ash,  2  parts  of  oil  of  vitriol,  and  16  parts  of  water,  are 
intimately  mixed  and  digested  together  for  some  considerable  time;  the  liquid, 
which  then  contains  acid  phosphate  of  lime,  is  separated  by  straining  through 
linen  from  the  insoluble  sulphate  of  lime,  concentrated  to  a  thick  syrup,  and 
afterwards  mixed  with  f  part  of  charcoal,  when  it  assumes  a  doughy  consistence. 
The  mass  is  then  strongly  heated  in  an  iron  vessel,  being  kept  constantly  stirred 
until  perfectly  dry,  and  afterwards  transferred,  when  cool,  as  rapidly  as  possible, 
into  an  iron  or  stoneware  retort,  to  the  neck  of  which  is  adapted  a  wide  tube, 
bent  at  right  angles,  and  passing  to  the  bottom  of  a  receiver  containing  water, 
and  provided  with  an  outlet  for  the  gaseous  products.  The  receiver  should  also 
be  surrounded  with  water.  The  phosphoric  acid  is  acted  upon  by  the  charcoal 
in  the  following  manner : — 4 

P05+C5=5CO+P; 

but  only  the  excess  of  phosphoric  acid  contained  in  the  acid  phosphate  of  lime 
is  acted  upon  by  the  charcoal,  ordinary  phosphate  of  lime  being  left  in  the  retort. 
The  phosphorus  is  condensed  by  the  water  in  the  receiver,  as  it  distils  over ;  the 
carbonic  oxide  evolved  is  generally  mixed  with  some  phosphuretted  hydrogen, 
in  consequence  of  the  presence  of  a  small  quantity  of  water  in  the  mixture, 
which,  undergoes  decomposition,  the  hydrogen  uniting  with  a  portion  of  the 

1  $£;,  light,  <f>fgiiv,  to  bear.  *  Berzelius,  31.6;'  Schrotter,  31. 

3  Nearly  all  soils  contain  phosphorus  in  the  form  of  phosphoric  acid,  but  in  very  minute 
proportions ;  the  plants  which  grow  upon  these  soils  contain  it  in  larger  quantities,  since 
they  have  as  it  were  concentrated  it  within  their  tissues ;  the  animals  which  live  upon 
such  plants  contain  the  largest  proportion  of  phosphorus,  and  hence  they  form  the  source 
from  which  this  element  is  prepared. 

4  A  modification  of  the  above  process  has  been  proposed  by  Wohler,  which  consists  in 
adding  to  the  mixture  of  acid  phosphate  and  charcoal,  a  quantity  of  sand  (silicic  acid), 
which  combines  with  the  lime,  thus  liberating  the  whole  of  the  phosphoric  acid. 


PHOSPHORUS.  173 

phosphorus.  This  gas  being  spontaneously  inflammable,  there  is  some  little  risk 
of  explosion  attending  the  preparation  of  phosphorus,  unless  the  mixture  has 
been  most  carefully  dried.  After  the  phosphorus  has  distilled  over,  it  is  melted 
under  warm  water  and  pressed  through  chamois  leather,  by  which  process  it  is 
freed  from  adhering  charcoal  and  red  oxide  of  phosphorus ;  it  is  then  once  more 
melted,  and  introduced  into  glass  tubes,  closed  at  one  end  with  a  cork.  When 
the  phosphorus  is  cool,  it  is  easily  pushed  out  in  the  form  of  a  stick.  Phosphorus 
must  be  preserved  under  water  in  a  tightly-closing  vessel;  it  is  also  advisable  to 
keep  it  in  the  dark. 

Properties. — Phosphorus  is,  when  pure,  a  colorless,  or  faintly  yellow,  trans- 
parent, or  semi-opaque  solid,  possessing  the  appearance  and  consistence  of  wax. 
It  crystallizes  in  regular  octohedra  and  rhomboidal  dodecahedra.  It  fuses  at 
113°  F.  (45°  C.)>  becoming  a  transparent  oily  liquid,  which  frequently  may  be 
cooled  down  far  below  the  melting  point  without  solidifying,  as  it  does,  however, 
the  moment  it  is  brought  into  contact  with  a  solid  substance.  The  boiling  point 
of  phosphorus  is  554°  F.  (290°  C.);  its  vapor  is  colorless,  and  possesses  a  den- 
sity of  4.355.  It  volatilizes  at  far  below  its  boiling  point,  and  is  even  slightly 
volatile  at  ordinary  temperatures.  Phosphorus  is  itself  devoid  of  taste  or  smell, 
but  when  exposed  to  the  air  it  undergoes  a  slow  combustion,  appearing  luminous 
in  the  dark,  and  giving  off  white  vapors,  which  consist  of  phosphorous  acid  (said 
to  be  mixed  with  phosphoric  acid),  at  the  same  time  emitting  a  peculiar  odor, 
something  like  garlic.1  This  smell  is  partly  owing  to  the  production  of  ozone 
(see  §  72).  Phosphorus  is  insoluble  in  water,  but  soluble  in  alcohol,  ether, 
bisulphide  of  carbon,  essential  oils,  and  terchloride  of  phosphorus.  When  in 
solution  it  has  an  acrid,  unpleasant  taste;  it  acts  as  a  violent  irritant  poison. 

Phosphorus  is  highly  inflammable;  when  heated  in  air  it  soon  takes  fire, 
burning  with  a  white  brilliant  light,  and  evolving  white  vapors  consisting  of 
phosphoric  acid.  A  piece  of  wood  or  paper  cannot  easily  be  kindled  in  the  flame 
of  phosphorus,  since  the  phosphoric  acid  condenses  upon  its  surface,  thus  pro- 
tecting it  from  the  action  of  the  flame.  When  dry,  phosphorus  may  also  inflame 
spontaneously,  especially  in  warm  weather,  or  if  repeatedly  handled;  it  is  there- 
fore necessary  to  manipulate  with  this  substance  under  water;  or,  if  this  be 
impracticable,  the  hands  and  phosphorus  should  both  be  immersed  in  cold  water 
from  time  to  time. 

The  inflammability  of  phosphorus  is  much  increased  when  it  is  in  a  finely 
divided  state;  this  is  well  seen  if  some  phosphorus  be  dissolved  in  bisulphide  of 
carbon  at  a  very  gentle  heat,  and  the  solution  poured  upon  a  piece  of  filtering- 
paper.  The  bisulphide  of  carbon  evaporates  rapidly,  leaving  a  thin  film  of 
phosphorus  upon  the  surface,  which  inflames  as  soon  as  the  paper  is  dry.  Phos- 
phorus may  also  be  kindled  by  friction,  or  percussion. 

Phosphorus  is  capable  of  existing  in  three  modifications,  differing  from  each 
other  to  a  considerable  extent  in  many  of  their  properties,  though  identical  in 
their  chemical  character.  These  are — 1st,  the  ordinary  phosphorus,  the  proper- 
ties of  which  have  just  been  described;  2d,  white  phosphorus;  and  3d,  red, 
or  amorphous  phosphorus.  The  two  latter  are  termed  allotropic3  modifications 
of  phosphorus. 

White  Phosphorus. — If  phosphorus  be  exposed  under  water,  to  sunlight,  or 
diffused  daylight,  it  becomes  coated,  after  a  time,  with  a  white  opaque  crust,  the 

1  This  gradual  oxidation  of  phosphorus  may  be  prevented  by  the  presence  of  a  small 
quantity  of  olefiant  gas,  ether-vapor,  or  some  essential  oil ;  in  fact,  it  is  said  that  phos- 
phorus may  be  distilled  in  an  atmosphere  containing  a  considerable  quantity  of  turpen- 
tine-vapor.    In  pure  oxygen,  at  a  temperature  of  60°  F.  (15°.5  C.),  no  oxidation  of  phos- 
phorus takes  place;  it  commences  at  once,  however,  if  the  gas  be  rarefied,  or  diluted 
with  hydrogen,  nitrogen,  or  carbonic  acid. 

2  See  I  103. 


174  PHOSPHORUS. 

specific  gravity  of  which  is  1.515.  It  may  be  dried  without  alteration  over  oil 
of  vitriol,  but  is  converted  into  ordinary  phosphorus  at  a  temperature  even  below 
122°  F.  (50°  C.),  unaccompanied  by  loss  of  weight  or  production  of  water,  showing 
that  this  white  substance  is  only  phosphorus  in  an  altered  state  of  aggregation. 

Red,  or  Amorphous  Phosphorus. — This  modification  of  phosphorus  is  likewise 
produced  by  the  action  of  light  on  the  ordinary  modification,  under  water  or  alco- 
hol, or  in  carbonic  acid  and  gases  containing  no  oxygen ;  it  was  formerly  regarded 
as  an  oxide  of  phosphorus.  Berzelius  was  the  first  to  consider  it  as  allotropic 
phosphorus.  It  has  recently  been  more  completely  examined  by  Schrbtter,  who 
has  found  that  it  may  be  readily  obtained  by  exposing  phosphorus,  for  a  length 
of  time,  in  an  atmosphere  free  from  oxygen  or  moisture,  to  a  temperature  ranging 
between  464°  and  482°  F.  (240°  and  250°  C.) ;  the  fused  phosphorus,  which 
at  first  is  transparent  and  colorless,  will  gradually  become  red  and  opaque,  and 
may  be  finally  freed  from  any  small  portion  of  ordinary  phosphorus  by  digestion 
in  bisulphide  of  carbon,  in  which  this  amorphous  modification  is  perfectly  insoluble. 

When  dry,  amorphous  phosphorus  is  a  scarlet,  or  carmine,  lustreless  powder, 
which  becomes  darker  when  heated.  It  is  also  obtained  on  the  large  scale  in 
dark  dense  masses  of  a  red,  and  sometimes  blackish-brown  color. 

Its  specific  gravity  is  1.964  at  50°  F.  (10°  C.)  It  does  not  become  luminous 
in  the  dark  until  heated  to  a  temperature  closely  approaching  that  at  which  it 
inflames  (500°  F.  260°  C.);  and,  under  all  circumstances,  this  substance  is  much 
less  inflammable  than  ordinary  phosphorus.  It  is  insoluble  in  most  of  the  sol- 
vents for  phosphorus,  and  has  been  found  devoid  of  the  poisonous  properties  of 
that  substance  in  its  ordinary  condition. 

When  distilled  in  an  atmosphere  of  carbonic  acid  at  a  temperature  of  500°  F. 
(260°  C.),  it  is  reconverted  into  ordinary  phosphorus. 

Phosphorus  combines  with  oxygen  to  form  suboxide  of  phosphorus,  P30, 
hypophosphorous  acid,  PO,  phosphorous  acid,  P03,  and  phosphoric  acid,  P05;  with 
hydrogen  it  forms  three  peculiar  compounds  (which  will  be  subsequently  de- 
scribed); it  also  forms  compounds  with  nitrogen,  chlorine,  bromine,  iodine, 
sulphur,  and  selenium. 

The  affinity  of  phosphorus  for  the  metals  is  inferior  to  that  of  sulphur.  The 
compounds  it  forms  are  termed  phosphides  (phosphurets),  and  are  somewhat 
analogous  to  the  sulphides. 

The  phosphorus  of  commerce  frequently  contains  arsenic  and  sulphur.  In 
order  to  detect  these  impurities,  the  phosphorus  may  be  heated  with  moderately 
concentrated  nitric  acid  (when  arsenic  is  sometimes  left  as  a  black  powder);  the 
nitric  solution  is  evaporated  nearly  to  dryness,  and  divided  into  two  parts — one 
to  be  tested  for  arsenic  by  boiling  with  sulphite  of  ammonia,  evaporating  to  expel 
sulphurous  acid,  and  passing  sulphuretted  hydrogen,  when  the  yellow  sulphide 
of  .arsenic  will  be  precipitated — the  other  portion  is  diluted  considerably  with 
water,  and  tested  with  chloride  of  barium,  in  the  presence  of  hydrochloric  acid ; 
if  a  white  precipitate  of  sulphate  of  baryta  is  obtained,  the  presence  of  sulphur 
in  the  phosphorus  may  be  inferred. 

Uses  of  Phosphorus.— This  element  is  extensively  used  for  the  manufacture 
of  lucifer  matches,  for  which  the  red  modification  has  of  late  been  employed, 
since  it  is  less  dangerous  to  handle,  and  is  not  so  liable  to  spontaneous  inflam- 
mation. Phosphorus  is  also  sometimes  employed  in  small  quantities  medicinally; 
and  in  Germany  it  is  generally  substituted  for  arsenic,  as  a  poison  for  rats,  &c. 


HYPOPHOSPHOROUS   ACID.  175 


PHOSPHORUS   AND   OXYGEN. 

Suboxide  of  phosphorus     .     P30  Phosphorous  acid 


Hypophosphorous  acid       .     PO 


Phosphoric  acid 


SUBOXIDE  OF  PHOSPHORUS,  P30.     Eq.  72. 

§  114.  Preparation. — This  compound  is  produced  by  throwing  a  stream  of 
oxygen  upon  phosphorus  fused  under  water.  Vivid  flashes  of  light  are  produced, 
and  some  phosphoric  acid  is  simultaneously  formed ;  this,  being  soluble  in  water, 
may  be  easily  separated,  by  washing,  from  the  pulverulent  suboxide  of  phospho- 
rus, which  is  dried  over  oil  of  vitriol.  Any  unoxidized  phosphorus  may  be 
extracted  by  means  of  bisulphide  of  carbon. 

Properties. — Suboxide  of  phosphorus  is  a  red  powder,  which  is  insoluble  in 
ether,  alcohol,  volatile  and  fixed  oils ;  and,  when  heated  in  close  vessels,  is  con- 
verted into  phosphoric  acid,  and  phosphorus : — 

5P30=P05+P9. 

If  heated  nearly  to  redness  in  air,  it  takes  fire,  being  converted  into  phosphoric 
acid ;  it  oxidizes  gradually  when  moist,  or  in  damp  air ;  it  takes  fire  in  chlorine, 
and  also  when  brought  into  contact  with  nitric  acid,  by  which  it  is  immediately 
converted  into  phosphoric  acid.  It  is  also  decomposed  by  solutions  of  the  alka- 
lies, hypophosphite  of  the  alkali,  and  phosphuretted  hydrogen  being  produced. 

A  hydrate  of  this  suboxide  also  exists,  but  cannot  be  preserved,  since  it  parts 
with  its  water,  yielding  the  red  suboxide,  directly  an  attempt  is  made  to  dry  it, 
even  at  ordinary  temperatures.  It  is  a  yellow  substance,  slightly  soluble  in  water. 

HYPOPHOSPHOROUS  ACID,  PO.    Eg.  40. 

Preparation. — When  the  phosphides  of  the  alkaline  metals,  or  of  barium, 
strontium  and  magnesium,  are  acted  upon  by  water,  hypophosphites  are  produced. 
It  may  also  be  obtained  by  boiling  phosphorus  with  aqueous  solutions  of  the  al- 
kalies, milk  of  lime,  or  baryta-water. 

Phosphoric  acid  and  phosphuretted  hydrogen  are  simultaneously  produced : — 
6(BaO.HOHP4=3BaO.P05+3BaO.PO+2PH3. 

The  best  method  of  obtaining  a  solution  of  the  acid  consists  in  boiling  phos- 
phorus with  baryta-water  in  an  open  wide-mouthed  flask,  and  separating  the 
precipitated  phosphate  of  baryta  by  filtration;  a  slight  excess  of  sulphuric  acid 
is  added  to  the  solution  to  separate  the  baryta,  the  filtered  liquid  digested  with 
oxide  of  lead  in  the  cold,  filtered,  and  the  clear  solution  of  hypophosphite  of 
lead  thus  produced,  decomposed  by  hydrosulphuric  acid;  the  liquid  is  then  freed 
from  sulphide  of  lead  by  filtration,  and  concentrated  by  evaporation. 

Properties. — Hypophosphorous  acid  does  not  exist  in  the  anhydrous  state; 
upon  concentrating  the  aqueous  solution,  a  very  acid,  viscid  liquid  is  obtained, 
which  is  a  hydrate  of  the  acid,  of  the  formula,  3HO.PO.     When  heated,  it  is 
decomposed  into  phosphoric  acid,  and  phosphuretted  hydrogen  gas : — 
2(3HO.PO)=3HO.P05+PH3. 

Hypophosphorous  acid  is  a  powerful  reducing  agent,  being  easily  converted 
into  phosphoric  acid  at  the  expense  of  the  oxygen  contained  in  the  other  sub- 
stance. This  acid  appears  to  be  tribasic. 

The  hypophosphites  are,  most  of  them,  crystallizable,  and  appear  to  exist  com- 
bined with  a  certain  amount  of  water.  When  heated,  they  are  decomposed  into 
phosphates  and  phosphuretted  hydrogen  (a  little  suboxide  of  phosphorus  appears 
likewise  to  be  produced).  These  salts  are  all  soluble  in  water,  and  some  are  solu- 
ble in  alcohol;  they  are  converted  into  phosphates  by  boiling  in  contact  with  air. 


176  PHOSPHORIC   ACID. 

PHOSPHOROUS  ACID,  P03.    Eq.  56. 

This  acid  is  produced  by  the  slow  and  imperfect  combustion  of  phosphorus. 

Preparation. — The  anhydrous  acid  is  obtained  by  heating  phosphorus  gently 
in  a  narrow  glass  tube,  drawn  out  to  a  long  narrow  point,  through  which  a  very 
slow  stream  of  dry  air  is  passed;  the  acid  forms  a  white  sublimate  in  the  anterior 
part  of  the  tube;  phosphoric  acid  and  suboxide  of  phosphorus  are  simultaneously 
formed. 

Properties. — Phosphorous  acid  forms  white  bulky  flakes,  deliquescing  in 
damp  air.  It  is  capable  of  being  sublimed,  and  does  not  redden  dry  litmus-paper. 
When  heated  in  close  vessels,  it  is  converted  into  anhydrous  phosphoric  acid  and 
phosphorus : — 

5(P03)=3P05+P3. 

The  hydrate,  P03.3HO,  is  prepared  by  decomposing  the  terchloride  of  phos- 
phorus by  water : — 

PC13  +  6HO=P03.3HO + 3HC1. 

The  hydrochloric  acid  simultaneously  produced  is  expelled  by  a  gentle  heat,  and 
the  solution  of  acid  concentrated,  until  it  yields  a  mass  of  deliquescent  crystals; 
if  evaporated  still  further  (in  vacuo),  it  yields  a  thick  uncrystallizable  syrup. 
When  heated  in  this  state,  it  is  decomposed  into  phosphoric  acid,  phosphuretted 
hydrogen,  and  water : — 

4(3HO.P03) =3(3HO.P05)  +  PH3. 

Phosphorous  acid  also  acts  as  a  reducing  agent,  on  account  of  its  affinity  for  oxy- 
gen. It  may  be  detected  in  the  water  under  which  phosphorus  has  been  kept  for 
some  time,  by  testing  with  solution  of  nitrate  of  silver,  when  a  black  precipitate 
of  metallic  silver  is  obtained. 

Phosphorous  acid  is  a  tribasic  acid;  it  does  not  possess  very  powerful  affinities 
for  bases. 

The  phosphites  appear  always  to  exist  in  combination  with  water.  Some  are 
soluble  in  the  latter,  and  those  which  are  insoluble  may  be  dissolved  in  the  pre- 
sence of  excess  of  acid.  Phosphites  are  not  oxidized  by  exposure  to  air  at  ordi- 
nary temperatures;  they  are,  however,  converted  into  phosphates  by  chlorine, 
nitric  acid,  and  many  metallic  oxides.  Solutions  of  these  salts  produce  no  pre- 
cipitate in  a  mixture  of  chloride  of  ammonium,  ammonia,  or  sulphate  of  magnesia, 
whereby  they  are  easily  distinguished  from  phosphates. 

Another  acid,  intermediate  between  phosphorous  and  phosphoric  acid  has  been 
described  by  Pelletier,  to  which  the  names  hypophosphoric  acid  and  phosphatic 
acid  have  been  given. 

It  is  also  formed  by  the  slow  combustion  of  phosphorus,  and  is  prepared  by 
introducing  sticks  of  phosphorus  into  tubes  elongated  at  the  bottom,  and  placed 
side  by  side  in  a  funnel,  the  neck  of  which  dips  in  a  bottle  placed  in  a  vessel 
containing  water;  this  arrangement  should  be  kept  in  a  cool  place,  and  the  mouth 
of  the  funnel  should  be  partly  covered  with  a  glass  plate. 

The  acid  drops  into  the  bottle  as  it  is  formed;  it  appears  as  a  syrupy  liquid, 
possessing  a  faint  garlic  smell. 

The  composition  of  this  acid  is  not  thoroughly  established;  it  appears  to  pos- 
sess the  formula  Pa00,  being  intermediate  between  phosphorous  and  phosphoric 
acids. 

PHOSPHORIC    ACID  (anhydrous*),  P05.    Eq. 72. 

§  115.  Phosphoric  acid  is  found  abundantly  in  the  mineral  kingdom,  in  com- 
bination with  various  metallic  oxides,  as  already  mentioned.  It  exists  in  several 
igneous  rocks;  and  in  all  rocks  of  primitive  origin.  It  is  also  found  in  the  animal 


PHOSPHORIC   ACID. 


.  . 


kingdom,  as  phosphates  of  lime,  magnesia,  and  ammonia,  and  in  the  ashes  of 
many  plants. 

ANHYDROUS  PHOSPHORIC  ACID  is  produced  by  the  rapid  combustion  of  phos- 
phorus in  dry  air  or  oxygen.  It  is  thus  obtained  in  white  light  flakes,  which 
fuse  to  a  vitreous  mass  at  a  red  heat,  and  sublime  at  a  still  higher  temperature. 
It  does  not  appear  to  possess  acid  properties,  until  it  has  combined  with  water. 
It  unites  with  the  latter  with  great  energy,  a  hissing  noise  being  produced  when 
water  is  dropped  upon  it;  it  does  not,  however,  disappear  immediately,  but  forms* 
a  flocculent  hydrate,  which  gradually  dissolves. 

It  is  decomposed  by  charcoal  at  a  red  heat,  and  also  by  potassium,  sodium,  iron, 
and  some  other  metals,  phosphides  of  the  metals  and  phosphates  of  the  metallic 
oxides  being  generally  produced.1 

HYDRATES  OF  PHOSPHORIC  ACID. — There  exist  three  different  hydrates  of 
phosphoric  acid  (besides  modifications  of  these  lately  discovered).  Several  views 
are  taken  of  the  true  constitution  of  these  hydrates,  which  differ  remarkably  from 
each  other  in  their  properties.  They  are  considered  either  as  anhydrous  phos- 
phoric acid  in  combination  with  various  proportions  of  water,  or,  according  to  the 
theory  of  hydrogen-acids,  as  perfectly  different  compounds  of  the  formulae  P06H, 
P07H2,  P08H3.  Though  the  latter  view  affords  a  better  explanation  of  the  pro- 
perties and  constitution  of  these  acids,  the  former  is  still  generally  adopted 
among  chemists.  These  acids  are  termed  mono-,  bi-  and  tri-basic  phosphoric  acids, 
or  metaphosphoric,  pyrophosphoric,  and  common  phosphoric  acids. 

MONOBASIC,  OR  METAPHOSPHORIC  ACID,  HO.P05. 

This  acid  is  formed  by  adding  water  to  the  anhydrous  acid.  It  is  best  obtained 
by  the  following  process :  1  part  of  phosphorus  is  cut  into  small  pieces,  and  in- 
troduced into  a  retort  connected  with  a  receiver,  and  containing  13  parts  of  nitric 
acid,  spec.  grav.  1.2 ;  the  retort  is  moderately  heated  on  a  sand-bath,  and  the  nitric 
acid  which  distils  over  returned  to  it  from  time  to  time,  until  the/  phosphorus 
has  disappeared ;  the  greater  part  of  the  nitric  acid  is  then  distilled  off,  and  the 
residual  liquid  evaporated  in  a  platinum  capsule  as  long  as  any  water  is  evolved ; 
upon  cooling,  the  phosphoric  acid  appears  as  a  colorless  glass  (frequently  termed 
glacial  phosphoric  acid),  which  dissolves  slowly  in  water,  and  is  volatilized  to 
some  extent  when  heated  to  redness.  The  acid  obtained  by  this  method  sometimes 
contains  traces  of  arsenic,  which  may  be  detected  by  Reinsch's  test  (see  Analysis). 

A  solution  of  this  acid  may  be  also  obtained  by  preparing  the  metaphosphate 
of  lead  from  the  soda-salt,  produced  by  igniting  ammonio-phosphate  of  soda, 
microcosmic  salt  (NaO.NH4O.HO.P05),  decomposing  the  lead-salt  by  means  of 
hydrosulphuric  acid,  and  heating  the  solution,  separated  from  the  sulphide  of 
lead,  to  expel  the  excess  of  the  gas. 

The  solution  of  this  acid  gives,  with  nitrate  of  silver,  a  white  crystalline  pre- 
cipitate; it  also  coagulates  albumen,  and  forms  a  difficultly- soluble  salt  when 
mixed  with  a  solution  of  potassa.  If  kept  for  some  days,  or  when  boiled  for  some 
time,  it  combines  with  an  additional  equivalent  of  water,  forming  pyrophosphoric 
acid,  and  afterwards  passes  into  ordinary  or  tribasic  phosphoric  acid.  The  water 
of  hydration  of  this  acid  cannot  be  expelled  by  heat. 

Metaphosphoric  acid  forms  with  bases  only  one  class  of  salts,  having  the  gene- 
ral formula  MO.P05.  The  soluble  metaphosphates  have  a  slightly  acid  reaction. 
They  yield  a  white  precipitate  with  nitrate  of  silver. 

[The  behavior  of  metaphosphoric  acid  with  bases  under  various  circumstances 
has  been  submitted  to  close  examination  by  Maddrell,  Henneberg,  and  Fleitmann. 

1  The  powerful  affinity  of  anhydrous  phosphoric  acid  for  water  renders  it  very  useful 
as  a  dehydrating  agent ;  it  is  especially  employed  in  organic  investigations. 
12 


178  PHOSPHORIC   ACID. 

The  last-named  chemist  has  come  to  the  conclusion  that  there  exist  five  poly- 
meric modifications  of  metaphosphoric  acid,  which  he  distinguishes  as  follows  : — 
Mono- metaphosphoric  acid       ....       P05.HO 

Di-metaphosphoric  acid 2P05.2HO 

Tri-metaphosphoric  acid  .  *.&&&&.  3P05.3HO 
Tetra-metaphosphoric  acid  ....  4POS.4HO 
Hexa-metaphosphoric  acid  ....  6P05.6HO 

The  following  is  his  view  regarding  the  formation  of  these  various  modifications : 
J/cwo-metaphosphoric  acid  is  produced  when  equal  equivalents  of  potassa  and 
metaphosphoric.  acid  are  united  together;  c^-metaphosphoric  acid  is  formed  when 
equal  equivalents  of  metaphosphoric  acid  and  protoxide  of  copper,  zinc,  or  man- 
ganese, are  heated  together;  /n'-metaphosphoric  acid  is  only  produced  when  a 
mixture  of  equal  equivalents  of  metaphosphoric  acid  and  soda  is  allowed  to  crys- 
tallize by  gradual  cooling;  tetra- metaphosphoric  acid  is  obtained  by  the  action  of 
teroxide  of  bismuth  and  the  protoxides  of  lead  and  cadmium  upon  metaphos- 
phoric acid;  and  hexa- metaphosphoric  acid  is  produced  by  igniting  the  hydrate 
of  phosphoric  acid,  by  rapidly  cooling  the  fused  soda-salt,  and  also  by  the  action 
of  protoxide  of  silver.] 

PYROPHOSPHORIC  ACID,  2HO.P05. 

If  tribasic  phosphoric  acid  is  evaporated  in  a  platinum  vessel  until  the  tem- 
perature reaches  415°  F.  (213°  C.),  it  is  converted  into  pyrophosphoric  acid, 
which,  when  concentrated,  forms  a  soft  viscid  glass,  very  soluble  in  water.  A 
solution  of  this  acid  may  be  obtained  by  precipitating  pyrophosphate  of  soda 
(2NaO.P05)  with  acetate  of  lead,  diffusing  the  washed  precipitate  through  water, 
decomposing  it  with  hydrosulphuric  acid,  and  freeing  the  filtered  solution  from  the 
latter  by  evaporation.  A  solution  of  this  acid  does  not  coagulate  albumen  nor 
precipitate  the  chlorides  of  barium  and  calcium,  and  yields  (only  upon  neutraliz- 
ing with  ammonia)  a  white  flaky  precipitate  with  nitrate  of  silver.  A  solution 
of  this  acid  may  be  preserved  for  some  time  in  the  cold,  but  is  converted  by  heat 
into  tribasic  phosphoric  acid. 

Pyrophosphoric  acid  forms  two  classes  of  salts  with  metallic  oxides ;  the  acid 
pyrophosphates,  MO.HO.P05,  and  the  neutral  pyrophosphates  2MO.PO-.  The 
latter  salts  possess  a  slightly  alkaline  reaction.  When  a  pyrophosphate  is  heated 
with  excess  of  base,  it  is  converted  into  a  tribasic  phosphate. 

TRIBASIC,  OR  ORDINARY  PHOSPHORIC  ACID. 
3HO.P05. 

Preparation. — It  has  already  been  stated  that  when  solutions  of  the  preceding 
acids  are  heated  for  some  time,  they  are  converted  into  ordinary  phosphoric  acid. 
This  acid  may  therefore  be  prepared  by  burning  phosphorus  gradually  in  air, 
under  a  bell  jar,  heating  the  resulting  product  with  nitric  acid,  to  convert  any 
oxide  of  phosphorus  or  phosphorous  acid  into  phosphoric  acid,  expelling  the  nitric 
.acid  by  evaporation,  and  dissolving  the  resulting  glacial  mass  in  hot  water. 

A  method  commonly  used  for  preparing  this  acid,  is  to  decompose  the  acid 
phosphate  of  lime  (obtained  according  to  the  method  given  in  the  preparation  of 
phosphorus)  with  ammonia  and  carbonate  of  ammonia,  the  former  of  which  de- 
composes the  acid  phosphate  of  lime,  while  the  latter  precipitates  the  lime  from 
the  sulphate. 

The  solution  containing  phosphate  and  sulphate  of  ammonia  is  evaporated  to 
dryness  and  the  residue  ignited,  when  both  the  salts  are  decomposed,  and  glacial 
phosphoric  acid  remains ;  if  this  be  boiled  with  water,  it  gives  the  tribasic  acid. 
It  is  said  that  the  phosphoric  acid  thus  prepared  always  contains  a  little  am- 
monia. 


PHOSPHORUS  AND  HYDROGEN.  179 

Properties. — If  a  solution  of  ordinary  phosphoric  acid  be  evaporated  to  a  thin 
syrup,  hard  transparent  crystals  of  trihydrate  of  phosphoric  acid  are  obtained. 
Tribasic  phosphoric  acid  parts  with  its  water  very  slowly  at  320°  F.  (160°  C.) 
If  heated  for  some  time  to  415°  F.  (213°  C.),  it  loses  one  equivalent  of  its  basic 
water,  becoming  converted  into  pyrophosphoric  acid,  2HO.P05;  at  a  red  heat  it 
loses  a  second  equivalent,  becoming  metaphosphoric  acid,  HO.P05.  A  solution 
of  tribasic  phosphoric  acid  does  not  coagulate  albumen,  nor  does  it  precipitate  a 
solution  of  nitrate  of  silver ;  but  when  a  small  quantity  of  ammonia  is  added,  . 
a  yellow  precipitate  of  tribasic  phosphate  of  silver  is  obtained. 

Ordinary  phosphoric  acid  forms  with  bases  three  different  classes  of  salts ; 
the  neutral  tribasic  phosphates  of  the  formula  3MO.P05;  the  common  phos- 
phates containing  two  equivalents  of  base,  and  one  of  basic  water,  to  one  of 
acid,  2MO.HO.P05;  and  the  acid  tribasic  phosphates,  containing  one  equivalent 
of  base,  and  two  of  basic  water,  to  one  equivalent  of  acid,  M0.2HO.P05.  The 
neutral  tribasic  phosphates  of  the  alkalies  have  a  strongly  alkaline  reaction;  the 
common  phosphates  of  the  alkalies  are  feebly  alkaline;  when  ignited  they  are 
converted  into  pyrophosphates ;  the  acid  phosphates  are  converted  by  ignition 
into  metaphosphates. 

The  different  equivalents  of  basic  water  of  tribasic  phosphoric  acidj  may  be 
replaced  by  equivalents  of  different  bases.  All  soluble  tribasic  phosphates  yield 
a  yellow  precipitate  with  nitrate  of  silver. 

Fleitmann  and  Henneberg  have  discovered  two  new  classes  of  phosphates,  in 
which  the  base  is  combined  with  acid  according  to  the  formulae,  3M0.2PO,  and 
6M0.5P05. 

The  soda-salts  of  these  series  will  be  described  in  the  article  upon  soda. 

Liebig  considers  the  relations  between  the  different  modifications  of  phosphoric 
acid  to  be  exhibited  in  the  most  simple  manner,  by  regarding  the  composition  of 
their  salts  in  such  a  light  as  to  compare  quantities  of  these  containing  an  equal 
amount  of  base ;  the  following  table  would  represent  the  general  formulae  of  the 
various  phosphates  according  to  this  view : — 

3MO.P05       Common,  or  tribasic  phosphates     .     .     6M0.2P05 

2MO.P05       Pyrophosphates 6M0.3P05 

3M0.2P05>  Fleitmann  and  Henneberg's  new  phos-  f  6M0.4P05 

6M0.5POJ      phates .  { 6M0.5P05 

MO.P05       Metaphosphates 6M0.6P05 


PHOSPHORUS  AND  HYDROGEN. 

Solid  phosphuretted  hydrogen     ....     P3H 
Liquid  phosphuretted  hydrogen  P  H3 

Gaseous  phosphuretted  hydrogen      .     .     .     P  H3 

SOLID  PHOSPHURETTED  HYDROGEN,  PHOSPHIDE  or  HYDROGEN.    P3H. 

§  116.  Upon  decomposing  by  water  the  phosphide  of  potassium,  formed  by 
fusing  phosphorus  and  potassium  together  under  naphtha,  a  yellow  powder  pre- 
cipitates, which  has  been  shown  to  be  the  solid  phosphide  of  hydrogen. 

This  substance  may  also  be  produced  in  other  ways;  first,  by  exposing  the 
phosphuretted  hydrogen  gas,  obtained  by  heating  phosphorus  with  milk  of  lime, 
to  strong  daylight,  in  bottles  with  the  necks  immersed  in  water.  Yellow  flakes 
are  deposited  after  a  time,  the  gas  losing  the  spontaneous  inflammability  which 
it  at  first  possessed.  Secondly,  it  may  be  obtained  by  acting  upon  phosphide  of 
calcium  (Ca2P)  with  strong  hydrochloric  acid,  phosphuretted  hydrogen  gas  being 
simultaneously  produced.  In  both  of  these  cases  it  appears  that  a  second  com.- 


180  PHOSPHORUS  AND  HYDROGEN. 

pound,  the  liquid  phosphide  of  hydrogen,  to  be  presently  described,  is  produced, 
which  resolves  itself  into  gaseous  and  solid  phosphides,  according  to  the  follow- 
ing equation : — 

5PH3  =  3PH3  +  P2H 

Liquid  phosphide  Gaseous  phosphide  Solid  phosphide. 

Properties. — This  substance,  when  freshly  prepared,  is  yellow,  but  assumes  an 
orange  color  by  exposure  to  light;  it  is  inodorous,  not  luminous  in  the  dark, 
and  takes  fire  at  392°  F.  (200°  C.),  and  also  when  struck  with  a  hammer  upon 
an  anvil.  It  is  decomposed  by  water  in  the  presence  of  an  alkali,  with  the 
evolution  of  hydrogen,  and  the  formation  of  a  hypophosphite : — 

P8H+2HO  +  6KO=2(3KO.PO)  +  H8. 

In  decomposing  phosphide  of  calcium  by  water,  a  greenish  substance  is  fre- 
quently observed,  which  appears  to  be  isomeric  with  this  solid  phosphide. 

LIQUID  PHOSPHIDE  OF  HYDROGEN,  PH3. 

This  compound  is  obtained  by  passing  the  gas  evolved  by  the  action  of  water 
on  phosphide  of  calcium  at  140°  F.  (60°  C.),  through  an  U-shaped  tube  im- 
mersed in  a  freezing  mixture. 

It  is  a  colorless  liquid,  which  does  not  solidify  at  — 4°  F.  ( — 20°  C.),  but  which 
is  volatilized  and  decomposed  at  a  temperature  of  86°  F.  (30°  C.);  it  is  insolu- 
ble in  water,  and  refracts  light  powerfully.  It  is  resolved,  by  the  action  of  light, 
into  solid  and  gaseous  phosphides  of  hydrogen. 

Alcohol  and  oil  of  turpentine  appear  to  dissolve  it,  but  immediately  decom- 
pose it  in  the  above  manner.  It  takes  fire  spontaneously  on  exposure  to  air, 
burning  with  a  bright  light.  When  mixed  in  the  smallest  proportion  with  phos- 
phuretted  hydrogen,  carbonic  oxide,  hydrogen,  or  any  other  inflammable  gas,  it 
renders  them  spontaneously  inflammable. 

GASEOUS  PHOSPHIDE  OF  HYDROGEN,  PHOSPHURETTED  HYDROGEN  GAS. 
PH3.     Sp.  Gr.  1.185. 

Composition  by  Volume. — 1  volume  of  phosphorus  and  6  volumes  of  hydrogen 
condensed  into  4  volumes. 

This  gas  may  be  obtained  in  a  state  of  purity  by  heating  crystallized  phos- 
phorous acid  in  a  green  glass  retort  (if  a  white  glass  retort  be  employed  the  gas 
will  contain  a  little  free  hydrogen,  an  alkaline  phosphite  being  produced  by  the 
action  of  the  phosphorous  acid  on  the~glass). 

Hydrated  phosphorous  acid  is  decomposed  according  to  the  following  equa- 
tion : — 

4(3HO.P03)=PH3-f3(3HO.P05). 

It  may  also  be  obtained  as  already  stated,  together  with  the  solid  compound, 
by  acting  upon  phosphide  of  calcium  with  concentrated  hydrochloric  acid: — 
5Ca.2P+10HCl==10CaCl+P2H-f3PH3. 

When  prepared  by  either  of  these  methods,  this  gas  is  colorless,  possessed  of 
a  disagreeable  alliaceous  odor,  and  is  not  spontaneously  inflammable,  but  burns 
when  a  light  is  applied  to  it,  being  converted  into  water  and  phosphoric  acid. 
A  slight  admixture  of  air,  though  producing  no  effect  at  first,  will  sometimes  cause 
it  to  explode  spontaneously  after  a  time.  It  is  slightly  soluble  in  water. 

Gaseous  phosphuretted  hydrogen  may  also  be  obtained  in  a  spontaneously 
inflammable  state,  by  boiling  phosphorus  together  with  water  and  hydrate  of 
lime,  or  with  a  strong  solution  of  potassa.  A  small  flask  is  filled  to  about  three- 
fourths  with  the  solution  of  potassa  (or  milk  of  lime),  a  few  fragments  of  phos- 


PHOSPHORUS   AND   CHLORINE.  181 

phorus  are  introduced,  and  the  flask  heated  on  a  sand-bath.  As  soon  as  the  gas 
evolved  burns  at  the  mouth,  a  delivery-tube  is  attached,  and  the  phosphuretted 
hydrogen  collected  over  water.  When  a  bubble  is  allowed  to  escape  into  the 
air,  it  will  inflame  with  a  slight  detonation,  producing  a  white  wreath  of  smoke 
(phosphoric  acid),  which  gradually  expands  as  it  ascends. 

The  effect  of  the  simultaneous  action  of  phosphorus  and  an  alkaline  base  upon 
water  is  the  production  of  a  hypophosphite,  together  with  phosphuretted  hydro- 
gen (see  §  114). 

The  spontaneously  inflammable  gas  may  also  be  obtained  by  acting  upon 
phosphide  of  calcium  with  water. 

When  preserved  for  some  time  this  gas  loses  its  spontaneous  inflammability, 
in  consequence  of  the  decomposition  of  the  small  quantity  of  liquid  phosphide  of 
hydrogen  (as  already  described)  to  which  it  owes  this  property.  Many  sub- 
stances which  possess  the  property  of  decomposing  the  liquid  phosphide  (such  as 
hydrochloric  acid,  or  oil  of  turpentine)  deprive  the  gas  at  once  of  its  spontaneous 
inflammability,  which  may,  however,  be  restored  by  acting  upon  the  uninflam- 
mable gas  with  an  oxidizing  agent  (such  as  binoxide  of  nitrogen),  which,  by 
abstracting  a  portion  of  hydrogen,  reproduces  a  small  quantity  of  the  liquid 
compound,  which  remains  diffused  through  the  gas. 

Phosphuretted  hydrogen  gas  (when  spontaneously  inflammable)  also  takes  fire 
in  chlorine  gas,  burning  with  a  greenish-white  light,  and  yielding  hydrochloric 
acid  and  pentachloride  of  phosphorus.  Many  metals  extract  the  phosphorus 
from  this  gas  at  high  temperatures,  yielding  metallic  phosphides  and  free  hydro- 
gen. Some  metallic  solutions  decompose  phosphuretted  hydrogen ;  with  sulphate 
of  copper  a  black  precipitate  is  formed ;  the  gas,  however,  is  not  entirely  absorbed, 
but  loses  its  inflammability. 

The  analogy  of  this  compound,  in  some  respects,  to  ammonia  (to  which  it 
corresponds  in  composition)  is  remarkable.  It  unites  with  hydriodic  acid, 
forming  a  crystalline  compound  analogous  to  chloride  of  ammonium,  which  is 
decomposed  by  water  with  evolution  of  phosphuretted  hydrogen. 

It  also  unites,  like  ammonia,  with  the  higher  oxides  of  tin,  antimony,  iron, 
and  other  metals,  forming  white  saline  compounds. 


PHOSPHORUS  AND  CHLORINE. 

§  117.  These  two  elements  unite  with  considerable  energy,  producing  two 
different  compounds,  the  terchloride  and  pentachloride  of  phosphorus. 

TERCHLORIDE  OF  PHOSPHORUS,  PC13.     Sp.  Gr.  1.45. 

This  chloride  is  formed  by  passing  dry  chlorine  gas  into  or  upon  fused  phos- 
phorus, in  a  retort  moderately  heated  in  a  sand-bath,  until  nearly  the  whole  of 
the  phosphorus  is  converted  into  terchloride,  which  distils  over  into  a  receiver.1 

It  is  a  colorless  transparent  limpid  liquid  which  has  a  pungent  odor,  resem- 
bling that  of  hydrochloric  acid,  and  fumes  when  exposed  to  the  air ;  it  boils  at 
172°.4  F.  (78°  C.) 

When  mixed  with  water,  it  is  gradually  decomposed  into  hydrochloric  and 
phosphorous  acids : — 

PC13  +  3HO=P03+3HC1. 

Terchloride  of  phosphorus  dissolves  a  small  quantity  of  phosphorus  with  the 
aid  of  heat,  the  solution  depositing  a  film  of  phosphorus  as  the  liquid  evaporates. 

1  Since  the  amorphous  phosphorus  has  been  introduced  into  general  use,  the  danger 
attending  the  preparation  of  both  chlorides  of  phosphorus  has  been  considerably  dimi- 
nished. 


182  PHOSPHORUS   AND   CHLORINE. 

PENTACHLORIDE  or  PHOSPHORUS,  PC15. 

This  compound  is  produced  by  allowing  phosphorus  to  burn  in  excess  of  dry 
chlorine  gas  (which  it  does  spontaneously  at  ordinary  temperatures),  or  by  acting 
upon  the  terchloride  of  phosphorus  with  chlorine,  which  gradually  converts  it 
into  the  solid  pentachloride.  The  latter  is  a  snow-white,  flocculent  substance, 
which  volatilizes  below  212°  F.;  its  vapor  density  is  4.85  at  365°  F.  (185°  C.); 
it  may  be  fused  under  pressure,  and  crystallizes,  upon  cooling,  in  transparent 
prisms.  It  fumes  on  exposure  to  air,  and  is  decomposed  by  water  into  phos- 
phoric and  hydrochloric  acids  : — 

PC15+5HO=P05+5HC1. 

It  forms,  with  metallic  oxides,  chloride  of  the  metal  and  phosphate  of  the  oxide. 
Pentachloride  of  phosphorus,  like  phosphoric  acid,  is  sometimes  employed  as  a 
dehydrating  agent ;  it  has  also  lately  been  used  for  producing  chlorine  compounds 
of  organic  derivation.1 

OXYCHLORIDE  OP  PHOSPHORUS,  PCl3Oa.       Sp.    Gr.  1.7. 

Pentachloride  of  phosphorus  is  gradually  converted  by  aqueous  vapor  into 
hydrochloric  acid  and  the  above  compound : — 

PCl5+2HO=PCl303-f2HCl. 

This  substance  is  always  produced  after  a  time,  if  pentachloride  of  phosphorus 
be  preserved  in  an  imperfectly-stoppered  bottle. 

It  is  a  colorless  liquid,  very  limpid,  and  of  high  refracting  power.  It  boils  at 
230°  F.  (110°  C.),  yielding  a  vapor  of  the  density  5.40;  its  odor  is  similar  to 
that  of  terchloride  of  phosphorus.  It  fumes  in  air,  and  is  decomposed,  by  con- 
tact with  water,  into  hydrochloric  and  phosphoric  acids. 

CHLOROSULPHIDE  or  PHOSPHORUS,  PC1S3. 

When  dry  hydrosulphuric  acid  is  passed  over  pentachloride  of  phosphorus,  or 
when  the  latter  is  agitated  in  a  vessel  filled  with  the  dry  gas,  a  colorless  liquid 
of  the  above  composition  is  obtained,  which  boils  at  262°  F.  (128°  C.);  it  is 
slowly  decomposed  by  water  into  hydrochloric,  hydrosulphuric,  and  phosphoric 
acids  : — 

PC13SS+5HO=P05+3HC1+2HS. 

It  is  converted  into  sulplwplwspJioric  add  by  alkalies,  a  metallic  chloride  being 
simultaneously  produced : — 

PC13S3+6KO=3KC1+3KO.P03S3. 

The  sulphophosphates  may  be  crystallized  ;  they  correspond  to  the  tribasic 
phosphates,  the  formula  of  sulphophosphate  of  soda  being — 

3NaO.P03S3-f24IIO. 

This  acid  may  be  replaced  in  its  combinations  with  bases  by  the  weakest  acids; 
when  thus  liberated,  it  is  at  once  decomposed  into  hydrosulphuric  and  phosphoric 

acids : — 

3(HO.PS303)+2HO=3(HO.P05)  +  2HS.* 

PHOSPHORUS  AND  BROMINE. 
When  phosphorus  and  bromine  are  brought  into  contact  in  a  vessel  filled  with 

1  Compounds  of  pentachloride  of  phosphorus  with  various  acids  (e.  g.  sulphuric,  phos- 
phoric, arsenious,  and  tungstic  acids)  have  been  obtained. 

2  By  the  action  of  sulphur  on  pentachloride  of  phosphorus,  Gladstone  has  obtained  a 
liquid  compound  to  which  he  ascribes  the  formula  PS4CL. 


PHOSPHORUS  AND  SULPHUR.  183 

carbonic  acid,  they  unite  instantaneously,  with  incandescence,  the  products  being 
a  solid  or  a  liquid,  according  to  the  proportions  used. 

Terbromide  of  Phosphorus  (P13r3)  may  be  obtained  by  adding  phosphorus,  in 
very  small  pieces,  to  perfectly  anhydrous  bromine,  until  the  color  of  the  latter 
disappears  perfectly ;  excess  of  phosphorus  may  be  separated  by  distillation. 

It  is  a  colorless,  very  volatile,  pungent  liquid,  which  does  not  solidify  at  10°. 4 
F.  ( — 12°  C.) ;  when  in  contact  with  air  it  emits  white  fumes;  and  is  decomposed 
by  water,  with  considerable  evolution  of  heat,  into  hydrobromic  and  phosphorous 
acids.  It  has  also  the  property  of  dissolving  phosphorus. 

Pentabromide  of  Phosphorus  (PBr5)  may  be  formed  by  mixing  the  terbromide 
with  bromine,  or  by  bringing  a  small  excess  of  the  latter  in  contact  with  phosphorus. 

It  is  a  lemon-yellow  solid  substance,  which  crystallizes  in  the  rhomboidal  form 
after  fusion,  and  may  be  obtained  in  needles  by  sublimation.  It  evolves  dense 
fumes  in  air,  and  is  converted  by  water  into  hydrobromic  and  phosphoric  acids. 

An  orybromide  of  pJiospJioruSj  analogous  to  the '  oxychloride,  of  the  formula 
PBr303,  also  exists. 

PHOSPHORUS  AND  IODINE. 

These  two  substances  unite  with  energy  at  ordinary  temperatures,  the  phos- 
phorus bursting  into  flame  if  air  have  access.  The  phosphorus  appears  to  unite 
with  iodine  in  several  proportions  ;  1  of  the  former  to  24  of  the  latter  forms  a 
black  mass,  fusing  at  104°. 8  F.  (46°  C.) ;  1  to  16  forms  a  dark  gray  crystalline 
substance,  fusing  at  84°. 2  F.  (29°  C.);  and  1  to  8  an  orange-yellow  mass,  fusing 
at  212°  F.  (100°  C.)  ;  all  three  are  decomposed  by  water,  yielding  hydriodic 
acid  ;  and  in  addition,  the  first  yields  phosphoric  acid,  the  second  phosphorous 
acid,  and  the  third  phosphorous  acid  and  phosphorus. 

PHOSPHORUS  AND  NITROGEN. 

Ammoniacal  gas  is  absorbed  by  both  the  chlorides  of  phosphorus. 

The  terchloride  of  phosphorus  yields  a  white  solid  which  is  sparingly  soluble 
in  water,  and  has  the  composition  PC13.5NH3.  When  this  compound  is  heated 
in  a  current  of  carbonic  acid,  it  is  resolved  into  hydrogen,  ammonia,  phosphorus, 
and  phosphide  of  nitrogen,  N3P.  This  last  is  a  white  amorphous  powder,  inso- 
luble in  all  menstrua ;  it  is  infusible  and  does  not  volatilize  at  a  red  heat  if  air 
be  excluded,  but  is  slowly  oxidized  when  heated  in  air;  when  heated  in  hydrogen 
it  yields  ammonia.  It  is  but  slowly  affected  by  powerful  oxidizing  agents. 

Gerhardt  states  that  this  compound  contains  hydrogen,  and  assigns  to  it  the 
formula  PN2H,  with  the  name  pliospliam. 

When  the  pentachloride  of  phosphorus  is  saturated  with  ammoniacal  gas,  chlo- 
ride of  ammonium  is  produced,  together  with  a  white  insoluble  substance,  of  the 
formula  N2P.2HO,  to  which  the  names  phosphamide  and  ht/drated pJioapkide  of 
nitrogen  have  been  given.  When  boiled  with  water,  especially  in  presence  of 
acids  and  alkalies,  it  yields  phosphoric  acid  and  ammonia. 

When  heated  out  of  contact  with  air,  it  evolves  ammonia,  and  leaves  a  gray 
insoluble  residue,  which  fuses,  but  is  not  decomposed  when  further  heated ;  its 
formula,  according  to  Gerhardt,  is  PN03. 

When  the  mass  obtained  by  the  action  of  moist  ammonia  upon  pentachloride 
of  phosphorus  is  distilled  with  water,  a  white  substance  passes  over,  which  crys- 
tallizes in  regular  prisms;  it  fuses  below  212°  F.,  and  may  be  distilled  unchanged; 
it  is  insoluble  in  water  and  acids,  but  dissolves  easily  in  alcohol  and  ether,  and 
appears  to  possess  great  stability. 

This  body  has  been  named  the  chlorophosphide  of  nitrogen :  its  formula  is 
N.P.CI, 

PHOSPHORUS  AND  SULPHUR. — These  elements  combine  in  a  number  of  dif- 
ferent proportions ;  if  phosphorus  and  sulphur  be  very  gently  heated  together, 


184  CARBON. 

/ 

they  unite  with  disengagement  of  much  heat,  and  frequently  with  explosion. 
The  safest  method  of  causing  them  to  combine  is  by  fusing  the  phosphorus  in  a 
flask  under  water,  and  then  introducing  gradually,  small  fragments  of  sulphur. 
Compounds  of  a  pale  yellow  color  are  thus  produced,  which  have  been  shown  by 
Berzelius  to  consist  of  a  series  of  sulphides  of  phosphorus,  analogous  to  the  oxides 
of  that  element,  as  is  seen  by  the  following  comparison  : — 

Subsulphide  of  phosphorus      P2S     Suboxide  of  phosphorus    .     P20 

Protosulphide  "  PS      Hypophosphorous  acid      .     PO 

Tersulphide  "  PS3     Phosphorous  acid     .     .     .     P03 

Pentasulphide          "  PS5     Phosphoric  acid  ....     P05 

Persulphide  "  PS^    No  analogous  oxygen  compound. 

They  are  prepared  by  fusing  together  the  two  elements,  in  the  proper  proportions, 

in  the  manner  described.     They  are  insoluble  in  water,  alcohol,  and  ether ;  of 

the  first  two  there  are  red  modifications.    They  combine  with  alkaline  sulphides, 

and  give  rise  to  the  production  of  sulphur-salts,  analogous  to  the  corresponding 

salts  of  the  oxides  of  phosphorus. 

PHOSPHORUS  AND  SELENIUM  appear  likewise  to  be  miscible  in  all  proportions, 
at  a  temperature  "approaching  the  fusing  point  of  phosphorus. 

No  formulae  have  yet  been  assigned  to  the  selenides  of  phosphorus. 

METALLIC  PHOSPHIDES. — The  affinity  of  phosphorus  for  metals  is  not  so 

powerful  as  that  of  sulphur;  nevertheless,  it  unites  with  the  greater  number, 

producing  phosphides.    These  may  be  obtained  by  direct  union  of  the  metal  and 

phosphorus  at  elevated  temperatures,  or  by  heating  the  phosphates  with  charcoal: — 

3MO.P05+C8=8CO+M8P. 

They  may  also  be  formed  by  heating  metallic  oxides  with  phosphorus,  or  by 
bringing  gaseous  phosphuretted  hydrogen  in  contact  with  salts  of  the  metals. 
They  are  solid,  opaque,  and  frequently  possess  metallic  lustre.  Many  of  them 
part  with  their  phosphorus  at  high  temperatures,  the  corresponding  phosphates 
being  sometimes  produced  at  the  same  time,  if  air  be  allowed  access.  They  are 
converted,  by  nitric  and  hypochlorous  acids,  into  phosphates.  The  alkaline  phos- 
phides are  decomposed  by  water,  phosphuretted  hydrogen  being  evolved,  and 
hypophosphite  of  the  metallic  oxide  produced. 


CARBON. 

Sym.  C.     Eq.  6.     Sp.  Gr.j  as  diamond,  3.5  to  3.55  (as  graphite,  1.9  to  2.3). 

§  118.  Lavoisier  was  the  first  to  show  that  carbonic  acid  consisted  of  oxygen 
and  another  element,  carbon  ;  and  that  this  element  existed  in  the  pure  state  as 
the  diamond.  Carbon  is  also  found,  nearly  pure,  in  plumbago,  or  graphite,  and 
in  anthracite.  In  coal  it  is  associated  with  iron,  hydrogen,  earthy  and  alkaline 
compounds,  &c.  In  most  vegetable  and  animal  substances  it  is  the  principal  con- 
stituent ;  it  also  occurs  in  many  minerals,  in  combination  with  oxygen  (as  car- 
bonic acid). 

The  DIAMOND  occurs  principally  at  Golconda,  in  Borneo,  and  Brazil.  It  is 
found  in  gravel  or  sand,  or  in  a  kind  of  conglomerate  of  fragments  of  chalcedony, 
jasper,  and  quartz.  Diamonds  are  generally  found  rough,  and  coated  with  a  crust 
which  renders  them  but  slightly  translucent;  on  removing  this,  however,  they  are 
very  brilliant,  and  generally  colorless  and  transparent,  though  they  also  occur  black, 
yellowish  or  brcmn,  blue,  green,  and  rose-colored.  They  refract  light  powerfully. 
The  regular  octohedron  is  the  primitive  form  of  the  diamond ;  its  most  general 
form,  however,  is  that  of  the  octohedron,  of  which  the  planes  are  replaced  by  low 
pyramids  of  three  planes,  so  that  the  figure  presents  twenty-four  planes,  and  is 


COAL.  185 

therefore  almost  spherical  in  form.  The  surfaces  of  the  crystal  are  seldom  flat, 
having  generally  become  curved,  in  consequence  of  the  continued  attrition  to  which 
they  have  been  subjected  in  the  motion  of  the  alluvial  materials  with  which  it  is 
associated ;  in  fact,  the  action  of  this  attrition  is  so  considerable,  as  frequently  to 
have  reduced  crystals  of  the  form  just  described  to  that  of  an  octohedron  with 
convex  faces.1 

The  diamond  is  the  hardest  of  all  gems,  its  natural  facets  being  harder  than 
those  produced  by  polishing.  The  glazier,  in  choosing  the  diamond  for  cutting 
glass,  makes  use  of  an  edge  of  the  crystal  formed  by  naturally  curved  surfaces, 
since  the  edges  formed  by  flat  planes  merely  scratch  the  glass  without  producing 
any  fissure. 

The  diamond  may  be  cleaved  in  the  direction  of  the  octohedral  plane ;  it  can 
only  be  polished  by  means  of  its  own  dust.  The  diamond  may  be  exposed  to  a 
white  heat  in  a  closed  crucible  without  undergoing  any  change.  When  heated 
in  air,  it  begins  to  burn  at  about  the  fusing-point  of  silver.  If  it  be  placed  between 
the  two  charcoal  points  of  a  very  powerful  battery,  it  becomes  so  brilliant  from 
incandescence  that  the  eye  is  dazzled  when  looking  at  it ;  but  if  viewed  through 
a  smoked  glass  it  will  be  observed  to  swell  up  considerably  and  divide  into  frag- 
ments. When  cold,  it  is  no  longer  transparent,  but  metallic  gray  in  appearance, 
and  very  friable,  resembling  coke  formed  from  bituminous  coal.  Fused  nitre 
rapidly  oxidizes  the  diamond,  the  carbonic  acid  produced  being  retained  by  the 
potassa  in  the  nitre.  Its  examination  according  to  this  method  affords  the  best 
proof  of  its  being  pure  carbon. 

GRAPHITE,  BLACK-LEAD,  OR  PLUMBAGO,  is  another  crystalline  modification 
of  carbon,  very  different  in  appearance  and  physical  properties  to  the  diamond. 
It  is  found  imbedded,  in  the  form  of  rounded  masses,  in  strata  of  limestone, 
mica-schist,  and  granite.  The  most  celebrated  locality  for  this  mineral  is  Bor- 
rowdale,  in  Cumberland.  The  crystalline  form,  in  which  it  is  occasionally  found, 
is  the  six-sided  table;  it  generally  consists,  however,  of  aggregates  of  small  gray 
metallic  scales,  perfectly  opaque,  soft,  and  unctuous  to  the  touch;  it  may  be 
easily  cut,  and  produces  a  lead-gray  mark  upon  paper.  It  always  contains  an 
admixture  of  manganese  and  iron  (existing  apparently  as  oxides,  combined  with 
silicic  and  titanic  acids).  Some  specimens  contain  as  much  as  28  per  cent,  of 
these  impurities,  while  in  others  only  traces  are  found.  .Graphite,  like  the  dia- 
mond, is  unalterable  by  heat.  It  may  be  prepared  artificially  by  bringing  an 
excess  of  charcoal  in  contact  with  fused  cast-iron;  a  portion  of  the  carbon  dis- 
solves, and  separates  out  again  on  cooling,  in  large  scales. 

§  119.  COAL. — The  form  in  which  carbon  is  found  most  abundantly  in  nature 
is  that  of  coal,  in  which  substance  it  is  associated  with  other  bodies,  very  variable 
in  their  nature. 

Microscopic  examination  of  the  various  kinds  of  coal  leaves  no  doubt  that  they 
are  of  vegetable  origin;  even  the  most  massive  coals  exhibit  some  evidence  of 
vegetable  structure,  and  in  others  of  inferior  order,  the  complete  forms  of  various 
portions  of  plants  are  frequently  found  compressed  between  the  layers,  more  or 
less  perfectly  transformed  into  coal.  These  observations,  added  to  the  results  of 
careful  researches  on  the  subject,  render  it  evident  that  coal  has  been  produced 
by  the  combined  action  of  heat  and  pressure  upon  vegetable  matter;  in  short, 
that  it  consists  of  the  vegetation  of  former  ages,  which  has  been  buried  beneath 
waters,  and  subsequently  become  gradually  transformed  into  coal  by  the  effect  of 
heat,  generated  by  the  action  of  moisture,  assisted  by  the  pressure  of  deposits  of 
mud,  sand,  or  clay,  which  had  gradually  displaced  the  water.  This  process  of 
subterraneous  combustion  appears,  indeed,  to  have  been  analogous  to  that  ob- 

1  Diamond  in  the  amorphous  state,  of  a  brownish-black  color,  has  been  found  in  Brazil, 
and  also  in  some  parts  of  Switzerland. 


CARBON. 

served  when  vegetable  matter,  such  as  hay,  flax,  &c.,  is  closely  packed  in  a  moist 
state,  when  it  is  found  gradually  to  undergo  a  species  of  fermentation,  or  slow 
combustion,  evolving  inflammable  vapors,  and  becoming  ultimately  carbonized. 

All  vegetable  matter,  if  exposed  in  a  moist  state  to  very  considerable  pressure, 
the  escape  of  the  gaseous  matter  being  thus,  to  a  great  extent,  prevented,  would 
become  converted  into  bitumen,  lignite,  brown  coal,  or  even  perfect  coal,  accord- 
ing to  the  intensity  and  duration  of  the  action.  Gaseous  compounds,  rich  in 
carbon,  evolved  by  the  first  action  of  heat,  would,  under  these  circumstances,  be 
,robbed  of  a  portion  of  that  constituent  as  the  temperature  increased,  or  even 
suffer  entire  decomposition  with  deposition  of  carbon  (see  §  129). 

In  laying  bare  or  removing  deposits  of  coal,  quantities  of  inflammable  gas, 
known  as  fire-damp  (carburetted  hydrogen),  are  continually  found  pent  up  in 
fissures,  or  gradually  escaping  from  the  pores  of  the  coal,  in  which  it  has  re- 
mained for  ages  compressed.  The  inflammable  gas  frequently  found  escaping 
from  morasses  and  stagnant  pools,  to  which  the  name  marsh-gas  has  been  given, 
evidently  results  from  the  same  species  of  fermentation,  or  partial  combustion  of 
vegetable  matter  inclosed  under  water  in  the  slime  and  mud;  the  resulting 
gaseous  products -(carburetted  hydrogen,  carbonic  acid,  &c.,  making  their  escape 
to  the  surface  of  the  water,  since  the  pressure  exerted  upon  them  is  insufficient 
to  retain  them.  After  a  time,  the  mass  covering  the  surface  of  the  earth  in  such 
localities  is  found  to  consist  of  imperfectly-charred  vegetable  matter,  to  which  the 
name  peat,  or  turf,  is  given,  and  which  evidently  represents  the  coal  in  its  first 
stage  of  formation. 

Upon  examining  the  different  kinds  of  coal,  they  are  found  to  vary  consider- 
ably in  composition  and  appearance,  according  to  the  temperature  to  which  they 
have  been  exposed,  and  the  period  of  their  formation. 

The  more  perfect  the  conversion  of  vegetable  matter  into  mineral  charcoal  has 
been,  the  smaller  is  the  proportion  of  elements  (hydrogen  and  oxygen)  found  in 
the  coal,  which  originally  existed  as,  or  are  easily  convertible  into,  volatile  com- 
pounds. 

The  brown-coal,  or  lignite,  represents  the  earliest  stage  of  the  process  of  car- 
bonization, and  is  the  coal  of  most  recent  formation.  It  has  a  brown,  earthy, 
and  sometimes  fibrous  and  woody  appearance;  large  masses  of  it  are  found 
retaining  the  original  form  of  the  trunks  of  trees,  and  others  containing  very 
perfect  forms  of  leaves,  &c.  This  coal  contains  from  57  to  70  per  cent,  of  car- 
bon, from  6  to  8  per  cent,  of  hydrogen,  and  from  14  to  37  per  cent,  of  oxygen, 
besides  nitrogen,  and  earthy  and  alkaline  salts.  Some  varieties  (particularly 
alum-shale],  contain  a  large  quantity  of  alumina,  and  are  employed  extensively 
for  the  manufacture  of  alum. 

The  blade-coal,  or  pit-coal,  is  in  a  far  more  advanced  state  of  carbonization 
than  the  lignites,  but  still  contains  a  considerable  amount  of  bituminous  matter. 

Under  this  head  are  classed  many  varieties  of  coal.  The  most  bituminous  of 
these  is  the  cannel  coal;  it  is  dense,  black,  devoid  of  lustre,  exhibiting  a  con- 
choidal  fracture,  and  capable  of  receiving  a  high  polish.  When  held  in  the 
flame  of  a  candle,  it  easily  ignites,  burning  with  a  steady,  bright  flame.  This 
coal  has  of  late  come  into  very  extensive  use  for  the  manufacture  of  illuminating 
gas,  of  which  it  yields  a  better  quality  than  other  species  of  coal.1  The  other 
varieties  of  pit  coal  also  possess  a  laminated  structure,  and  more  or  less  brilliancy; 
the  principal  kinds  have  received  the  names,  pitch-coal,  cubical  coal,  splint  coalf 

1  A  species  of  cannel-coal  (the  bog-head  coal)  found  at  Bathgate,  in  Scotland,  has  lately 
received  extensive  application.  When  submitted  to  distillation,  it  yields  a  large  quantity 
of  oily  matter,  which  is  very  valuable  as  a  lubricating  agent,  and  from  which  a  peculiar 
crystalline  solid,  termed  paraffine,  may  be  separated.  This  latter  has  been  proposed  as 
an  illuminating  material. 


COAL.  187 

and  caking  coal.  When  exposed  to  beat,  they  soften  (some  swelling  up  con- 
siderably), burn  with  a  bright  flame,  and  leave  but  little  ash.  The  caking  coal 
is  the  most  readily  inflammable,  burns  the  longest,  and  easily  agglutinates  when 
heated  in  large  masses  (whence  its  name).  It  is  therefore  employed  for  the 
manufacture  of  gas  and  coke,  in  preference  to  the  other  kinds  of  pit  coal. 

Pit  coals  contain  from  74  to  89  pe.r  cent,  of  carbon :  impressions  of  leaves 
and  plants,  or  a  fibrous  woody  structure,  frequently  appear  in  some  of  them; 
almost  every  species  contains,  in  addition  to  the  ordinary  mineral  constituents, 
iron-pyrites  (bisulphide  of  iron),  sometimes  in  layers  of  distinct  crystals,  and 
sometimes  very  finely  disseminated.  This  is  the  most  objectionable  of  all  con- 
stituents met  with  in  coal,  as  will  be  presently  noticed. 

The  glance-coal  or  anthracite  (  Welsh  coaF)  is  the  oldest  of  all  kinds  of  fossil 
charcoal,  and  must  be  regarded  as  the  last  stage  of  carbonization;  hence  it  dif- 
fers very  considerably,  both  in  its  composition  and  nature,  from  the  other  kinds 
of  coal.  It  is  homogeneous,  and  totally  devoid  of  impressions  of  plants,  has  a 
massive  structure,  conchoidal  fracture,  a  vitreous  lustre,  and  frequently  exhibits 
a  powerful  play  of  color  (e..  g.  the  so-called  peacock  coal).  It  contains  from  90 
to  95  per  cent,  of  carbon.  It  is  of  all  kinds  of  coal  the  most  difficult  of  com- 
bustion,1 and  only  burns  with  a  flame  in  a  powerful  current  of  air. 

Jet  is  also  a  species  of  coal  of  this  class :  it  is  bituminous,  and  sometimes  goes 
by  the  name  of  pitch  coal. 

§  120.  Decomposition  of  Coal. — That  the  action  of  heat  upon  the  organic 
portion  of  coal  must  vary  considerably,  according  to  circumstances,  is  obvious. 
When  subjected  to  heat  in  confined  spaces  (i.  e.  destructive  distillation),  a  great 
variety  of  products,  more  or  less  volatile  and  inflammable,  escape,  and  a  porous 
substance,  consisting  of  carbon,  together  with  the  inorganic  constituents  of  coal, 
remains  behind,  to  which  the  name  of  coke  is  given.  A  detailed  account  of  this 
decomposition  will  be  found  in  the  article  on  coal-gas  (§  126). 

The  most  simple  decomposition  which  coal  undergoes,  is  its  conversion  by 
heat,  and  an  unlimited  supply  of  air  or  oxygen,  into  the  ultimate  products,  car- 
bonic acid  and  water,  and  a  small  quantity  of  ammonia;  but  even  this  result 
may  be  modified,  if  the  whole  mass  of  coal  acted  upon  does  not  undergo  simul- 
taneous combustion;  the  carbonic  acid  becoming  partially  reduced  to  carbonic 
oxide  as  it  comes  into  contact  with  that  portion  of  the  coal  which  is  highly 
heated,  but  not  supplied  with  the  oxygen  necessary  for  its  combustion.  (§  123.) 

The  burning  of  coal,  in  an  ordinary  fire,  for  example,  is,  however,  a  process 
of  far  more  complicated  nature.  The  heat  produced  by  the  first  burning  por- 
tion (i.  e.  the  outer  surface),  subjects  the  greater  mass  of  coal  to  dry  distillation, 
a  variety  of  volatile  products  being  thus  formed,  mostly  of  an  inflammable  nature, 
which  therefore  burst  into  flame  as  they  come  into  contact  with  the  burning  coal 
and  with  oxygen.  Some  of  these,  being  rich  in  carbon,  burn  with  a  bright 
flame,  the  results  being  water,  carbonic  acid,  and  a  considerable  amount  of  un- 
consutned  carbon,  which  is  carried  off  in  a  finely  divided  state,  together  with  the 
products  of  combustion  and  other  volatile  matters  which  escape  the  action  of 
heat  and  oxygen,  thus  producing  what  is  called  smoke,  and  depositing  itself  par- 
tially upon  cool  surfaces  in  the  form  of  soot.  If  the  combustion  of  the  coal  be 
not  carried  to  the  fullest  extent,  a  porous  cinder,  similar  to  coke,  will  remain 
behind,  which  no  longer  contains  any  constituents  volatilizable  by  the  action  of 
a  bright  red  heat,  but  consists  of  carbon  and  the  ash  of  the  coal.  This  cinder 
will  gradually  glow  away,  if  maintained  at  a  sufficient  temperature,  until  the 
inorganic  constituents  of  coal  alone  remain  in  the  form  of  an  ash. 

Inorganic  Constituents  of  Coal. — The  nature  of  the  inorganic  or  mineral  por- 

1  Anthracite  is  now  extensively  used  as  fuel,  not  only  on  a  large  scale  (in  smelting  pro- 
cesses), but  also  on  a  small  scale  in  metallurgic  operations. 


188  CARBON. 

tion  of  the  coal  is  greatly  influenced  by  the  species  of  rock  near  which  the  seam 
runs;  it  is  found  generally  to  contain,  besides  the  ordinary  mineral  constituents 
of  plants,  those  derived  from  portions  of  the  rock  which  have  been  gradually 
carried  into  the  pores  of  the  coal.  The  mineral  substances  most  generally  found 
in  greater  or  less  abundance  in  different  kinds  of  coal,  are  potassa,  lime,  magne- 
sia, iron,  manganese;  silicic,  phosphoric,  and  sulphuric  acids;  sulphur,  chlorine, 
and  sometimes  traces  of  iodine.  Of  some  of  these  it  is  difficult  to  say  how  they 
originally  exist  in  coal,  since,  in  obtaining  the  ash  in  which  they  are  detected  by 
burning  the  coal,  their  combinations  amongst  each  other  must  undergo  important 
modifications. 

Iron  exists,  as  already  stated,  chiefly  as  iron-pyrites  (FeS2),  which,  when 
heated,  parts  with  one  portion  of  its  sulphur,  becoming  (proto-)  sulphide  of 
iron,  the  sulphur  being  converted  into  sulphurous  and  other  acids.1  The  sulph- 
ide is  partially  oxidized,  yielding  sulphate  of  iron,  and  also  sesquioxide  of  iron. 
The  sulphur  undergoes  various  degrees  of  oxidation;  hyposulphurous  and  hypo- 
sulphuric  acids,  in  combination  with  potassa  or  lime,  are  sometimes  found  in  the 
ash  of  coal.  Sulphate  of  lime  exists  in  large  quantities  in  some  kinds  of  coal, 
and  is  always  found  in  coal-ash.  The  potassa  and  a  portion  of  the  earths,  as 
also  iron  and  manganese,  are  found  in  the  ash  as  carbonates.  Some  ashes  con- 
tain likewise  chloride  of  potassium. 

Estimation  of  the  Value  of  Fuel. — It  is  of  the  highest  importance  that  we 
should  be  enabled  to  arrive  at  an  accurate  idea  of  the  value  of  different  kinds  of 
coal  or  fuel  in  general,  with  reference  to  their  heating  qualities;  in  other  words, 
with  regard  to  the  amount  or  intensity  of  heat  produced  by  their  perfect  com- 
bustion in  air.  The  means  presented  for  this  purpose  by  what  are  called  pyro- 
meters, furnish  by  no  means  results  to  be  depended  upon ;  the  most  simple 
method  is,  therefore,  to  determine  the  relative  heating  powers  of  different  fuel. 
This  may  be  easily  effected  by  ascertaining  the  amount  of  water  raised  from  the 
temperature  of  32°  F.  (0°  C.)  to  212°  F.  (100°  C.),  by  combustion  of  a  stand- 
ard weight  of  the  different  kinds  of  fuel :  thus,  it  has  been  found  that 

Part  by  Weight.  Water  raised  from  32°  to  212°. 

1  pure  carbon     ...     78  parts  by  weight. 

1  wood  charcoal       .     .     75  " 

1  dry  wood     .     .     «     .     36  « 

1  good  coal    ....     60  « 

It  is  obvious  that  in  this  way  the  relative  value  of  different  kinds  of  fuels  may 
easily  be  measured  and  calculated. 

Another  method  of  determining  the  heating  power,  is  to  ascertain  the  amount 
of  oxygen  necessary  for  the  combustion  of  a  certain  amount  of  coal.  This  is 
effected  by  mixing  the  finely  divided  fuel  with  a  substance  containing  oxygen, 
which  is  not  expelled  by  mere  application  of  heat,  but  is  very  easily  abstracted 
by  substances  having  an  affinity  for  it  at  an  elevated  temperature.  The  method 
adopted  is  to  mix  the  pounded  and  dried  coal  with  pure  litharge  (PbO),  and  to 
maintain  the  mixture  in  a  state  of  fusion  for  some  time  in  a  Hessian  crucible, 
which,  when  the  mass  has  subsequently  become  cool,  is  broken,  and  the  lead, 
reduced  from  the  oxide  by  the  action  of  the  carbon  and  hydrogen,  is  found  at 
the  bottom ;  from  the  quantity  of  lead  reduced,  the  amount  of  oxygen  consumed 
in  the  combustion  or  oxidation  of  the  coal  is  easily  calculated.3 

1  The  presence  of  iron-pyrites  in  coal  is  exceedingly  injurious  to  furnaces,  or  any  metal 
work  with  which  the  hot  coal  comes  in  contact,  since  it  easily  parts  with  a  portion  of  its 
sulphur,  thus  acting  rapidly  upon  the  metal.     Coke  prepared  from  coal  containing  much 
pyrites,  acts  injuriously  in  the  same  manner. 

2  The  estimation  of  the  value  of  coal,  however,  is  not  complete  without  some  experi- 
ments upon  its  mechanical  nature.     To  ascertain,  for  example,  what  quantity  of  coal 


ANALYSIS   OP   COAL.  189 

The  carbon  and  hydrogen  (which  are  the  two  heating  constituents  in  coal) 
may  also  be  separately  determined  from  the  amount  of  carbonic  acid  and  water 
produced  by  the  complete  oxidation  of  a  known  weight  of  coal  j  this  is  effected 
by  burning  the  powdered  coal  with  oxide  of  copper  (the  action  of  which  is 
sometimes  aided  by  the  addition  of  free  oxygen),  and  collecting  the  products  in 
the  manner  usually  adopted  in  organic  analysis. 

The  nitrogen  in  coal,  which  varies  in  amount  from  1  to  2  per  cent,  may  be 
determined  according  to  the  method  of  Will  and  Varrentrapp. 

Determination  of  the  Sulphur. — About  20  grains  of  finely-powdered  coal  are 
mixed  with  an  equal  weight  of  pure  carbonate  of  soda;  the  resulting  powder  is 
then  well  mixed  with  one  part  of  pure  nitrate  of  potassa,  and  four  parts  of  pure 
chloride  of  sodium;  the  mixture  is  introduced  into  a  platinum  crucible  (which 
should  not  be  more  than  half-filled),  and  maintained  in  a  state  of  gentle  fusion 
until  the  whole  of  the  carbon  has  been  oxidized  by  the  nitre,  and  the  mass 
appears  white.  The  crucible  is  then  allowed  to  cool,  and  afterwards  immersed 
in  a  beaker  containing  distilled  water,  acidified  with  hydrochloric  acid,  whereby 
the  fused  mass  is  dissolved,  and  the  carbonic  acid  liberated.  The  sulphuric  acid 
now  in  solution,  which  has  been  produced  by  the  oxidation  of  the  sulphur  by  the 
nitre,  may  be  determined  by  precipitation  as  sulphate  of  baryta  (see  Quantitative 
Analysis).  From  the  amount  of  sulphuric  acid  formed,  the  percentage  of 
sulphur  present  in  the  coal  is  easily  calculated. 

The  following  is  also  a  very  neat  method  of  determining  the  sulphur :  A 
weighed  quantity  of  dried  coal  is  mixed  with  twice  its  weight  of  carbonate  of 
magnesia,  and  the  mixture  placed  in  a  tube  of  Bohemian  glass,  which  is  then 
strongly  heated  while  a  slow  current  of  oxygen  is  allowed  to  pass  over  the  mix- 
ture. The  organic  matter  is  soon  oxidized,  and  the  sulphur  converted  into  sul- 
phuric acid,  which  unites  with  the  magnesia,  expelling  the  carbonic  acid.  As 
soon  as  the  heated  mass  has  become  quite  white,  the  tube  is  allowed  to  cool, 
broken  up,  and  digested  in  warm  water ;  the  sulphate  of  magnesia  is  thus  extracted 
from  the  mass,  and  the  amount  of  sulphur  determined  in  the  aqueous  solution, 
as  directed  above. 

Of  the  agents  employed  in  the  first  of  the  above  methods,  the  most  important 
member  is  the  nitre,  which  oxidizes  the  carbon,  hydrogen,  and  sulphur  in  the 
coal ;  if  used  alone,  however,  its  action  on  the  coal  would  be  very  intense,  and 
much  loss  would  ensue  in  consequence  of  the  violent  effervescence  of  the  liquid 
mass ;  this  action  is  moderated  by  the  addition  of  the  chloride  of  sodium,  which 
being  a  substance  of  no  active  properties,  and  at  the  same  time  tolerably  fusible, 
serves  as  a  capital  diluent. 

Estimation  of  Ash. — From  10  to  20  grains  of  the  finely-pulverized  coal  are 
dried  perfectly  by  exposure  in  the  air-bath  to  a  temperature  of  248°  F.  (120°  C.), 
and  then  carefully  ignited  in  a  platinum  crucible  over  a  gas-flame,  or  that  of  a 
roaring-lamp,  until  the  whole  of  the  combustible  matter  is  consumed.  The 
crucible,  being  supported  by  a  wire  triangle,  is  placed  in  a  slanting  position,  the 
mouth  is  closed  by  loosely  placing  the  lid  upon  it,  until  no  more  volatile  matter 
is  observed  to  escape,  when  the  orifice  is  partly  opened,  in  order  to  allow  of  the 
entrance  of  air  into  the  crucible.  The  ash  should  be  stirred  about,  from  time  to 
time,  by  means  of  a  piece  of  thin  platinum  wire,  so  as  to  expose  a  fresh  surface 
to  the  action  of  the  air  that  enters  the  crucible.  When  the  whole  of  the  organic 
matter  appears  to  be  burnt  off,  the  crucible  is  allowed  to  cool,  and  weighed,  after 
which  it  is  once  more  strongly  ignited,  and  reweighed ;  this  is  repeated  until  the 

would  be  likely  to  be  disintegrated  by  carriage ;  how  much  coal  could  be  stowed  away  in 
a  certain  space,  &c.  &c. 

Certain  patent  fuels,  presenting  considerable  advantages  as  far  as  facility  of  stowage  is 
concerned,  have  been  lately  manufactured,  by  mixing  coal-dust  and  waste  with  bitumin- 
ous matters,  and  moulding  the  resulting  mass  into  bricks. 


190  CARBON. 

numbers  from  two  consecutive  weighings  are  alike.  It  is  found  very  difficult, 
in  many  instances,  to  burn  off  the  last  traces  of  carbon  from  the  ash  of  coal, 
particularly  if  it  be  a  caking  coal ;  in  such  cases,  it  is  necessary  to  resort  to  an 
auxiliary  agent,  in  order  to  obtain  a  perfectly  pure  ash. 

One  method  is,  to  cover  the  crucible  containing  the  ash,  with  a  lid  having  a 
perforation  in  the  centre,  through  which  a  tube  of  porcelain,  or  of  platinum,  may 
be  allowed  to  enter  the  crucible.  By  means  of  this  tube,  which  is  connected 
with  a  gas-holder  containing  oxygen,  a  very  moderate  current  of  that  gas  may 
be  allowed  to  enter  the  crucible,  and  by  coming  in  contact  with  the  ash  at  a  low 
red  heat,  to  oxidize  rapidly  the  last  traces  of  carbon.  The  surface  of  the  ash  in 
the  crucible  must  be  changed,  from  time  to  time,  in  the  manner  directed. 

A  perfect  oxidation  of  the  carbon  may  also  be  effected  by  mixing  the  ash,  after 
it  is  burnt  as  thoroughly  as  possible  with  a  small  quantity  of  pure  oxide  of  mer- 
cury, and  then  applying  a  moderate  heat,  when  the  carbon  will  be  rapidly  oxi- 
dized at  the  expense  of  the  oxygen  in  the  oxide,  the  mercury  being  at  the  same 
time  volatilized.  This  operation  is  conducted  in  an  open  crucible  or  capsule. 

Estimation  of  Coke. — About  100  grains  of  the  dried  coal  are  exposed,  in  a 
covered  porcelain  crucible,  inclosed  in  a  Hessian  crucible,  to  a  bright  red  heat 
for  about  an  hour. 

The  proximate  analysis  of  coal — i.  e.  the  determination  of  the  products  of  its 
destructive  distillation,  may  be  executed  in  the  following  manner  (Bunsen  and 
Playfair)  : — 

A  weighed  quantity  of  coal  is  heated  in  a  tube  of  hard  glass,  and  the  coke 
remaining  after  the  operation  is  weighed  in  the  tube. 

The  products  of  the  distillation  are  collected  in  the  following  apparatus : — 

1.  A  cooled  receiver  for  condensing  the  tar,  water,  and  ammonia. 

2.  A  tube  filled  with  chloride  of  calcium,  to  retain  any  water  and  ammonia 
which  may  have  escaped. 

3.  A  bulb-apparatus  containing  a  solution  of  oxide  of  lead  in  potassa,  to  retain 
sulphuretted  hydrogen  and  carbonic  acid. 

4.  A  drying-tube,  with  chloride  of  calcium. 

5.  A  bulb-apparatus,  containing  pentachloride  of  antimony,  to  absorb  olefiant 
gas  and  vapors  of  hydrocarbons. 

6.  A  bulb-apparatus  containing  an  alcoholic  solution  of  potassa,  to  absorb  any 
volatile  chlorinated  products. 

7.  A  drying-tube  containing  sulphuric  acid. 

8.  A  graduated  tube,  filled  with  mercury,  for  collecting  the  uncondensed  gases. 
§  121.    Charcoal. — Carbon  may  be  obtained  from  the  substances  in  which  it 

exists  in  large  quantities,  under  a  great  variety  of  forms,  the  principal  of  which 
are,  gas-carbon,  coke,  wood-char coal ',  lampblack,  and  ivory-black. 

Gas-carbon  is  produced  by  the  gradual  deposition  of  carbon  from  coal-gas  at 
a  high  temperature,  upon  the  inner-surface  of  the  gas-retorts,  which  it  frequently 
covers  to  a  considerable  thickness,  forming  very  compact,  hard  masses,  of  a 
metallic  lustre,  and  mammillated,  or  fibrous  structure,  somewhat  resembling 
graphite.  Its  specific  gravity  is  1.76. 

Coke  is  a  dense  charcoal,  resembling  that  of  wood,  and  valuable  as  a  fuel,  from 
the  high  temperature  resulting  from  its  combustion,  and  also  on  account  of  the 
much  smaller  amount  of  sulphur  which  it  contains,  compared  with  coal,  from 
which  it  is  prepared  according  to  various  methods.  The  oldest  method  of  pre- 
paring coke  consists  in  burning  the  coal  in  large  heaps,  without  excluding  the 
air,  until  the  coke  is  produced,  when  its  further  consumption  is  prevented  by 
covering  the  heap  with  a  coating  of  dust.  Sometimes  mounds  are  constructed 
round  a  conical  brick  opening,  in  building  which  a  brick  is  left  out  from  time  to 
time,  so  that  the  inner  part  of  this  channel  is  connected  by  apertures  with  the 
surrounding  heap  of  coal  throughout  the  structure.  The  heaviest  pieces  of  coal 


WOOD    CHARCOAL.  191 

are  placed  at  the  base  of  the  mound,  and  care  is  taken  in  constructing  the  latter, 
to  have  free  channels  leading  from  the  apertures  in  the  chimney  to  the  circum- 
ference. The  outer  surface  of  the  mound  is  covered  with  a  coating  of  cinders. 
The  ignition  is  effected  by  the  chimney,  into  which  burning  coals  are  thrown, 
which  communicate  their  flames  to  the  mound  through  the  apertures.  Air  is 
allowed  to  pass  into  the  mound  through  spaces  at  the  foot,  and  escapes  through 
the  chimney.  As  soon  as  the  whole  mass  becomes  redhot,  the  mouth  of  the 
chimney  and  the  other  apertures  are  closed,  and  the  coke  allowed  to  cool. 

Coke  is  also  very  frequently  prepared  in  furnaces  of  brick,  provided  with  doors 
or  slides,  by  which  the  access  of  air  may  be  regulated.  These  furnaces  are  kept 
in  operation  day  and  night,  receiving  fresh  charges  of  coal  directly  one  charge  of 
coke  is  withdrawn,  while  the  furnace  is  still  redhot,  whereby  the  fresh  charge 
of  coal  is  ignited. 

In  the  processes  above  mentioned,  the  secondary  products  of  the  coking,  such 
as  tar  and  gaseous  matter,  are  not  taken  into  consideration.  Coke  is,  however, 
obtained  in  large  quantities,  as  a  secondary  product,  in  the  manufacture  of  gas, 
where  the  coal  is  submitted  to  destructive  distillation  in  closed  iron  retorts.  Good 
coke  should  be  compact  and  in  large  pieces,  not  liable  to  crumble  away.  It  yields 
upon  incineration  about  2  or  3  per  cent,  of  earthy  ash,  and  has  a  specific  gravity 
varying  from  1.6  to  2. 

Wood  Charcoal. — The  temperature  resulting  from  the  combustion  of  charcoal 
is  much  higher  than  that  from  burning  wood,  in  consequence  of  the  absence  of 
the  large  quantity  of  water  which  wood  contains,  amounting  to  between  50  and 
60  per  cent.  The  object  of  charring  wood  is  therefore  the  removal  of  moisture, 
and,  what  is  also  of  great  importance,  the  concentration  of  the  heating  power  of 
the  wood  to  a  smaller  space,  and  the  expulsion  of  those  matters  contained  in  it 
which  become  volatile  before  they  are  burned,  thus  rendering  a  large  amount  of 
heat  latent. 

Charcoal  is  prepared  either  by  allowing  the  volatile  constituents  of  the  wood 
alone  to  undergo  combustion,  or  by  heating  the  wood  in  closed  vessels,  when,  the 
air  being  excluded,  all  matters  volatile  at  a  high  temperature,  are  expelled  without 
undergoing  combustion. 

Charcoal  is  obtained,  according  to  the  first  plan,  in  a  similar  manner  to  coke, 
by  constructing  heaps  or  mounds  of  wood,  inclosed  in  a  coating  of  charcoal-powder 
or  sand,  and  supplied  with  fissures  for  the  admission  of  air  into  the  mass,  which 
may  be  closed  at  pleasure,  as  the  charring  proceeds.  The  second  method  is  that 
of  charring  the  wood  in  furnaces  or  retorts,  the  volatile  products  being  conducted 
into  condensing  apparatus,  and  thus  preserved.  In  this  manner,  acetic  or  pyro- 
ligneous  acid,  wood  naphtha,  or  pyroligneous  ether,  and  tar,  are  obtained  as 
secondary  products. 

The  method  and  precautions  adopted  in  charring  wood,  as  also  the  choice  of 
wood,  depend  much  upon  the  use  to  which  the  charcoal  is  to  be  applied.  If  wood 
is  heated  in  confined  spaces  beyond  a  certain  period,  it  is  found  that  the  amount 
of  combustible  matter  in  a  given  volume  no  longer  increases,  but  suffers  an  abso- 
lute loss;  or,  that  when  charcoal  containing  the  maximum  amount  of  combustible 
matter  is  required,  the  wood  is  only  incompletely  charred ;  in  this  state  it  is 
called  red  charcoal  (ckarbon  roux],  and  in  economical  respects  possesses  great 
advantages  over  the  black  charcoal  obtained  by  the  complete  charring  of  wood ; 
which  being,  however,  more  dense  and  compact  than  the  latter,  possesses  the 
advantages  of  greater  conducting  power.1  Wood  which  has  been  previously  dried, 
yields  a  greater  quantity  of  charcoal  than  the  corresponding  amount  of  damp 

1  For  further  particulars  respecting  the  comparative  value  of  charbon  roux  and  black 
charcoal,  see  article  on  Gunpowder. 


192  CARBON. 

wood,  as,  in  the  latter  case,  carburetted  hydrogen,  and  carbonic  oxide  are  evolved 
when  the  wood  is  charred. 

The  most  perfect  charcoal  is  that  which  is  prepared  for  the  manufacture  of 
gunpowder,  for  which  purpose  only  certain  kinds  of  wood  are  employed  :  viz. 
the  alder,  dogwood,  poplar,  maple,  and  walnut.  The  wood  is  charred  in  iron 
cylindrical  retorts,  which  admit  of  the  most  accurate  regulation  of  heat  through- 
out the  operation.  They  are  sometimes  connected  with  condensing  apparatus  for 
the  reception  of  the  volatile  products,  and  are  supplied  with  tubes  in  which 
pieces  of  test-wood  are  placed,  and  examined  from  time  to  time  to  ascertain 
accurately  the  period  of  requisite  carbonization. 

Frequently,  instead  of  charging  the  retorts  directly  with  the  wood  to  be  char- 
red, it  is  packed  into  sheet-iron  cylindrical  cases  (slips)  provided  with  lids,  and 
of  such  dimensions  as  to  fit  easily  into  the  retort.  A  great  saving  of  time  and 
heat  is  effected  by  their  use,  as,  when  the  wood  has  been  properly  charred,  the 
case  or  slip  containing  it  may  be  easily  withdrawn,  and  another  containing  a  fresh 
charge  of  wood  at  once  introduced  into  the  retort,  without  allowing  the  latter  to 
cool  down,  as  would  otherwise  be  necessary. 

When  the  charcoal  is  withdrawn  from  the  retort,  it  is  at  once  transferred  into 
iron  cases,  provided  with  closely  fitting  covers,  and  is  there  allowed  to  remain 
until  it  has  cooled  down  sufficiently  to  prevent  its  smouldering  when  exposed  to 
the  air.  These  cases  are  called  the  extinguishers. 

The  bark,  small  branches,  leaves,  and  knots  afford  a  dense  hard  charcoal  dif- 
ficult of  combustion,  chiefly  on  account  of  the  greater  amount  of  ash  (silicates) 
which  they  contain,  and  which  agglutinates  at  a  high  temperature.  In  preparing 
powder-charcoal,  these  portions  are  carefully  removed  before  the  wood  is  intro- 
duced into  the  retort,  and  the  resulting  charcoal  is  again  looked  over,  as  portions 
of  this  dense  coal  are  frequently  formed  by  the  trickling  down  of  drops  of  tar, 
which  have  condensed  on  the  upper  surface  of  the  retort,  upon  the  hot  charcoal. 

The  charbon  roux,  already  referred  to,  or,  in  other  words,  the  charcoal  contain- 
ing the  maximum  amount  of  inflammable  matter,  is  produced  at  a  comparatively 
low  temperature  (about  540°  F.);  this  has  led  to  the  proposal  of  a  method  (which 
has  been  carried  out  successfully),  for  preparing  charcoal  of  this  kind  by  means 
of  heated  steam  of  a  certain  pressure.  The  plan  adopted  consists  in  conducting 
steam  from  a  boiler  into  a  serpentine  iron  pipe,  in  which  its  temperature  and 
tension  are  raised  to  the  proper  point  by  external  application  of  heat ;  the  heated 
steam  is  then  allowed  to  pass  into  a  copper  cylinder  inclosing  a  second,  in  which 
the  wood  to  be  charred  is  packed.  The  steam  passing  round  the  latter  cylinder, 
heats  the  wood  to  such  an  extent  as  to  liberate  the  tar  and  volatile  matters ;  it 
is  then  allowed  to  enter  the  inner  cylinder,  when  it  thoroughly  penetrates  into 
the  pores  of  the  wood,  expelling  the  volatile  substances,  which  it  carries  with  it 
as  it  escapes  from  another  portion  of  the  cylinder.  The  charcoal  thus  obtained 
is  of  a  red-brown  color,  and  is  the  kind  generally  used  in  France  (where  this 
method  was  worked  out)  for  the  manufacture  of  gunpowder. 

The  temperature  to  which  the  steam  is  heated  in  the  serpentine  tube,  is  ascer- 
tained and  regulated  by  introducing  into  a  large  copper  tube  closed  at  one  end 
(and  reaching  from  the  exterior  of  the  outer  cylinder  into  the  inner  one),  small 
cylinders  of  tin,  lead,  or  an  alloy  which  will  fuse  at  a  certain  temperature;  upon 
these  rest  long  thin  iron  rods  surmounted  by  weights,  which  cause  the  rods  to 
sink  into  the  metal  as  soon  as  it  softens  or  melts.  By  fixing  into  the  cylinder 
several  of  these  tubes  containing  alloys  of  different  fusing-points,  a  proper  range 
of  temperature  is  obtained. 

Thoroughly  burned  charcoal  is  brownish  or  bluish-black,  presenting,  when 
powdered,  a  smooth,  velvet-like  appearance.  Its  specific  gravity  varies  exceed- 
ingly, according  to  its  porosity. 

Charcoal  possesses  the  remarkable  property  of  absorbing  and  condensing  within 


ANIMAL   CHARCOAL.  193 

its  pores,  many  times  its  volume  of  different  kinds  of  gases,  more  particularly 
those  liquefiable ;  thus  it  absorbs,  of  ammoniacal  gas,  90  times  its  volume ;  of 
hydrosulphuric  acid,  35;  of  oxygen,  9.25  its  volume;  of  nitrogen  7.5,  and  of 
hydrogen  1.75  volumes.  It  likewise  absorbs  moisture  from  the  air,  and  condens- 
able vapors  and  effluvia  of  all  descriptions  (coke  possesses  the  same  property, 
though  in  a  less  degree).  Freshly  calcined  charcoal  also  considerably  retards 
the  putrefaction  of  organic  matter,  if  placed  in  contact  with  it.  The  interior  of 
wine  and  of  water  casks  is  frequently  charred  before  the  introduction  of  the 
liquids;  the  wine  being  found  to  be  improved  in  quality,  and  water  to  remain 
sweet,  when  thus  placed  in  contact  with  charcoal.  Spirits  may  also  be  easily 
deprived  of  the  empyreumatic  oil  they  frequently  contain,  by  passing  them 
through  coarsely  pounded  charcoal.  A  property  also  possessed  by  charcoal,  of 
absorbing  various  coloring  matters,  will  be  more  particularly  noticed,  when  we 
treat  of  animal  charcoal.  When  vapor  of  water  is  passed  over  charcoal  at  a  red 
heat,  it  is  decomposed,  a  mixture  of  hydrogen,  carbonic  oxide,  carbonic  acid,  and 
light  carburetted  hydrogen  being  produced. 

Lampblack  is  the  carbon  deposited  from  combustible  substances  imperfectly 
burnt;  such  as  tar,  resins,  oils,  or  gas.  It  may  be  obtained  in  the  purest  form 
by  passing  the  vapor  of  alcohol  or  a  volatile  oil  through  a  porcelain  tube,  heated 
to  redness.  On  a  large  scale,  lampblack  is  prepared  by  burning  a  resinous  mat- 
ter in  large  chambers  with  imperfect  access  of  air;  the  product  is  collected  on 
cloths  hung  round  the  chamber.  A  charcoal  of  the  same  description,  though 
containing  traces  of  hydrogen  and  oxygen,  is  obtained  by  igniting,  in  close  ves- 
sels, sugar,  starch,  and  substances  of  a  similar  nature. 

Bone-black,  ivory-black,  or  animal  charcoal,  is  the  charcoal  obtained  by  cal- 
cining bones  in  close  vessels.  This  charcoal  contains  about  ten  times  its  own 
weight  of  bone-earth  in  admixture,  whereby  it  is  distributed  over  a  considerable 
surface.  It  possesses  the  property,  to  a  high  degree  (common  also  to  wood-char- 
coal to  a  less  extent), of  absorbing  organic  coloring  matters;  the  charcoal  obtained 
by  calcining  dried  blood,  hoofs,  and  horns,  and  hide-clippings,  with  carbonate  of 
potassa,  and  afterwards  extracting  the  calcined  mass  with  water,  possesses  this 
property  in  the  highest  degree.  It  is  very  remarkable  that  this  property  of 
charcoal,  though  merely  a  mechanical  attraction  of  surface,  frequently  overcomes 
chemical  affinities  of  considerable  intensity.  Most  organic  bitter  principles,  as 
also  organic  bases,1  when  in  combination  with  acids,  are  withdrawn  from  solutions 
by  animal  charcoal.  The  substances  thus  removed  remain  evidently  upon  the 
surface  of  the  charcoal ;  the  indigo  is  withdrawn  from  a  neutral  solution  of  that 
substance  in  sulphuric  acid,  upon  its  being  passed  through  animal  charcoal;  the 
latter,  however,  again  yields  up  the  coloring  matter  when  treated  with  solution 
of  potassa.  Animal  charcoal  has  also  the  property  of  removing  certain  inorganic 
substances  from  their  solutions ;  such  as  soluble  subsalts  of  lead;  iodine  from 
its  solution  in  iodide  of  potassium ;  lime  and  hydrosulphuric  acid  from  their  solu- 
tions; and  metallic  oxides  from  their  solutions  in  caustic  alkalies;  several  of  the 
former  being  speedily  reduced  to  the  metallic  state,  apparently  by  the  action  of 
carbon  in  the  very  close  state  of  proximity  into  which  they  are  brought  with  it. 
Neutral  ^alts  are  not  affected  to  any  extent  by  animal  charcoal.  If  the  animal 
charcoal  is  deprived  of  the  bone-earth  it  contains,  by  treatment  with  an  acid,  its 
decolorizing  and  abstracting  properties  are  considerably  diminished,  probably  in 
consequence  of  its  being  rendered  more  compact.  When  animal  charcoal  is  heated 
in  chlorine  water,  it  gradually  disappears,  being  converted  into  carbonic  acid. 

§  122.  General  Properties  of  Carbon. — Carbon  is  a  dimorphous  substance 
(crystallizing  in  two  different  forms,  as  graphite  and  diamond) ;  it  is  a  bad  con- 

1  This  property  was  recently  applied  by  Graham  and  Hofmann  in  the  examination  of 
bitter  ales  for  strychnine. 
13 


194  CARBON. 

ductor  of  heat,  and  ordinary  wood-charcoal  is  also  a  bad  conductor  of  electricity ; 
but  when  calcined  at  a  high  temperature,  it  becomes,  like  graphite,  a  very  good 
electric  conductor.  When  submitted  to  the  action  of  a  very  powerful  battery, 
carbon  becomes  softer  by  the  intense  heat ;  it  then  slightly  vaporizes.1  Upon 
exposure  to  a  temperature  of  this  description,  all  kinds  of  carbon  are  converted 
into  a  soft,  friable  coke,  similar  to  graphite.  Though  carbon,  in  the  various 
modifications  in  which  it  occurs,  is  possessed  of  very  different  properties,  its 
general  chemical  character  is,  under  all  circumstances,  the  same. 

The  only  instance  of  the  artificial  crystallization  of  carbon  which  we  possess, 
is  the  manner  in  which  it  separates  from  its  solution  in  fused  iron,  as  already 
noticed.  Carbon  is  not  possessed  of  active  chemical  properties  at  low  tempera- 
tures; it  is  remarkable  for  its  non-volatility  and  insolubility;  it  cannot  be  dis- 
solved unless  oxidized,  as  by  nitric  or  sulphuric  acid,  or  chlorine  water.  The 
hypothetical  density  of  carbon  vapor,  calculated  from  the  densities  of  carbonic 
oxide  and  carbonic  acid,  is  0.414.  Carbon  burns  readily  in  air  or  oxygen,  when 
raised  to  a  certain  temperature  (varying  with  the  density  of  the  different  varie- 
ties), the  product  being  carbonic  acid,  a  colorless  gas.  When  burnt  in  a  limited 
supply  of  air  or  oxygen,  carbon  is  converted  into  carbonic  oxide,  which  consists 
of  equal  equivalents  of  carbon  and  oxygen.  Carbon  also  combines  with  chlorine, 
phosphorus,  and  sulphur,  and  unites  with  some  of  the  metals  at  high  tempera- 
tures, producing  metallic  carbides  or  carburets. 

The  powerfully  deoxidizing  action  of  carbon,  even  at  ordinary  temperatures, 
has  recently  been  demonstrated  in  a  striking  manner  by  Schbnbein.  He  suc- 
ceeded in  reducing  solutions  of  several  salts  of  the  sesquioxide  of  iron  to  the 
corresponding  salts  of  the  oxide,  by  simple  agitation  of  their  solutions  with  char- 
coal powder.  By  the  same  method,  chloride  of  mercury  was  reduced  to  sub- 
chloride,  and  the  nitrate  of  oxide  to  that  of  the  suboxide. 

Uses  of  Carbon. — This  element,  in  its  various  forms,  meets  with  a  most  ex- 
tensive application  in  the  arts  and  manufactures.  Its  powerful  affinity  for  oxygen 
at  a  high  temperature,  and  the  further  advantages  which  it  presents  in  being 
infusible  at  the  highest  furnace-heat,  and  in  forming  gaseous  products  of  com- 
bustion, render  it  the  most  suitable  substance  for  effecting  the  reduction  of  me- 
tallic oxides.2  The  various  modifications  of  carbon  also  meet  with  many  special 
applications.  The  diamond  is  not  only  highly  valued  as  the  most  precious  of 
gems,  but  on  account  of  its  hardness  is  used  for  cutting  and  engraving  glass,  and 
in  the  state  of  dust  for  polishing  hard  metals  and  gems.  Graphite  is  of  the 
highest  importance  in  the  arts,  being  used  for  the  manufacture  of  black  lead- 
pencils.  A  more  impure  kind  is  also  extensively  employed  for  imparting  a 
polished  surface  to  iron,  and  protecting  it  from  the  action  of  air  and  moisture. 
Graphite,  as  well  as  highly  calcined  charcoal  or  coke,  is  used  for  surrounding 
the  extremities  of  lightning-conductors,  to  facilitate  the  passage  of  electricity  to 
the  earth,  in  consequence  of  the  good  conducting  powers  of  these  forms  of  car- 
bon. Coke  and  charcoal  have  long  since  become  indispensable  as  fuel;  the 
choice  of  either  will  depend  upon  the  heat  required,  or  other  circumstances;  the 
advantages  they  possess,  in  many  respects,  over  wood  and  coal,  have  already 
been  stated.  Coke  is  also  used  for  constructing  the  carbon  cylinders  of  Bunsen's 
Carbo-zinc  Galvanic  Batteries.  Powdered  coal  is  coked  in  an  iron  mould  of  the 
proper  form,  and  a  great  degree  of  compactness  is  afterwards  given  to  the  porous 

1  Despretz  has  succeeded  in  volatilizing  and  subliming  carbon,  by  means  of  a  Bunsen's 
battery  of  four  hundred  and  ninety  six  cells. 

2  The  indestructibility  of  charcoal  under  the  influence  of  air  and  moisture  receives 
many  useful  applications;  thus  it  is  customary  to  char  the  ends  of  stakes,  piles,  &c.,  be- 
fore fixing  them  in  the  ground.     Masses  of  charcoal  were  formerly  buried  as  enduring 
landmarks. 


CARBONIC   OXIDE.  195 

cylinder  thus  obtained,  by  soaking  it  in  a  syrup  and  calcining  it  a  second  time. 
Charcoal  points  for  the  poles  of  batteries  may  be  made  in  a  similar  manner. 

The  most  important  use  of  charcoal  is  its  application  in  the  manufacture  of 
gunpowder :  it  is  also  used,  in  the  freshly  calcined  state,  as  a  deodorizer  and 
disinfectant,  in  consequence  of  its  power  of  absorbing  effluvial  vapor;  the  puri- 
fication of  water  by  charcoal  filters  is  an  example  of  this. 

Lampblack  is  frequently  of  great  use  to  the  chemist,  since  it  presents  to  him 
very  finely-divided  carbon  in  a  tolerably  pure  state.  It  is  also  used  extensively 
by  colormen,  and  in  the  manufacture  of  blacking. 

The  decolorizing  properties  of  animal  charcoal,  or  bone-black,  render  it  of 
considerable  importance  in  manufactures;  for  example,  in  sugar-refining,  in  the 
manufacture  of  tartaric  acid,  &c. 

The  liquids  to  .be  decolorized  are  generally  filtered  hot  through  beds  of 
coarsely-grained  animal-charcoal,  two  or  three  feet  in  thickness.  Several  substi- 
tutes for  bone-black,  in  which  its  composition  is  imitated,  are  employed  success- 
fully. Thus,  100  parts  of  pipeclay,  made  up  into  a  thin  paste  with  water,  £Aid 
thoroughly  mixed  with  500  parts  of  finely-powdered  coal  and  20  parts  of  tar, 
afford,  when  dried  and  calcined,  a  mass  which  is  not  much  inferior  in  its  decolor- 
izing properties  to  bone-black.  The  recalcination  of  bone-black  once  used  has 
been  found  considerably  to  diminish  the  decolorizing  power,  which  arises  from 
the  deposition  of  a  dense  coating  of  charcoal  upon  its  surface,  produced  by  the 
decomposition  of  the  organic  coloring-matter  absorbed.  By  allowing  the  sugar- 
filters  to  ferment,  whereby  the  coloring  matter  is  decomposed,  the  charcoal  will, 
after  being  washed  and  recalcined,  recover  its  power  to  a  very  great  extent. 

Since  animal  charcoal  contains  several  inorganic  constituents  (phosphate  and 
carbonate  of  lime,  &c.),  it  is  necessary  to  purify  it  before  employing  it  for 
chemical  purposes.  This  is  effected  by  boiling  it  two  or  three  times  with  hydro- 
chloric acid  in  excess,  until  the  acid  solution  is  no  longer  precipitated  by  ammo- 
nia, and  subsequently  washing  with  water  until  all  acid  is  removed,  its  deco- 
lorizing properties  are,  however,  greatly  weakened  by  this  purification. 

The  property  which  animal  charcoal  has  of  abstracting  the  salts  of  organic  bases 
from  their  solutions,  renders  it  also  available  as  an  antidote  to  vegetable  poisons. 


CARBON  AND   OXYGEN. 

Carbonic  oxide CO. 

Carbonic  acid CO,,.1 

CARBONIC  OXIDE. 

CO.     Eq.  14.     Sp.  Gr.  0.967. 

Composition  ly  Volume. — 2  volumes  of  carbon-vapor  and  1  volume  of  oxygen 
form  2  volumes  carbonic  oxide. 

§  123.  This  gas  is  produced  when  carbonic  acid  is  passed  over  charcoal,  or  some 
metals,  at  a  high  temperature;  also  when  vapor  of  water  is  passed  over  well-burnt 
charcoal  at  a  red  heat,  in  an  iron  or  porcelain  tube;  or  by  igniting  chalk,  or  other 
carbonates,  with  the  proper  proportion  of  charcoal,  or  easily  oxidizable  metals. 

Carbonic  oxide  is  produced  by  the  combustion  of  fuel  in  almost  every  furnace 
or  fire.  The  first  result  of  the  action  of  the  air  upon  the  fuel  at  a  high  temperature 
is  the  production  of  carbonic  acid  gas ;  but  as  it  passes  upwards  through  the  re- 

1  Oxalic  acid  (C203),  which  is  sometimes  classed  with  the  oxides  of  carbon,  is  not 
enumerated  in  this  list,  since  it  is  not  known  to  exist  in  the  separate  (anhydrous)  state. 


190  CARBON  AND   OXYGEN. 

maining  fuel,  which  is  highly  heated,  but  does  not  come  in  contact  with  air,  the 
carbonic  acid  is  reduced  to  carbonic  oxide,  a  portion  of  the  fuel  being  likewise 
converted  into  this  gas  by  the  other  equivalent  of  oxygen.  The  gas  thus  produced 
is  inflamed  as  it  comes  in  contact  with  the  air  at  the  upper  part  of  the  fire,  and  is 
thus  reconverted  into  carbonic  acid. 

Carbonic  oxide  is  likewise  produced  by  the  dry  distillation  of  many  organic 
substances,  and  by  the  decomposition  of  oxalic  acid,  or  ferrocyanide  of  potassium, 
by  concentrated  sulphuric  acid. 

Preparation. — The  two  last-named  substances  are  most  generally  employed  for 
the  production  of  carbonic  oxide.  Oxalic  acid  consists  of  two  equivalents  of  carbon 
and  three  of  oxygen  (or  of  two  groups,  CO  and  C03),  combined  with  one  equiva- 
lent of  water.  When  heated  with  strong  sulphuric  acid,  the  latter  seizes  the  water 

Fig.  66. 


of  hydration,  which  appears  essential  to  the  existence  of  oxalic  acid,  for,  on  its 
abstraction,  the  latter  is  immediately  resolved  into  equal  volumes  of  carbonic  acid 
and  carbonic  oxide : — 

C,08.HO+HO.S08fe2HO.SO.+CO+COa. 

The  resulting  mixture  of  gases  is  passed  through  milk  of  lime,  or  through 
solution  of  potassa,  which  retain  the  carbonic  acid. 

When  ferrocyanide  of  potassium  is  heated  with  8  or  10  times  its  weight  of 
concentrated  sulphuric  acid,  it  yields  a  large  quantity  of  carbonic  oxide,  being 
decomposed,  together  with  the  water,  by  the  action  of  the  acid,  according  to  the 
following  equation : — 

K2FeC6N3+6(HO.S03)+6HO=6CO+2(KO.S03)+FeO.S03+3(NH4O.S03). 

Properties. — Carbonic  oxide  is  a  colorless  inodorous  gas,  which  has  not  yet  been 
liquefied,  and  burns,  when  in  contact  with  air,  with  a  blue  flame,  being  thereby 
converted  into  carbonic  acid.1  It  does  not  support  combustion  or  respiration ;  it  is, 
indeed,  highly  poisonous,  producing  coma  almost  immediately,  when  inhaled  pure. 

According  to  Leblanc,  one  per  cent,  of  carbonic  oxide  diffused  through  the  air 

1  The  affinity  of  carbonic  oxide  for  oxygen  at  a  high  temperature  is  turned  to  advantage, 
upon  an  enormous  scale,  in  the  reduction  of  some  metals  (particularly  iron)  from  their  ores. 


CARBONIC  ACID.  197 

is  sufficient  to  render  it  irrespirable  (see  §  124).  Carbonic  oxide  has  no  action  on 
vegetable  colors ;  it  is  a  neutral  body,  similar  to  water ;  it  does  not,  however, 
combine  either  with  acids  or  bases,  like  that  substance.  It  is  but  slightly  soluble 
in  water. 

Carbonic  oxide,  when  mixed  with  an  equal  volume  of  dry  chlorine,  and  exposed 
to  the  action  of  the  sun's  rays,  unites  with  that  element,  producing 

CHLOROXICARBONIC  ACID,  CHLOROCARBONIC  ACID,  or  PHOSGENE  GAS,  which 
has  the  formula  COC1. 

It  is  colorless,  and  possesses  a  peculiar  sweet  but  suffocating  odor.  It  is  also 
produced  without  the  influence  of  solar  radiation,  when  carbonic  oxide  is  passed 
through  pentachloride  of  antimony,  the  latter  being  thereby  reduced  to  the  ter- 
chloride.  Its  production  in  this  manner  affords  a  ready  means  of  testing  for 
carbonic  oxide,  since  the  smallest  quantity  of  phosgene  gas  produced  is  easily 
recognizable  by  its  peculiar  odor.  Water  decomposes  this  gas,  producing  carbonic 
and  hydrochloric  acids  : — 

COCl+HO=COa+HCl. 
Carbonic  oxide  is  decomposed  by  potassium  and  sodium  at  a  high  temperature. 

These  metals,  however,  absorb  a  quantity  of  the  gas  at  a  lower  temperature, 
hence  they  are  employed  to  separate  it  from  mixtures  of  hydrogen  and  carbo- 
hydrogen  with  carbonic  oxide.  In  the  preparation  of  potassium,  where  that  metal 
and  carbonic  oxide  are  the  chief  products,  there  are  produced  small  quantities  of 
peculiar  compounds  of  carbonic  oxide,  which,  when  heated  with  water,  yield  two 
acids,  to  which  the  names  croconic  and  rhodizonic  acids  have  been  given.  These, 
and  other  compounds,  in  which  the  existence  of  carbonic  oxide  as  a  radical  is 
assumed,  form  a  class  termed  the  carbonic  oxide  series,  of  which  the  following 
are  the  members : — 

(Carbonic  oxide  CO.) 

Carbonic  acid CO-f-0 

Chlorocarbonic  acid CO  +  Cl 

Oxalic  acid "  .     .  2CO-f  0 

Oxamide 2CO-f-NH3 

Carbonoxide  of  potassium 7CO-f-K3 

llhodizonic  acid 7CO  +  3HO 

Croconic  acid 5CO  +  H 

Melliticacid 4CO  +  H 

CARBONIC  ACID. 
C02.    ^.22.    Sp.  Gr.  1.529. 

Composition  ~by  Volume. — Two  volumes  of  carbon-vapor,  and  two  volumes  of 
oxygen  condensed  to  two  volumes. 

§  124.  Carbonic  acid  occurs  in  the  atmosphere  (as  a  product  of  combustion, 
respiration,  and  decay  of  various  kinds);  in  considerable  quantities  in  the  mine- 
ral kingdom,  combined  with  metallic  oxides;  also  in  all  spring  and  river  water, 
either  in  combination  with  earthy  and  alkaline  bases,  or  dissolved  in  the  water  in 
an  uncombined  state.  Carbonic  acid  issues  from  the  ground  in  various  localities 
(e.g.  in  Brohl,  the  Grotto  del  Cane,  and  in  Pyrmont).  It  forms  the  deadly  choke- 
damp  of  coal-mines. 

Carbonic  acid  is  produced  by  the  combustion  of  all  carbonaceous  substances  in 
oxygen  or  in  air,  or  by  submitting  them  to  the  action  of  oxidizing  agents  at  a 
more  or  less  elevated  temperature. 

It  is  also  a  product  of  respiration,  fermentation,  and  putrefaction;  and  is 
formed  when  carbonic  oxide  is  burnt  in  air,  or  mixed  with  half  its  volume  of 
oxygen,  and  inflamed  or  ignited  by  the  electric  spark  or  prepared  platinum. 


198  CARBON   AND    OXYGEN. 

Preparation. — Carbonic  acid  gas  is  obtained  by  the  action  of  a  mineral  acid 
upon  a  carbonate ;  and  is  most  readily  procured  by  pouring  moderately  concen- 
trated hydrochloric  acid  upon  fragments  of  marble  in  a  gas-generating  apparatus. 
The  carbonate  of  lime  is  thus  converted  into  chloride  of  calcium;  carbonic  acid 
escaping  with  effervescence : — 

CaO.C03+HCl=CaCl+COa+HO. 

It  may  also  be  prepared  by  acting  upon  chalk  with  dilute  sulphuric  acid.1 
Hydrochloric  acid  is,  however,  much  to  be  preferred,  since  the  sulphate  of  lime, 
which,  in  the  above  instance,  is  the  resulting  product,  is  very  insoluble  in  water, 
and  even  more  so  in  the  presence  of  free  sulphuric  acid,  and  being  therefore  depo- 
sited upon  the  chalk  or  marble,  prevents  further  action  of  the  acid.  Chloride  of 
calcium,  on  the  contrary,  is  exceedingly  soluble.  Carbonic  acid  may  be  collected 
over  cold  water,  but  cannot  be  retained  over  it  for  any  length  of  time  without 
some  loss,  on  account  of  its  solubility.  Being  considerably  heavier  than  air,  it 
may  be  easily  collected  by  downward  displacement. 

When  pure  gas  is  required,  it  should  be  first  allowed  to  pass  through  a  small 
quantity  of  water,  to  retain  any  hydrochloric  acid  vapor  that  may  be  carried  over 
mechanically,  and  afterwards  through  a  drying  tube  filled  with  chloride  of  calcium. 

Properties. — Carbonic  acid  may  exist  in  the  solid,  liquid,  and  gaseous  states. 
It  is  liquefied  by  pressure  of  30  atmospheres  at  a  temperature  of  32°  F.,  the 
amount  of  pressure  required  to  liquefy  it  decreasing  with  the  temperature. 

Liquid  carbonic  acid  may  be  obtained  on  a  small  scale  by  generating  the 
gas  in  a  Faraday's  condensing-tube,  by  the  action  of  sulphuric  acid  on  carbonate 
of  ammonia,  the  tube  being  kept  at  a  very  low  temperature;  it  is  prepared  in 
larger  quantities,  according  to  the  method  described,  §  37. 

Liquid  carbonic  acid  is  colorless,  and  very  mobile,  possessing  an  elastic  force 
of  38.5  atmospheres  at  32°  F.  Its  specific  gravity  at  that  temperature  is  0.83  ; 
it  is  possessed  of  remarkable  dilating  power.  Liquid  carbonic  acid  is  insoluble 
in  water  and  fatty  oils,  but  is  miscible  in  all  proportions  with  alcohol,  ether,  bi- 
sulphide of  carbon,  naphtha,  or  oil  of  turpentine;  it  is  solidified  at  about  — 94° 
F.  (  — 70°  C.),  forming  a  perfectly  transparent,  vitreous  mass.  If  allowed  to 
escape  into  air,  liquid  carbonic  acid  evaporates  with  great  rapidity,  one  portion 
passing  over  into  the  gaseous  state  immediately,  whereby  the  other  portion  is 
cooled  down  to  so  low  a  temperature  as  to  become  frozen. 

Solid  carbonic  acid  is  most  readily  obtained  according  to  Thilorier's  or  Nat- 
terer's  method  (§  37);  it  then  presents  the  appearance  of  snow,  and  is  compres- 
sible like  that  substance.  It  is  a  bad  conductor  of  heat ;  hence,  although  its 
temperature  is  probably  as  low  as  — 148°  F.  (  — 100°  C.),  it  may  be  handled 
without  injury;  if  pressed  upon  the  skin,  however,  it  produces  a  blister  similar 
to  that  caused  by  a  burn.  It  may  be  preserved  for  some  hours  in  the  air  in  large 
masses,  if  surrounded  by  any  non-conducting  substance.  When  mixed  with 
ether,  it  forms  a  soft,  semi-fluid  mass,  which  evaporates  rapidly,  producing  the 
most  intense  cold,  whereby  mercury  may  be  frozen  in  large  quantities;  a  still 
more  intense  cold  may  be  obtained  by  placing  a  mixture  of  the  above  description 
under  the  receiver  of  an  air-pump,  and  rapidly  exhausting  the  air  and  gaseous 
carbonic  acid.  When  obtained  by  exposing  liquid  carbonic  acid  to  a  low  tempe- 
rature, the  solid  carbonic  acid  resembles  ice;  it  appears  to  melt  at  about  — 97°. 6 
F.  (_72°C.) 

Gaseous  carbonic  acid  is  colorless;  it  possesses  a  slightly  pungent,  acidulous 
odor,  is  incombustible,  and  does  not  support  the  combustion  of  most  substances. 
It  imparts  to  tincture  of  litmus  a  peculiar  wine-red  color,  differing  considerably 

1  This  method  is  always  preferred  when  the  carbonic  acid  is  required  for  making 
aerated  waters,  since  the  hydrochloric  acid  is  liable  to  be  carried  off  in  vapor,  which 
condenses  in  the  water. 


CARBONIC   ACID.  199 

from  the  onion-skin  red  produced  by  sulphuric  acid  ;  the  blue  color  is,  however, 
restored  by  exposure  of  the  liquid  to  air,  as  the  carbonic  acid  evaporates.  At  the 
ordinary  temperature,  water  dissolves  about  an  equal  volume  of  carbonic  acid; 
but  this  solubility  is  considerably  increased  by  the  application  of  pressure.  It 
has  been  shown,  however,  that  a  volume  of  water  always  dissolves  the  same  vo- 
lume of  carbonic  acid  under  all  pressures,  and  that  the  greater  amount  absorbed 
is  dependent  upon  the  condensation  of  the  gas.  Upon  the  removal  of  the  pres- 
sure, the  extra  amount  of  gas  absorbed  escapes. 

Solution  of  carbonic  acid  has  an  agreeably  acid  taste;  it  exerts  a  slight  solvent 
action  upon  several  salts,  otherwise  insoluble  in  water  (e.  g.  carbonate  and  phos- 
phate of  lime).  It  is  probable  that  the  phosphate  of  lime  contained  in  plants 
is  supplied  to  them  through  the  medium  of  the  water  percolating  through  the 
soils,  since  water  is  always  more  or  less  charged  with  carbonic  acid  absorbed 
from  the  atmosphere  or  other  sources! 

The  great  density  of  carbonic  acid  admits  of  its  being  poured  from  one  vessel 
to  another,  like  a  liquid,  provided  the  surrounding  air  be  not  agitated. 

When  inhaled  pure,  or  even  mixed  with  a  considerable  amount  of  air,  carbonic 
acid  produces  asphyxia  and  death;  acting  as  a  narcotic  poison.1  It  is  frequently 
believed  that  such  mixtures  of  air  and  carbonic  acid  as  will  allow  a  candle  to 
burn,  may  be  breathed  safely  by  man  or  animals;  hence  the  practice  of  lowering 
a  candle  into  pits,  wells,  or  other  places  supposed  to  contain  vitiated  air.  It  is, 
however,  found  that  mixtures  in  which  a  candle  may  burn,  will,  if  inhaled,  pro- 
duce, if  not  immediate  insensibility,  ultimately  the  most  dangerous  consequences. 
It  is  now  generally  allowed  that  the  accidents  resulting  from  charcoal  fires  in 
close  apartments,  are  due  rather  to  the  carbonic  oxide  evolved  by  the  incomplete 
combustion,  than  to  the  carbonic  acid ;  the  latter  is  not  generally  produced  in 
sufficient  quantity  to  cause  death. 

Carbonic  acid  may  be  shown  to  be  a  product  of  respiration,  by  breathing  through 
a  tube  into  lime  or  baryta  water,  which  are  almost  immediately  rendered  turbid 
by  the  production  of  the  carbonates. 

Carbonic  acid  is  decomposed  into  carbonic  oxide  and  oxygen  by  the  continued 
action  of  the  electric  spark ;  the  products  are,  however,  induced  to  reunite  by 
the  same  agent.  It  is  similarly  decomposed,  the  oxygen  becoming  fixed  or  com- 
bined, when  subjected  to  a  high  temperature  in  contact  with  carbon,  hydrogen, 
iron,  or  zinc,  or  to  the  electric  spark  in  contact  with  hydrogen  or  with  some 
metals.  When  potassium  is  heated  in  an  atmosphere  of  carbonic  acid,  it  becomes 
incandescent,  and  abstracts  the  whole  of  the  oxygen  from  the  gas,  the  result 
being  potassa  and  a  deposition  of  carbon.  Sodium  acts  in  a  similar  manner, 
though  less  violently.  Phosphorus,  sulphur,  and  similar  inflammable  substances, 
do  not  possess  this  property,  and  are  extinguished  if  immersed,  while  burning,  ia 
the  gas. 

A  few  words  may  be  said  respecting  the  method  employed  for  determining  the 
composition  of  carbonic  acid,  since  it  may  be  effected  with  ease  and  exactness, 
and  is,  both  chemically  and  generally,  as  important  as  the  determination  of  the 
composition  of  water.  A  small  portion  of  carbon,  as  pure  and  dry  as  possible,3 
contained  in  a  little  boat  or  cradle  of  platinum,  is  accurately  weighed,  and  intro- 
duced into  a  porcelain  tube,  a,  I  (Fig.  67),  which  is  heated  to  redness  in  a  fur- 
nace, and  contains  in  b,  the  portion  opposite  to  that  in  which  the  carbon  is  intro- 
duced, some  porous  oxide  of  copper  (retained  within  a  certain  distance  from  the 
opening  of  the  tube  by  a  plug  of  asbestos).  The  extremity,  a  of  the  tube  at 
which  the  carbon  was  introduced,  is  connected  with  a  gas-holder,  from  which  a 

1  Animals  or  persons  rendered  insensible  or  thrown  into  convulsions  by  inhaling  this 
gas,  may  frequently  be  restored  by  sudden  immersion  in  cold  water. 

2  Diamond  has  been  used  in  the  most  accurate  determinations  of  this  question. 


200 


CARBON   AND   OXYGEN. 


stream  of  pure  oxygen  may  be  supplied,  which  is  dried  previously  to  its  entrance 
into  the  tube  by  passing  through  an  U-tube,  E,  containing  fragments  of  pumice 
moistened  with  oil  of  vitriol.  The  other  extremity  of  the  porcelain  tube  at  which 
the  oxide  of  copper  is  situated  is  connected  with  a  similar  U-tube,  A,  to  the  other 
end  of  which  is  attached  a  bulb  absorption-apparatus,  p,  containing  solution  of 


Fig.  67. 


potassa ;  this  is  again  connected  with  an  U-tube,  C,  containing  pumice  moistened 
with  strong  solution  of  potassa,  and  likewise  attached  to  a  third  tube,  D,  similar 
to  the  first.  The  bulbs  and  these  two  tubes  are  accurately  weighed  together  before 
they  are  attached  to  the  apparatus.  The  tubes  being  all  securely  connected  in 
the  usual  manner,  the  oxygen  is  allowed  to  enter  the  apparatus  and  expel  the  air 
slowly.  The  porcelain  tube  is  then  heated  to  redness,  when  the  carbon  soon 
ignites,  and  is  converted  into  carbonic  acid,  which  is  absorbed  by  the  caustic 
potassa  in  the  bulbs  and  U-tube,  as  it  is  carried  into  them  by  the  continuous 
current  of  oxygen. 

A  small  amount  of  moisture  may  be  carried  off  mechanically  by  the  latter  in 
its  passage  through  these  tubes;  this  is  retained  by  the  sulphuric  acid  in  the  last 
weighed  U-tube  as  the  gas  passes  off  through  it  into  the  atmosphere.  Should 
any  carbonic  oxide  be  produced  in  the  combustion  of  the  carbon,  which  is  some- 
times the  case,  it  is  immediately  converted  into  carbonic  acid  as  it  comes  in  con- 
tact with  the  redhot  oxide  of  copper  contained  in  the  end  of  the  tube.  The 
current  of  oxygen  through  the  apparatus  is  allowed  to  continue  for  some  little 
time  after  the  combustion  of  the  carbon,  to  insure  the  perfect  collection  of  the 
resulting  carbonic  acid.  When  the  operation  is  completed,  the  three  tubes  are 
once  more  weighed  together,  the  amount  of  carbonic  acid  produced  being  indicated 
by  their  increase  of  weight.  The  small  boat  is  then  carefully  removed  from  the 
tube  and  reweighed,  together  with  any  small  amount  of  residue  or  ash,  resulting 
from  the  combustion  of  the  carbon,  and  consisting  of  the  earthy  impurities  which 
it  may  have  contained.  This  weight,  deducted  from  the  original  weight  of  the 
boat  and  carbon,  will  furnish  the  amount  of  pure  carbon  employed  in  the  expe- 
riment. 

The  weight  of  the  carbonic  acid  (inferred  from  the  increase  in  the  weight  of 
the  absorption-tubes),  minus  that  of  the  carbon  employed  in  the  experiment,  gives 
the  quantity  of  oxygen  contained  in  the  gas. 

Combinations  of  Carbonic  Acid. — This  acid  unites  with  metallic  oxides,  pro- 
ducing salts,  which  are  termed  carbonates.  It  is,  however,  a  very  feeble  acid, 
being  easily  replaced  by  all  other  acids,  except  hydrocyanic  acid.  The  carbonates 
of  alkalies  have,  in  consequence,  a  strong  alkaline  reaction.  The  hydrate  of 
carbonic  acid  does  not  appear  to  exist  in  the  free  state;  it  is,  however,  contained 


LIGHT   CARBURETTED    HYDROGEN.  201 

in  the  bicarbonates  of  the  alkalies,  the  general  formula  for  which  is  MO.COa, 
I!O.COa.  Carbonic  acid  escapes  from  all  its  salts,  with  the  exception  of  those 
of  the  neutral  carbonates  of  the  alkalies,  when  they  are  exposed  to  the  action  of 
heat.  When  replaced  in  its  combinations  by  other  acids,  it  escapes  with  effer- 
vescence. 

Uses  of  Carbonic  Acid. — Liquid  carbonic  acid  is  employed  for  the  production 
of  the  solid  acid,  which,  when  mixed  with  ether,  or  bisulphide  of  carbon,  is  a 
powerful  refrigerator,  exceedingly  important  in  all  experiments  on  condensation 
of  gases,  and  without  which  many  of  the  most  interesting  results  obtained  in  this 
direction  by  Faraday  and  others,  would  probably  not  have  been  arrived  at.  Car- 
bonic acid  gas  is  most  extensively  employed  in  the  preparation  of  aerated  waters. 
The  liquid  to  be  charged  with  gas  is  contained  in  very  strong  vessels,  made  of 
copper,  well-tinned,  into  which  the  gas  is  forced  with  considerable  pressure. 

Iron  must  not  be  employed  in  the  construction  of  these  vessels,  since  a  solu- 
tion of  carbonic  acid  has  considerable  action  on  that  metal.  The  carbonic  acid 
evolved  by  fermentation,  is  often  employed  on  a  large  scale  for  the  preparation 
of  certain  carbonates,  such  as  carbonate  of  lead,  bicarbonate  of  soda,  &c. 

Carbonic  acid  is  frequently  employed  by  the  chemist  for  replacing  the  air  in 
vessels  or  apparatus  in  which  the  absence  of  free  oxygen  is  absolutely  necessary 
(e.  g.  in  the  conversion  of  phosphorus  into  the  allotropic  modification).  A  mix- 
ture of  carbonic  acid  with  aqueous  vapor  and  nitrogen,  disengaged  under  con- 
siderable pressure,  has  also  been  employed  for  extinguishing  fires  j  the  disengag- 
ing apparatus  (the  fire-annihilator)  being  furnished  with  a  hose  whereby  the 
gaseous  mixture  may  be  directed  to  any  particular  point. 

In  medicine,  carbonic  acid  is  administered  in  the  form  of  aerated  saline  drinks. 

Alkaline  carbonates  are  also  frequently  administered. 


CARBON   AND    HYDROGEN. 

Light  carburetted  hydrogen CaH4 

Olefiantgas C4H4 

All  other  compounds  of  carbon  and  hydrogen,  of  which  there  are  a  great  num- 
lerjfall  strictly  within,  the  province  of  organic  chemistry. 

LIGHT  CARBURETTED  HYDROGEN,  Marsh  gas  or  Fire-damp. 
C2H4.     Sp.  Gr.  0.556.     %  16. 

§  125.  Composition  by  Volume. — 4  volumes  of  carbon-vapor  and  8  volumes  of 
hydrogen  condensed  to  4  volumes. 

This  gas,  being  a  product  of  the  decomposition  or  putrefaction  of  vegetable 
matter  (wood,  &c.)  under  water,  frequently  escapes  in  considerable  quantities 
from  the  bottom  of  stagnant  pools,  or  may  be  made  to  rise  to  the  surface  by  stir- 
ring the  mud  about.  Hence  its  name  of  marsh-gas.  It  may  be  easily  collected 
in  such  localities  by  inverting,  over  the  water  where  it  escapes,  a  bottle  filled 
with  water,  in  the  neck  of  which  is  fixed  a  funnel. 

The  gas  thus  obtained  contains  a  considerable  amount  of  carbonic  acid  and  a 
little  nitrogen.  It  may  be  purified  from  the  former  by  agitation  with  lime- 
water. 

Considerable  quantities  of  the  same  gas  are  also  found  to  issue  from  the  earth 
in  some  localities,  emanating  from  coal  deposits ;  in  working  coal-mines  it  is  also 
frequently  met  with,  inclosed  in  cavities,  rendering  the  atmosphere  inflammable 
by  its  admixture,  and  being  hence  frequently  the  cause  of  dangerous  explosions, 
in  consequence  of  which  the  name  of  fire-damp  was  given  to  it.  Serious  acci- 


202  CARBON   AND   HYDROGEN. 

dents  also  happen  occasionally,  in  consequence  of  the  evolution  of  fire-damp  from 
the  cavities  existing  in  coal  stored  on  board  ship. 

It  is  also  the  product  of  the  destructive  distillation  of  coal,  and  of  the  action 
of  a  high  temperature  on  the  vapor  of  alcohol. 

Preparation. — The  best  method  of  obtaining  this  gas  is  to  heat  in  a  copper  or 
coated  glass  retort,  an  intimate  mixture  of  4  parts  of  dried  acetate  of  soda,  4  parts 
of  fused  potassa,  and  6  parts  of  quicklime. 

It  may  be  collected  over  water.     . 

NaO.C4H303+KO.HO=C2H4+KO.C03+NaO.C02. 


Acetate  of  soda.  Marsh-gas. 

Properties. — Light  carburetted  hydrogen  is  a  colorless  and  inodorous  gas,  burn- 
ing with  a  pale  blue  and  white  flame ;  the  results  of  the  combustion  are  carbonic 
acid  and  water.1  It  is  but  very  slightly  soluble  in  water.  Chlorine  has  no  action 
upon  it  in  the  dark,  but  when  a  mixture  of  the  gases  is  exposed  to  diffused  day- 
light in  the  presence  of  moisture,  hydrochloric  and  carbonic  acids  are  produced : — 

C3H4+CI8+4HO=2COa+8HCl. 

When  mixed  with  a  small  quantity  of  air,  light  carburetted  hydrogen  explodes 
but  feebly  or  not  at  all ;  but  if  the  proportion  of  air  be  about  the  quantity  neces- 
sary for  its  complete  combustion  (about  10  volumes  to  1  of  the  gas),  the  mixture 
explodes  very  violently.  As  the  quantity  of  air  increases  beyond  that  proportion, 
the  explosive  power  diminishes,  until  at  last  the  gaseous  mixture  merely  burns 
round  the  flame  of  a  candle  or  lamp.3  The  frequent  and  lamentable  accidents 
occurring  in  coal  mines  in  consequence  of  the  formation  of  fire-damp,  or  explosive 
mixture  of  air  and  light  carburetted  hydrogen,  led  Sir  H.  Davy  to  make  a  close 
examination  of  this  gas,  with  reference  to  its  combustible  properties,  in  connec- 
tion with  some  beautiful  researches  of  his  on  the  power  possessed  by  the  metals, 
in  consequence  of  their  conducting  properties,  of  cooling  down  gases  in  a  state  of 
combustion  to  such  an  extent  as  to  extinguish  flame. 

Davy  found  that  flame  could  not  be  communicated  through  a  narrow  glass  tube 
to  an  explosive  mixture  of  marsh-gas  and  air,  the  cooling  power  of  the  sides  of 
the  tube  preventing  the  gas  from  attaining  a  sufficiently  high  temperature. 
Metallic  tubes  naturally  possessed  this  power  to  a  higher  degree,  in  consequence 
of  their  good  conducting  properties,  and  it  was  found  that  even  metallic  wires, 
held  within  a  certain  distance  of  each  other,  or,  more  conveniently,  wire  gauze 
of  a  certain  fineness,  possessed  the  power  of  obstructing  the  passage  of  flame,  or 
of  protecting  an  explosive  mixture  from  ignition  by  flame.  Thus,  by  allowing  a 
stream  of  coal-gas  to  pass  through  a  ^>iece  of  moderately  fine  wire  gauze  (contain- 
ing not  less  than  400  meshes  to  the  square  inch),  it  may  be  kindled  on  the  upper 
side  without  the  flame  being  thereby  communicated  to  it  below  the  gauze.  The 
development  of  these  principles  led  Davy  to  the  construction  of  the  safety -lamp, 
by  the  use  of  which  the  miner  is  protected  from  danger,  and  at  the  same  time 
warned  of  the  existence  of  a  pernicious  atmosphere.  It  consists  merely  of  an  oil 
lamp,  the  wick  of  which  is  inclosed  in  an  iron  wire  gauze  cage,  of  which  the 
upper  part  is  double;  a  wire,  bent  into  a  hook  at  the  upper  extremity,  passes 
upwards  through  the  lamp,  by  which  it  may  be  trimmed  to  some  extent  without 
removing  the  gauze  cage. 

When  this  lamp  is  introduced,  while  burning,  into  an  inflammable  atmosphere, 
the  flame  of  the  lamp  will  be  extinguished,  while  a  bluish  flame  will  be  seen 

1  The  carbonic  acid  formed  by  the  explosion  of  fire-damp  in  coal  mines  is  technically 
called  "after-damp,"  and  is  more  fatal  to  the  miners  than  even  the  explosion  itself. 

2  No  explosion  takes  place  if  the  volume  of  air  be  less  than  6  or  more  than  14  times 
the  volume  of  the  gas. 


COAL-GAS.  203 

•within  the  gauze  cage,  arising  from  the  combustion  of  the  gas  as  it  penetrates ; 
by  this,  therefore,  the  miner  is  immediately  made  aware  of  the  presence  of  fire- 
damp. The  lamp  may  even  be  allowed  to  remain  in  this  state  in  an  atmosphere 
of  light  carburetted  hydrogen  until  the  wire  gauze  is  heated  to  dull  redness  by 
the  heat  of  the  burning  gases  inside ;  for,  although  kindled  immediately  by  flame, 
this  gas  requires  a  higher  temperature  for  its  ignition  than  most  other  inflamma- 
ble gases.  An  iron  rod  heated  to  dull  redness  will  set  fire  to  olefiant  gas,  hydro- 
gen, carbonic  oxide,  &c.,  while  the  temperature  of  iron  must  be  almost  a  white 
heat  before  it  will  inflame  light  carburetted  hydrogen. 

COAL-GAS. 

§  126.  The  gaseous  product  of  the  distillation  of  coal  contains  light  carburet- 
ted hydrogen  in  much  larger  proportion  than  any  other  gas;  it  will,  therefore, 
not  be  out  of  place  to  enter  here  into  a  brief  account  of  the  preparation  and 
nature  of  coal-gas. 

By  submitting  coal  to  distillation  in  closed  iron  retorts,  three  principal  pro- 
ducts are  obtained  :  a  dark,  oily,  viscid  fluid,  known  as  coal-tar,  containing  a 
variety  of  substances;  an  aqueous  liquid,  containing  ammonia  and  its  salts;  and 
a  gaseous  mixture,  the  principal  constituent  of  which  is  light  carburetted  hydro- 
gen, but  which  contains  besides,  variable  quantities  of  olefiant  gas,  carbonic 
oxide,  hydrogen,  carbonic  acid,  and  nitrogen,  and  smaller  quantities  of  sulphu- 
retted hydrogen,  bisulphide  of  carbon,  vapor  of  volatile  liquid  hydrocarbons,  am- 
monia, cyanogen,  hydrochloric  acid,  and  aqueous  vapor.  The  four  first-named 
products  form  the  main  bulk  of  the  gas,  together  with  the  vapors  of  the  volatile 
liquids;  the  hydrogen  and  carbonic  oxide  are  evidently  produced  by  the  decom- 
position of  moisture  in  the  coal,  or  of  water  produced  in  the  distillation,  the 
vapor  of  which,  passing  over  the  redhot  coal,  yields  these  two  gases.  All  coal 
contains  more  or  less  sulphur  (generally  existing  as  iron-pyrites),  which  is  con- 
verted during  the  distillation  into  hydrosulphuric  acid,  and  vapor  of  bisulphide 
of  carbon. 

The  nitrogen  existing  in  coal  is  expelled  as  ammonia,  cyanogen  (C3N),  and  a 
combination  of  the  latter  substance  with  sulphur,  sulphocyanogen  (C2NS3);  any 
free  nitrogen  is  due  to  the  atmospheric  air  contained  in  the  retorts  at  the  com- 
mencement of  the  operation.  The  only  absolutely  essential  constituents  of  coal- 
gas,  obtained  in  the  ordinary  process  of  manufacture,  are  light  carburetted 
hydrogen  and  olefiant  gas.  Its  illuminating  power  is  mainly  owing  to  the  lattar, 
and  to  the  vapors  of  liquid  hydrocarbons  which  the  gas  contains,  while  the  light 
carburetted  hydrogen,  though  burning  with  but  a  pale  flame,  evolves  much  more 
heat  by  its  combustion  than  the  olefiant  gas,  and  thus,  by  imparting  a  very  high 
temperature  to  the  small  particles  of  carbon  separated  during  the  combustion  of 
the  illuminating  constituents  (§  65),  contributes  considerably,  though  indirectly, 
to  the  luminosity  of  the  gas-flame. 

There  are,  however,  considerable  objections  to  the  presence  of  large  quantities 
of  both  light  carburetted  hydrogen  and  carbonic  oxide,  as  diluents  in  coal-gas,  in 
consequence  of  the  large  amount  of  carbonic  acid  generated  by  their  combustion  ; 
the  excessive  amount  of  heat  evolved  during  the  combustion  of  light  carburetted 
hydrogen  is  also  a  great  drawback  to  the  use  of  such  gas,  containing  a  large 
quantity  of  this  constituent,  for  the  illumination  of  apartments;  though,  on  the 
other  hand,  when  the  gas  is  employed  solely  as  a  source  of  heat,  its  value  is 
much  increased  from  the  same  cause.  It  would,  however,  greatly  add  to  the 
general  utility  of  gas,  if  the  light  carburetted  hydrogen  could  be  entirely,  or  in 
part,  replaced  by  hydrogen,  since  this  gas  evolves  much  less  heat  in  proportion 
to  its  volume,  and  its  product  of  combustion  is  perfectly  innocuous.  This  object 
appears  to  be  to  a  great  extent  attained,  by  the  application  of  a  new  process  for 
the  manufacture  of  gas,  which  we  shall  presently  notice. 


204 


CARBON   AND    HYDROGEN. 


The  peculiar  property  which  chlorine  possesses,  of  forming,  when  mixed  with 
coal-gas,  oily  substances  with  those  of  its  compounds  to  which  it  owes  its  illu- 
minating properties,  namely,  olefiant  gas,  and  the  vapors  of  hydrocarbons,  affords 
a  ready  means  of  testing  its  illuminating  power,  which  is,  of  course,  in  direct 
proportion  to  the  decrease  in  volume  of  the  gas  when  mixed  with  chlorine. 
From  experiments  made  by  Henry,  it  has  been  proved  that  the  gaseous  products 
of  the  distillation  of  coal  differ  very  considerably  at  the  various  periods  of  the 
operation.  Before  the  coal  arrives  at  a  cherry-red  heat,  the  products  consist 
almost  entirely  of  hydrogen  and  tar,  together  with  the  atmospheric  air  from  the 
retort.  When  the  retort  has  attained  the  stated  temperature,  illuminating  gas 
passes  over,  the  value  of  which  decreases  in  proportion  to  the  length  of  time 
for  which  the  coal  has  been  heated. 


Time  of  collection. 

Spec.  grav. 

Absorbed  by 
chlorine. 

Light 
carburetted 
hydrogen. 

Carbonic 
oxide. 

Hydrogen. 

Nitrogen. 

f  0.650 

In  100  parts  of  gas  from  Wigan  cannel  coal. 

13 

82.5 

3.2 

0 

1.3 

In  1st  hour      .     .     . 

\  0.620 

12 

72 

1.9 

8.8 

5.3 

[0.630 

12 

58 

12.3 

16 

1.7 

5  hours  after  com-  "1 
mencement  .     .     / 

0.500 

7 

56 

11 

21.3 

4.7 

10  hours  ditto.     .     . 

0.345 

0 

20 

10 

60 

10 

We  see  from  the  above  that  the  gas  evolved  towards  the  termination  of  the 
process,  only  serves  to  increase  the  total  volume  obtained  from  the  coal,  and  to 
deteriorate  by  dilution  the  illuminating  power  of  the  gas,  since  that  obtained  at 
the  expiration  of  the  tenth  hour  burns  with  merely  a  pale  blue  flame.  The 
large  amount  of  hydrogen  found  in  the  last  stage  of  the  operation  can  evidently 
no  longer  be  produced  by  the  decomposition  of  water,  but  must  be  due  to  the 
action  of  the  high  temperature  upon  the  compounds  of  carbon  and  hydrogen 
which  have  been  proved  to  be  resolved  into  their  elements  at  a  high  red  heat 
(§  129).  The  carbon  thus  liberated  is  found  deposited  on  the  sides  of  the  retort 
as  an  exceedingly  hard  and  dense  crust,  known  by  the  name  of  gas-carbon 
(§  121).  This  kind  of  decomposition  cannot,  under  any  circumstances,  be 
entirely  avoided,  since  the  gas,  as  it  is  evolved  from  coal  in  large  retorts,  must 
always  pass  over  a  redhot  surface;  it  may,  however,  be  much  diminished  by  a 
careful  moderation  of  the  temperature. 

The  cannel  coal  is  found  to  be  the  best  for  the  manufacture,  and  the  Scotch 
parrot  coal  the  next.  The  coal  should  be  as  dry  as  possible,  and  when  subjected 
to  distillation,  should  be  raised  as  rapidly  as  possible  to  a  cherry-red  heat,  at 
which  temperature  it  should  be  uniformly  maintained  throughout  the  distillation. 
The  operation  should  be  stopped  when  experiment  has  shown  that  the  illuminat- 
ing power  of  the  gas  evolved  decreases  rapidly.1 

The  retorts  used  are  of  cast-iron  ;2  their  forms  elliptical,  cylindrical,  or  slight 
modifications  of  these,  and  are  connected  with  necks,  from  which  conducting- 
pipes  pass  into  a  large  horizontal  tube,  termed  the  hydraulic  main,  where  a  large 

• 

1  The  period  of  the  distillation  varies  from  five  to  eight  hours,  according  to  the  nature 
of  the  coal  and  the  form  of  the  retort  used. 

2  Stone-ware  retorts  are  now  very  frequently  substituted  for  those  of  cast-iron. 


COAL-GAS.  205 

quantity  of  tar  and  araraoniacal  liquor  is  deposited  from  the  gas  as  it  passes  from 
the  retorts.  From  the  hydraulic  main  the  gas  is  conducted  into  a  series  of  iron 
tubes,  which  are  kept  cool  by  water,  and  in  which  the  chief  part  of  the  easily- 
condensable  impurities  is  separated  from  the  gas. 

In  some  of  the  large  works  the  gas  is  allowed  to  pass  from  the  condenser  into 
a  washing-apparatus,  consisting  of  a  very  long  iron  case  furnished  with  three  or 
four  shelves,  placed  at  intervals  of  about  one  foot,  and  attached  alternately  to 
either  side  of  the  case;  water  is  allowed  to  trickle  over  these  shelves,  and  a  large 
surface  being  thus  exposed  to  the  action  of  the  gas  flowing  in  an  opposite  direc- 
tion, a  large  quantity  of  the  gaseous  impurities  is  absorbed  by  it. 

In  another  ingenious  arrangement,  termed  the  scrubber,  the  gas  is  allowed  to 
enter  at  the  bottom  of  a  tall  cylindrical  case,  containing  perforated  shelves  charged 
with  fragments  of  coke,  over  which  water  is  allowed  to  trickle;  in 'this  way  a  still 
further  purification  of  the  gas  may  be  effected.  ' 

When  the  gas  leaves  the  washing-apparatus,  it  has  still  to  be  purified  from  the 
remainder  of  the  incondensable  constituents,  which  are  highly  detrimental  to  its 
quality,  such  as  ammonia,  sulphuretted  hydrogen,  &c.  The  method  exclusively 
employed,  till  very  recently,  for  the  removal  of  these  obnoxious  impurities,  was 
that  of  bringing  the  gas  into  contact  with  slaked  lime,  or  milk  of  lime.  When 
milk  of  lime  is  used,  the  gas  is  allowed  to  pass  through  a  considerable  bulk  in 
very  small  bubbles,  the  liquid  being,  at  the  same  time,  continually  agitated  with 
a  rouser  or  stirrer.  The  chemical  action  of  this  substance  is,  however,  insufficient 
to  effect  perfect  purification  of  the  gas;  the  most  effectual  means  of  retaining  not 
only  the  sulphur  compounds,  but  the  ammoniacal  salts,  is  evidently  the  use,  as 
purifiers,  of  salts  of  earths,  or  other  metallic  oxides,  which  will  effect  double  de- 
composition, and  produce  non-volatile  compounds.  Sulphate  of  lead  has  been 
employed  as  a  purifier,  sulphate  of  ammonia  and  sulphide  of  lead  being  the  chief 
results  of  its  action  on  the  gas ;  it  is,  however,  necessary  to  use  lime  together 
with  this  salt,  in  order  to  remove  the  carbonic  acid. 

The  sulphates  of  manganese  and  iron  are  more  efficacious,  but  the  best  purify- 
ing medium  known  at  present  appears  to  be  that  which  is  now  introduced  into 
several  large  metropolitan  gas-works,  namely,  sawdust,  saturated  with  chloride  of 
calcium.  The  purifying  material  may,  after  it  has  been  employed,  be  worked 
with  advantage  for  several  important  commercial  chemicals,  such  as  sulphate  and 
muriate  of  ammonia,  and  Prussian  blue,  &c. 

After  this  purification,  the  gas  passes  directly  into  the  gasometers,  whence  it 
is  distributed  to  the  various  mains. 

The  secondary  products  in  the  manufacture  of  gas  are  of  considerable  com- 
mercial importance.  The  tar,  by  distillation,  furnishes  a  liquid  known  as  coal- 
tar-naphtha,  which  is  a  mixture  of  various  acid,  basic,  and  neutral  hydrocarbons, 
the  description  of  which  falls  within  the  province  of  organic  chemistry.  The 
most  important  of  these  substances  is  a  volatile  liquid  known  as  benzol  (C^Hg), 
which  has  lately  been  employed  as  an  illuminating  material,  and  for  several 
other  purposes.  The  residue  after  the  distillation  of  tar  is  termed  pitch. 

The  ammoniacal  liquor,  which  is  very  rich  in  carbonate  of  ammonia,  is  em- 
ployed for  the  preparation  of  sulphate  of  ammonia,  and  chloride  of  ammonium. 
Other  chemical  products  (e.g.  Prussian  blue)  are  also  obtained  from  this  liquor. 

When  lime  is  used  as  a  purifying  agent,  it  is  withdrawn  from  the  purifiers 
after  a  certain  time,  and  is  used  as  a  manure  under  the  name  of  gas-lime. 

§  127.  ANALYSIS  OF  COAL-GAS. — The  rigorous  analysis  of  gases  requires  so 
much  accuracy  of  manipulation,  and  involves  so  many  operations  peculiar  to  itself, 
that  it  almost  deserves  to  be  considered  a  separate  branch  of  practical  chemistry. 
Sufficient  has  been  said  in  the  article  on  the  measurement  and  absorption  of  gases 
(§  36),  to  give  a  general  idea  as  to  the  manner  in  which  analyses  of  gas  are  con- 


206  CARBON  AND    HYDROGEN. 

ducted.     We  shall  therefore  confine  ourselves  in  this  place  to  an  outline  of  the 
method  usually  pursued  in  the  examination  of  coal-gas. 
The  following  are  the  substances  usually  determined : — 

Olefiant  gas  j  lllumlnati      constituentSt 

Vapors  of  hydrocarbons      ) 

Light  carburetted  hydrogen. 

Hydrogen. 

Carbonic  acid. 

Carbonic  oxide. 

Nitrogen. 

A  measured  volume  of  the  gas  standing  over  mercury,  is  agitated  with  solution 
of  potassa,  allowed  to  stand  for  some  time,  and  again  measured. 

The  difference  of  volume  indicates  the  amount  of  carbonic  acid. 

The  residual  gas  is  transferred,  in  the  pneumatic  (water-)  trough  to  a  gradu- 
ated tube,  carefully  measured,  mixed  with  half  its  volume  of  pure  chlorine,  and 
allowed  to  stand  for  twenty-four  hours  in  a  dark  place.  The  tube  is  then  placed 
in  a  jar  containing  solution  of  potassa,  and  agitated  for  some  time  to  remove  the 
excess  of  chlorine.  The  residue  is  then  measured. 

The  difference  between  this  volume  and  the  preceding,  indicates  the  volume  of 
olefiant  gas  and  vapors  of  hydrocarbons  (and  hence  is  a  measure  of  the  illuminat- 
ing value  of  the  gas). 

Another  method  consists  in  passing  up  a  pellet  of  coke,  moistened  with  fuming 
sulphuric  acid  (in  the  manner  described,  §  36),  into  a  known  volume  of  the  dry 
gas  over  mercury,  and  afterwards  removing  any  acid  vapor  by  a  similar  pellet  of 
fused  potassa. 

The  remaining  gas,  or  a  measured  portion  of  it,  is  introduced  into  a  small 
tube,  the  closed  end  of  which  is  bent  downwards,  standing  over  mercury.  (All 
moisture  must  be  removed  from  the  mercury  with  blotting-paper,  and  from  the 
gas  by  prolonged  contact  with  pellets  of  fused  hydrate  of  potassa.)  A  small 
pellet  of  potassium  is  introduced  into  the  closed  extremity  of  the  tube,  and  gen- 
tly heated,  so  that  it  may  absorb  the  carbonic  oxide. 

The  gas  is  then  again  transferred  to  a  graduated  tube,  over  water,  and  mea- 
sured. The  difference  in  volume  shows  the  amount  of  carbonic  oxide. 

The  remaining  gas,  after  the  removal  of  the  carbonic  oxide,  is  introduced  into 
an  eudiometer  (§32),  mixed  with  a  measured  quantity  (about  twice  the  volume 
of  the  gas)  of  oxygen,  and  exploded  by  the  electric  spark,  over  mercury. 

The  volume  of  the  residual  gas  (oxygen,  nitrogen,  carbonic  acid)  is  carefully 
noted,  and  agitated  with  solution  of  potassa,  which  absorbs  the  carbonic  acid, 
the  volume  of  which  is  equal  to  that  of  the  light  carburetted  hydrogen. 

The  remainder  is  exposed  to  the  action  of  phosphorus,  over  water,  for  24 
hours;  the  amount  of  oxygen  absorbed  is  then  deducted  from  the  total  quantity 
employed,  in  order  to  ascertain  the  amount  consumed  in  the  combustion.  By 
deducting  from  this  quantity  twice  the  volume  of  the  light  carburetted  hydrogen, 
we  obtain  the  measure  of  oxygen  consumed  by  the  free  hydrogen,  the  volume  of 
which  is  of  course  double  that  of  the  oxygen. 

Finally,  the  residue  consists  of  nitrogen. 

In  the  above  sketch,  we  have,  for  the  sake  of  simplicity,  omitted  to  mention 
the  corrections  for  temperature,  barometric  pressure,  and  aqueous  vapor,  so 
necessary  in  all  analyses  of  gaseous  mixtures.  For  the  methods  of  effecting 
these  corrections,  we  refer  to  §  8. 

§  128.  OiL-GAS. — Refuse  fat,  train  oil,  and  impure  oils  of  various  kinds, 
which  are  not  adapted  for  burning,  are  sometimes  used  for  the  production  of  gas. 
Experiments  made  by  Henry,  have  shown  that  the  gas  obtained  by  distilling 
various  oils  at  a  comparatively  low  temperature  (a  dull  red  heat)  possesses  illu- 


OLEFIANT   GAS.  207 

initiating  powers  far  superior  to  coal-gas,  the  amount  of  gaseous  matter  absorbed 
by  chlorine  being  considerably  greater;  a  portion  of  this  consists  of  a  peculiar 
gas  discovered  by  Faraday,  to  be  presently  described  (§  129).  The  gas  is  pre- 
pared from  oil  by  allowing  the  latter  to  flow  into  a  retort  (similar  to  a  coal-gas 
retort)  filled  with  bricks  or  lumps  of  coke,  heated  to  dull  redness.  Gas  is  also 
obtained  for  illuminating  purposes  from  resin,  which  is  first  fused,  and  then,  like 
the  oil,  allowed  to  fall  upon  heated  lumps  of  coke  or  brick.1  Even  the  gases 
obtained  by  the  distillation  of  animal  matters,  flesh,  bones,  soap-waste,  and  in 
the  manufacture  of  bone-black,  are  here  and  there  used  for  illuminating  pur- 
poses. 

WATER-GAS. — Among  various  more  recent  methods  of  preparing  illuminating 
gas,  we  may  mention  that  which  consists  in  passing  steam  over  heated  charcoal 
or  coke,  .and  conducting  the  resulting  gases,  consisting  of  hydrogen,  carbonic 
oxide,  and  carbonic  acid,  together  with  a  considerable  quantity  of  aqueous  vapor, 
into  a  second  retort,  in  which  illuminating  gas  is  being  generated,  either  from 
coal  or  resin.  The  great  advantages  of  this  process  appear  to  be  the  following: 
1.  That  the  olefiant  gas  and  vapor  of  hydrocarbons  are  rapidly  removed  from  the 
retort  by  the  current  of  water-gas,  and  are  therefore  not  exposed  to  a  tempera- 
ture sufficiently  high  to  decompose  them,  as  is  generally  the  case;  2.  That  the 
aqueous  vapor  appears  to  be  decomposed  in  coming  in  contact,  at  an  elevated 
temperature,  with  the  tarry  hydrocarbons,  in  such  a  manner  as  to  convert  their 
carbon  into  carbonic  oxide,  and  to  liberate  the  hydrogen,  which  advantageously 
replaces,  as  above  noticed,  a  part  of  the  light  carburetted  hydrogen  in  ordinary 
gas;  3.  That  the  carbonic  acid  produced  in  the  first  retort  is  reduced  in  the 
second  to  carbonic  oxide,  by  contact  with  the  carbonaceous  matter  at  a  high 
temperature;  4.  That  certain  coals  which  generally  yield  a  gas  burning  with  a 
smoky  flame,  from  a  superabundance  of  carbon,  may  be  made  to  furnish  a  gas 
sufficiently  diluted  for  illuminating  purposes. 

It  is  at  once  apparent  that  the  quantity  of  gas  obtained  by  this  process  from  a 
given  amount  of  coal  is  considerably  increased,  as  is  also  the  total  illuminating 
power;  although  the  amount  of  light  obtained  by  the  combustion  of  a  given 
volume  of  this  gas  must  obviously  be  less  than  that  yielded  by  an  equal  volume 
of  coal-gas. 

OLEFIANT  GAS,  BICARBURETTED  HYDROGEN. 
C4H4.     Eq_.  28.     Sp.  Gr.  0.985. 

Composition  1y  Volume. — 2  volumes  of  carbon-vapor  and  2  volumes  of  hydro- 
gen condensed  to  1  volume. 

§  129.  This  carburetted  hydrogen  is  produced  in  variable  quantities,  as  already 
stated,  by  the  distillation  of  coal,  the  luminosity  of  coal-gas  being  mainly  de- 
pendent upon  its  presence. 

Preparation. — It  may  be  obtained  by  heating  together,  in  a  capacious  retort, 
a  mixture  of  1  measure  of  alcohol  and  3  measures  of  concentrated  sulphuric  acid. 
The  mixture  soon  blackens,  and  effervescence  ensues,  when  the  temperature  must 
be  moderated,  or  the  action  becomes  very  intense.  The  gas  may  be  obtained  in 
larger  quantity  an.d  of  greater  purity,  according  to  the  directions  of  Graham,  by 
mixing,  in  a  capacious  flask,  28  ounces  of  water  with  twice  their  volume  of  oil 
of  vitriol,  and  adding  to  the  diluted  acid,  while  hot,  24  measures  of  alcohol. 
The  mixture  is  allowed  to  stand  for  some  hours,  and  then  maintained  in  a  state 
of  gentle  ebullition. 

1  The  furnaces  are  so  arranged  that  the  resin  is  melted  in  a  reservoir,  placed  above 
the  retort,  and  exposed  to  the  waste  heat  of  the  flue.  A  pipe,  provided  with  a  plug  or 
stopcock,  connects  the  cistern  with  the  retort ;  the  melted  resin  is  supplied  to  the  latter 
through  this  pipe. 


208  CARBON   AND   HYDROGEN. 

The  principal  result  of  the  action  of  sulphuric  acid  upon  alcohol  in  this  in- 
stance is  the  conversion  of  the  latter  into  olefiant  gas  and  water  : — 

C4H803=C4H4-f2HO. 

There  are,  however,  several  secondary  reactions,  resulting  in  the  decomposition 
of  the  sulphuric  into  sulphurous  acid,  the  formation  of  carbonic  acid,  and  of  a 
considerable  quantity  of  ether.1  It  is  therefore  necessary  to  submit  the  gas  ob- 
tained to  purification,  which  is  effected  by  passing  it  first  through  water,  to  retain 
the  principal  quantity  of  ether  and  the  alcohol  which  distils  over  unchanged,3 
and  afterwards  through  a  solution  of  potassa,  to  retain  the  sulphurous  and  car- 
bonic acids,  and  finally  through  oil  of  vitriol  to  remove  water.  The  gas  may  be 
collected  over  water,  which  absorbs  about  one-eighth  of  its  volume. 

Properties. — Olefiant  gas  is  colorless,  and  has  a  peculiar  alliaceous  odor.  It 
burns  with  a  brilliant  white  flame,  requiring  three  times  its  volume  of  oxygen 
for  complete  combustion. 

It  may  be  converted  by  cold  and  pressure  into  a  colorless  liquid,  which  cannot 
be  solidified  at  the  lowest  attainable  temperature.  Fuming  sulphuric  acid  and 
pentachloride  of  antimony  have  the  power  of  absorbing  considerable  quantities  of 
this  gas,  producing  peculiar  compounds. 

It  is  generally  found  that  these  liquids  leave  certain  impurities  in  olefiant  gas 
uncondensed,  which  consist  principally  of  light  carburetted  hydrogen  gas. 

Olefiant  gas  burns  in  an  atmosphere  of  chlorine,  yielding  hydrochloric  acid 
and  carbon.  When  mixed  with  an  equal  volume  of  that  gas  in  a  moist  state,  it 
combines  with  it  to  produce  an  oily  liquid  of  the  formula  C4H4C12  (see  Chloride 
of  Carbon,  §  131),  to  which  the  name  Dutch  liquid  has  been  given,  in  conse- 
quence of  its  having  been  discovered  by  the  associated  Butch  chemists,  who  gave 
the  name  of  olefiant  gas  to  bicarburetted  hydrogen,  on  account  of  this  property.3 

When  olefiant  gas  is  passed  through  a  porcelain  tube,  heated  nearly  to  white- 
ness, it  is  decomposed  into  carbon  and  hydrogen ;  if  a  lower  temperature  be 
employed,  only  a  part  of  the  carbon  is  separated,  light  carburetted  hydrogen 
being  formed. 

'.--•.'.  * 

BICARBURETTED  HYDROGEN  or  FARADAY,  or  Gas  of  Oil. 

C8H8-    E<1-  56-     Sp-  Gr-  1-926.* 

This  gas  has  already  been  referred  to  as  one  of  the  products  of  the  destructive 
distillation  of  fatty  oils.  It  may  be  liquefied  at  a  temperature  of  0°  F.  ( — 18°  C.), 
or  by  subjecting  oil-gas  to  considerable  pressure.  Its  specific  gravity  is  double 
that  of  olefiant  gas.  It  is  only  slightly  soluble  in  water,  but  more  so  in  alcohol 
and  fatty  oils;  fuming  sulphuric  aci<J  absorbs  as  much  as  100  times  its  volume. 
It  has  already  been  stated  that  chlorine  unites  with  all  the  compounds  of  carbon 
and  hydrogen  that  possess  the  same  percentage  composition  as  olefiant  gas. 

This  gas  produces  a  compound  with  chlorine  somewhat  similar  to  Dutch  liquid. 
When  inflamed,  it  burns  with  a  brilliant  light;  it  requires  for  its  combustion  6 
volumes  of  oxygen. 

1  At  times  also  the  olefiant  gas  is  contaminated  by  light  carburetted  hydrogen,  and  also 
by  higher  compounds  of  carbon  and  hydrogen. 

2  A  peculiar,  oily,  ethereal  liquid,  termed  oil  of  wine,  condenses  in  tne  first  wash-bottle. 

3  Berzelius  has  also  given  the  name  Elayle  to  this  gas  (from  sXatw,  the  source  of  an  oil). 

4  Composition  by  Volume. — 4  volumes  of  carbon-vapor  and  4  volumes  of  hydrogen  con- 
densed to  1  volume. 


CYANOGEN.  209 


CARBON   AND   NITROGEN. 

BICARBIDE  OP  NITROGEN,  CYANOGEN. 
CaN  or  Cy.     Eq.  26.     Sp.  Gr.  1.806. 

Composition  ~by  Volume. — 1  volume  of  cyanogen  contains  2  volumes  of  carbon- 
vapor  and  1  volume  of  nitrogen. 

§  130.  This  substance  is  of  considerable  importance,  inasmuch  as  it  is  the  type 
of  those  bodies  known  as  compound  salt-radicals  (§  12),  and  was  the  first  of  these 
discovered,  in  1814,  by  Gay-Lussac. 

Cyanogen  is  always  produced,  in  combination  with  an  alkali-metal,  when  nitro- 
genized  organic  matter  is  heated  with  an  alkaline  carbonate. 

Cyanide  of  potassium  is  formed  when  nitrogenized  organic  bodies  are  heated 
with  potassium,  or  when  nitrogen  (or  atmospheric  air)  is  passed  over  charcoal,  in 
presence  of  potassa,  at  a  high  temperature.  It  is  probably  by  the  latter  method 
that  cyanide  of  potassium  is  formed  in  the  blast-furnaces  in  which  iron  is  reduced 
from  its  ores. 

When  ammoniacal  gas  is  passed  over  charcoal  at  a  high  temperature,  cyanide 
of  ammonium  is  formed. 

Preparation. — Cyanogen  is  prepared  by  heating  pure  dry  cyanide  of  mercury 
in  a  retort  or  tube  of  hard  glass ;  the  gas  may  be  collected  over  mercury,  or,  with 
some  loss,  by  downward  displacement. 

The  cyanide  of  mercury  is  not  entirely  volatilized  in  this  experiment,  a  small 
quantity  of  a  brown  substance  is  left,  which  has  the  same  percentage  composition 
as  cyanogen,  and  is  termed  paracyanoyen. 

The  cyanide  of  mercury  must  not  contain  any  oxycyanide,  or  the  cyanogen 
will  be  contaminated  with  carbonic  acid  and  nitrogen. 

If  any  moisture  be  present  in  the  cyanide,  carbonate  of  ammonia  and  cyanide 
of  ammonium  will  be  formed. 

Properties. — Cyanogen  is  a  colorless  gas,  having  a  peculiar  and  characteristic 
pungent  odor.  It  condenses  to  a  colorless  liquid  at  the  ordinary  temperature, 
under  a  pressure  of  4  atmospheres.  Liquid  cyanogen  may  be  obtained  by  heating 
cyanide  of  mercury  in  one  limb  of  a  closed  bent  tube,  the  other  limb  of  which  is 
surrounded  with  a  mixture  of  ice  and  salt.  The  specific  gravity  of  liquid  cyanogen 
is  0.9.  It  may  be  solidified  by  the  aid  of  a  mixture  of  solid  carbonic  acid  and  ether. 

Cyanogen  is  combustible;  it  burns  with  a  remarkable  peach-colored  flame, 
yielding  carbonic  acid  and  nitrogen.  A  mixture  of  cyanogen  and  oxygen  is  ex- 
ploded by  contact  of  flame,  or  of  the  electric  spark. 

Water  dissolves  about  4  times  its  volume  of  cyanogen,  but  it  is  much  more 
soluble  in  alcohol,  which  is  capable  of  absorbing  about  25  volumes.  The  gas 
may  be  easily  expelled  from  these  solutions  by  heat. 

An  aqueous  solution  of  cyanogen  may  be  kept  unchanged  for  a  long  time  in 
the  dark,  but,  if  exposed  to  light,  it  deposits  a  brown  matter,  containing  the  ele- 
ments of  cyanogen  and  water,  while  the  solution  contains  carbonate  of  ammonia 
(NH4O.C03),  cyanide  of  ammonium  (NH4C3N),  oxalate  of  ammonia  (NH4O.C303), 
formiate  of  ammonia  (NH4O.C3H03),  and  urea  (C2H4N303).  It  will  be  seen  that 
these  various  compounds  contain  only  the  elements  which  exist  in  cyanogen  and 
water ;  the  explanation  of  this  most  interesting  decomposition  belongs  strictly  to 
organic  chemistry. 

Cyanogen  is  absorbed  by  solutions  of  the  alkalies,  which  it  decomposes  in  the 
same  manner  as  chlorine,  giving  rise  to  cyanides  of  the  metals,  and  cyanates  of 
the  alkalies. 

2KO+Cy3=KO.CyO+KCy. 
14 


210  CARBON   AND   CHLORINE. 

Cyanogen  combines  directly  with  potassium  and  sodium  at  a  slightly  elevated 
temperature. 

Combinations  of  cyanogen  are  known,  with  oxygen,  hydrogen,  chlorine,  brom- 
ine, iodine,  sulphur,  and  most  metals.  The  history  of  these  compounds  is,  how- 
ever, so  interwoven  with  that  of  many  others  belonging  to  the  department  of 
organic  chemistry,  that  its  consideration  belongs  more  appropriately  to  that 
branch  of  the  science. 

We  subjoin  a  list  of  some  of  the  principal  compounds  of  cyanogen. 

Cyanic  acid          .         .         .         .         .         .         .  CyO 

Fulrninic  acid      .         .         .         .         .         .         .  Cy003 

Cyan  uric  acid      .         .         .     '    .         .         .         .  Cy303 

Hydrocyanic,  or  prussic  acid          .         .         .         .  HCy 

Gaseous  chloride  of  cyanogen         ....  CyCl 

Liquid        «  "  .        .        .  Cy2Cl3 

Solid  «  «  .  V     .  Cy3Cl3 

Bromide       1  :  "  ....  CyBr 

Iodide,  «  ....  Cyl 

Bisulphide  "  (sulphocyanogen)  CySa 

Ferrocyanogen     .......  Cy3Fe  ' 

Ferricyanogen      .....       x  ._•'•"•     .  CyeFe3 

Cobalticyanogen  ......  CyeCoa 

Manganicyanogen         ......  Cy6Mn3 

Chromicyanogen  ....        *•?'•*'     .  Cy6Cr3 

Platinocyanogen  ......  Cy3Pt 

Palladiocyanogen          ......  Cy2Pd 

Iridiocyanogen    .         .         .         .         .         .         .  Cy3Ir 

The  last  nine  compounds  are  themselves  quasi-elements,  or  compound  salt- 
radicals,  which  have  not  been  isolated,  but  are  known  to  exist  in  a  well-defined 
series  of  compounds. 

Mellon,  C6N4,  is  another  salt-radical,  the  description  of  which  must  be  reserved 
for  organic  chemistry. 


CARBON    AND    CHLORINE. 

Protochloride  of  carbon     ;.  .  ^  '      .         .     C4C14  (4CC1) 
Sesquichloride  of  carbon     .        -."         .         .     C4C16  (2C2CI3) 
Bichloride  of  carbon          N.         .         .         .     C3C14  (2CC12) 

§  131.  These  elements  do  not  unite  directly,  but  their  compounds  are  pro- 
•duced  by  the  action  of  chlorine  on  combinations  of  carbon  with  other  non-metallic 
substances.  The  description  of  their  formation,  though  more  frequently  included 
in  organic  chemistry,  may  be  briefly  entered  into  here,  since  it  is  in  close  con- 
inection  with  the  subject  of  carbohydrogens,  of  which  we  have  just  been  treating. 

It  has  already  been  mentioned,  that  when  olefiant  gas  is  mixed  with  an  equal 
Tolume  of  chlorine,  an  oily  substance,  known  as  Dutch  liquid,  is  obtained.  It 
is  a  colorless  liquid,  possessing  a  peculiar,  sweet,  agreeable  odor;  its  specific 
gravity  is  1.24 ;  it  boils  at  67°. 6  F.  (84°.5  C.),  yielding  a  vapor  of  specific  gra- 
vity 3.448.  The  empirical  formula  is  C4H4C12;  but  a  closer  study  shows  that  it 
must  be  represented  by  the  formula  C4H3C1.HC1,  being,  in  fact,  a  compound  of 
what  is  called  the  chloride  of  acetyle  (or  dichloracetyle),  C4H3C1,  with  hydro- 
chloric acid;  and,  indeed,  if  Dutch  liquid  is  subjected  to  the  action  of  an  alco- 
holic solution  of  potassa,  chloride  of  potassium  is  produced  by  the  decomposition 
of  the  hydrochloric  acid,  and  the  body  C4H3C1  obtained,  as  a  very  volatile,  lim- 
pid liquid. 


CHLORIDES   OF   CARBON.  211 

If  Dutch  liquid  be  submitted  to  the  action  of  a  current  of  dry  chlorine,  it 
absorbs  a  considerable  quantity;  a  second  equivalent  of  hydrogen,  existing  ori- 
ginally in  the  olefiant  gas,  is  converted  into  hydrochloric  acid,  and  replaced  by 
an  equivalent  of  chlorine,  the  substance  C4H2C13.HC1  being  produced,  from 
which  an  alcoholic  solution  of  potassa  separates  the  body  C4H3C13. 

The  hydrochlorate  of  this  second  substance  is  again  acted  upon  in  a  similar 
manner  by  chlorine  gas,  a  third  equivalent  of  hydrogen  is  abstracted  and  re- 
placed by  chlorine;  the  resulting  compound  is  the  hydrochlorate  of  a  third  sub- 
stance in  this  series,  containing  now  only  one  equivalent  of  hydrogen,  its  formula 
being  C4HC13.HC1.  (This  compound  may  likewise  be  decomposed  by  potassa  in 
a  similar  manner  to  the  others.)  This  substance,  once  more  acted  upon  by 
chlorine,  yields  a  compound  of  the  formula  C4HC15,  or  C4C14.HC1,  which  is  there- 
fore the  hydrochlorate  of  the  quadrichloride,  or  what  was  originally  called  the 
protochloride  of  carbon,  C4C14.  By  the  action  of  alcoholic  potassa,  this  chloride 
may  be  separated  from  the  hydrochloric  acid;  we  shall  proceed  to  its  description 
immediately. 

When,  finally,  this  last  hydrochlorate  (C4HC15)  is  submitted  to  the  action  of 
excess  of  chlorine  under  the  influence  of  the  sun's  rays,  the  last  equivalent  of 
hydrogen  which  it  contains  is  replaced  by  chlorine,  and  the  sesquichloride  of 
carbon  C4Clfi=2(C3Cl3)  is  obtained. 

In  the  above  reactions,  therefore,  the  hydrogen  in  olefiant  gas  is  gradually  re- 
placed, equivalent  after  equivalent,  by  chlorine,  hydrochlorates  of  the  various 
substances  being  produced  as  follows : — 

C4H4  Olefiant  gas. 

C4  -j  ™3     obtained  as  the  hydrochlorate      C4  -j  ™3,  HC1. 

v  V. 

^2,HC1. 

H  J  H 

01,  4  1  01,' 

C4C14    '  "  "  C4C14,HC1. 

Finally,   the  hydrochlorate  of  the  last  substance  yields  up  its  hydrogen  for 
chlorine,  thus: — 

C4Cl4.HCl-f  C1=C4C14C13  or  C4C16. 

This  view  regarding  the  constitution  and  formation  of  the  chlorides  of  carbon 
has  been  established  by  the  observation  of  their  vapor-densities. 

PROTOCHLORIDE  OR  QUADRICHLORIDE  OF  CARBON. 

C4C14.   Sp.  Gr.  1.5. 

§  132.  This  compound  is  obtained  by  passing  the  vapor  of  sesquichloride  of 
carbon  through  a  redhot  glass  tube,  filled  with  fragments  of  glass.  Chlorine  is 
liberated  in  this  reaction,  and  a  colorless  liquid  is  obtained,  which,  when  purified, 
boils  at  240°  F.  (120°  C.),  and  has  a  composition  corresponding  to  equal  equiva- 
lents of  chlorine  and  of  carbon,  whence  its  name,  protochloride;  its  true  formula 
is,  however,  proved  to  be  C4C14,  by  an  examination  of  its  vapor-density,  which 
was  found  to  be  5.820  by  direct  experiment: — 

8  volumes  carbon-vapor  .     .    3.371 
8        "       chlorine  .19.523 


22.894 

Density     =5.724. 

4 
This,  therefore,  establishes  its  character  as  a  derivative  of  olefiant  gas,  C4H4. 


212  CARBON   AND    SULPHUR. 

SESQUICHLORIDE  OF  CARBON,  C4C18.    Sp.  Gr.  2. 

This  substance  is  obtained  by  acting  upon  Dutch  liquid  with  chlorine,  under 
the  influence  of  solar  radiation,  as  Long  as  any  more  of  the  gas  is  absorbed.  It 
is  a  white  crystalline  solid,  of  a  peculiar  aromatic  odor,  somewhat  resembling 
camphor.  It  may  easily  be  purified  by  crystallization  from  boiling  alcohol.  It 
is  volatile,  fusing  at  320°  F.  (160°  C.),  and  boiling  at  365°  F.  (185°  C.) 
The  density  of  its  vapor  is  8.157. 

PERCHLORIDE  OF  CARBON,  C3C14.    Sp.  Gr.  1.6. 

Regnault  obtained  this  substance  by  the  action  of  excess  of  chlorine  upon 
chloroform  (C3HC13),  and  regards  it  as  the  final  product  of  the  substitution  of 
chlorine  for  hydrogen  in  light  carburetted  hydrogen,  CaH4,  analogous  to  the  pro- 
duct C4C14  from  olefiant  gas,  C4H4;  since,  by  the  action  of  excess  of  chlorine,  in 
sunlight,  upon  light  carburetted  hydrogen,  he  obtained,  besides  chloroform  and 
other  compounds  of  a  similar  nature,  a  portion  of  the  compound  CSC14,  or  per- 
chloride  of  carbon. 

It  is  also  obtained  by  passing  a  mixture  of  chlorine  gas  and  bisulphide  of 
carbon  vapor  through  a  redhot  porcelain  tube  containing  fragments  of  porcelain. 
Chloride  of  sulphur  is  simultaneously  produced.  The  perchloride  of  carbon  is  a 
colorless,  limpid  liquid,  possessing  a  peculiar  alliaceous  odor,  and  boiling  at  172° 
F.  (78°  C.)  Its  vapor-density  is  5.415. 

Regnault  obtained  another  sesquichloride  of  carbon,  the  vapor-density  of 
which  was  only  4.082,  by  passing  the  vapor  of  the  above  chloride  through  a 
tube  heated  to  low  redness. 

By  the  action  of  chlorine  upon  the  crystalline  hydrocarbon  naphthaline,  al- 
ready mentioned,  another  crystalline  chloride  of  carbon,  of  the  formula  C^Clg 
has  been  obtained. 

Carbon  with  Bromine  and  Iodine. — No  compounds  of  carbon  with  bromine 
and  iodine  have  been  obtained.  Olefiant  gas  unites  with  them  to  produce  com- 
pounds analogous  to  Dutch  liquid;  the  bromine  compound  maybe  robbed  of  one 
other  equivalent  of  hydrogen,  but  the  action  does  not  proceed  further;  with 
iodine,  not  even  the  second  substance  can  be  obtained. 


CARBON  AND   SULPHUR. 

BISULPHIDE  OF  CARBON,  OR  SULPHO-CARBONIC  ACID. 
CS3.    Eq.  38.     Sp.  Gr.  1.263. 

§  133.  When  a  mixture  of  sulphur  and  carbon  is  heated,  they  do  not  unite; 
but  if  sulphur- vapor  be  passed  over  charcoal  in  a  porcelain  tube  heated  to  bright 
redness,  they  combine,  producing  a  substance  analogous  in  composition  to  car- 
bonic acid. 

Preparation. — The  best  method  of  obtaining  the  bisulphide  of  carbon  is  to 
fill  a  large  earthenware  tubulated  retort  a  (Fig.  68)  with  small  dry  fragments 
of  charcoal ;  into  the  tubulure  of  the  retort  is  fitted  with  luting  a  porcelain  tube 
b,  passing  nearly  to  the  bottom  of  the  retort.  The  latter  is  heated  in  a  furnace 
capable  of  surrounding  its  body;  the  neck  is  connected  with  a  Liebig's  condenser 
Cj  dj  in  which  the  water  is  constantly  changed;  the  extremity  of  its  conducting- 
tube  passes  down  to  the  lower  part  of  a  bottle,  which  is  also  surrounded  by  cold 
water,  and  contains  itself  a  little  of  that  liquid.  When  the  retort  is  raised  to 
the  proper  temperature,  fragments  of  sulphur  are  gradually  introduced  through 
the  tube,  the  opening  of  which  is  immediately  closed  with  a  stopper  after  each 
introduction.  The  sulphur  being  at  once  converted  into  vapor,  passes  over  the 


BISULPHIDE   OF   CARBON. 


213 


redhot  charcoal,  and  is  converted  into  bisulphide  of  carbon,  which  condenses  in 
the  receiver. 

Fig.  68. 


The  product  thus  obtained  generally  contains  a  little  excess  of  sulphur  in  solu- 
tion, besides  the  water  placed  in  the  receiver  to  retard  its  evaporation.  It  may 
be  purified  from  the  former  by  rectification  over  a  water-bath,  when  the  sulphur 
remains  behind.  Digestion  over  fused  chloride  of  calcium,  and  subsequent  rec- 
tification, will  free  it  from  water. 

This  substance  may  also  be  prepared  by  heating,  in  an  earthenware  retort,  a 
mixture  of  charcoal  and  metallic  sulphides  (iron  or  copper  pyrites),  which  part 
with  their  sulphur  pretty  readily. 

Properties. — Bisulphide  of  carbon  is  a  colorless,  very  volatile  liquid,  refracting 
light  powerfully.  It  possesses  a  fetid  odor.  It  boils  at  113°  R  (45°  C.),  and 
by  the  rapidity  with  which  it  evaporates,  especially  in  vacuo,  is  capable  of  pro- 
ducing a  great  degree  of  cold.1  The  density  of  its  vapor  is  2.67.  Bisulphide 
of  carbon  is  but  very  slightly  soluble  in  water,  but  dissolves  to  any  extent  in 
alcohol  and  ether.  It  is  exceedingly  inflammable,  burning  with  a  pale-blue 
lambent  flame;  the  products  of  combustion  are  carbonic  and  sulphurous  acids. 
If  a  few  drops  of  bisulphide  of  carbon  are  introduced  into  a  vessel  containing 
oxygen  or  nitric  oxide,  its  vapor  diffuses  itself  at  once  through  the  gases,  pro- 
ducing very  combustible  mixtures,  which  burn  with  a  brilliant  flash  of  light  and 
explosion,  when  flame  is  applied. 

Sulphur,  phosphorus,  and  iodine  are  easily  soluble  in  bisulphide  of  carbon ;  the 
two  former  substances  are  frequently  crystallized  (as  specimens)  from  their  solu- 
tion in  this  liquid,  by  very  gradual  spontaneous  evaporation. 

If  a  solution  of  phosphorus  in  bisulphide  of  carbon  be  poured  upon  a  piece  of 
paper,  the  film  of  phosphorus,  deposited  by  the  almost  instantaneous  evaporation 
of  the  solvent,  will  be  acted  upon  with  such  rapidity  by  the  oxygen  of  the  air, 
that  the  heat  generated  will  cause  it  to  burst  into  flame. 

This  solution  is  employed  in  electrotyping  objects,  which  are  coated  by  jts 
means  with  a  film  of  phosphorus,  and  thereby  rendered  capable  of  receiving  a 
metallic  covering  when  introduced  into  a  solution  of  copper. 

The  vapor  of  bisulphide  of  carbon  consists  of  2  volumes  of  carbon-vapor  and 
f  volume  of  sulphur- vapor,  condensed  to  2  volumes ;  being  in  this  respect  analo- 
gous to  carbonic  acid. 

It  has  already  been  stated  that  when  bisulphide  of  carbon  and  chlorine  are 


cold. 


A  mixture  of  solid  carbonic  acid  and  bisulphide  of  carbon  produces  the  most  intense 


214  BORON. 

passed  together  through  a  redhot  tube,  the  former  is  converted  into  chloride  of 
sulphur  and  perchloride  of  carbon. 

When  kept  for  a  long  time  under  water,  in  vessels  containing  air,  bisulphide 
of  carbon  acquires  a  yellow  color,  from  partial  oxidation  and  separation  of  sulphur 
which  is  held  in  solution ;  a  small  quantity  of  sulphuric  acid  is  also  formed,  be- 
sides carbonic  acid. 

Bisulphide  of  carbon  unites  with  sulphides  or  sulphur-bases,  producing  salts 
analogous  to  the  carbonates,  which  are  called  sulpho-carbonates,  their  general 
formula  being  MS.CS2.  It  may  therefore  be  called  a  sulphur-acid.  Some  me- 
tallic oxides  are  gradually  converted  by  it  into  a  mixture  of  carbonate  and  sulpho- 
carbonate,  thus: — 

3KO+3CS3=KO.C03-f2(KS.CS2). 

Bisulphide  of  carbon  may  be  analyzed  by  allowing  it  to  undergo  combustion 
with  chromate  of  lead,  whereby  it  is  converted  into  carbonic  and  sulphuric  acids, 
the  former  being  determined  in  the  ordinary  manner,  the  sulphur  by  difference. 
Or,  the  latter  may  be  directly  determined  by  passing  the  vapor  of  bisulphide  of 
carbon  through  a  combustion-tube,  containing  a  mixture  of  oxide  of  copper  and 
carbonate  of  soda,  heated  to  redness.  The  carbon  escapes  as  carbonic  acid, 
accompanied  by  an  equal  volume  of  the  gas  evolved  by  the  action  of  the  sulphuric 
acid  produced,  upon  the  carbonate  of  soda. 

In  preparing  bisulphide  of  carbon  by  passing  sulphur-vapor  through  a  redhot 
tube  containing  charcoal,  the  residual  portion  of  the  latter  is  found  to  contain 
some  sulphur  which  cannot  be  expelled  by  heat. 

Berzelius  considered  that  there  was  a  solid  compound  of  sulphur  with  the  car- 
bon, formed  in  this  experiment. 

When  bisulphide  of  carbon-vapor  is  passed  over  a  quantity  of  redhot  iron  or 
copper,  insufficient  for  its  perfect  decomposition,  it  is  converted  into  a  rose- 
colored,  thin,  sharp-tasting  liquid,  which  is  said  to  contain  probably  protosidphide 
of  carbon. 

CARBON  AND  THE  METALS. — Carbon,  though  possessing  no  active  affinity  for 
metals,  may  be  made  to  unite  with  several,  particularly  with  iron,  producing 
metallic  carburets  or  carbides.  These  compounds  are  easily  decomposed  into 
carbonic  acid  and  the  metallic  oxides,  when  heated  in  contact  with  air. 


BORON. 

St/m.  B.    Eq.  10.9. 

§  134.  In  1808,  Gay-Lussac  and  Thenard,  and  directly  afterwards,  Davy,  de- 
composed boracic  acid  (discovered  in  borax  by  Homberg,  in  1702)  into  boron 
and  oxygen. 

The  first-named  chemists  obtained  this  element  by  heating  boracic  acid  and 
potassium ;  while  Davy  procured  it  by  the  action  of  a  powerful  voltaic  battery  on 
boracic  acid. 

Boron  is  one  of  the  rarer  non-metallic  elements  ;  it  exists  in  nature  only  in 
the  form  of  boracic  acid  (in  hot  springs  and  lagoons),  and  in  combinations  of  this 
acid  with  metallic  oxides,  as  tincal  (crude  borax)  datolite,  boracite,  &c. 

Preparation. — When  vitrified  boracic  acid  is  powdered  and  heated  in  a  tube 
of  glass,  iron,  or  copper,  with  an  equal  weight  of  potassium,  cut  up  into  small 
pieces,  the  oxygen  in  the  acid  is  seized  by  the  metal,  and  a  portion  of  boron  thus 
reduced,  while  borate  of  potassa  is  formed.  This  may  be  removed  by  treatment 
with  hot  water,  and  the  boron  is  obtained  in  a  state  of  powder. 


BORACIC  ACID.  215 

The  best  method  of  obtaining  boron  is  to  prepare  the  double  fluoride  of  boron 
and  potassium  (3KF.2BF3),  by  saturating  hydrofluoric  acid  with  boracic  acid, 
and  then  gradually  adding  fluoride  of  potassium.  The  difficultly  soluble  double 
compound  thus  produced  is  collected  and  dried  at  a  temperature  nearly  approach- 
ing to  redness. 

This  compound  is  then  powdered,  and  introduced  into  an  iron  tube  closed  at 
one  end,  together  with  an  equal  weight  of  potassium,  whereupon  heat  is  applied 
sufficient  to  melt  the  latter,  and  the  mixture  of  the  two  substances  is  effected  by 
stirring  with  an  iron  wire.  Upon  the  mass  being  exposed  to  a  red  heat,  the 
potassium  abstracts  the  fluorine.  The  fluoride  of  potassium  may  afterwards  be 
removed  by  heating  the  mass  with  a  solution  of  chloride  of  ammonium,  which 
converts  the  free  potassa  into  chloride  of  potassium,  and  thus  prevents  the  oxida- 
tion of  the  boron,  which  takes  place  in  the  presence  of  fixed  alkali;  the  chloride 
of  ammonium  adhering  to  the  boron  may  be  afterwards  removed  by  treatment 
with  alcohol. 

Properties. — Boron  is  obtained  by  the  above  methods  as  a  dark,  greenish-brown 
powder,  both  tasteless  and  inodorous,  and  very  similar  in  external  characters  to 
carbon. 

Boron  is  not  dissolved  by  any  simple  solvent.  Oxidizing  agents,  such  as  nitric 
acid,  dissolve  it  in  the  form  of  boracic  acid;  hydrofluoric  acid  converts  it  into 
fluoride  of  boron,  hydrogen  being  evolved. 

It  does  not  fuse  when  exposed  to  a  red  heat  in  hydrogen,  but  may  be  liquefied 
between  the  poles  of  a  galvanic  battery.  Boron,  like  carbon,  has  never  been 
converted  into  vapor.  It  burns  with  a  bright  light  and  scintillation,  if  heated 
in  air  or  oxygen,  boracic  acid  being  produced,  which  is  the  only  oxide  of  boron, 
known. 

When  heated  with  nitrate  of  potassa,  it  is  rapidly  oxidized,  being  converted 
into  borate  of  potassa;  the  action  is  sometimes  accompanied  by  violent  deflagra- 
tion. Borate  of  potassa  is  also  formed  when  boron  is  heated  with  carbonate  of 
potassa,  carbon  being  separated. 

Boron  unites  with  considerable  energy  with  chlorine  and  sulphur;  its  combi- 
nation with  fluorine  has  already  been  referred  to. 

BOEACIC  ACID,  B03.     Eq.  34.9.     Sp.  Gr.  1.83. 

§  135.  This  acid  occurs,  as  already  stated,  in  several  minerals,  particularly  as 
tinea!.,  or  crude  biborate  of  soda  (borax),  which  is  found  in  the  form  of  incrusta- 
tions in  the  beds  of  small  lakes  in  Thibet,  where  it  is  dug  up  during  the  hot 
season.1 

The  greatest  quantity  of  this  acid  is  obtained  from  the  volcanic  districts  of 
Tuscany,  where  numerous  jets  of  vapor  (suffioni)  ascend  in  thick  volumes  into 
the  air,  charged  with  boracic  acid,  which  the  vapor  holds  in  mechanical  suspen- 
sion; the  apertures  whence  the  vapor  escapes  are  exposed  in  some  places,  and  in 
others  are  covered  by  small,  muddy  lakes  (lagoons). 

It  appears  that  the  acid  is  brought  up  to  the  surface  by  the  water  in  these 
lakes,  which  penetrates  occasionally  into  the  mouths  of  the  apertures,  and  dis- 
solves out  the  acid  principally  deposited  there  by  the  vapor  as  it  makes  its 
escape.  Advantage  is  taken  of  this  fact  for  obtaining  boracic  acid  from  these 
jets  of  vapor,  in  the  following  manner : — 

A  series  of  artificial  lagoons,  in  connection  with  each  other,  is  constructed  of 
rough  brickwork  lined  with  clay,  over  the  mouths  of  one  or  more  fissures.  They 
are  generally  built  one  above  the  other,  on  the  side  of  a  hill,  the  upper  one 
being  supplied  with  water  from  neighboring  springs,  which,  when  partly  saturated 

1  Small  quantities  of  boracic  acid  have  been  detected  in  several  mineral  waters  in 
France. 


216  BORON. 

there,  is  allowed  to  run  into  the  lower  lagoon,  and  subsequently  from  thence  to 
another,  and  so  on  until  it  has  become  sufficiently  impregnated  with  acid  from 
the  vapors  escaping  from  the  earth  at  the  bottom  of  these  reservoirs,  to  pay  the 
expense  of  working.  When  withdrawn  from  the  lowest  lagoon,  the  liquor  is 
allowed  to  clarify  by  standing,  and  is  then  evaporated  in  leaden  pans,  a  quantity 
of  sulphate  of  lime,  which  is  deposited  during  the  evaporation,  being  removed 
with  rakes.  When  a  liquor  of  the  spec.  grav.  1.07  to  1.08  is  obtained,  it  is 
transferred  to  round  wooden  tubs,  lined  with  lead,  where  the  acid  is  allowed  to 
crystallize  out;  it  is  afterwards  drained  in  a  basket,  and  dried  in  chambers 
heated  by  steam.1 

The  boracic  acid  thus  obtained  is  very  impure,  containing  only  about  76  or 
77  per  cent,  of  the  acid:  its  chief  impurities  are  the  sulphates  of  ammonia,  and 
the  metallic  oxides.  This  crude  acid  is  employed  for  the  preparation  of  borax, 
the  manufacture  of  which  is  described  §  173. 

Pure  boracic  acid  is  prepared  by  dissolving  1  part  of  pure  biborate  of  soda  in 
2  £  parts  of  water,  and  adding  hydrochloric  acid  until  the  liquid  is  powerfully 
acid.  As  the  solution  cools,  the  boracic  acid  crystallizes  out  in  small  plates, 
while  chloride  of  "sodium  remains  in  solution.  The  crystals  are  washed  with  a 
little  cold  water,  and  then  recrystallized  from  boiling  water. 

Properties. — Boracic  acid  crystallizes  in  thin,  colorless,  lustrous  plates,  which 
contain  43.6  per  cent,  of  water  of  crystallization.  When  heated, -they  first  part 
with  their  water,  and  then  fuse  to  a  colorless  liquid,  solidifying  upon  cooling  to 
a  very  hard,  brittle,  transparent,  colorless  glass,  which  becomes  opaque  when 
kept  for  some  time,  even  in  hermetically-sealed  tubes,  in  consequence,  apparently, 
of  the  arrangement  of  the  atoms  in  the  form  of  crystallization  proper  to  the 
ordinary  temperature. 

Boracic  acid  volatilizes  when  exposed  to  a  very  high  temperature  f  it  passes 
off  in  considerable  quantity  with  the  vapor  of  water,  or  of  alcohol,  being  depo- 
sited again  upon  a  cool  surface  in  small,  colorless,  micaceous  plates.  It  is  not 
corrosive;  its  taste  is  not  acid,  but  somewhat  bitter;  its  action  upon  litmus  is 
not  powerful;  like  carbonic  acid,  it  imparts  to  it  a  wine-red  tint;  it  turns  tur- 
meric brown,  in  a  similar  manner  to  the  alkalies. 

In  its  affinities,  it  is  slightly  more  powerful  than  carbonic  acid,  which  it  re- 
places in  its  combinations.  Crystallized  boracic  acid  contains  three  equivalents 
of  water,  one  of  which  is  constitutional;  its  formula  is  therefore  HO.B03-f-2Aq. 
One  part  of  the  acid  dissolves  in  25.66  parts  of  water  at  60°  F.  (15°. 5  C.),  and 
in  2.97  at  212°  F.  (100°  C.)  It  is  soluble  in  alcohol,  its  solution  burning  with 
a  green  flame. 

Boracic  acid  has  the  property  of  imparting  to  many  substances  a  high  degree 
of  fusibility,  uniting  with  them  generally  to  produce  a  glass;  it  is  to  this  pro- 
perty that  biborate  of  soda  owes  its  application  as  a  flux  (borax,  §  58). 

Boracic  acid  unites  with  metallic  oxides  to  produce  borates.  Though  so  feeble 
an  acid  that  it  only  replaces  carbonic  acid  at  ordinary  temperatures,  it  has  the 
power  of  expelling  all  acids  volatile  at  a  red  heat.  Most  borates  fuse  to  trans- 
parent glasses,  which  possess  the  property  of  dissolving  many  metallic  oxides, 
yielding  with  them  various  colors.  With  the  exception  of  the  alkaline  borates, 
all  salts  of  this  acid  are  soluble  with  difficulty  in  water. 

1  Since  fuel  is  very  scarce  in  Tuscany,  the  liquor  is  evaporated,  and  the  crystals  are 
dried,  by  the  heat  of  the  vapor  from  the  suffioni. 

2  When  the  solutions  of  certain  metallic  oxides  in  fused  boracic  acid  are  exposed  to  a 
very  high  temperature,  the  boracic  acid  is  gradually  volatilized,  and  the  oxides  deposited 
in  a  crystalline  state.     By  this  method,  several  crystallized  minerals  have  been  artificially 
produced,  \vhich  possess  all  the  properties  of  their  natural  prototypes.     Thus  spinelle 
(MgO.Al203)  has  been  obtained  by  dissolving  alumina  and  magnesia  in  fused  boracic 
acid. 


TERFLUORIDE   OF   BORON.  217 

BORON  AND  NITROGEN. — A  porous  white  substance  may  be  produced  by 
heating  together  two  parts  of  chloride  of  ammonium  and  one  part  of  dried  borax, 
which  appears  to  be  nitride  of  boron,  having  the  formula  BN.  It  is  purified  by 
repeated  treatment  with  hot  dilute  hydrochloric  acid.  It  may  be  exposed  in  a 
closed  crucible  to  a  high  temperature  without  undergoing  alteration ;  it  is  not 
acted  upon  by  acids  or  alkaline  solutions,  but  if  fused  with  hydrate  of  potassa  it 
is  converted  into  borate  of  potassa  and  ammonia.  When  heated  to  redness  in  a 
current  of  aqueous  vapor,  it  is  converted  into  boracic  acid  and  ammonia. 

Nitride  of  boron  is  decomposed  when  heated  together  with  easily  reducible 
metallic  oxides  (e.  g.  the  oxides  of  lead,  copper,  or  mercury),  binoxide  of  nitro- 
gen being  evolved. 


BORON   AND    CHLORINE. 

TERCHLORIDE  OF  BORON,  BC13.     Sp.  Gr.  3.942. 

Composition  by  Volume. — 2  volumes  of  boron-vapor  and  6  of  chlorine  con- 
densed to  4  volumes. 

This  substance  is  obtained  by  passing  dry  chlorine  over  heated  boron,  or  over 
an  intimate  mixture  of  boracic  acid  and  charcoal,  heated  to  redness  in  a  porce- 
lain tube.     In  the  latter  case  it  is  mixed  with  carbonic  oxide : — 
B03-fC3+Cl3=BCl3+3CO. 

It  must  be  collected  over  mercury. 

Properties. — The  terchloride  of  boron  is  a  colorless  gas,  producing  white  fumes 
when  exposed  to  the  air,  in  consequence  of  its  immediate  decomposition  by 
moisture  into  hydrochloric  and  boracic  acids.  When  passed  through  a  very 
small  quantity  of  water,  it  forms  a  solid  hydrate. 


BORON   AND   FLUORINE. 

TERFLUORIDE  OF  BORON,  BF3.     Sp.  Gr.  2.31. 

This  compound,  which  is  a  colorless  gas  similar  to  the  chloride,  may  be  ob- 
tained by  heating  a  mixture  of  1  part  of  fused  boracic  acid,  2  parts  of  fluor-spar, 
and  12  of  concentrated  sulphuric  acid. 

Terfluoride  of  boron  fumes  when  in  contact  with  air,  and  has  a  powerfully 
suffocating  odor.  It  chars  organic  substances  rapidly ;  it  may  be  condensed  by 
intense  cold  to  a  clear  colorless  liquid.  WTater  dissolves  about  700  or  800  times 
its  volume  of  this  gas;  a  concentrated  solution  is  best  obtained  by  distilling  to- 
gether with  concentrated  sulphuric  acid,  a  mixture  of  equal  parts  of  fluor-spar 
and  borax,  previously  fused  together  and  powdered.  The  distillate  is  a  very 
concentrated  aqueous  solution  of  the  fluoride,1  which  is  decomposed  if^diluted  con- 
siderably, boracic  acid  being  produced,  together  with  hydrofluoloracic  acid, 
which  is  probably  analogous  to  hydrofluosilicic  acid  (§  139),  possessing  therefore 
the  formula,  3HF.2BF3.  Its  formation  would  then  be  represented  by  the  equa- 
tion : — 

3BF3  +  3HO=3HF.2BF3+B03. 

1  When  water  is  completely  saturated  with  terfluoride  of  boron,  an  acid  is  formed  to 
which  the  name  fluoboracic  acid  has  been  given ;  it  is  composed  of  boracic  and  hydrofluoric 
acids  (3HF.B03),  and  its  production  mav  be  explained  by  the  equation: — 

BF34-3HO=3HF-hB03. 

It  may  be  prepared  directly  by  dissolving  boracic  acid  in  hydrofluoric  acid ;  it  is  a  syrupy 
liquid,  of  sp.  gr.  1.58,  very  acid,  and  capable  of  charring  organic  substances. 


218 


SILICON. 


BORON  AND  SULPHUR. — When  boron  is  heated  to  redness  in  vapor  of  sulphur, 
it  burns  a  white  or  grayish  substance  being  produced,  which  is  sulphide  of  boron. 
This  substance  is  rapidly  decomposed  by  water,  hydrosulphuric  and  boracic  acids 
being  produced. 


SILICON   (SILICIUM). 

Sym.  Si.     Eq.  21.3. 

§  136.  Pure  silicon  was  first  obtained  by  Berzelius,  in  1823.  It  is,  next  to 
oxygen,  the  most  abundant  substance  in  nature,  but  is  only  found  in  the  form 
of  teroxide,  as  silica,  which  occurs,  not  merely  in  the  greater  number  of  mineral 
substances  (being  almost  the  sole  constituent  of  several,  such  as  quartz  and 
sandstone),  but  also  in  small  quantities  both  in  the  vegetable  and  animal 
kingdom. 

Preparation. — Silicon  is  obtained  in  a  similar  manner  to  boron,  by  heating 
the  double  fluoride  of  potassium  and  silicon  with  sufficient  potassium  to  combine 
with  the  whole  of  the  fluorine,  according  to  the  method  given  at  §  134,  and 
afterwards  washing  the  mass  with  cold  water,  until  no  alkaline  reaction  is  ob- 
servable, then  boiling  with  water  to  decompose  any  of  the  double  fluoride  which 
may  not  have  been  acted  upon,  and,  finally,  washing  the  silicon  perfectly  with 
hot  water.  Care  must  be  taken  not  to  employ  too  much  potassium,  since,  in 
that  case,  a  silicide  of  that  metal  is  produced,  which,  when  acted  upon  by  water, 
is  decomposed  into  silicon  and  potassa,  with  evolution  of  hydrogen  (a  portion  of 
the  latter  being  absorbed  by  the  silicon,  from  which  it  may  again  be  separated 
by  a  dull  red  heat) ;  the  alkaline  solution  which  would  thus  be  produced  has  a 
solvent  action  upon  the  silicon,  more  particularly  if  warm  water  be  employed ; 
the  silicon  then  becomes  converted  into  silica,  hence  the  necessity  of  first  wash- 
ing with  cold  water. 

Silicon  may  also  be  obtained  by  passing  the  vapor  of  chloride  or  fluoride  of 
silicon  over  heated  potassium,  and  afterwards  washing  the  mass  with  cold  water; 
or  by  heating  silica  with  potassium ;  in  the  latter  case,  however,  a  considerable 
amount  of  silicide  of  potassium  is  produced,  and  the  large  quantity  of  potassa, 
resulting  on  the  subsequent  treatment  with  water,  dissolves  the  greater  part  of 
the  silicon,  whereby  it  is  reconverted  into  silica. 

Properties. — Silicon,  when  pure,  \is  a  dark  brown  powder,  heavier  than  water, 
devoid  of  lustre,  which  stains  the  fingers,  and  is  infusible  before  the  blowpipe ; 
it  is  non-volatile;  it  increases  in  density  when  powerfully  ignited,  and  assumes 
a  chocolate  tint ;  it  appears  to  be  thus  converted  into  an  allotropic  modification, 
differing  considerably  in  several  of  its  properties  from  the  silicon  as  it  is  origi- 
nally obtained.  The  latter  burns  with  a  bright  flame  when  moderately  heated 
in  oxygen  or  air,  being  partially  converted  into  silicic  acid ;  it  unites  with  sul- 
phur by  the  aid  of  heat,  and  is  volatilized  when  heated  with  hydrofluoric  acid. 
The  chocolate  modification  may  be  heated  to  whiteness  without  burning,  is  not 
acted  upon  by  hydrofluoric  acid,  and  does  not  unite  with  sulphur.  Berzelius 
concludes  that  the  silicon  contained  in  quartz,  and  all  insoluble  varieties  of  silica, 
is  the  allotropic  modification,  while  the  element  exists  in  its  original  physical 
condition  in  soluble  compounds  of  silicon. 

When  fused  with  dry  carbonate  of  potassa,  both  modifications  of  this  element 
are  completely  converted  into  silicic  acid,  the  carbonic  acid  being  decomposed, 
and  carbon  separated : — 

3(KO.C03)+S52=2(KO.Si03)+KO+C3. 


SILICIC   ACID.  219 

Silicon  forms  only  one  compound  with  oxygen,  silicic  acid,  or  silica  Si03;  it 
unites  with  hydrogen,  chlorine,  bromine,  fluorine,  and  sulphur,  and  enters  also 
into  direct  combination  with  potassium,  producing  a  silicide  in  the  manner 
already  described. 

This  element,  like  boron;  exhibits  a  great  similarity  to  carbon. 


SILICON  AND  OXYGEN. 

SILICIC  ACID,  SILICA,  Si03.     Uq.  45.3.     Sp.  Gr.  2.66. 

§  137.  This  substance  is  found  in  nature  perfectly  pure,  or  very  nearly  so,  as 
rock-crystal,  quartz,  flint,  sand,  chalcedony,  opal,  tripoli,  agate,  jasper,  &c.,  and 
is  an  important  constituent  of  a  very  large  class  of  minerals.1 

It  may  be  obtained  by  fusing  1  part  of  finely-powdered  quartz  or  sand  in  a 
platinum  crucible,  with  2.5  parts  of  a  mixture  of  equivalent  weights  of  the  car- 
bonates of  potassa  and  of  soda,  the  mineral  being  added  to  the  fused  mass  from 
time  to  time,  in  small  quantities,  as  long  as  effervescence  is  observed.  The  fused 
substance,  when  cold,  is  dissolved  in  very  dilute  hydrochloric  acid,  the  liquid 
separated  by  filtration  from  any  insoluble  portions,  and  evaporated  to  perfect  dry- 
ness;  the  residue  is  once  more  heated  with  hydrochloric  acid,  it  is  then  thrown 
upon  a  filter,  washed  with  hot  water,  and  afterwards  dried  and  ignited. 

Silica  may  also  be  obtained,  in  a  state  of  very  minute  division,  by  passing  the 
terfluoride  of  silicon  into  water,  when  hydrofluosilicic  acid  is  simultaneously  pro- 
duced (§  139).  It  may  be  prepared  sufficiently  pure,  for  many  purposes,  by 
igniting  colorless  rock-crystal,  and  immersing  it  while  hot  in  water ;  after  this 
treatment,  the  mineral  may  easily  be  pulverized. 

Artificially  crystallized  silicic  acid  may  be  obtained  by  dissolving  the  silicate 
of  copper,  obtained  by  adding  silicate  of  potassa  to  chloride  of  copper,  in  hydro- 
chloric acid,  precipitating  the  copper  by  hydrosulphuric  acid,  and  evaporating  in 
vacua  the  filtered  solution  of  silica  in  hydrochloric  acid.  White  transparent 
needles  of  hydrate  of  silica  are  thus  obtained,  together  with  amorphous  silica. 

Properties. — Silicic  acid,  in  the  naturally  crystallized  state,  is  found  as  rode- 
crystal,  in  the  form  of  six-sided  prisms,  terminated  by  six-sided  pyramids,  and  is 
possessed  of  great  hardness,  though  considerably  inferior  in  this  point  to  diamond 
or  topaz.  In  the  amorphous  state,  it  occurs  pure  as  opal  (which  contains  in 
addition  only  a  small  quantity  of  water). 

In  the  finely-divided  state,  as  obtained  by  the  above-mentioned  process,  it  is  a 
white  powder,  tasteless,  but  gritty.  If  strongly  heated,  it  becomes  very  mobile 
and  light,  being  easily  dispersable  by  a  slight  current  of  air.  It  does  not  fuse 
at  any  furnace  temperature,  but  may  be  liquefied  by  the  flame  of  the  oxybydro- 
gen  blowpipe,  or  of  a  spirit-lamp,  into  which  is  forced  a  jet  of  oxygen,  and  also 
by  means  of  a  powerful  voltaic  battery.  A  clear  glass  is  then  obtained. 

When  silicic  acid  is  precipitated  from  its  combination  with  an  alkali,  by  gra- 
dual addition  of  an  acid,  it  assumes  a  gelatinous  form  (being  then  a  hydrate), 
but  passes  over,  when  dried,  into  the  pulverulent  state. 

When  once  separated  from  its  solutions,  silicic  acid  is  not  dissolved  to  any 

1  Way  has  lately  discovered,  at  Farnliam,  large  deposits  of  silica,  in  the  condition  in 
which  it  is  readily  soluble  in  hot  solutions  of  caustic  potassa  or  soda.  These  beds  are 
situated  at  the  base  of  the  chalk  formation,  between  the  upper  green  sand  and  the  gait 
clay.  The  discoverer  proposes  to  employ  these  beds  as  a  convenient  source  of  silicate  of 
lime  for  agi-icultural  purposes.  He  finds  that  a  mixture  of  slaked  lime  with  the  powdered 
rock,  when  made  into  a  thin  paste  and  left  for  several  weeks,  is  entirely  converted  into 
silicate  of  lime.  The  action  is  promoted  by  the  presence  of  2  or  3  per  cent,  of  carbonate 
of  soda,  the  latter  appearing  to  act  as  a  carrier  between  the  silica  and  the  lime.  Similar 
deposits  had  been  previously  found  by  Sauvage  in  the  Department  des  Ardennes. 


220  SILICON   AND   OXYGEN. 

extent  either  by  water  or  acids  (with  the  exception  of  hydrofluoric  acid);  but  if 
a  large  excess  of  concentrated  hydrochloric,  nitric,  or  sulphuric  acid  be  at  once 
added  to  the  solution  of  an  alkaline  silicate,  the  silicic  acid  is  completely  held  in 
solution,  appearing  to  combine  chemically  with  the  acid  at  the  moment  of  libe- 
ration. The  silicic  acid  may  be  precipitated  from  solutions  of  this  description 
by  the  gradual  addition  of  an  alkali,  or  of  carbonate  of  ammonia. 

The  gelatinous  silicic  acid  obtained  by  the  decomposition  of  fluoride  of  silicon 
by  water,  is  considerably  soluble  in  the  latter,  yielding  a  tasteless  solution,  which 
possesses  no  acid  reaction,  and  deposits  the  silicic  acid,  upon  evaporation,  as  a 
white  amorphous  powder,  soluble  again  in  water.  Addition  of  hydrochloric  acid 
to  the  solution  renders  the  silicic  acid  insoluble. 

All  waters  are  found  to  contain  a  larger  or  smaller  proportion  of  silicic  acid, 
which  is  deposited  upon  evaporation.  In  some  waters  it  exists  in  combination 
with  alkaline  bases.  Deposits  of  silica  are  formed  from  the  waters  of  several  hot 
springs,  such  as  the  Geysers. 

A  gelatinous  hydrate  of  silica,  of  the  formula  Si03.HO,  which  has  already 
been  mentioned,  is  produced  by  gradually  adding  chloride  of  ammonium,  or  a 
mineral  acid,  to  a  solution  of  silicate  of  potassa,  or  by  precipitating  a  solution  of 
silica  in  an  acid  by  an  alkali  or  its  carbonate ;  or,  finally,  by  slowly  and  partially 
evaporating  the  solution  of  silica  in  hydrochloric  acid.1  It  is  purified  by  wash- 
ing with  hydrochloric  acid  and  water.  If  allowed  to  dry  in  air,  at  ordinary  tem- 
peratures, it  gradually  loses  its  gelatinous  appearance,  and  forms  a  mass  like 
gum,  which  finally  passes  over  to  a  white  powder.  When  this  hydrate  is  heated 
to  212°  F.  (100°  C.),  it  parts  with  one-half  of  its  water,  yielding  a  second 
hydrate  of  the  composition  2Si03.HO. 

By  exposing  silicic  ether  to  the  action  of  moist  air,  Ebelmen  has  obtained  hard 
transparent  masses  of  hydrated  silicic  acid,  similar  in  appearance  to  rock-crystal, 
and  having  the  composition  2Si03.3HO. 

Silicic  acid  is  capable  of  displacing  carbonic  acid  from  its  combinations  at  an 
elevated  temperature.  When  fused  with  an  alkaline  carbonate  before  the  blow- 
pipe, it  forms  a  clear  glass,  the  carbonic  acid  escaping  with  effervescence.3  Sul- 
phates even  are  decomposed  by  silicic  acid  at  a  high  temperature,  especially  if 
carbon  be  present,  which  then  exerts  a  reducing  action  upon  sulphuric  acid,  con- 
verting it  into  sulphurous  acid,  which  is  of  course  far  more  readily  expelled. 

Silicic  acid  forms,  with  the  more  powerful  bases,  a  class  of  salts  termed  sili- 
cates; they  are  generally  produced  by  fusing  silicic  acid  with  the  bases.  The 
proportions  in  which  this  acid  unites  with  bases  are  unusually  various ;  it  also 
forms  numerous  double-salts,  those  of  the  silicate  of  alumina  with  other  silicates 
being  the  most  abundant.  The  silicates  in  which  the  acid  predominates  are  in- 
soluble in  water,  and  constitute  the  different  varieties  of  glass,  to  be  presently 
described. 

It  seems  probable,  from  the  remarkable  difference  in  the  properties  of  ignited 
and  unignited  silicic  acid,  that  these  are  allotropic  modifications  of  the  same  sub- 
stance, and  that  each  modification  has  its  own  particular  class  of  salts. 

The  silicates  are  decomposed  the  more  readily  by  strong  acids,  the  more  power- 
ful the  base,  the  less  silicic  acid,  and  the  more  water  they  contain.  All  silicates 
are  gradually  decomposed  by  digestion  with  sulphuric  acid;  after  fusion  with  a 
carbonate  of  an  alkali  or  an  alkaline  earth,  they  are  also  soluble  in  hydrochloric 
acid. 

1  If  this  evaporation  be  conducted  in  vacua,  crystals  of  silicic  acid  are  obtained,  as 
already  mentioned. 

2  Finely-powdered  silica  has  been  found  to  decompose  alkaline  carbonates  and  bicar- 
bonates,  even  when  boiled  for  some  time  with  their  solutions.     The  carbonates  of  lime 
(prot-)  oxide  of  iron  and  magnesia,  appear  also  to  be  decomposed  by  silica  under  similar 
circumstances. 


GLASS.  221 

Those  mineral  silicates  which  are  decomposed  by  the  action  of  hydrochloric 
acid  are  termed  zeolitic. 

Uses  of  Silicic  Acid.— This  substance,  more  particularly  in  combination  with 
alkalies  or  earths  (e.  g.  in  the  form  of  slays),  is  extensively  used  in  metallurgic 
operations,  as  a  flux,  for  effecting  the  decomposition  of  metallic  compounds  by 
the  solution  of  certain  of  their  constituents,  or  for  promoting  the  fusion  of  the 
slag,  and  thus  aiding  the  separation  of  the  metal. 

It  receives  its  most  extensive  application,  however,  in  the  manufacture  of  glass, 
porcelain,  and  earthenware ;  the  two  latter  will  be  treated  of  under  the  head  of 
alumina,  §  211 ;  we  shall  therefore  confine  ourselves  at  present  to  a  brief  con- 
sideration of  the  nature  and  properties  of  glass,  its  composition,  and  different 
varieties. 

GLASS.1 

§  138.  This  substance,  so  invaluable  in  all  departments  of  science,  arts,  and 
manufactures,  is  a  combination  of  two  or  more  silicates,  one  of  which  is  a  silicate 
of  an  alkali,  while  the  other  may  be  either  silicate  of  lime,  baryta,  oxide  of  lead, 
or  (prot-)  oxide  of  iron. 

Glass  differs  from  most  natural  silicates  in  being  perfectly  amorphous ;  it  is 
produced  by  the  fusion,  at  a  more  or  less  elevated  temperature,  of  silicic  acid 
together  with  various  metallic  oxides,  such  as  potassa,  soda,  magnesia,  lime, 
baryta,  the  (prot-)  oxides  of  iron  and  manganese,  the  sesquioxides  of  iron  and 
aluminum,  the  binoxides  of  manganese  and  tin,  &c.  The  fused  substance,  being 
allowed  to  cool,  solidifies  to  a  transparent,  amorphous  mass,  either  colorless  or 
not,  according  to  the  metallic  oxides  employed.  The  high  temperature,  assisting 
the  comparatively  weak  affinities  of  silicic  acid,  induces  it  to  unite  with  the  bases, 
producing  silicates  of  various  composition. 

Glass  is  possessed  of  high  elasticity,  considerable  hardness  and  brittleness, 
and  the  power  of  resisting  the  action  of  the  air  and  most  other  gases,  and,  to  a 
great  extent,  that  of  water  and  a  large  number  of  powerful  chemical  agents.3 
In  addition  to  these  general  properties,  the  various  kinds  of  glass  possess  certain 
special  characters,  varying  of  course  with  their  .composition  and  the  nature  of 
the  base  they  contain  :  it  will  therefore  be  advisable  to  take  a  brief  survey  of  the 
special  properties  of  the  various  silicates  employed  in  the  manufacture  of  glass. 

The  alkaline  silicates,  although  the  most  fusible,  vary  considerably  in  this 
respect,  according  to  the  amount  of  base  they  contain.  A  mixture  of  £  of  silicic 
acid  with  2  or  3  times  its  weight  of  alkali,  will  fuse  at  a  red  heat,  yielding  a 
product  easily  soluble  in  cold  water.  As  the  proportion  of  silica  increases,  the 
fusibility  of  the  product  diminishes,  as  does  likewise  its  solubility  in  water;  those 
richest  in  silica  are  indeed  scarcely  attacked  by  the  most  powerful  acids.  Some 

1  We  have  to  acknowledge  the  assistance  afforded  to  us  by  Knapp's  Technology,  in 
writing  the  following  history  of  glass. 

2  It  has  not  yet  been  found  possible  to  prepare  a  glass,  however  carefully,  that  is  capa- 
ble of  withstanding  perfectly  the  action  of  various  agents,  even  of  water.     The  liquid 
obtained  by  digesting  powdered  window  or  tube  glass  with  a  little  water,  has  been  found 
to  be  alkaline,  and  to  contain  silica.    Glass  vessels,  and  the  glazings  of  porcelain  or  earthen- 
ware dishes,  are  all  more  or  less  attacked,  if  retained  for  some  time  in  contact  with  boiling 
water.     Glass  that  is  exposed  to  the  continued  action  of  weather  for  a  number  of  years, 
becomes  more  or  less  corroded.     Acids  will  extract  the  bases  from  glass,  separating  the 
silica,  and  alkaline  solutions  will  dissolve  the  silica,  or  at  any  rate  loosen  it,  from  the 
surface  of  the  glass,  to  a  considerable  extent.     Lead-glass  is  easily  blackened  if  exposed 
to  the  action  of  sulphuretted  hydrogen  or  soluble  sulphides,  and,  if  heated  in  a  flame 
rich  in  carbon,  is  at  once  blackened,  the  lead  being  reduced  by  the  action  of  the  latter. 
Glass  is  most  powerfully  attacked  by  hydrofluoric  acid,  which  acts  both  upon  the  silica 
and  the  bases. 


222  GLASS. 

of  the  alkaline  silicates  possess  the  property  of  cooling,  after  fusion,  to  a  perfectly 
amorphous  mass,  passing  over  gradually  from  the  liquid,  through  an  intermediate 
pasty  state,  to  solidification.  This  property  is  retained  by  them  even  when  they 
are  mixed  with  other  silicates  which  crystallize ;  nay  more,  they  exert  an  influ- 
ence over  these,  preventing  their  crystallization,  and  thus  rendering  them  man- 
ageable in  the  hands  of  the  glassblower.1 

The  silicates  of  the  alkaline  earths  fuse  only  at  a  very  high  temperature.  The 
silicates  of  lime  and  magnesia  which  correspond  about  to  the  formula  MO.Si03 
are  the  most  fusible,  requiring,  however,  the  highest  heat  of  a  blast-furnace.  The 
silicate  of  lime  of  that  composition  assumes  a  crystalline  structure  as  it  cools. 
The  silicates  of  alumina  are  still  more  infusible;  that  corresponding  to  the  for- 
mula Ala03.3SiO?,  which  appears  the  most  fusible,  cannot  be  liquefied  in  a  blast- 
furnace.2 The  silicates  of  iron  and  manganese  are  far  more  easily  fusible,  but 
become  crystalline  on  cooling ;  the  silicates  of  lead  are  the  more  readily  fusible, 
in  proportion  to  the  amount  of  oxide  of  lead  they  contain. 

With  regard  to  the  silicates  obtained  in  the  manufacture  of  glass,  it  is  difficult 
to  say  whether  they  are  really  in  chemical  combination;  thus  much  is  certain, 
that  the  properties  of  different  simple  silicates  undergo  considerable  modifications 
when  mixtures  are  made;  thus,  we  have  already  stated  that  the  presence  of  alka- 
line silicates  will  prevent  the  silicates  of  iron  and  manganese  from  assuming  a 
crystalline  structure;  again,  it  is  found  that  the  temperature  at  which  a  complex 
silicate  fuses  is  always  below  the  mean  of  the  fusing  point  of  its  component  sili- 
cates; indeed,  sometimes  even  below  that  of  the  most  fusible  of  the  silicates 
present. 

The  choice  of  bases,  as  also  the  proportions,  employed  in  the  manufacture  of 
glass,  must  of  course  be  regulated  by  the  application  which  the  product  is  to 
receive.  The  effect  produced  upon  the  nature  of  glass  by  the  different  metallic 
oxides  already  mentioned  may  be  briefly  stated  to  be  as  follows: — 

Potassa  and  soda  render  the  glass  easily  fusible ;  the  soda  adding  to  its  bril- 
liancy, but  imparting  to  it  a  greenish  tint;  potassa  does  not  tint  the  glass,  but 
yields  a  somewhat  less  brilliant  product. 

Lime  does  not  affect  the  color  of  the  glass,  but  adds  to  its  lustre,  and  also 
increases  its  hardness,  while  it  decreases  its  fusibility.  Alumina  diminishes  the 
fusibility  of  glass  more  than  any  other  metallic  oxide,  while,  on  the  other  hand, 
oxide  of  lead  renders  it  easily  fusible,  and  also  imparts  to  it  a  great  degree  of 
softness  and  brilliancy.  Lead  glass  is  also  the  most  colorless,  and  possesses  the 

1  It  may  be  mentioned  under  this  head,  that  the  so-called  soluble  glass  is  an  alkaline 
silicate,  and  is  prepared  by  fusing  together,  in  an  earthen  crucible,  15  parts  of  sand,  10 
parts  of  pearl-ashes  (crude  carbonate  of  potassa),  and  1  part  of  charcoal.     The  charcoal 
aids  the  production  of  the  silicate,  by  the  conversion  of  the  carbonic  acid  into  carbonic 
oxide,  which  escapes  more  readily,  and  also  by  the  reduction  of  sulphuric  acid,  which  is 
present  in  pearl-ashes.     Cold  water  does  not  dissolve  the  resulting  mass,  it  only  removes 
any  foreign  alkaline  salts  that  may  be  present.     Upon  boiling  the  silicate  thus  purified 
with  5  parts  of  water,  it  gradually  dissolves  completely;  the  solution  maybe  concentrated 
to  a  syrupy,  sticky  liquid  which  gelatinizes  on  cooling,  and  on  exposure  to  air  becomes  a 
transparent,  colorless,  brittle,  but  not  very  hard  glass,  possessing  an  alkaline  reaction  ;  it 
is  itself  unalterable  by  exposure  to  air,  but  becomes  coated  with  a  film  of  alkaline  salt 
(carbonate),  which  may  be  removed  by  cold  water. 

This  substance  has  been  applied  for  diminishing  the  combustibility  of  wood,  stuffs,  paper, 
&c.,  by  coating  such  substances  with  it,  whereby  they  become  protected  from  air.  It 
may  also  be  employed  as  an  excellent  cement  for  glass  and  porcelain,  and  finally  for  silici- 
fying  objects  made  of  chalk  and  gypsum,  by  impregnating  them  with  a  solution  of  the 
glass,  and  afterwards  exposing  them  to  the  air.  A  considerable  degree  of  hardness  may 
thus  be  imparted  to  such  objects  ;  they  are  even  thereby  rendered  susceptible  of  a  high 
polish. 

2  The  only  means  by  which  these  refractory  silicates  may  be  perfectly  fused,  is  by  the 
flame  of  the  oxy-hydrogen  blowpipe. 


GLASS.  223 

highest  refractive  power.  The  action  of  laryta  is  similar  to  that  of  lead.  The 
fusibility  of  glass  is  also  increased  by  iron  and  manganese,  but  iron  is  liable  to 
color  the  glass,  particularly  if  it  is  present  as  protoxide,  the  green  color  thereby 
produced  being  more  intense  than  the  brown  color  afforded  by  an  equal  quantity 
of  sesquioxide.  Hence,  glass  which  has  a  green  tint,  from  the  presence  of  pro- 
toxide of  iron,  may  be  almost  decolorized  by  oxidation.  A  small  quantity  of 
binoxide  of  manganese,  when  added  to  a  glass  containing  protoxide  of  iron, 
destroys  the  green  color  imparted  by  the  latter,  whilst  the  protoxide  of  manga- 
nese produced  does  not  impart  any  color  to  the  glass;  if  more  binoxide  of  man- 
ganese be  used  than  is  necessary  to  oxidize  the  protoxide  of  iron,  an  amethyst 
color  is  imparted  to  the  glass. 

Various  other  metallic  oxides  are  frequently  used  in  the  manufacture  of  glass, 
not  so  much  to  alter  its  nature  as  to  impart  to  it  various  tints;  we  shall  pre- 
sently return  to  a  brief  consideration  of  these.  It  is  found,  in  accordance  with 
the  above  observations,  that  those  kinds  of  glass  which  possess  a  high  specific 
gravity  (from  2.8  to  3.6,  in  consequence  of  the  great  density  of  the  silicates  they 
contain)  are  the  softest,  and  also  possess  the  greatest  brilliancy  and  refractive 
power,  while  those  varieties  that  are  far  less  fusible,  possess  less  brilliancy  and  a 
lower  specific  gravity  (2.37  to  2.6). 

It  appears  that  the  composition  of  a  glass  is  not  only  dependent  upon  the  pro- 
portion of  the  ingredients  mixed  together,  but  upon  the  temperature  employed; 
the  tendency  possessed  by  silicic  acid  to  unite  in  large  proportions  with  bases 
being  somewhat  counteracted  by  the  difficult  fusibility  of  high  silicates.  A  very 
high  temperature  tends  also  to  volatilize  portions  of  the  alkaline  bases  from  glass; 
thus  complex  silicates  are  found  to  decrease  gradually  in  fusibility  by  continued 
exposure  to  a  high  temperature ;  this  is  not  only  owing  to  the  volatilization  of 
the  alkalies,  but  also  to  the  extraction  of  alumina  from  the  glass-pots  by  the 
silica  liberated.  Excess  of  base  in  glass  is  equally  prone  to  act  upon  the  pots 
in  the  opposite  manner,  extracting  the  silica. 

We  have  already  stated  that  glass  (in  the  extended  sense  of  the  word)  is  amor- 
phous; when  in  its  most  liquid  state  (at  the  highest  heat  of  the  furnace)  it  is  of 
the  consistence  of  thin  syrup,  and  may,  when  in  that  state,  be  cast  into  moulds 
or  sheets.  As  the  temperature  cools  down  to  a  bright  red  heat,  the  glass  be- 
comes very  tough  and  tenacious,  and  may,  when  in  that  state,  be  blown  into  any 
form,  or  drawn  out  into  threads. 

If  a  mass  of  glass  be  allowed  to  cool  in  the  air,  the  outer  portion  solidifies  first, 
and  forms  a  coating  which  resists  any  change  of  position  that  might  otherwise 
be  assumed  by  the  interior  particles  in  the  act  of  cooling;  hence  these  latter 
exert  a  certain  degree  of  tension  upon  the  external  layer  of  glass,  and  a  slight 
concussion  of  the  latter,  insufficient  of  itself  to  destroy  its  continuity,  will  deter- 
mine the  rupture  of  the  mass.1  In  order  to  avoid  this  inconvenience,  glass  ves- 
sels are  generally  .annealed  by  slow  cooling  in  ovens,  the  temperature  of  which 
is  very  gradually  diminished;  here  the  whole  mass  of  glass  solidifies  almost 
simultaneously,  and  a  state  of  permanent  equilibrium  is  established  among  the 
particles. 

The  devitrification  of  glass,  which  is  observed  in  masses  which  are  exposed  for 
a  length  of  time  to  a  temperature  approaching  to  fusion,  depends  mainly  upon 
the  volatilization  of  alkali,  but  partly,  also,  upon  a  molecular  change  in  the 
structure  of  the  glass,  resulting  in  a  crystalline  arrangement  of  the  particles. 
Reaumur's  porcelain,  as  perfectly  devitrified  glass  has  been  termed,  possesses  a 
remarkable  opacity  and  hardness,  striking  fire  with  steel. 

1  If  a  drop  of  melted  glass  is  allowed  to  fall  into  cold  water,  it  assumes  an  elongated 
form,  terminating  in  a  point,  as  is  well  known  in  the  case  of  the  Rupert's  drop.  If  the 
thin  extremity  be  broken,  the  tension  existing  between  the  particles  will  be  immediately 
exerted,  and  the  whole  drop  will  fall  to  powder. 


22-4  GLASS. 

Having  briefly  noticed  the  general  nature  and  properties  of  glass,  we  shall 
confine  ourselves  to  an  account  of  the  materials  employed  by  the  glass-maker, 
and  of  the  composition  of  the  principal  varieties  of  glass,  referring  the  reader  to 
special  works  on  the  subject  for  the  practical  details  of  glass-making. 

Sand  is  the  most  general  source  of  silica,  since  it  requires  less  preparation 
than  other  varieties  of  silicious  minerals.  Ordinary  sands  generally  contain 
iron,  lime,  and  clay,  and  sometimes  organic  matter.  The  clay  is  removed  by 
levigation,  the  lime  is  harmless,  but  the  iron  is  objectionable  in  most  cases  ; 
though  easily  removed  by  hydrochloric  acid,  the  expense  is,  in  many  instances, 
too  great;  hence,  sand  free  from  iron,  such  as  is  found  at  Alum  Bay  (in  the  Isle 
of  Wight),  in  Norfolk,  Lancashire,  Sydney,  and  New  Holland,  is  always  preferred. 

The  sand  is  generally  heated  in  reverberatory  furnaces  before  use,  to  expel 
organic  matter,  and  to  reduce  it  to  a  fine  state  of  division. 

Rock-crystal,  massive  quartz,  and  flint,  are  used  for  some  kinds  of  glass;  the 
fragments  are  heated  to  redness,  and  then  thrown  into  water,  when  they  may  be 
very  easily  reduced  to  powder. 

The  potassa  used  is  either  common  ashes  or  crude  potashes,  according  to  the 
quality  of  the, glass.  For  soda,  barilla  or  soda-ash  is  generally  employed; 
soap-boilers'  waste  is  also  used  for  common  kinds  of  glass;  the  sulphates  of  soda 
and  potassa  may  likewise  be  advantageously  employed,  the  sulphuric  acid  being 
reduced  by  means  of  a  little  carbon,  and  thus  more  readily  expelled  by  the  silica. 

The  lime  may  be  furnished  by  limestone  of  any  description,  if  not  too  poor,  or 
too  rich  in  alumina  and  magnesia.  An  excess  of  lime  in  the  manufacture  of 
glass  is  avoided,  since  it  extracts  the  silica  from  the  pots,  thus  speedily  destroy- 
ing them.  Lead-glass  is  made  from  litharge  or  red-lead,  the  latter  being  preferred, 
since  it  is  in  a  finer  state  of  division,  and  furnishes  available  oxygen  for  the  oxida- 
tion of  impurities.  As  these  oxides,  in  the  commercial  state,  both  contain  iron 
and  copper,  red-lead  is  generally  purified  for  glass-making.  Too  much  lead  is 
also  injurious  to  glass,  rendering  it  too  soft,  and  coloring  it  yellow.  When  lead 
is  employed,  potassa  is  used  exclusively  as  alkali,  since  soda  imparts  a  bluish 
tint  to  lead-glass. 

When  baryta  is  required  (as  in  bottle-glass,  to  increase  its  fusibility),  heavy 
spar  (sulphate  of  baryta)  is  added. 

Some  silicious  minerals,  which  are  more  or  less  easily  fusible,  are  used  at 
times  in  the  manufacture  of  glass.  The  principal  are  basalt,  clinkstone,  loam, 
marl, pumice-stone,  &c.  Some  may  be  used  alone  as  glass,  such  as  basalt;  others 
require  the  addition  of  lime  or  alkali  to  increase  their  fusibility. 

The  presence  of  impurities  in  some  of  the  materials  employed  in  glass-making, 
and  which  frequently  impart  a  color  \to  the  product,  renders  the  use  of  decoloriz- 
ing agents  necessary  at  times.  The  principal  substances  used  are,  binoxide  of 
manganese,  arsenious  acid,  and  saltpetre,  all  of  which  effect  the  oxidation  of  the 
impurities  (such  as  carbon  or  iron). 

Finally,  broken  glass  (cullet)  is  always  ground  up  and  mixed  with  the  mate- 
rials for  glass  of  a  similar  kind,  before  their  introduction  into  the  pots,  the  fusion 
of  the  mass  being  much  assisted  by  its  presence. 

The  production  and  fusion  of  glass  is  effected  in  reverberatory  furnaces  of 
various  kinds,  by  hot  flame-fires  (the  fuel  employed  is  coal,  or  baked  wood). 
The  glass,  or  metal,  as  it  is  termed,  is  fused  in  large  crucibles,  or  pots,  of  very 
refractory  fire-clay,  which  have  been  very  carefully  annealed  before  use. 

The  different  varieties  of  glass  may  be  divided  into  two  classes  :  first,  those 
which  consist  mainly  of  silica,  lime,  and  alkali,  of  which  the  principal  are  crown- 
glass,  icindow -glass,  the  various  kinds  of  bottle-glass,  and  plate-glass  ;*  the  second 

1  Bohemian  glass,  which  belongs  to  this  class,  and  is  indispensable  to  the  chemist  on  ac- 
count of  its  difficult  fusibility  and  power  of  resisting  sudden  changes  of  temperature,  owes 
its  properties  especially  to  the  circumstance  of  its  containing  only  silica,  potassa,  and  lime. 


GLASS. 


225 


class  comprises  those  glasses  of  which  lead  is  an -important  ingredient,  of  these 
the  principal  are  flint-glass,  of  which  a  kind  is  especially  manufactured  for  optical 
purposes;  strass  or  glass-paste,  used  for  artificial  gems,  and  glass-enamel. 

The  following  tables  exhibit  the  percentage  composition  of  the  principal  kinds 
of  glass,  as  determined  from  the  analyses  of  various  specimens : — 

FIRST  CLASS. 


Crown 

glass. 

Window 
glass. 

Bohemian 
glass.1 

76 

15 

*8 

'l 

Plate 

glass. 

74.4 
1  17.2 
5.4 

2.*9 
1.4 

BOTTLl 
^>  ' 

ordinary. 

58.4 
3.7 
22.4 

0.8 
7.8 
4.4 

3  GLASS 

*•—  •  —  ^ 

medicinal. 

62.8 
22.1 

12.5 
2.6 

69.1 

13.3 
12.9 

4.5 

66.4 
12.1 

13.7 
2.8 
1.5 
3.3 

i'.'s 

Potassa            

Protoxide  of  manganese     . 

Sesquioxide  of  iron  .     .     . 
Protoxide  of  lead      .     .     . 

SECOND  CLASS. 


Flint  glass,  or 
crystal. 

Strass,  or  paste. 

Enamel. 

54.9 

38.5 

31.6 

9.5 

7.9 

8.3 

Protoxide  of  lead    .         .       '."."*''.' 
Alumina           .         .        '.        •»"'''  ;.'T^.i".  * 
Sesquioxide  of  iron           .        •-»   •  :  .    .:o*<,j 

35.1 
1.1 
0.6 

53.0 
1.0 

50.3 
9  8 

We  have  already  referred  to  the  property  possessed  by  various  metallic  oxides, 
of  imparting  different  colors  to  glass ;  the  extensive  application  it  has  received 
from  the  earliest  times  in  the  production  of  colored  or  stained  glass,  painted 
glass,  and  glass-paste,  renders  an  enumeration  of  the  various  coloring  substances 
necessary. 

Sesquioxide  of  iron,  suboxide  of  copper,  and  gold  (either  in  the  state  of  purple 
of  Cassius,  terchloride  of  gold,  or  fulminating  gold),  are  employed  for  obtaining 
a  red  color ;  the  first  of  these  three  yields  a  brownish-red  glass ;  the  coloring 
power  of  the  suboxide  of  copper  is  very  intense,  the  smallest  quantity  rendering 
glass  opaque;  hence,  in  coloring  glass  with  this  oxide,  the  red  glass  is  first  pre- 
pared, and  colorless  glass  coated  with  a  thin  layer  of  it  (by  what  is  termed  flash- 
ing). The  suboxide  will  readily  seize  oxygen  during  the  fusion  of  the  glass, 
producing  the  protoxide,  which  yields  a  green  glass ;  hence  reducing  substances 
are  generally  added  in  fusions  of  this  kind  of  glass. 

Various  shades  of  red,  from  carmine  to  rose,  are  obtained  by  the  use  of  gold. 

Yellow  glass  is  obtained  by  means  of  glass  of  antimony,  consisting  of  a  mixture 
of  tersulphide  of  antimony  and  antimonious  acid,  produced  by  incomplete  roast- 
ing of  the  former.  Antimoniate  of  potassa  is  also  used.  Charcoal  is  sometimes 
used  for  imparting  a  brownish-yellow  tint  (in  some  kinds  of  bottle-glass),  the  color 
being  produced  by  the  distribution  of  carbon  in  a  fine  state  of  division  through 

1  The  composition  of  Bohemian  hard  glass  tubing  (combustion-tubing),  has  been  found 
by  Rowney  to  be  as  follows: — 

Silicic  acui  73.13,  lime  10.43,  alumina  0.30,  sesquioxide  of  iron  0.13,  magnesia  0.26,  prot- 
oxide of  manganese  0.46,  soda  3.07,  potassa  11.49. 
15 


226  GLASS. 

the  mass.  Chloride  of  silver  yields  a  brilliant  yellow  with  glass  containing  alu- 
mina. Sesquioxide  of  uranium  is  now  extensively  employed  for  coloring  glass 
yellow  ;  it  yields  a  brilliant  color,  exhibiting  a  greenish  tinge. 

A  green  color  is  obtained,  as  already  stated,  by  (prot-)  oxide  of  iron,  but  the 
color  obtained  by  means  of  oxide  of  copper  is  far  more  brilliant  and  beautiful, 
particularly  if  the  glass  to  be  colored  contains  lead.  If  the  glass  is  dull  or  trans- 
lucent, the  color  produced  by  oxide  of  copper  is  not  green,  but  blue. 

Sesquioxide  of  chromium  yields  the  finest  green  color.  Oxide  of  cobalt  is  the 
only  substance  used  to  impart  a  Hue  color  to  glass.  The  ores  of  cobalt  contain 
a  number  of  other  substances  (arsenic,  sulphur,  copper,  nickel,  iron,  &c.),  which 
it  is  necessary  to  remove  as  far  as  possible,  since  they  exert  great  influence  over 
the  blue  color  yielded  by  the  cobalt.  The  ores  are  levigated,  roasted,  and  after- 
wards fused  with  proper  proportions  of  finely-divided  quartz  and  potashes.  A 
deep  blue  glass  is  thus  obtained,  which,  when  ground  and  washed,  receives  the 
name  of  cobalt  smalts,  and  is  employed  for  coloring  glass. 

Other  colors  (called  mixed  colors')  are  imparted  to  glass  by  using  mixtures  of 
the  substances  just  enumerated.  Thus  binoxide  of  manganese  and  smalt  yield  a 
brown  garnet  color  ;  orange  is  obtained  by  the  use  of  silver  and  iron;  flesh-color 
by  iron  and  alumina,  &c. 

These  various  colors  are  either  introduced  into  the  fused  glass,  or  a  colored 
glass  is  first  prepared,  with  which  the  colorless  glass  is  coated,  or  lastly,  colored 
lead-glasses  are  prepared  and  finely  ground  as  pigments,  with  which  paintings 
are  made  on  the  glass,  and  afterwards  burnt  in. 

In  the  manufacture  of  artificial  gems,  a  very  brilliant  colorless  flint-glass,  con- 
taining a  great  quantity  of  lead,  is  prepared  and  carefully  fused  with  the  various 
colors  employed.  Topaz  is  obtained  by  the  use  of  Sesquioxide  of  iron,  purple  of 
Cassius,  and  glass  of  antimony;  a  ruby  color  is  produced  by  purple  of  Cassius ; 
beryl,  by  oxide  of  cobalt  and  glass  of  antimony ;  garnet,  by  purple  of  Cassius, 
antimony,  and  binoxide  of  manganese;  emerald,  by  the  oxides  of  copper  and 
chromium,  &o. 

Enamel-glasses ,  employed  extensively  for  coating  vessels  of  various  kinds,  either 
for  ornament  or  protection,  consist  of  easily  fusible  lead-glass,  which  is  either 
transparent  or  colored  as  above,  or  rendered  opaque  or  milky,  by  the  uniform 
dissemination,  throughout  its  mass,  of  fine  particles  of  some  substance  which 
cannot  be  fused  at  the  temperature  at  which  the  glass  is  made.  The  substances 
generally  employed  for  producing  opaque,  or  opalescent  enamels,  are  bone-earth, 
binoxide  of  tin,  or  teroxide  of  antimony. 

Enamels  may  also  be  applied,  like  the  colored  glasses,  as  pigments,  for  which 
purpose  they  are  reduced  to  a  fine  state  of  division,  and  are  burnt  on  to  the  ves- 
sels, which  are  exposed  to  the  necessary  heat  in  muffles. 

For  the  analysis  of  glass,  see  Quantitative  Analysis,  Special  Methods.       ;., ... 

§  139.  SILICON  AND  HYDROGEN. — In  the  description  of  the  preparation  of 
silicon,  mention  was  made  of  the  retention  of  hydrogen  by  that  substance,  ob- 
tained by  the  action  of  potassium  on  the  fluoride,  when  it  is  washed  with  water. 
A  chemical  compound,  the  silicide  of  hydrogen,  appears  to  be  formed,  which, 
when  freed  from  silicic  acid,  by  treatment  with  hydrofluoric  acid,  burns  with 
brilliancy  in  oxygen  or  air,  water  being  always  produced.  It  parts  with  its 
hydrogen,  yielding  silicon,  when  very  strongly  heated  in  a  covered  crucible. 

SILICON  AND  CHLORINE. — When  heated  in  chlorine,  silicon  takes  fire,  forming 
terchloride  of  silicon,  SiCl3,  as  a  vapor,  which  condenses,  upon  cooling,  to  a 
mobile  liquid. 

This  compound  may  also  be  prepared  by  passing  chlorine  over  an  intimate 
mixture  of  charcoal  and  flocculent  silica,  strongly  heated  in  a  porcelain  tube,  or 
earthenware  retort.  It  is  purified  from  excess  of  chlorine  by  agitation  with  mer- 
cury, and  distillation.  It  is  then  obtained  as  a  transparent,  colorless  liquid,  of 


SILICON   AND   FLUORINE. 


227 


sp.  gr.  1.52,  which  boils  at  122°  F.  (50°  C.),  and  does  not  solidify  at  — 4°  F. 
( — '20°  C.)j  it  evaporates  directly  on  exposure  to  air.  Its  vapor  is  suffocating, 
and  is  decomposed  by  moisture,  forming  dense  clouds  of  hydrochloric  acid,  and 
depositing  silicic  acid.  If  the  liquid  is  placed  in  contact  with  water,  it  is  decom- 
posed in  a  similar  manner,  the  resulting  silica  remaining  dissolved  in  hydrochloric 
acid. 

SILICON  AND  BROMINE. — These  elements  unite  to  produce  a  compound  similar 
in  appearance  and  properties  to  terchloride  of  silicon,  which  is  rapidly  decomposed 
by  water. 


SILICON    AND    FLUORINE. 

TERFLUORIDE  OF  SILICON,  SiF3,  is  formed  when  hydrofluoric  acid  comes  in 
contact  with  silicic  acid,  or  a  silicious  substance,  such  as  glass.  The  etching  of 
glass  by  hydrofluoric  acid  (see  §  102),  is  dependent  upon  the  production  of  ter- 
fluoride of  silicon. 

This  substance  is  prepared  by  heating  in  a  glass  or  earthenware  vessel,  a  mix- 
ture of  equal  parts  of  finely-powdered  fluor-spar  and  glass,  with  6  or  8  parts  of 
concentrated  sulphuric  acid.  In  this  reaction  the  oxygen  in  the  silicic  acid  of 
the  glass  is  replaced  by  the  fluorine  of  the  fluor-spar,  according  to  the  following 
equation : — 

3CaF+Si03+3(HO.S03)=SiF3-f3(CaO.S03)-f3HO. 

The  sulphuric  acid  employed  should  be  as  strong  as  possible,  and  great  care 
should  be  taken  to  have  the  apparatus  perfectly  dry,  since  the  fluoride  is  easily 
decomposed. by  water.  It  must,  therefore,  be  collected  over  mercury. 

Properties. — Terfluoride  of  silicon  is  a  colorless  gas,  of  spec.  grav.  3.6,  which 
forms  very  dense  fumes  when  in  contact  with  a  damp  atmosphere. 

When  this  gas  is  allowed  to  come  in  contact  with  water,  it  is  at  once  partially 
decomposed,  together  with  a  certain  quantity  of  the  latter,  silicic  acid  being 
separated,  and  hydrofluoric  acid  liberated,  which  immediately  unites  with  a 
second  portion  of  the  terfluoride  of  silicon,  producing  a  peculiar  acid,  termed 
hydrofluosilicic  acid. 

HYDROFLUOSILICIC  ACID,  3HF.2SiF3. — The  formation  of  this  acid  is  shown 
by  the  following  equation  :  — 

3SiF,+3HO=3HF.2SiF,+Si08. 

In  order  to  obtain  a  solution  of  this  acid,  the  fluoride  of  silicon  obtained  as 
above  is  transmitted  into  water;  the  mouth  of  the  delivery- tube,  however,  must 
not  be  allowed  to  come  in  contact  with  the  water,  since  it  would  very  soon  be- 
come choked  up  with  the  silicic  acid  liberated 
by  the  decomposition  of  the  gas.  A  little  mer- 
cury, or  a  small  cup  containing  some  of  that 
metal  (Fig.  69),  is  therefore  placed  at  the  bot- 
tom of  the  vessel  of  water,  into  which  the  ex- 
tremity of  the  tube  is  allowed  to  dip.  As  each 
bubble  of  gas  ascends  through  the  mercury  and 
enters  the  water,  it  becomes  inclosed  in  a  coat- 
ing of  gelatinous  silicic  acid,  which  rises  to  the 
surface,  and  then  disperses  as  the  gas  is  ab- 
sorbed by  the  water ;  when  the  liquid  through 
which  the  gas  is  passed  is  perfectly  tranquil, 
tubes  of  the  gelatinous  silica  are  sometimes 
formed,  through  which  the  gas  escapes  unde- 
composed;  it  is  necessary,  therefore,  to  agitate 


Fig.  69. 


228  SILICON   AND   FLUORINE. 

the  liquid,  from  time  to  time,  with  a  glass  rod.  When  the  water  is  saturated,  it 
appears  as  a  gelatinous,  semi-transparent  mass,  owing  to  the  quantity  of  the  silicic 
acid  separated.  Upon  the  removal  of  the  silica  by  filtration,  a  very  acid  liquid 
is  obtained,  which  has  the  property  of  producing,  in  pretty  concentrated  neutral 
solutions  of  potassa,  soda,  and  lithia,  gelatinous,  transparent  precipitates;  and 
in  solutions  of  salts  of  baryta,  a  white  precipitate,  becoming  crystalline  after 
some  time.  Compounds  resembling  these  in  constitution,  are  formed  with  many 
metallic  oxides  when  they  are  employed  in  sufficient  quantity  only  to  neutralize 
the  hydrofluosilicic  acid.  It  appears  that,  under  these  circumstances,  the  hydro- 
Igen  in  the  acid  is  replaced  by  metal,  double  fluorides  of  the  metal  and  of  silicon 
being  produced : — 

3KO+3HF.2SiF3=3KF.2SiF3  +  3HO. 

The  general  formula  of  these  salts,  therefore,  is  3MF.2SiF3.  If  the  bases  be 
added  in  excess,  simple  metallic  fluorides  are  produced,  together  with  silicic 
acid : —  . 

3HF.2SiF3+9KO=9KF-f  2Si03+3HO. 

Upon  allowing  a  solution  of  hydrofluosilicic  acid,  containing  the  silica  sepa- 
rated in  its  formation,  to  evaporate  slowly  in  a  warm  place,  the  whole  disappears 
after  a  time;  the  hydrofluoric  acid,  reacting  upon  the  silicic  acid,  gives  rise  to 
the  formation  of  fluoride  of  silicon.  If  a  clear  solution  of  hydrofluosilicic  acid 
be  allowed  to  evaporate  in  a  glass  or  porcelain  vessel,  it  will  also  become  recon- 
verted into  fluoride  of  silicon,  the  silicic  acid  necessary  to  the  reaction  being 
supplied  by  the  material  of  the  vessel,  which  therefore  becomes  etched. 

SILICON  AND  SULPHUR. — A  combination  of  these  substances  may  be  produced 
by  heating  silicon  in  vapor  of  sulphur;  the  union  is  attended  with  evolution  of 
heat  and  light.  A  white,  earthy  substance  is  obtained,  which  burns  slowly  when 
heated  in  air,  yielding  silicic  and  sulphurous  acids;  on  exposure  to  moist  air,  at 
ordinary  temperatures,  it  is  gradually  converted  into  silicic  acid,  hydrosulphuric 
acid  being  evolved. 

A  chlorosiilpliide  of  silicon,  of  the  formula  SiSCl3,  has  been  obtained  by  pass- 
ing the  vapor  of  terchloride  of  silicon  and  dry  hydrosulphuric  acid  together 
through  a  porcelain  tube,  heated  to  redness.  It  is  a  colorless  liquid,  evolving 
pungent  fumes  on  exposure  to  air;  it  boils  at  about  212°  F.  (100°  C.),  and  has 
a  sp.  gr.  of  1.45.  It  is  decomposed  by  water  into  hydrochloric,  hydrosulphuric, 
and  silicic  acids,  together  with  a  small  quantity  of  sulphur. 

It  appears  that  the  second  and  third  equivalents  of  chlorine  in  terchloride  of 
silicon  may  also  be  replaced  by  sulphur.  The  existence  of  a  compound  of  the 
formula,  SiS3Cl  has  not  yet  been  properly  established,  but  the  tersulphide  of 
silicon  SiS3  has  been  obtained  pure.  It  is  obtained  as  a  residue  when  crude 
chlorosulphide  of  silicon  is  distilled. 


THE    METALS. 


§  140.  IN  treating  of  the  second  class  of  elements,  the  metals,  we  shall  divide 
these  bodies  into  groups  according  to  the  deportment  exhibited  by  them,  or 
by  their  oxides,  with 'particular  reagents;  this  classification  is  the  same  as  that 
employed  in  the  analytical  section,  and  is  adopted  in  this  place,  in  order  that  it 
may  be  impressed  upon  the  memory  of  the  student;  since,  however,  this  group- 
ing of  the  inetals  is  of  far  greater  importance  in  analysis  than  in  their  general 
history,  it  is  fully  explained  in  the  introduction  to  that  branch  of  study,  and 
thither  we  must  now  refer  for  further  information,  though,  for  our  present  pur- 
pose, it  is  really  unnecessary,  and  indeed  premature,  to  understand  the  principles 
of  such  a  classification,  the  reader  being  called  upon  only  to  bear  in  mind  that  it 
exists. 

We  have  already  shown  in  what  consists  the  difference  between  a  metal  and  a 
non-metallic  element,  and  will  now  merely  recapitulate  the  chief  points  of 
dissimilarity. 

A  metal  is  a  better  conductor  of  heat  and  electricity  than  a  non-metallic  body. 

Metals  are  capable  of  forming  bases  by  combining  with  oxygen. 

Generally  speaking,  metals  have  a  greater  affinity  for  non-metallic  substances 
than  these  have  for  each  other,  and  the  result  of  the  combination  of  a  metal  with 
a  non-metallic  body  usually  exhibits  the  properties  of  a  salt. 

The  combinations  of  metals  with  each  other  are  termed  alloys,  except  when 
mercury  enters  into  the  compound,  which  is  then  known  as  an  amalgam. 

Were  we  to  enter  here  into  the  general  description  of  the  relations  of  the 
metals  to  oxygen,  sulphur,  and  other  non-metallic  bodies,  we  should  only  have 
to  instance  and  describe  examples  which  would  be  of  necessity  repeated  in  the 
history  of  the  particular  metals  to  which  such  examples  belong,  and  hence  we 
shall  pass  on  at  once  to  the  special  consideration  of  the  metals. 


230 


POTASSIUM. 


METALS   OF   THE   FIRST   GROUP. 

(Metals  of  the  Alkalies.} 


POTASSIUM. 

St/m.  K.     Eq.  39.     Sp.  Gr.  0.865. 

§  141.  Potassium  was  discovered  by  Sir  H.  Davy,  in  1807.  It  occurs  in 
nature  always  in  combination;  many  minerals  contain  this  metal;  we  may 
especially  notice  feldspar,  which  is  a  double  silicate  of  alumina  and  potassa 
(KO.Si03.  Al3033Si03).  It  is  also  found  in  sea-water  and  in  most  mineral  waters, 
in  soils,  and  hence  also  in  plants,  which  contain  potassa,  sometimes  as  silicate, 
and  more  generally  in  the  form  of  salts  with  organic  acids,  which  upon  incinera- 
tion, furnish  carbonic  acid,  with  which  the  potassa  is  found  in  combination  in  the 
ashes  of  such  plants;  the  ashes  of  land-plants  are  much  richer  in  potassa  than 
those  of  marine  plants.  Potassa  is  also  found,  in  combination  with  nitric  acid, 
forming  nitre,  or  saltpetre,  as  an  incrustation  on  the  soil  in  certain  hot  climates. 

The  chief  source  whence  potassium  itself  is  obtained  is  the  bitartrate  of  potassa 
(KO.HO.C8H4010),  which  is  known  in  commerce  under  the  names  of  argol  and 
cream  of  tartar,  and  is  the  salt  deposited  in  large  quantity  during  the  fermenta- 
tion of  the  grape-juice  in  the  preparation  of  wines. 

Preparation. — Potassium  was  originally  prepared  by  its  discoverer  by  subject- 
ing one  of  the  oxides,  potassa,  to  the  action  of  a  powerful  galvanic  battery,  the 
negative  pole  of  which  was  in  contact  with  mercury;  the  oxygen  of  the  alkali 
was  disengaged  at  the  positive  pole,  and  the  metal  at  the  negative  pole,  where  it 
entered  into  combination  with  the  mercury,  forming  an  amalgam  which  was  sub- 
jected to  distillation,  when  the  potassium  was  left  behind  in  the  retort.  This 
metal  may  also  be  prepared  in  small  quantity  by  passing  hydrate  of  potassa,  in 
a  state  of  vapor,  over  iron  heated  to  whiteness. 

In  practice,  however,  potassium  is  now  always  prepared  by  the.  deoxidation  of 
potassa,  by  means  of  charcoal  at  a  high  temperature.  In  order  to  effect  this,  an 
intimate  mixture  of  carbonate  of  potassa  and  charcoal  is  prepared  by  calcining 
the  bitartrate  of  potassa  in  a  covered  crucible;  when  the  salt  KO.HO.C8H4010  is 
heated  in  close  vessels,  it  evolves  water,  together  with  certain  vapors  resulting 
from  the  decomposition  of  the  tartaric  acid,  whilst  one  part  of  the  carbon  remains 
behind,  as  carbonic  acid,  in  combination  with  the  potassa,  and  another  part  in 
the  free  state,  mechanically  mixed  with  the  carbonate. 

The  mixture  of  carbonate  of  potassa  and  carbon  thus  obtained,  is  mixed  with 
an  additional  quantity  of  ordinary  wood-charcoal,  and  introduced  into  an  iron 
mercury-bottle,  covered  with  clay  to  enable  it  to  resist  the  action  of  the  fire ;  an 
iron  tube  is  tightly  screwed  into  the  bottle,  and  communicates  with  a  receiver  of 
a  particular  construction,  containing  a  quantity  of  petroleum  in  which  the  potas- 
sium is  condensed,  and  provided  with  an  exit-tube  for  the  gas  evolved;  the  iron 


POTASSA.  231 

bottle  is  very  strongly  heated  in  a  furnace  with  a  good  draught,  when  the  potas- 
sium distils  over  into  the  receiver,  which  is  kept  cool  by  a  stream  of  water.  The 
action  of  the  carbon  upon  the  carbonate  of  potassa  is  very  simple  : — 

KO.COd+Ca=K+3CO; 

but  when  the  vapor  of  potassium  and  the  carbonic  oxide  pass  from  the  retort 
into  the  tube,  in  which  they  are  subjected  to  a  lower  temperature,  a  decomposi- 
tion of  the  carbonic  oxide  takes  place,  and  a  peculiar  solid  compound  containing 
potassium  is  formed,  which  not  only  entails  a  considerable  loss  of  this  metal,  but 
is  very  liable  to  stop  up  the  tube,  thus  giving  rise  to  the  most  dangerous  explo- 
sions; hence  it  is  necessary  that  this  tube  be  unstopped  from  time  to  time;  in 
fact,  very  many  precautions  are  necessary  in  the  preparation  of  potassium,  and 
we  have  only  given  an  outline  of  the  process,  as  far  as  it  possesses  a  general 
interest,  referring  to  larger  works  for  a  more  detailed  description  of  the  difficulties 
to  be  overcome  in  practice.  In  order  to  purify  the  potassium  obtained  in  this 
process,  it  is  fused  under  petroleum  and  strained  through  linen;  it  may  then  be 
redistilled  in  the  vapor  of  petroleum,  and  preserved  in  small  bottles  filled  with 
this  liquid  or  with  benzol. 

Properties. — Potassium  is  a  bluish  white  lustrous  metal,  which  oxidizes  very 
rapidly  when  exposed  to  air,  becoming  converted  into  potassa,  on  which  account 
it  is  always  preserved,  as  above  directed,  in  a  liquid  free  from  oxygen;  it  is 
brittle  at  low  temperatures,  but  at  the  ordinary  temperature  may  be  cut  like 
wax;  it  fuses  at  25°  C.  (136°.4  F.),  and  may  be  distilled  unchanged  in  an 
atmosphere  free  from  oxygen,  at  a  red  heat;  the  vapor  of  potassium  has  a  green 
color.  The  specific  gravity  of  this  metal  being  only  0.865,  it  floats  upon  the 
surface  of  water,  which  it  decomposes  even  at  the  ordinary  temperature,  com- 
bining with  the  oxygen  with  such  energy  that  the  metal  is  raised  to  a  tempera- 
ture sufficiently  high  to  kindle  the  liberated  hydrogen,  which  burns  with  a 
violet  flame,  from  the  presence  of  a  little  vapor  of  potassium;  after  this  experi- 
ment, the  water  will  of  course  present  an  alkaline  reaction,  due  to  the  potassa 
which  it  now  holds  in  solution.  When  potassium  is  heated  in  air,  it  burns  with 
a  fine  violet  flame,  being  converted  into  potassa.1 

The  powerful  affinity  for  oxygen  which  potassium  exhibits,  renders  it  very 
useful  in  many  operations;  thus,  it  will  be  remembered  that  this  metal  is  em- 
ployed in  the  preparation  of  boron  and  silicon,  and  we  shall  hereafter  have  occa- 
sion to  mention  its  use  in  reducing  various  metallic  oxides.  In  experiments 
upon  organic  substances,  potassium  is  also  found  useful  for  removing  oxygen, 
chlorine,  bromine,  &c. 


POTASSIUM   AND    OXYGEN. 

Potassa KO. 

Teroxide  of  potassium      K03. 

§  142.  Berzelius  believed  that  the  gray  substance  produced  when  potassium 
is  burnt  in  an  insufficient  supply  of  air,  or  when  thin  plates  of  the  metal  are 
exposed  to  a  moist  atmosphere,  consists  of  a  suloxide  of  potassium ,  K30.  When 
placed  in  contact  with  water,  it  is  converted  into  potassa,  with  disengagement  of 
hydrogen,  which  does  not  inflame. 

POTASSA,  KO.     Eq.  47. 
Preparation. — Anhydrous  potassa  may  be  obtained  by  heating  the  hydrate 

1  The  combustion,  however,  is  never  complete,  since  the  metal  becomes  covered  with 
a  film  of  potassa,  which  protects  it  from  further  oxidation. 


232  POTASSIUM   AND    OXYGEN. 

KO.HO  with  an  equivalent  weight  of  potassium,  in  an  atmosphere  free  from 
oxygen ;  decomposition  of  the  water  then  takes  place,  and  two  equivalents  of 
potassa  are  produced;  thus: — 

KO.HO  +  K=2KO  +  H. 

Properties. — Anhydrous  potassa  is  a  hard  gray  solid,  fusible  at  a  little  above 
a  red  heat,  and  convertible  into  vapor  at  a  very  high  temperature.  When  this 
substance  is  added  to  an  equivalent  quantity  of  water,  very  energetic  combination 
takes  place,  and  so  much  heat  is  developed  that  the  resulting  hydrate  of  potassa 
fuses  and  becomes  redhot.  Since  the  anhydrous  potassa  has  received  no  appli- 
cation, it  need  not  further  occupy  our  attention. 

HYDRATE  OF  POTASSA,  CAUSTIC  POTASSA. 
KO.HO.     Eq.  56. 

§  143.  This  is  a  compound  of  very  great  importance,  since  it  is  constantly 
employed  in  chemical  operations. 

Preparation. — Hydrate  of  potassa  is  generally  prepared  from  the  carbonate. 
One  part  of  carbonate  of  potassa  is  dissolved  in  ten  parts  of  water,  in  a  clean 
iron  pan,  and  the  solution  raised  to  the  boiling  point ;  to  this  solution  is  now 
added,  by  small  portions  at  a  time,  a  quantity  of  milk  of  lime,  prepared  by 
slaking  one  part,  at  least,  of  good  quicklime  with  warm  water,  in  a  covered  pan; 
the  mixture  should  be  allowed  to  boil  for  a  minute  or  two  after  each  addition  of 
lime,  and  the  water  which  evaporates  should  be  replaced;  when  all  the  lime  has 
been  added,  a  small  portion  of  the  liquid  is  removed  from  the  pan,  and  allowed 
to  stand  till  the  lime  has  subsided;  the  clear  liquid  is  then  decanted,  and  mixed 
with  excess  of  dilute  hydrochloric  acid;  should  any  considerable  effervescence  be 
produced,  fresh  portions  of  milk  of  lime  are  added  to  the  boiling  liquid  till  this 
is  no  longer  the  case;  the  pan  is  then  covered,  and  the  mixture  boiled  for  a 
quarter  of  an  hour,  after  which  it  is  removed  from  the  fire,  and  allowed  to  stand 
until  all  the  solid  particles  have  subsided;  the  clear  liquid  may  be  drawn  off  with 
a  siphon  (those  portions  which  are  still  turbid  may  be  set  aside  in  stoppered 
bottles  of  green  glass),  and  rapidly  evaporated,  in  a  silver  basin,  either  to  the 
requisite  state  of  concentration,  or,  if  the  solid  hydrate  be  required,  until  the 
hydrate  itself  begins  to  pass  off  in  white  fumes,  when  it  may  be  poured  upon  a 
clean  iron  plate,  and  allowed  to  cool.  If  a  scum  of  carbonate  of  potassa  be 
formed  upon  the  surface  of  the  fused  hydrate,  it  should  be  removed  before  pour- 
ing the  latter  from  the  pan. 

The  decomposition  is  thus  represented  : — 

KO.C02+CaO.HO=KO.HO+CaO.C03. 

In  this  process,  simple  though  it  appears,  considerable  care  is  required  to  in- 
sure a  good  result ;  thus,  if  too  small  a  quantity  of  water  be  present,  the  carbo- 
nate of  potassa  will  not  be  decomposed  by  the  lime;  in  fact,  a  strong  solution  of 
potassa  is  capable  of  withdrawing  the  carbonic  acid  from  carbonate  of  lime. 
Again,  if  the  mixture  be  not  boiled  after  each  addition  of  milk  of  lime,  the  car- 
bonate of  lime  will  not  subside  readily,  and  the  resulting  solution  of  potassa  will 
be  turbid.  It  is  important  that  the  pan  in  which  the  potassa  is  prepared  be 
made  of  untinned  iron,  or  of  silver,  since  tin  and  copper  would  be  acted  upon  by 
the  alkali;  the  vessel  in  which  the  solution  is  allowed  to  subside  should  be 
covered,  for  the  potassa  is  very  prone  to  be  reconverted  into  carbonate  by  ab- 
sorption of  carbonic  acid  from  the  air.  The  solution  of  potassa  should  be  pre- 
served in  stoppered  bottles,  the  glass  of  which  is  free  from  oxide  of  lead,  since 
this  latter  is  soluble  in  potassa;  bottles  of  German  glass,  or  of  common  green 
glass,  are  the  best. 

The  hydrate  of  potassa  thus  prepared  is  liable  to  contain  various  impurities, 


HYDRATE   OF  POTASSA.  233 

derived  from  the  lime  and  carbonate  of  potassa;  these  are  particularly  noticed, 
and  the  method  of  discovering  them  described,  in  the  section  upon  reagents.  A 
purer  variety  of  hydrate  of  potassa,  known  as  alcohol-potash,  is  prepared  by 
agitating  the  syrupy  hydrate  with  alcohol,  decanting  the  alcoholic  solution,  and 
evaporating.  Pure  potassa  is  also  prepared  from  carbonate  of  potassa  obtained 
by  incinerating  well-washed  bitartrate  of  potassa;  the  lime  for  this  purpose  is 
generally  obtained  by  the  calcination  of  oyster-shells  in  an  open  fire.1 

Properties. — Hydrate  of  potassa,  when  perfectly  pure,  is  a  white,  hard  solid 
(as  met  with  in  commerce,  it  is  often  in  the  form  of  thin  sticks  (potassa  fusa), 
which  have  been  cast  in  moulds,  and  have  a  bluish-green  color,  due  to  the  pre- 
sence of  manganate  of  potassa).  It  fuses  below  a  red  heat,  and  at  a  higher  tem- 
perature volatilizes  in  white  vapors.  The  water  cannot  be  expelled  by  heat. 
Placed  in  water,  it  dissolves  rapidly,  with  disengagement  of  heat  and  a  slight 
hissing  sound.  It  also  dissolves  very  readily  in  alcohol,  which,  after  a  short 
time,  it  decomposes,  yielding  a  brown  solution.  When  exposed  to  the  air,  it 
deliquesces  to  a  syrupy  liquid,  which  gradually  absorbs  carbonic  acid,  and  passes 
into  carbonate  of  potassa. 

Hydrate  of  potassa  is  the  most  powerful  alkali  which  we  possess;  its  solution 
in  water  has  a  very  soapy  feeling  on  the  skin,  and  immediately  restores  the  blue 
color  to  reddened  litmus,  or  imparts  a  brown  color  to  turmeric.  When  brought 
in  contact  with  acids,  the  water  is  displaced,  and  the  potassa  combines  with  the 
acid  to  form  a  potassa-salt.  The  salts  formed  by  potassa  with  strong  acids,  when 
neutral  in  constitution,  are  also  neutral  in  reaction.  These  salts  are,  with  few 
exceptions,  soluble  in  water. 

The  aqueous  solution  of  potassa  (liquor  potassae),  which  is  so  very  useful  both 
as  a  chemical  and  medicinal  agent,  is  prepared  by  arresting  the  evaporation  of 
the  liquid  obtained  by  decomposing  the  carbonate  of  potassa  with  lime,  as  soon 
as  it  has  attained  a  certain  strength  ;  this  is  indicated  by  the  specific  gravity  of 
the  solution,  the  amount  of  hydrate  of  potassa  in  which  increases  with  its  den- 
sity. By  reference  to  the  tables  given  in  larger  chemical  works,  we  may  ascer- 
tain the  amount  of  potassa  contained  in  solutions  of  various  densities.  The 
liquor  potassae  used  in  medicine  has  a  specific  gravity  of  1.06,  and  appears  to 
contain  about  5  per  cent,  of  real  alkali.  The  ordinary  solution  employed  in  the 
laboratory  contains  about  25  per  cent.,  and  has  a  specific  gravity  1.27. 

Solution  of  potassa  boils  at  a  higher  temperature  than  water,  and  the  stronger 
the  solution  the  higher  will  be  its  boiling-point ;  this  solution,  and  all  other 
strong  alkaline  solutions,  should  never  be  heated  in  vessels  of  glass  or  porcelain, 
since  they  readily  attack  these  materials.  Solution  of  potassa  attacks  cork,  and 
must  therefore  be  preserved  in  stoppered  bottles. 

A  solution  of  hydrate  of  potassa  in  a  very  small  quantity  of  hot  water,  if 
allowed  to  cool  in  a  stoppered  bottle,  deposits  small  rhombohedral  crystals  of  the 
formula  KO  +  5HO,  which  dissolve  in  water  with  production  of  cold.  Potassa, 
as  has  been  already  mentioned,  may  be  decomposed  by  a  powerful  galvanic  cur- 
rent; certain  metals,  iron  and  zinc,  for  example,  at  a  high  temperature,  are  also 
capable  of  abstracting  its  oxygen.  Hydrate  of  potassa,  when  fused  with  sawdust 
and  many  other  organic  matters,  oxidizes  them  at  the  expense  of  the  water  which 
it  contains,  hydrogen  being  evolved,  and  the  potassa  remaining  as  carbonate,  the 
carbonic  acid  being  formed  by  the  oxidation  of  the  carbon  of  the  organic  matter. 
We  have  seen  that  potassa  is  reduced  by  carbon  at  a  high  temperature.  If  chlo- 
rine be  passed  over  potassa  at  a  red  heat,  it  displaces  the  oxygen,  chloride  of 
potassium  being  formed ;  whilst,  if  chlorine  be  allowed  to  act  upon  a  solution  of 
potassa,  we  obtain  chloride  of  potassium,  and  a  salt  of  potassa  with  an  oxygen- 

1  Pure  potass  is  sometimes  prepared  by  decomposing  sulphate  of  potassa  with  hydrate 
of  baryta. 


234  NITRATE   OF   POTASSA. 

acid  of  chlorine ;  the  same  is  the  case  with  bromine  and  iodine ;  an  analogous 
reaction  takes  place  between  potassa  and  sulphur  or  phosphorus,  a  sulphide  or 
phosphide  of  potassium  being  formed,  together  with  a  salt  of  potassa  with  one  of 
the  oxygen-acids  of  these  elements. 

Uses  of  Potassa. — The  solid  hydrate  of  potassa  is  extensively  used  by  the 
chemist  for  drying  gases,  for  decomposing  mineral  silicates  and  various  organic 
substances.  It  is  also  applied  in  surgery  as  a  caustic.  Solution  of  hydrate  of 
potassa  is  extensively  used  by  the  soap-maker  for  preparing  soft  soap,  and  is  con- 
stantly employed  in  the  laboratory,  where  its  very  powerful  alkaline  properties 
render  it  useful  for  displacing  weaker  bases,  and  for  absorbing  acid  gases,  for 
example,  carbonic  acid,  in  organic  analysis.  In  medicine,  the  solution  of  sp.  gr. 
1.06  is  administered  as  an  antacid,  and  as  a  solvent  of  uric  acid  in  cases  of 
gravel,  &c. 

NITRATE  OF  POTASSA,  NITRE,  SALTPETRE.  KO.N05. 

§  144.  This  salt  occurs  in  nature  as  an  incrustation  upon  the  surface  of  the 
earth  in  hot  climates,  such  as  India,  Arabia,  and  South  America.  It  is  also 
found  in  certain  caverns  in  Ceylon  and  other  parts ;  these  natural  excavations 
occur  in  a  limestone,  which  contains  magnesia  and  feldspar.  Some  of  these  caves 
are  the  resort  of  innumerable  bats,  whose  excrement  collects  in  them,  and  doubt- 
less is  a  great  source  for  the  production  of  nitre  in  these  localities. 

Saltpetre,  as*  it  is  found  in  these  crusts  or  deposits,  is  always  more  or  less  con- 
taminated with  the  nitrates  of  lime,  magnesia,  and  soda,  besides  their  chlorides 
and  sulphates. 

Nitrate  of  potassa  is  also  found  in  small  quantities  in  the  juices  of  plants,  and 
in  some  waters. 

In  some  of  those  localities  where  nitre-incrustations  are  found,  this  salt  ap- 
pears to  exist  in  small  quantities  in  the  soil,  being  collected  upon  its  surface  by 
the  heat  of  the  sun,  which  causes  the  superficial  moisture  to  evaporate,  and 
deposit  the  salt  dissolved  in  it,  while  the  crust  of  earth,  thus  becoming  very  dry 
and  porous,  draws  up  fresh  quantities  of  moisture,  containing  nitrates,  from  be- 
neath, which  is  in  turn  evaporated ;  in  this  manner  the  crust  of  salt  deposited 
gradually  increases  in  thickness. 

In  other  localities,  however  (e.g.  in  some  of  the  caverns  above  alluded  to),  the 
saltpetre  is  evidently  formed  gradually,  by  the  decomposition  of  animal  and 
vegetable  matter,  in  contact  with  certain  bases. 

Many  examples  might  be  quoted  of  the  production  of  nitrates  in  this  manner ; 
we  may  mention,  as  one,  the  production  of  the  so-called  saltpetre-rot,  a  plumose 
incrustation  of  nitrates  which  is  frequently  observed  upon  the  base  of  the  exter- 
nal walls  of  buildings  in  crowded  cities,  imperfectly  drained,  when  nitrogenized 
organic  matter  (manure)  mixes  with  earthy  salts  in  the  street,  or  attaches  itself 
to  the  mortar  of  the  buildings.1 

§  145.  It  has  already  been  stated  that  the  production  of  nitric  acid,  from 
organized  substances,  appears  to  depend  upon  the  oxidation  of  the  ammonia 
produced  in  the  putrefaction  of  nitrogenized  bodies,  at  the  expense  of  the  atmo- 
sphere, in  the  presence  of  powerful  bases,  with  which  the  nitric  acid  thus  formed 
may  combine j  thus: — 

NH3  +  08=3HO-fN05. 

The  existence  of  the  bases  in  a  porous  condition  is  believed  to  assist  the 
formation  of  nitric  acid,  probably  by  the  great  condensing  power  which  porous 

1  This  species  of  incrustation  must  not  be  confounded  with  a  similar  efflorescence  fre- 
quently observed  on  the  walls  of  new  buildings  (particularly  if  these  are  plastered  over), 
and  which  consists  of  sulphates  and  carbonates  of  the  alkalies  contained  in  the  building 
materials,  and  gradually  brought  to  the  surface  as  the  structure  dries. 


PREPARATION   OP    NITRE.  235 

substances  are  known  to  exert  over  gases,  thus  bringing  them  within  the  sphere 
of  action  of  chemical  affinity.1  This  argument  receives  great  support  from  the 
fact  that  ammonia  may  be  converted  into  peroxide  of  nitrogen,  by  passing  it 
over  spongy  platinum  heated  to  572°  F.  (300°  C.)  It  is  obvious  that,  if  that 
oxide  can  be  thus  formed,  there  is  no  obstacle  to  its  final  conversion  into  nitric 
acid. 

Artificial  production  of  Nitrates. — In  countries  where  nitre  does  not  occur, 
or  where  it  is  not  easily  imported,  large  quantities  are  prepared  artificially,  by 
what  is  termed  the  process  of  nitrification,  the  conditions  necessary  for  the  forma- 
tion of  nitrates  being  carefully  attended  to. 

Vegetable  and  animal  refuse  containing  nitrogen,  such  as  the  sweepings  of 
slaughter-houses,  dung,  weeds,  &c.,  is  made  into  heaps  with  earth,  limestone,  old 
mortar,  and  ashes ;  these  heaps  are  sheltered  from  rain,  and  are  moistened  from 
time  to  time  with  urine;  after  several  months,  an  incrustation  of  nitrates  forms 
on  the  surface;  when  sufficiently  rich  (or  ripe),  the  nitrified  ear tli,  as  it  is  termed, 
is  extracted  in  the  manner  to  be  presently  described.3 

In  the  Prussian  saltpetre  plantations,  the  nitre-beds  are  constructed  in  such  a 
manner  that  they  are  never  completely  removed.  That  side  of  the  mound  which 
is  exposed  to  the  prevailing  wind  is  perpendicular,  while  the  back  portion  is 
built  up  in  steps.  The  heap  is  watered  from  behind,  while,  as  the  front  wall  is 
exposed  to  the  desiccating  action  of  the  wind  and  sun,  the  nitrates  are  there 
collected,  and  the  rich  outer  coating  is  removed  from  time  to  time,  fresh  portions 
of  material  being  added  to  the  heap  from  behind. 

In  Sweden,  where  nitre  is  a  revenue-tax,  most  of  the  peasants  possess  a  nitre- 
plantation  on  a  small  scale.  Heaps  are  constructed  in  sheds,  of  the  materials 
enumerated  above,  watered  from  time  to  time  with  urine,  and  maintained  in  a 
porous  condition  by  the  insertion  of  twigs.  The  mass  is  turned  occasionally, 
and  allowed  to  remain  generally  about  two  years. 

In  other  countries  (e.g.  in  Switzerland,  where  the  stables  are  erected  against 
the  sides  of  the  mountains),  the  liquid  manure  that  penetrates  through  the 
roughly  boarded  floors  of  the  stables,  is  collected  beneath,  in  pits  filled  with  a 
mixture  of  the  above-mentioned  substances. 

The  time  required  for  the  production  of  nitrates,  in  any  quantity,  varies  con- 
siderably with  the  temperature  of  the  atmosphere.  It  has  been  observed  that 
from  59°  to  68°  F.  is  the  temperature  most  favorable  to  the  production  of  nitrates, 
while  their  formation  is  completely  checked  at  32°  F. 

PREPARATION  AND  PURIFICATION  OF  NITRE. — The  separation  of  the  nitrates 
from  the  earth  is  effected  by  lixiviation.  The  nitrified  earth  is  broken  up  into 
small  lumps,  and  placed  in  large  tubs  or  troughs  with  false  perforated  bottoms, 
and  lateral  openings  below  these,  stopped  with  plugs  until  required.  The  per- 
forated bottom  is  covered  with  a  layer  of  straw  or  small  twigs,  to  prevent  the 
holes  from  becoming  stopped  up  by  portions  of  the  earth.  Sufficient  water  is 
added  to  cover  the  earth,  and  allowed  to  remain  together  with  it  for  about  twelve 
hours,  in  order  that  the  salts  may  be  thoroughly  extracted.  The  solution  or  lye 

1  Some  chemists  imagine  this  power  capable  even  of  inducing  the  nitrogen  and  oxygen 
of  the  air  to  unite  directly  to  form  nitric  acid,  provided  some  impulse  be  imparted  to  their 
particles  by  the  presence  of  organic  matter  undergoing  decomposition,  or  of  ready-formed 
ammonia.     In  support  of  their  argument,  they  call  attention  to  the  large  amount  of  ani- 
mal matter  required  to  produce  any  quantity  of  nitric  acid,  and  to  the  circumstance  that 
ammonia  continually  escapes  into  the  atmosphere,  whence  it  may  be  rapidly  absorbed  by 
porous  earth  or  rocks,  being  one  of  those  gases  over  which  such  bodies  exert  their  influ- 
ence in  the  most  powerful  manner. 

2  One  thousand  cubic  inches  of  good  nitrified  earth  yield  about  five  ounces  of  saltpetre. 
The  surface  of  the  mounds  upon  which  the  nitrates  collect  is  removed  from  time  to  time, 
and  set  aside  for  lixiviation.    It  is  generally  about  three  years  before  a  large  nitre-mound 
is  completely  removed. 


236  PURIFICATION   OP   NITRE. 

is  afterwards  allowed  to  run  off  from  the  openings  at  the  bottom  of  the  vessel.1 
Generally,  the  liquor  obtained  from  one  quantity  of  earth  is  poured  upon  a  second, 
and  even  a  third,  in  order  that  a  tolerably  concentrated  solution  of  nitrates  may 
be  obtained.  This  lye,  which  contains  the  nitric  acid  in  combination  with  lime, 
magnesia,  potassa,  soda,  and  ammonia,  besides  considerable  quantities  of  chlorides 
and  sulphates  of  these  bases,  is  now  mixed  with  a  strong  solution  of  carbonate  or 
sulphate  of  potassa,  when  the  whole  of  the  nitric  acid  is  converted  into  nitrate  of 
potassa. 

The  solution  is  allowed  to  stand  until  clear,  when  it  is  decanted,  and  trans- 
ferred to  a  boiler,  where  it  is  rapidly  boiled  down  until  it  has  attained  a  certain 
strength.  A  large  quantity  of  the  impurities  are  separated  in  this  operation; 
small  quantities  of  earthy  salts  are  first  deposited,  and  as  the  solution  becomes 
more  concentrated,  the  chlorides  of  potassium  and  sodium  (of  which  it  contains 
very  considerable  quantities)  separate  in  small  crystals,  the  solubility  of  these 
salts  in  water  being  only  slightly  increased  by  heat,  when  compared  with  that  of 
nitre  under  similar  circumstances.3  When  the  liquor  has  attained  a  certain  spe- 
cific gravity,  it  is  drawn  off  from  the  boiler,  and  allowed  to  remain  undisturbed, 
in  large  pans,  at  a  temperature  of  about  122°  F.  (50°  C.)  until  the  chlorides 
have  separated  as  far  as  possible;  it  is  then  decanted  into  other  vessels,  and 
allowed  to  crystallize. 

The  nitre  thus  obtained  is  still  contaminated  with  small  quantities  of  alkaline 
chlorides  and  with  organic  coloring  matter.  It  is  now  digested  with  the  smallest 
quantity  of  hot  water  necessary  for  the  complete  solution  of  the  saltpetre  (whereby 
a  further  quantity  of  chlorides  is  sometimes  separated).  The  solution  is  then 
boiled  with  a  small  quantity  of  glue  or  gelatin,  which  possesses  the  property  of 
rendering  insoluble  the  whole  of  the  organic  matter  by  its  coagulation,  and  col- 
lects as  a  scum  upon  the  surface  of  the  liquid,  from  which  it  is  easily  removed. 
When  the  solution  is  sufficiently  concentrated,  it  is  allowed  to  run  through 
funnel-bags  into  crystallizing-pans,  where  it  is  continually  agitated  with  wooden 
stirrers,  until  crystals  are  no  longer  deposited.  The  object  of  this  may  be  ex- 
plained in  a  few  words  :  if  a  solution  of  nitre  is  allowed  to  crystallize  undisturbed, 
it  deposits  very  large  striated  crystals,  containing  considerable  cavities,  in  which 
are  inclosed  portions  of  the  mother  liquor;  if  the  latter  contain  any  impurities, 
they  will  consequently  be,  to  some  extent,  retained  by  the  crystals.  But  if  a 
solution  of  nitre,  as  it  crystallizes,  be  continually  stirred,  the  salt  is  deposited  in 
very  fine  grains  (called  saltpetre-flour),  which  may  be  very  easily  freed  from  any 
trifling  quantity  of  impurity  that  may  adhere  to  their  surfaces. 

In  order  to  avoid  loss  of  product  by  washing  this  saltpetre-flour  with  water 
(which  must,  of  course,  dissolve  a  considerable  quantity),  recourse  is  had  to  a 
very  ingenious  method  of  purification,  dependent  upon  the  power  possessed  by 
water  of  exerting  its  solvent  action  upon  several  salts  simultaneously,  the  amount 
of  one  salt  present  in  a  quantity  of  water  not  preventing  the  solubility  of  another, 
or  of  a  third  salt,  in  the  same  water. 

The  saltpetre-flour  is  placed  in  a  trough,  similar  to  that  employed  in  the  pro- 
cess of  lixiviation ;  a  saturated  solution  of  pure  nitre  is  then  poured  upon  it,  and 
allowed  to  remain  in  contact  with  it  for  a  short  time.  Any  chlorides  that  may 

1  The  lixiviated  earth  still  retains  a  small  quantity  of  nitrates,  and  is  used,  in  the  salt- 
petre plantations,  for  the  construction  of  fresh  mounds. 

2  The  solubility  of  nitre  at  212°  F.  (100°  C.)  is  about  14  times  greater  than  it  is  at 
ordinary  temperatures,  while  that  of  chloride  of  potassium  is  only  about  twice  as  great, 
and  that  of  chloride  of  sodium  is  but  slightly  increased.     If,  therefore,  a  solution  contain- 
ing these  three  salts  be  concentrated,  the  greater  quantities  of  the  chlorides  will  be  depo- 
sited as  the  water  decreases,  while  the  nitrate  of  potassa  will  not  exhibit  any  symptom  of 
crystallizing  out. 

The  crystals  of  chlorides  deposited  in  the  above  process  are  allowed  to  collect  in  a 
small  basket  suspended  in  the  lye. 


NITRATE    OF   POTASSA.  237 

still  have  been  retained  by  the  saltpetre  are  dissolved  in  this  way,  without  loss 
of  nitre.  The  solution  is  afterwards  drained  off,  and  the  washing  repeated  twice 
or  three  times,  when  the  nitre  is  obtained  absolutely  free  from  chlorides.  The 
solution  of  nitre  is  afterwards  employed  for  the  first  washing  of  a  fresh  portion 
of  saltpetre-flour.  The  latter  is  then  dried  at  a  moderate  temperature. 

At  Waltham  Abbey,  the  refining  of  saltpetre  is  effected  in  a  somewhat  different 
manner.  It  is  decolorized  by  boiling  its  solution  with  freshly-ignited  charcoal, 
and  is  afterwards  freed  perfectly  from  chlorides  by  repeated  recrystallization. 

§  146.  Properties  of  Nitre. — Nitrate  of  potassa  is  a  dimorphous  salt,1  crystal- 
lizing in  colorless,  six-sided  prisms,  and  in  flattened  rhombohedra,  neither  of 
which  contains  any  water  of  crystallization;  its  specific  gravity  is  1.933.  When 
heated,  the  crystals  of  nitre  first  decrepitate,  from  the  expansion  of  water  mecha- 
nically inclosed  by  them:  at  a  higher  temperature,  about  662°  F.  (350°  C.), 
they  fuse,  and  are  ultimately  decomposed,  yielding,  at  first,  oxygen,  the  residue 
consisting  of  nitrite  of  potassa  (KO.N03) ;  if  this  be  further  heated,  nitrogen  and 
oxygen  are  evolved,  and  a  mixture  of  potassa  and  peroxide  of  potassium  (K03) 
remains. 

Fused  nitrate  of  potassa  is  translucent,  and  possesses  a  fibrous,  crystalline 
structure;  it  is  known  in  pharmacy  by  the  name  of  sal prunelle. 

Nitrate  of  potassa  has  a  saline,  cooling  taste ;  it  dissolves  in  about  5  parts  of 
cold  water  (causing  considerable  depression  of  temperature),  and  in  less  than  its 
own  weight  of  boiling  water.  Nitrate  of  potassa  is  very  slightly  soluble  in 
alcohol. 

This  salt  acts,  at  high  temperatures,  as  a  very  powerful  oxidizing  agent;  thus 
sulphur  and  carbon,  when  dropped  into  fused  nitre  of  a  pretty  high  temperature, 
are  oxidized  with  great  violence,  sulphate  and  carbonate  of  potassa  being  formed ; 
in  these  and  similar  cases,  the  nitrogen  is  either  evolved  in  the  free  state,  or  as 
an  inferior  oxide.  Even  silver,  gold,  and  platinum,  cannot  resist  the  oxidizing 
action  of  nitrate  of  potassa. 

§  147.  Uses  of  Nitre. — This  salt  receives  its  most  important  application  in  the 
manufacture  of  gunpowder,2  and  in  pyrotechny;  it  is  also  used  for  some  kinds  of 
instantaneous  matches. 

The  powerfully  oxidizing  properties  of  nitre  have  been  applied  from  a  very 
early  period  for  the  preparation  of  explosive  mixtures.  Besides  gunpowder,  the 
period  of  the  discovery  of  which  cannot  be  satisfactorily  traced,  we  may  mention 
a  mixture  possessed  of  powerfully  explosive  properties,  known  by  the  name  of 
pulvis  fulminans,  which  consists  of  3  parts  of  nitre,  2  parts  of  dry  carbonate  of 
potassa,  and  1  part  of  sulphur.  This  mixture  explodes  powerfully,  when  dry,  if 
heated  upon  an  iron  plate. 

Saltpetre  is  also  used  for  the  preservation  of  meat.  It  is  sometimes  employed 
for  the  manufacture  of  nitric  acid,  and  is  of  great  value  to  the  chemist  as  a  pow- 
erful oxidizing  agent.  In  medicine,  nitre  is  also  extensively  used. 

Baume's  flux  consists  of  3  parts  of  nitre,  1  part  of  sulphur,  and  1  part  of 
sawdust;  it  is  capable  of  inducing  the  fusion  of  different  metals,  partly  on  account 
of  the  heat  evolved  by  its  deflagration,  and  partly  because  it  converts  a  portion 
of  the  metal  into  a  more  fusible  sulphide. 

1  The  dimorphism  exhibited  by  nitre  is  similar  to  that  of  carbonate  of  lime ;  the  pris- 
matic crystals  being  very  nearly  the  same  as  those  of  arragonite,  while  the  rhombohedra 
are  almost  identical  with  those  of  calcareous  spar. 

2  Nitrate  of  potassa,  when  pure,  does  not  attract  any  moisture  from  the  air ;  it  is  in 
consequence  of  this  absence  of  deliquescent  properties,  and  the  comparative  facility  with 
which  it  may  be  purified  from  deliquescent  salts,  that  it  is  employed  in  the  manufacture 
of  gunpowder,  in  preference  to  nitrate  of  soda,  which  occurs  in  much  greater  abundance, 
but  is  a  very  deliquescent  salt. 


238  REFRACTION  OP  NITRE. 

•    EXAMINATION  OF  NITRE. 

§  148.  It  is  of  great  importance  to  possess  some  good  means  of  ascertaining  the 
value  of  samples  of  nitre.  The  following  are  the  principal  methods  employed 
for  this  purpose. 

The  most  simple  of  these,  and  the  one  that  is  most  extensively  employed  for 
the  rough  estimation  of  the  value  of  nitre,  is  that  of  examining  the  fracture  of 
the  fused  salt. 

It  has  been  mentioned  that  fused  nitre  possesses  a  peculiar  fibrous  structure ; 
the  presence  of  foreign  salts  affects  this  structure  to  a  greater  or  less  degree, 
according  to  their  quantity.  A  slight  percentage  of  chloride  of  sodium,  for 
example,  gives  rise  to  small  nodules  in  the  mass;  in  long-practised  hands,  the 
percentage  of  nitre  can  be  ascertained,  by  this  physical  examination,  with  suffi- 
cient accuracy  for  mercantile  purposes ;  no  reliance  can,  however,  be  placed  in 
it  by  a  casual  experimenter.  A  cube  of  nitre,  of  1  or  2  inches  in  thickness,  is 
cast  in  an  iron  mould;  it  is  afterwards  broken  in  halves,  and  the  fracture 
examined. 

The  examination  of  nitre  by  this  method  is  called  the  refraction  of  nitre,  which 
name  is  also  applied  in  general  to  the  examination  of  nitre  by  any  of  the  pro- 
cesses in  common  use. 

There  are  two  other  physical  methods  of  examining  nitre ;  one  of  these  con- 
sists in  "washing  a  known  weight  of  the  dried  salt  with  a  saturated  solution  of 
pure  nitre,  upon  a  filter  of  known  weight,  until  no  reaction  is  obtained  with 
nitrate  of  silver  in  the  washings;  afterwards  carefully  spreading  the  filter  open 
upon  a  porous  tile,  in  order  that  as  much  as  possible  may  be  absorbed  of  the 
solution  that  is  mechanically  retained,  and  finally  drying  in  the  water-bath.  The 
loss  in  weight  which  the  nitre  and  filter  will  have  sustained,  indicates  the  amount 
of  impurities  in  the  nitre.  This  method  is  tedious,  and  always  yields  results 
from  1  to  2  per  cent,  too  high,  in  consequence  of  the  addition  to  the  substance 
operated  upon,  of  a  small  quantity  of  nitre,  left  by  evaporation  of  that  portion  of 
the  solution  which  is  inevitably  retained  by  the  surfaces  of  the  crystals,  and  by 
the  filter.  The  error  may  be,  to  a  great  extent,  corrected  by  weighing  the  filter 
and  contents,  before  and  after  desiccation,  and  deducting  from  the  second  weight 
the  amount  of  nitre  known  to  correspond  to  the  quantity  of  water  evaporated. 

Another  source  of  error  arises  from  the  increased  solubility  of  nitre  in  a  solu- 
tion containing  chloride  of  sodium,  in  consequence  of  the  mutual  decomposition 
of  these  salts  giving  rise  to  chloride  of  potassium,  and  nitrate  of  soda ;  tables 
have  been  constructed,  from  direct  experiments,  to  enable  the  analyst  to  make 
the  requisite  correction. 

The  second  physical  method  is  based  upon  the  principle  that  the  solution  of  a 
crystallizable  salt  in  a  certain  amount  of  hot  water,  upon  being  allowed  to  cool 
down,  first  commences  to  deposit  crystals  at  a  temperature  standing  in  direct 
relation  to  the  amount  of  salt  dissolved ;  and  that  this  temperature  is  the  same, 
whether  the  solution  contain  other  salts  in  addition  or  not. 

A  scale  is  first  constructed  of  temperatures  at  which  cooling  solutions  of  nitre 
of  different  strength  commence  to  crystallize,  a  fixed  amount  of  water  (100  parts) 
being  taken  in  each  observation.  A  known  weight  of  the  sample  to  be  exa- 
mined is  dissolved  in  a  beaker,  at  about  140°  F.  (60°  C.),  in  the  same  amount 
of  water  as  that  employed  in  constructing  the  table;  a  thermometer  indicating 
J°  is  then  introduced,  and  the  temperature  noted  at  which  the  first  symptom  of 
crystallization  is  perceptible.  By  simple  comparison  of  this  temperature  with 
the  table,  the  amount  of  nitre  in  the  solution  is  at  once  ascertained. 

An  inaccuracy  in  this  determination  may  arise  from  the  presence  of  chloride 
of  sodium,  which  would  tend  to  depress  the  temperature  of  the  crystallizing- 


GUNPOWDER.  239 

point,  by  decomposing  a  certain  quantity  of  the  nitre  in  the  manner  above 
alluded  to. 

Gay-Lussac's  method  of  examining  nitre  consists  in  mixing  about  20  grains 
(accurately  weighed)  of  the  dried  specimen,  with  about  10  grains  of  charcoal- 
powder  and  80  grains  of  chloride  of  sodium ;  this  mixture  is  introduced  by  small 
portions  into  an  iron  crucible  heated  to  redness;  the  fused  mass  is  dissolved  in 
water,  the  solution  colored  with  litmus,  and  dilute  sulphuric  acid  of  known 
strength  added  from  a  graduated  glass  until  a  slight  excess  has  been  employed, 
which  is  known  by  the  peculiar  bright-red  tint  assumed  by  the  solution.  The 
number  of  measures  of  acid  employed  is  then  observed,  and  the  amount  of  nitrate 
of  potassa  to  which  they  correspond,  calculated.  40  parts  (1  eq.)  of  sulphuric 
acid  (S03)  correspond  to  101  parts  (1  eq.)  of  nitrate  of  potassa,  as  may  be  seen 
by  the  following  equation,  which  exhibits  the  action  of  the  carbon  upon  the 
nitrate  of  potassa : — 

2(KO.N05)+C5=2(KO.C02)-fN3+3COa; 

where  it  will  be  seen  that  every  equivalent  of  nitrate  of  potassa  produces  an 
equivalent  of  carbonate,  which  requires  also  one  equivalent  of  sulphuric  acid  for 
its  neutralization.  The  chloride  of  sodium  is  merely  added  to  the  mixture  to 
moderate  the  violence  of  the  deflagration. 

A  fallacious  result  will  be  obtained  by  this  method,  if  the  specimen  examined 
contain  sulphates,  as  they  are  reduced  to  sulphides  by  fusion  with  charcoal ; 
these  being  decomposed  by  sulphuric  acid  (with  disengagement  of  hydrosulphuric 
acid),  their  presence  will  involve  the  use  of  an  excess  of  the  test  acid,  and  a  con- 
sequent excess  in  the  calculated  percentage  of  nitre.  If  hydrosulphuric  acid  is, 
therefore,  detected  upon  the  first  addition  of  acid  to  the  solution  of  the  fused 
mass,  recourse  must  be  had  to  some  one  of  the  other  methods. 

Pelouze's  method  consists  in  boiling  a  known  weight  of  the  salt  with  a  solu- 
tion of  chloride  of  iron  (FeCl)  containing  excess  of  hydrochloric  acid  (prepared 
by  dissolving  piano-wire  in  excess  of  acid),  diluting  largely  with  water,  and 
ascertaining,  by  the  careful  addition  of  a  standard  solution  of  permanganate  of 
potassa,  how  much  iron  has  been  converted  into  sesquichloride  by  the  nitrate  of 
potassa,  when  the  calculation  will  proceed  according  to  the  equation : — 

6FeCl+4HCl  +  KO.N05=3Fe3Cl3-f4HO-fKCl-fN03; 

which  shows  that,  for  every  6  equivalents  (168  parts)  of  iron  converted  into 
sesquichloride,  1  equivalent  (101  parts)  of  nitrate  of  potassa  is  present  in  the 
specimen. 

The  impurities  which  may  exist  in  commercial  nitre  are,  besides  organic  mat- 
ter, lime,  magnesia,  soda,  sulphuric  and  hydrochloric  acids.  In  testing  for  these 
substances,  the  course  prescribed  for  systematic  qualitative  analysis,  in  another 
part  of  this  work,  may  be  followed. 


GUNPOWDER. 

§  149.  Gunpowder  is  an  intimate  mixture  of  nitre,  charcoal,  and  sulphur,  the 
proportions  of  which  vary  somewhat  in  different  countries,  and  according  to  the 
uses  to  which  the  powder  is  applied.  The  action  of  this  substance  as  a  propel- 
ling agent  is  dependent  upon  the  rapid  oxidation  of  the  charcoal  by  the  nitre, 
and  the  consequent  sudden  evolution  of  a  large  volume  of  heated  gas.  In  a 
mixture  of  nitre  and  charcoal  alone  the  oxidation  (deflagration)  proceeds  with 
comparative  tardiness;  the  addition  of  sulphur  greatly  augments  the  combusti- 
bility of  the  mixture  (in  consequence  of  the  low  temperature  at  which  it  ignites); 


240 


GUNPOWDER. 


the  sulphur,  by  its  presence,  also  renders  available  for  the  oxidation  of  the  car- 
bon an  extra  amount  of  oxygen,  namely,  that  which  is  united  with  the  potassium, 
the  latter  being  at  once  converted  into  sulphide,  upon  ignition  of  the  powder. 

The  advantages  possessed  by  gunpowder,  as  a  propelling  agent,  over  all  other 
explosive  mixtures,  or  over  the  chemical  compounds  endowed  with  explosive 
properties,  with  which  we  are  at  present  acquainted,  are,  first,  the  comparative 
safety  with  which  it  may  be  manufactured,  handled,  and  transported,  and  second- 
ly, the  gradual  nature  of  its  decomposition,  when  compared  with  that  of  other 
explosives,  whereby  the  force  resulting  from  the  rapid  evolution  of  gas  in  a  con- 
fined space  has  sufficient  time  to  overcome  the  inertia  of  the  projectile,  which  is 
not  the  case  with  compounds,  the  conversion  of  which  into  gaseous  products  is 
instantaneous. 

The  gunpowder  which  is  most  powerful  as  a  propelling  agent  is  found  to  be 
that  which  corresponds  most  nearly  in  composition  to  the  formula 

KO.N05+C3-fS. 

The  theoretical  decomposition  of  a  powder  of  this  description  would  be  repre- 
sented by  the  equation : — 

KO.N05+C3+S=KS+3C02+N. 

In  practice,  it  is  found  that  small  quantities  of  many  other  products  are  inva- 
riably formed,  besides  carbonic  acid,  nitrogen,  and  sulphide  of  potassium,  among 
which  may  be  mentioned,  carbonic  oxide,  hydrosulphuric  acid,  bisulphide  of 
carbon  vapor,  carbonate  of  potassa,  cyanide  (and  sulphocyanide)  of  potassium, 
and  aqueous  vapor.1  The  most  important  products  of  a  careful  and  complete 
combustion,  on  a  small  scale,  of  powder  of  the  above  composition,  have,  however, 
been  found  to  correspond  pretty  closely  to  the  above  theoretical  expression. 

The  gases  disengaged  in  the  combustion  of  this  powder  would  occupy,  at  32° 
F.  (0°  C.),  a  volume  329  times  as  great  as  that  occupied  by  the  powder;  the 
force  exerted  by  the  evolution  of  these  gases  is,  however,  mainly  dependent  upon 
their  enormous  expansion,  at  the  instant  of  the  explosion,  by  the  heat  evolved 
in  the  action;  for  it  is  calculated  that  one  volume  of  powder  of  the  above  compo- 
sition yields,  at  the  moment  of  ignition,  at  least  2000  times  its  volume  of  gas.2 

If  gunpowder  contain  more  carbon  in  proportion  to  the  nitre  than  the  quan- 
tity above  stated,  a  proportionate  amount  of  carbonic  oxide  is  produced  in  its 
explosion ;  thus,  if  six  equivalents  of  carbon  be  employed,  instead  of  threef  to 
one  equivalent  of  nitre,  the  whole  of  the  oxygen  contained  in  the  latter  would 

1  The  great  heat  attending  the  explosion  converts  a  quantity  of  the  sulphide  of  potas- 
sium into  vapor,  which  takes  fire  with  a  flash  at  the  muzzle  of  the  gun,  and  is  converted 
by  the  oxygen  of  the  air  into  sulphate  of  potassa,  which  forms  the  white  smoke  observa- 
ble after  the  discharge. 

Chevreul  examined  the  products  obtained  by  the  combustion  of  pulverized  gunpowder 
in  a  small  copper  tube.  Gay-Lussac  obtained  the  gases  by  letting  the  powder  fall,  grain 
by  grain,  into  the  redhot  tube ;  in  both  cases  the  gases  were  collected  over  mercury. 
The  following  are  the  results  obtained  by  these  chemists : — 


GAY-LUSSAC. 

Carbonic  acid 53 

Carbonic  oxide 42 

Nitrogen 5 

100 


CHEVKEUL. 

Carbonic  acid 45.41 

Nitrogen         37.53 

Nitric  oxide 8.10 

Carbonic  oxide 4.87 

Carburetted  hydrogen       .     .  3.59 

Hydrosulphuric  acid    ...  0.50 

100.00 

2  The  temperature  evolved  by  the  combustion  of  gunpowder  has  been  found  to  be  suffi- 
ciently intense  to  fuse  gold  and  other  metals;  it  is  estimated  at  1200°  C.  (2192°  F.) 


4  GUNPOWDER.  241 

theoretically  be  evolved  as  carbonic  oxide  on  the  decomposition  of  the  powder, 
as  the  following  equation  shows : — 

KO.N03+C6-fS=KS-r-6CO+N. 

Now  since  the  space  occupied  by  equal  equivalents  of  carbonic  oxide  and  of 
carbonic  acid  is  the  same,  it  is  evident  that  a  much  larger  volume  of  gas  would 
be  evolved  (calculated  for  a  temperature  of  82  F.  and  ordinary  barometric  pres- 
sure) from  the  gunpowder  which  contained  the  larger  amount  of  charcoal.  But 
it  must  be  borne  in  mind  that  the  amount  of  heat  evolved  in  the  production  of 
carbonic  oxide  is  far  less  than  that  generated  when  carbonic  acid  is  produced, 
and  that,  consequently,  the  powder  which  contains  the  minimum  quantity  of 
charcoal  will  yield,  at  the  instant  of  explosion,  by  far  the  greatest  bulk  of  gas. 
That  this  expansion  of  the  gas  by  heat  is  of  the  greatest  importance,  is  very 
evident  from  what  has  already  been  stated;  it  has  been  ascertained  that  this 
expansion  increases  greatly  with  an  increase  of  temperature ;  thus,  for  example, 
200  volumes  of  gases  raised  to  a  temperature  of  2428°  F.,  occupy  the  same 
bulk  as  300  volumes  which  are  only  heated  to  1466°.6  F.,  namely,  1170 
volumes. 

It  will  be  readily  seen,  from  the  above  considerations,  why  a  powder  which 
approximates  most  nearly  in  composition  to  the  formula  KO.N05+C3-fS  should 
be  most  valuable  for  fire-arms.  The  percentage  composition  of  gunpowder  of 
this  description  would  be : — 

Nitre    .    '.  /T'.  .  .,„  ,  '..  ".'"  ..,.     74.82 
Charcoal    .........     13.83 

Sulphur  ;' /;;••>;  ;,,  ::;VJV':%  ,«;.;.-.   n.85 

'^    100.00 

Upon  comparing  the  composition  of  the  powders  prepared  in  different  coun- 
tries1 for  fire-arms,  they  will  be  found  to  agree  more  or  less  closely  with  the 
above  percentages ;  it  must  be  remembered,  however,  that  the  proportions  have 
been  arrived  at  by  experience,  in  most  cases  long  before  any  theory  concerning 
the  chemical  composition  or  action  of  powder  was  advanced.  In  some  cases  the 
deviations  from  the  theoretical  numbers  may  be  readily  explained ;  thus,  in  the 
manufacture  of  the  Waltham  Abbey  powder,  a  slight  excess  of  charcoal  is  always 
employed,  in  order  to  allow  for  the  small  quantity  of  foreign  matter  (ash)  always 
associated  with  carbon  in  that  form,  while  the  proportion  of  sulphur  is  reduced 
as  much  as  is  compatible  with  the  production  of  a  powerful  powder,  in  conse- 
quence of  the  injurious  action  of  that  substance  (and  even  of  sulphides,  in  the 
presence  of  moisture)  upon  metal. 

Some  kinds  of  powder,  manufactured  for  special  purposes  (e.g.  blasting-powder), 
contain  a  much  larger  proportion  of  charcoal;  the  expense  of  the  powder  is  there- 


1  The  following  table  shows  the  percentage  composition  of  gunpowder  of  different 
countries: — 

Nitre.         Charcoal.  Sulphur. 

English  ( Waltham  Abbey)     .     .     .     .  75.00  15.00  10.00 
France,               ) 

Prussia,              \ 75.00  12.50  12.50 

United  States,  J 

Russia 73.78  13.59  12.63 

Austria 76.00  11.50  12.50 

Spain 76.47  10.78  12.75 

Switzerland  (Champy  globular  poivder)  76.00  14.00  10.00 

Sweden 75.00  9.00  16.00 

China 75.00  14.40  9.60 

16 


242  GUNPOWDER. 

by  considerably  diminished,  a  matter  of  primary  importance  in  such  cases.  In 
the  decomposition  of  such  powder,  a  mixture  of  carbonic  oxide  and  carbonic  acid 
gases  is  evolved,  and  a  higher  sulphide  of  potassium  produced.  The  comparative 
force  exerted  by  a  powder  of  this  description  is  of  course  far  less  than  that 
exerted  by  good  fire-arm  powder. 

MANUFACTURE  OF  GUNPOWDER. — In  the  manufacture  of  gunpowder  the 
minute  state  of  division  and  intimate  mixture  of  the  ingredients  is  of  equal  im- 
portance with  the  proper  proportions ;  hence  considerable  care  must  be  bestowed 
upon  the  various  processes  through  which  the  constituents  and  the  powder  itself 
have  to  pass.  Different  methods  have  been  employed  from  time  to  time,  for 
attaining  the  desired  results.  We  shall  confine  ourselves  chiefly  to  an  outline  of 
the  manufacture  of  gunpowder,  as  conducted  at  the  Waltham  Abbey  mills. 

The  Ingredients. — The  greatest  care  is  taken  in  the  preparation  of  pure  ingre- 
dients for  gunpowder. 

The  presence  of  any  chloride  in  the  nitre  employed  must  be  avoided,  since  the 
deliquescent  nature  of  these  salts  would  act  very  injuriously  upon  powder,  causing 
it  to  absorb  moisture,  whereby  its  power  is  soon  greatly  weakened.  Saltpetre 
containing  more  -than  ^  -£-$•$  of  chlorides  is  rejected  as  unfit  for  use.  By  the 
method  adopted  at  Waltham  Abbey,  of  which  an  outline  has  already  been  given 
(§  145),  the  nitre  is  obtained  absolutely  pure.  In  order  to  free  it  perfectly  from 
moisture,  it  is  always  very  carefully  fused  and  cast  into  moulds.  In  this  opera- 
tion, the  application  of  too  high  a  temperature  is  guarded  against  with  care,  since 
the  production  of  a  small  quantity  of  caustic  potassa,  by  the  decomposition  of 
the  nitre,  would  impart  deliquescent  properties  to  the  latter.1 

Carefully  prepared  flowers  of  sulphur  are  employed  in  the  manufacture  of  gun- 
powder. The  method  of  obtaining  these  at  Waltham  Abbey  is  similar  to  that 
described  at  §  103.  When  the  walls  of  the  chamber  into  which  the  sulphur- 
vapors  are  conducted  become  too  warm  to  effect  their  proper  condensation  to 
flowers,  the  communication  between  the  chamber  and  the  retort  is  closed,  and 
another  one  opened,  leading  into  a  metal  receiver;  the  sulphur  is  allowed  to 
distil  over  into  this,3  until  the  chamber  has  become  sufficiently  cool,  and  the 
flowers  have  been  collected  from  its  sides,  when  the  vapors  are  once  more  allowed 
to  pass  into  it. 

Since,  at  the  commencement  of  the  distillation,  when  the  retort  and  condens- 
ing-chamber  still  contain  atmospheric  air,  the  first  portions  of  the  sulphur-vapor 
must  inflame,  sulphurous  acid  being  produced,  the  flowers  will  frequently  possess 
a  faint  acid  reaction  when  they  are  removed  from  the  chamber.  This  is  avoided 
by  allowing  the  sulphur  to  condense  upon  damp  cloths,  or  removed  by  allowing 
it  to  remain  between  such  cloths  for  #  short  time  previously  to  use. 

The  charcoal  for  powder  is  carefully  prepared  in  retorts  and  slips,  as  described 
at  §  121.  The  volatile  products  are  conducted  from  the  retorts,  by  pipes,  into 
the  fire  by  which  the  charring  is  effected,  and  there  consumed.  The  species  of 
wood  exclusively  employed  by  government  for  making  powder-charcoal,  are  alder, 
dogwood,3  and  willow.  About  twenty-five  to  thirty  per  cent,  of  charcoal  are 

1  The  following  is  a  delicate  test  for  the  over-fusion  of  nitre :  a  small  quantity  of  the 
fused  nitre  is  dissolved  in  water,  and  a  few  drops  of  a  neutral  solution  of  sulphate  of  copper 
added.  The  production  of  a  bright-green  tint  indicates  the  presence  of  nitrous  acid  (nitrite 
of  copper  being  produced),  and  shows  that  a  portion  of  the  nitre  has  at  any  rate  under- 
gone the  first  stage  of  decomposition  (see  Nitrate  of  Potassa) ;  if,  in  addition,  a  flocculent 
blue  precipitate  (hydrated  oxide  of  copper)  is  formed  immediately  upon  the  addition  of 
the  sulphate  of  copper,  or  is  deposited  after  a  short  time,  the  presence  of  caustic  potassa 
in  the  sample  is  indicated. 

*  The  massive  (crystalline)  sulphur  thus  obtained  is  employed  by  government  in  the 
manufacture  of  other  laboratory  compositions. 

8  Dogwood  charcoal  is  employed  exclusively  for  rifle-powder. 


GUNPOWDER.  243 

generally  obtained  in  successful  operations.1  Good  powder- charcoal  should  have 
a  bluish-black  appearance,  and,  when  powdered,  a  lustre  resembling  that  of  vel- 
vet ;  it  should  be  light,  sonorous,  firm,  and  slightly  flexible.  The  wood  used 
in  the  manufacture  of  powder-charcoal,  as  also  the  charcoal  itself,  must  be  care- 
fully picked  over,  as  directed  at  §  121  (Cylinder-charcoal').* 

Pulverization  and  intimate  mixture  of  the  Ingredients. — The  machine  or  mill 
by  which  the  ingredients  are  first  powdered,  and  afterwards  intimately  blended, 
or  incorporated,  as  it  is  termed,  consists  of  two  upright  mill-stones,  or  runners, 
of  smoothly  cut  marble  or  limestone,  or  of  iron  (about  7  feet  in  diameter,  and  12 
inches  thick,  and  weighing  from  3  to  4  tons  each),  which  turn  upon  one  common 
horizontal  axis,  while  this  again  turns  upon  a  vertical  axis,  placed  in  the  centre 
of  a  flat  bed,  of  the  same  material  as  the  runners  that  revolve  upon  it.8  The 

1  The  charge  for  a  retort,  at  Waltham  Abbey,  is  1|  cwt.,  which  is  burnt  from  three  and 
a  half  to  four  hours ;  the  charcoal  obtained  generally  amounts  to  40  Ibs. 

3  The  superiority  of  a  product  of  less  complete  carbonization  of  wood,  called  charbon 
roux  (red  charcoal),  over  the  black  charcoal,  for  the  manufacture  of  gunpowder,  has  been 
maintained  by  some  chemists,  particularly  in  France.  The  subject  still  requires  experi- 
mental investigation;  we  may  however  state,  in  a  few  words,  what  is  known  concerning 
it.  A  full  red  heat  yields  black  charcoal  containing  about  90  per  cent,  of  carbon,  and  7 
to  8  per  cent,  of  hydrogen  compounds.  A  temperature  approaching  red  heat  yields  char- 
bon  roux,  containing  70  to  72  per  cent,  of  carbon,  and  28  to  30  per  cent,  of  hydrogen  and 
oxygen.  The  latter  appears  to  be  charcoal  containing  the  maximum  amount  of  inflammable 
matter  in  wood. 

Powder  made  with  this  kind  of  charcoal  certainly  appears  to  burn  with  greater  energy 
than  that  made  with  black  charcoal ;  this  arises,  probably,  from  the  readier  inflammability 
of  the  charcoal. 

In  charbon  roux,  there  appear  to  exist  about  28  per  cent,  of  hydrogen  and  oxygen  in  the 
proportion  to  form  water,  besides  about  2  per  cent,  of  hydrogen  over  and  above  that  amount. 
A  larger  proportion  of  charcoal  must  therefore  be  employed  to  effect  the  proper  decomposi- 
tion than  if  black  charcoal  were  used,  since  the  large  percentage  of  hydrogen  and  oxygen 
above  alluded  to  does  not  enter  into  the  action ;  for  in  the  combustion  of  organic  sub- 
stances, the  heat  is  produced  by  th«  combustion  of  the  carbon  and  of  that  amount  of 
hydrogen  present  in  the  body,  over  and  above  the  quantity  required  to  produce  water  by 
the  oxygen  present  in  the  substance.  The  produce  thus  obtained  would  be  far  less  dense 
than  ordinary  powder,  it  would  therefore  occupy  a  greater  bulk,  and  would  be  liable  to 
dust  very  much,  and  also  attract  considerably  more  moisture  than  black  charcoal  powder. 
Moreover,  the  specific  heat  of  aqueous  vapor  is  very  high,  and  a  large  amount  of  the 
heat  generated  in  the  explosion  of  the  powder  would  consequently  be  absorbed  in  the 
conversion  of  the  water  into  vapor;  hence  it  is  impossible  that  the  expansion  of  the 
gases  should  be  equal  to  that  of  the  products  obtained  in  the  combustion  of  black 
charcoal  gunpowder. 

*  Other  forms  of  machinery  are  employed  in  different  parts  of  the  Continent  for  pul- 
verizing and  mixing  the  ingredients.  One  of  these  consists  of  a  drum  or  cylinder  of 
wood  or  leather,  strained  over  a  frame,  revolving  on  central  axes.  Projecting  ridges 
of  wood  are  fixed  on  the  internal  surface  of  the  drum,  at  a  short  distance  from  each 
other.  The  coarsely-crushed  ingredients  are  introduced  into  the  drum  through  a  flap- 
door,  together  with  a  number  of  small  balls  (of  bronze,  or  a  harder  alloy,  f  copper  to 
1  tin).  The  barrel  is  then  allowed  to  revolve  with  moderate  rapidity,  whereupon  the 
balls  are  raised  to  a  certain  height,  and  then  fall  back  from  ridge  to  ridge,  crushing 
the  material  with  which  they  meet.  This  is  termed  the  revolutionary  process,  having 
been  adopted  in  France  at  the  time  of  the  first  Revolution.  In  some  parts  of  the  Con- 
tinent, the  manufacture  of  powder  is  effected  by  stamping-mills,  which  consist  of  long 
rows  of  circular  mortars  of  iron  or  of  oak  (with  very  hard  wood  inserted  in  the  bot- 
toms) ;  long  pestles,  fitted  with  bronze  shoes  (weighing  about  60  pounds),  and  provided, 
at  the  centre  of  the  rod,  with  crosspieces,  are  lifted  to  a  certain  height  (about  1£  foot) 
by  the  projections  of  a  long  cog-wheel,  and  then  allowed  to  fall  upon  the  ingredients  in 
the  mortar.  The  pestle  is  lifted  about  sixty  times  in  a  minute  ;  the  mass  to  be  pulverized 
or  incorporated  is  moistened  with  water  from  time  to  time.  The  mortars  being  so  formed 
as  to  contract  gradually  from  the  centre  towards  the  opening,  the  mass,  as  it  is  forced 
up  the  sides  of  the  mortar  by  the  blows  of  the  pestle,  falls  back  again  to  the  bottom  ;  iu 
this  manner  the  mass  becomes  thoroughly  mixed ;  to  insure  this  result,  it  is,  however, 
necessary  to  loosen,  from  time  to  time,  the  hard  crust  that  will  always  form  at  the  bottom 
of  the  mortar. 


244  GUNPOWDER. 

cylinders  are  not  equidistant  from  the  vertical  axis;  they  do  not  consequently 
move  over  the  same  surface.1 

The  ingredients,  having  been  reduced  to  a  sufficiently  fine  state  of  division, 
are  weighed  out,  for  mixture,  in  the  following  invariable  proportions  : — 

Nitre     .     .    VY    .     .     31  Ibs.  8  oz. 

Charcoal    .     .  V  .  V      6."    4"    13  drms. 

Sulphur 4    "    3   "      3     " 


Together 42    "    0   "      0     " 

which  constitute  what  is  termed  a  charge,  or  the  quantity  of  material  placed  at 
one  time  upon  the  incorporating-mill.  These  quantities  are  then  introduced  into 
the  mixing-machine,  which  consists  of  a  wooden  box,  or  cylinder,  through  which 
passes  an  octagonal  shaft,  provided  with  a  number  of  fan-like  arms.  The  cylinder 
is  made  to  revolve  round  the  shaft,  which  turns  at  the  same  time  in  the  opposite 
direction.  From  five  to  ten  minutes  are  allowed  for  effecting  a  thorough  mixture 
of  the  ingredients  ;  the  powder  is  then  removed  from  the  cylinder  and  filled  into 
bags,  which  are  tied  firmly,  so  as  to  prevent  any  separation  of  the  ingredients 
from  each  other  in  their  transport  to  the  incorporating-nrills.3 

The  mixture  is  then  spread  upon  the  bed  of  the  incorporating-mill,  moistened 
with  distilled  water  to  such  an  extent  as  to  make  the  particles  cohere  firmly,3  and 
once  more  submitted  to  the  action  of  the  mill.  The  runners  are  not  allowed  to 
revolve  so  rapidly  as  in  the  first  instance,  when  the  ingredients  are  merely  ground, 
in  order  that  the  particles  may  be  uniformly  submitted  to  the  crushing  action 
and  pressure  of  the  rollers  for  a  longer  period.  Great  care  must  be  taken  that 
no  hard  or  gritty  particles  fall  upon  the  bed  of  the  mill,  and  the  mass  must  be 
retained  in  a  sufficiently  moist  state  throughout  the  incorporation,  which  lasts 
from  three  to  four  hours.  A  can  with  a  very  fine  rose  is  employed  for  moisten- 
ing the  powder ;  any  particles  that  are  pushed  by  the  rollers  beyond  their  track, 
are  carried  back  by  scrapers,  which  are  appropriately  fixed,  and  travel  round  with 
the  rollers.  Towards  the  close  of  the  operation,  the  latter  are  allowed  to  revolve 
only  very  slowly. 

The  mass  that  is  removed  from  these  mills  after  incorporation,  is  now  possessed 
of  all  the  chemical  properties  of  powder,  the  particles  having  become  most  uni- 
formly and  intimately  mixed.  It  soon  hardens,  forming  cakes  of  about  f  inch 
thick,  which  should  have  a  dark  grayish-black  appearance,  and  be  perfectly  homo- 
geneous, exhibiting  no  specks  whatever.  In  this  state  the  powder  is  called 
mill-cake. 

These  cakes,  before  they  are  thoroughly  dry,  are  reduced  to  coarse  powder,  in 
what  is  called  the  breaking-down  mill  (which  consists  of  two  sets  of  metal  rollers, 
furnished  with  teeth,  between  which  the  powder  passes);  this  is  then  placed  in 
layers  of  a  certain  thickness  between  copper  plates,  and  packed  in  very  stout 
boxes,  in  which  it  is  submitted  to  a  pressure  of  122  tons  on  the  square  foot,  by 
means  of  a  powerful  hydraulic  press.  When  the  powder  is  removed  from  be- 
tween the  plates,  it  presents  very  much  the  appearance  of  slate,  being  in  very 

1  Any  portions  of  the  ground  substance  adhering  to  the  rollers  is  removed,  as  they 
revolve,  by  scrapers  of  ^wood,  tipped  with  iron,  which  are  fixed  within  sufficiently  close 
proximity  to  the  surface  of  the  roller. 

a  If  a  mixture  of  this  description,  or  a  gunpowder  that  has  not  been  subjected  to 
sufficient  pressure,  be  but  loosely  packed,  the  comparative  densities  of  the  ingredients 
being  very  different,  they  will  gradually  separate  to  a  great  extent,  if  subject  to  any 
concussion  in  their  transport ;  the  light  charcoal-powder  will  collect  on  the  upper  sur- 
face, and  much  will  escape,  as  dust,  through  the  fissures  in  a  box,  or  between  the  inter- 
stices of  a  sack. 

3  The  quantity  of  water  required  for  this  purpose  varies  considerably  with  the  tempera- 
ture and  state  of  the  atmosphere. 


GUNPOWDER.  245 

dense  blackish  cakes,  about  £  inch  thick  (called  press-caJce).  By  subjecting  the 
powder  to  this  powerful  pressure,  several  important  results  are  attained.  The 
density  of  the  powder  is  very  greatly  increased,  and  consequently  a  certain  bulk 
of  the  pressed  powder  will  yield,  upon  combustion,  a  far  greater  volume  of  gas 
than  an  equal  bulk  of  powder  that  has  only  been  subjected  to  the  pressure  of  the 
incorporating-mill.  Moreover,  the  hardness  of  the  powder  is  naturally  increased 
in  a  similar  proportion,  whereby  it  is  better  enabled  to  withstand  the  action  of 
the  atmosphere,  and  is  also  far  less  liable  to  loss  from  dusting,  in  its  transport. 

Granulation  of  the  Powder. — By  this  process  the  powder  is  obtained  in  grains 
of  the  various  sizes  and  forms  required  for  fire-arms  of  different  descriptions,  or 
for  other  purposes  (e.  g.  in  blasting  operations),  the  fineness  of  the  powder 
determining  to  a  great  extent  the  rapidity  of  combustion,  which  requires  modifi- 
cation according  to  circumstances. 

A  very  ingenious  piece  of  machinery  is  employed  at  Waltham  Abbey  for  granu- 
lating the  powder,  and  separating  it  into  the  different  kinds,  known  as  large 
grain  (or  L.  G.^jine  grain  (or  F.  G.),  and  meal-powder,  or  dust.  It  does  not 
come  within  our  province  to  give  more  than  a  sketch  of  the  principle  of  this 
machine. 

A  continuous  supply  of  the  coarsely-crushed  press-cake  is  allowed  to  fall  upon 
a  pair  of  revolving  metal  rollers,  provided  with  large  teeth,  whereby  it  is  partly 
reduced  to  grains  of  different  sizes ;  the  powder,  as  it  passes  from  these  rollers,  is 
received  by  a  set  of  three  long,  sloping  screens,  or  sieves,  of  different  fineness, 
fitted  one  upon  the  other,  and  working  continually  backwards  and  forwards,  with 
a  trough,  running  their  whole  length  at  the  bottom.  The  powder  is  thus  sub- 
jected to  the  usual  sifting  motion ;  those  portions  that  are  retained  by  the  first 
sieve,  as  they  work  their  way  down  its  surface,  are  made  to  fall  between  a  second 
pair  of  rollers  with  finer  teeth,  the  powder  granulated  by  these  again  falls  upon 
the  upper  screen,  where  it  is  once  more  sifted ;  any  portions  that  may  still  be  too 
coarse  to  pass  through,  are  reduced  by  a  third,  still  lower,  set  of  rollers  with  very 
fine*  teeth.  The  powder,  on  passing  through  the  first  screen  falls  upon  the 
second,  where  the  large-grain  powder  is  retained,  being  separated  from  the  fine 
grains  and  dust  by  the  sifting  motion  to  which  it  is  subjected;  the  third  sieve 
retains  the  fine-grain  powder,  while  the  dust  or  meal-powder  falls  through  into 
the  trough  beneath.  Each  kind  of  powder,  as  it  travels  down  to  the  bottom  of 
the  screens,  is  collected  at  the  opening  in  boxes,  running  on  wheels  and  rails. 

Various  additional  contrivances  are  applied  to  this  piece  of  machinery,  to 
obviate  the  necessity  of  the  presence  of  workmen,  during  the  granulation  of  the 
powder,  in  case  of  an  accidental  explosion.1 

After  granulation,  the  powder  is  freed  from  dust  by  allowing  it  to  run  gradu- 
ally through  sloping  reels,  inclosed  in  boxes  and  covered  with  canvas,  or  with 
silk  of  about  fifty-six  meshes  to  the  inch,  according  to  the  size  of  the  grains 
introduced.  The  finest-grained  powder  is  afterwards  rounded  and  polished  by 
what  is  termed  the  glazing  process.  This  consists  in  subjecting  the  powder,  in  a 
sufficiently  moist  state,  to  a  rotary  motion  in  barrels  or  drums,  containing  arms 

1  On  the  Continent,  the  powder  is  chiefly  granulated  in  drum-sieves  of  different  fine- 
ness, fitting  one  in  the  other,  to  which  an  alternating  rotary  motion  is  imparted.  On  the 
upper  of  these  is  placed,  together  with  the  crushed  powder,  a  lenticular  disk  of  heavy 
wood  (sometimes  loaded  with  lead).  By  the  motion  of  the  drum,  this  disk  is  made  to 
travel  over  the  surface  of  the  upper  sieve,  crushing  the  particles  of  the  powder  with 
which  it  meets  until  they  are  all  sufficiently  fine  to  pass  through  the  first  sieve. 

The  so-called  Champy,  or  Swiss  globular  powder,  is  obtained  by  allowing  minute  drops 
of  distilled  water  to  fall  from  a  very  finely  perforated  tube  upon  meal-powder,  which  is 
made  to  revolve  in  a  drum,  such  ashas  been  already  described  as  used  sometimes  for  powder- 
ing and  mixing  the  ingredients.  Each  drop  of  water  thus  collects,  in  a  globular  form,  a  cer- 
tain quantity  of  the  powder  ;  the  grains  thus  formed  are  afterwards  separated  from  the 
dust  by  means  of  sieves. 


246  GUNPOWDER. 

similar  to  the  mixing-drums  already  described,  the  velocity  of  the  motion  being 
only  sufficient  to  allow  the  grains  to  roll  over  each  other  and  become  polished  by 
attrition.  Powder  thus  glazed  is  less  liable  to  dust  in  its  transport,  and  is  ren- 
dered more  impervious  to  the  action  of  atmospheric  moisture.  Very  coarse- 
grained powder  (blasting-powder)  is  sometimes  glazed  with  graphite. 

The  last  operation  which  the  powder  has  to  undergo,  is  that  of  desiccation.  It 
is  requisite  during  all  the  processes  enumerated  to  retain  the  powder  in  a  more 
or  less  moist  state ;  it  is,  however,  necessary  when  the  manufacture  is  completed 
to  expel  the  moisture.  For  this  purpose  the  powder  is  exposed  for  some  time 
to  a  temperature  of  134°  F.  in  a  chamber  heated  by  steam,  and  so  constructed 
that  there  shall  be  a  continual  change  of  atmosphere,  the  moist  air  escaping  as 
dry  air  enters. 

The  greatest  precautions  are  adopted  to  prevent  accidents  during  the  manu- 
facture of  powder,  or  at  any  rate  to  prevent  a  fire  in  one  part  of  the  factory 
extending  to  any  other  portion.  Each  process  is  conducted,  if  possible,  in 
detached  premises  at  some  distance  one  from  the  other,  and  in  some  cases  these 
are  flanked  by  high  buttresses  of  brick  or  stone,  of  great  thickness.  All  kinds  of 
grit  are  most  carefully  excluded  from  the  various  buildings,  the  floors  of  which 
are  frequently  covered  with  leather,  and  into  which  no  person  is  permitted  to 
enter  in  shoes  that  have  been  worn  out  of  doors.  Nevertheless,  terrible  accidents 
occur  at  times,  the  affinities  between  the  constituents  of  powder  being  balanced 
with  such  nicety  that  trifling  causes,  such  as  comparatively  slight  friction,  are 
sometimes  sufficient  to  impart  to  it  the  impulse  necessary  for  its  decomposition. 

Properties  of  Gunpowder. — Good  powder  should  exhibit  perfect  uniformity  of 
texture;  light  specks  or  glittering  points  indicate  an  incomplete  mixture.  The 
grains  should  be  sufficiently  hard  not  to  be  easily  crushed  between  the  fingers, 
and  not  to  soil  these  or  a  piece  of  paper  by  mere  contact.  Gunpowder  should 
burn  rapidly,  leaving  a  very  slight  residue.  If  inflamed  upon  white  paper,  it 
should  blacken  the  latter  but  slightly,  and  should  on  no  account  set  light  to  it. 
Powder  is  inflamed  by  any  burning  substance,  by  an  electric  spark,  or  recfhot 
metal,  or  by  violent  concussion.  It  does  not,  however,  ignite  if  exposed  to  a 
temperature  below  a  red  heat.  If  it  be  exposed  in  a  glass  vessel,  containing  an 
atmosphere  of  hydrogen  or  carbonic  acid,  to  a  gradually  increasing  temperature, 
the  sulphur  may  be  completely  separated,  subliming  upon  the  cool  portion  of  the 
vessel. 

It  has  been  proved  that  powder  may  be  inflamed  not  only  by  the  powerful 
concussion  of  iron  against  a  hard  substance,  but  by  the  concussion  of  compara- 
tively soft  bodies,  provided  it  be  sufficiently  powerful.  Experiment  has  shown 
that  powder  placed  upon  lead,  or  even  wood,  may  be  ignited  by  the  concussion 
of  a  leaden  bullet  fired  at  it. 

The  inflammability  of  powder  is  greatly  influenced  by  its  physical  nature,  as 
has  been  already  stated.  A  fine-grain  powder  will  burn  more  rapidly  than  large- 
grain  powder ;  the  greater  the  density  of  a  powder,  the  more  gradual  its  com- 
bustion. 

Angular  powder  will  burn  more  rapidly  than  round-grained  powder;  glazing 
also  decreases  the  inflammability  of  powder.  The  presence  of  moisture  naturally 
retards  the  inflammability  of  powder  considerably. 

Powder  in  which  the  theoretical  proportions  are  exact,  and  in  the  manufacture 
of  which  a  very  inflammable  charcoal  has  been  used,  the  ingredients  having  been 
mixed  without  the  application  of  very  great  pressure,  will  undergo,  when  ignited, 
an  almost  instantaneous  decomposition ;  such  a  powder  resembles  the  fulminates 
in  many  respects,  the  strain  which  it  exerts  upon  the  fire-arm  is  far  too  powerful, 
hence  it  is  not  so  generally  applicable  as  powder  which  undergoes  a  more  gra- 
dual decomposition. 

Gunpowder  always  attracts  moisture,  more  or  less,  since  charcoal,  however 


CHLORATE  OP  POTASSA.  247 

dense,  absorbs  moisture  from  the  air,  though  of  course  the  hygroscopic  property 
of  powder  is  considerably  increased  by  the  use  of  porous  charcoal  (such  as  char- 
bon-roux)  in  its  manufacture,  or  by  the  presence  of  any  considerable  quantity  of 
powder-dust.  Powder,  manufactured  with  perfectly  pure  nitre,  is  found,  if  pre- 
served in  dry  stores,  to  absorb  about  0.5  per  cent,  of  moisture;  the  amount 
naturally  increases  considerably  if  the  powder  is  kept  in  a  damp  situation.  Fine 
grain  powder  is  generally  found  to  absorb  moisture  more  rapidly  than  the  large- 
grain  powder. 

The  amount  of  ash  left  upon  the  ignition  of  powder  varies  considerably  with 
the  purity  of  the  ingredients,  with  the  proportions  employed,  and  particularly 
with  the  nature  of  the  charcoal  used.  Its  gradual  accumulation  in  a  fire-arm  is 
a  source  of  great  inconvenience,  since  it  soon  renders  it  foul  and  difficult  to 
charge,  thus  limiting  the  number  of  rounds  that  can  be  fired  in  rapid  succession, 
i.  e.  without  first  cleaning  out  the  fire-arm.  This  fouling,  as  it  is  termed,  is 
avoided  to  some  extent  by  the  use  of  a  small  quantity  of  some  fatty  substance, 
which  lubricates  the  barrel,  and,  by  preventing  the  adhesion  of  the  ash,  pro- 
motes its  expulsion  by  the  gases  as  they  make  their  escape. 

For  the  analysis  of  gunpowder,  see  Quantitative  Analysis,  special  methods. 

§  150.  NITRITE  OF  POTASSA  (KO.N03)  is  sometimes  employed  for  the  prepa- 
ration of  nitrogen;  it  may  be  obtained  sufficiently  pure  for  this  purpose  by 
maintaining  nitrate  of  potassa  at  a  red  heat  in  an  earthen  crucible,  until,  a  small 
portion  being  removed  and  dissolved  in  water,  the  solution  has  an  alkaiine  reac- 
tion, and  gives  a  brownish-white  precipitate  (a  mixture  of  nitrite  of  silver  and 
oxide  of  silver),  with  nitrate  of  silver,  showing  that  a  little  potassa  has  been  set 
free.  The  pure  salt  may  be  prepared  by  decomposing,  with  chloride  of  potas- 
sium, the  nitrite  of  silver  previously  purified  by  recrystallization. 

It  is  a  deliquescent  salt,  which  crystallizes  with  considerable  difficulty. 

CHLORATE  or  POTASSA,  HYPEROXYMURIATE  OF  POTASSA,  KO.C105 . 

§  151.  Preparation. — The  simplest  method  of  preparing  this  sMt  consists  in 
transmitting,  through  a  wide  tube,  a  current  of  washed  chlorine  into  a  concen- 
trated solution  of  potassa  or  its  carbonate;  the  solution,  when  saturated  with 
chlorine,  is  heated  for  some  time,  to  insure  the  complete  conversion  of  any  hypo- 
chlorate  into  chlorate,  and  allowed  to  cool,  when  chlorate  of  potassa  crystallizes 
out,  and  may  be  purified  by  recrystallization.  The  action  of  the  chlorine  upon 
the  potassa,  in  this  process,  is  thus  represented : — 

6KO+C]8=5KG1+KO.C105. 

A  more  economical  method  consists  in  passing  chlorine  over  a  somewhat  damp 
mixture  of  7.6  parts  of  carbonate  or  sulphate  of  potassa  and  16.8  of  hydrate  of 
lime;  the  mass  is  afterwards  treated  with  boiling  water,  and  the  chlorate  of 
potassa  separated  from  the  chloride  of  calcium  by  crystallization.1 

Properties. — Chlorate  of  potassa  crystallizes  in  colorless,  thin,  tabular  crystals, 
and,  more  rarely,  in  needles,  which  contain  no  water  of  crystallization,  and  are 

1  Calvert  has  proposed  an  improved  process  for  the  manufacture  of  chlorate  of  potassa, 
which  consists  in  employing  a  solution  of  caustic  potassa  of  spec.  grav.  1.11. — 3.1  parts 
of  this  solution  are  mixed  with  1  part  of  hydrate  of  lime,  previously  slaked ;  the  mixture 
is  slightly  heated,  and  rapidly  saturated  with  chlorine.  The  solution  is  filtered,  to  sepa- 
rate any  slight  insoluble  residue,  and  evaporated  to  crystallization. 

The  great  advantage  consists  in  the  circumstance  that  the  chlorine  is  oxidized  at  the 
expense  of  the  lime,  the  calcium  of  which  is  converted  into  chloride,  so  that  nearly  the 
whole  of  the  potassa  is  converted  into  chlorate: — 

KO+5CaO+Clc=KO.C106+5CaCl. 


248  CHLORATE  OF  POTASSA. 

unaltered  by  exposure  to  air.  When  heated,  they  decrepitate,  fuse  easily,  and 
at  a  temperature  below  redness  evolve  oxygen  (the  details  respecting  this  decom- 
position will  be  found  under  the  Preparation  of  Oxygen,  §  69). 

It  has  also  been  observed,  in  the  place  referred  to,  that  if  the  salt  be  mixed 
with  certain  substances,  especially  with  binoxide  of  manganese,  the  decomposi- 
tion is  promoted  in  a  very  remarkable  manner.  The  oxygen  evolved  from 
chlorate  of  potassa  has  generally  an  odor  of  chlorine. 

Chlorate  of  potassa  is  soluble  in  about  17  parts  of  water  at  the  ordinary  tem- 
perature (with  production  of  cold);  at  the  boiling  point,  it  dissolves  in  1.5  parts 
of  water,  so  that  the  greater  part  is  deposited  on  cooling ;  it  is  sparingly  soluble 
in  alcohol. 

The  chlorate,  like  the  nitrate  of  potassa,  possesses  oxidizing  properties,  but 
much  more  powerful  than  those  of  the  latter  salt;  if  sprinkled  upon  redhot  coals, 
it  gives  rise  to  vivid  deflagration.  If  a  mixture  of  chlorate  of  potassa  with  sul- 
phur be  triturated,  or  struck  with  a  hammer,  explosion  ensues;  various  metals, 
metallic  sulphides,  and  organic  substances  also  form  explosive  mixtures  with 
chlorate  of  potassa;  a  mixture  of  chlorate  of  potassa  and  sugar  is  inflamed  when 
moistened  with  oil  of  vitriol,  and  this  principle  was  formerly  taken  advantage  of 
in  the  preparation  of  the  Promethean  matches. 

When  acted  upon  with  cone,  sulphuric  acid,  an  experiment  which  requires 
great  caution,  chlorate  of  potassa  is  decomposed  with  violence,  yielding  perchlo- 
rate  of  potassa,  peroxide  of  chlorine,  and  sulphate  of  potassa;  thus: — 
3(?:0.0105)+2(HO.S03)=2(KO.S03)  +  2HO-fKO.C107+2C104. 

Nitric  acid  converts  it  into  a  mixture  of  nitrate  and  perchlorate  of  potassa, 
with  evolution  of  chlorine  and  oxygen  : — 

4(KO.C105)+3(HO.N05)=3(KO.N05)+KO.C107+C13+013. 

When  heated  with  hydrochloric  acid,  a  decomposition  takes  place  which  is  not 
perfectly  understood,  and  which  results  in  the  production  of  a  deep  yellow  pun- 
gent gas,  which  was  named  by  Davy  euchlorine  (see  §  94). 

A  mixture  of  chlorate  of  potassa  with  hydrochloric  acid  or  nitric  acid  is  fre- 
quently empbyed  as  an  oxidizing  solvent  in  analytical  operations. 

Ifses. — Chlorate  of  potassa  is  extensively  employed  for  the  manufacture  of 
lucifer  matches.  For  this  purpose  it  is  generally  mixed  with  nitrate  of  potassa, 
phosphorus,  minium,  and  gum.1  * 

The  intense  power  exhibited  by  chlorate  of  potassa  as  an  oxidizing  agent,  in 
which  respect  it  far  surpasses  the  nitrate  of  potassa,  has  induced  many  experi- 
menters, from  a  comparatively  early  period,  to  attempt  the  production  of  a  com- 
pound containing  chlorate  of  potassa  instead  of  nitre,  which  would  possess  all  the 
properties  of  gunpowder,  while  it  was  far  more  powerful,  effecting  results  which 
could  only  be  obtained  by  the  use  of  a  much  larger  comparative  amount  of  pow- 
der. All  experiments  hitherto  made  have  shown,  however,  that  explosive  mix- 
tures of  chlorate  of  potassa  with  easily  oxidizable  substances  (e.  g.  sulphur,  sul- 
phide of  antimony,  &c.),  resemble,  in  the  effect  they  produce,  the  fulminates 
much  more  than  they  do  gunpowder,  their  decomposition  being  too  instantaneous 
to  admit  of  their  use  in  fire-arms  (see  §  149) ;  the  strain  exerted  by  the  explosion 
of  the  least  powerful  of  such  mixtures  upon  the  barrel  of  a  gun  has  been  found 
too  great  to  be  withstood  by  the  metal  for  any  lengthened  period.  Several  mix- 
tures have  been  proposed  (e.  g.  the  so-called  white  gunpowder •,  consisting  of  chlo- 
rate of  potassa,  sulphur,  and  ferrocyanide  of  potassium),  particularly  for  blasting 
purposes,  where  they  might  meet  with  more  successful  application,  were  it  not 
for  the  very  great  risk  attending  their  manufacture  on  a  large  scale,  in  conse- 

1  In  matches  which  ignite  without  explosion,  the  chlorate  of  potassa  is  replaced  by  a 
mixture  of  nitrate  of  potassa  and  binoxide  of  lead. 


SULPHATE   OF  POTASSA.  249 

quence  of  the  slight  impulse  required  to  induce  the  violent  action  of  chlorate  of 
potassa. 

As  detonating  compounds,  however,  where  an  instantaneous  action  is  required 
(e.  y.  in  firing  a  charge  of  powder),  these  mixtures  are  very  useful,  and  receive 
extensive  application,  being  far  cheaper  than  the  fulminates. 

Thus,  the  composition  with  which  the  percussion-tubes  for  cannon  are  filled, 
consists  of  2  parts  of  chlorate  of  potassa,  2  parts  of  sulphide  of  antimony,  and  1 
of  powdered  glass  (to  increase  its  susceptibility).  Mixtures  of  this  description 
must  be  made  with  great  care.  The  ingredients  are  first  powdered  separately, 
and  then  mixed  with  a  feather,  or  some  comparatively  soft  body,  in  a  smooth 
vessel.  Chlorate  of  potassa  is  also  occasionally  used  in  medicine. 

§  152.  PERCHLORATE  OF  POTASSA,  KO.C107.  This  salt  exists  in  the  residue 
left  on  gently  heating  chlorate  of  potassa  till  the  evolution  of  oxygen  slackens  ; 
if  this  residue  be  boiled  with  water,  the  solution,  on  cooling,  deposits  crystals  of 
the  perchlorate. 

Perchlorate  of  potassa  forms  anhydrous,  colorless,  prismatic  crystals,  which  are 
decomposed  by  heat  into  chloride  of  potassium  and  oxygen.  They  are  sparingly 
soluble  in  cold,  but  more  so  in  hot  water ;  perchloric  acid  is  hence  occasionally 
employed  as  a  test  for  potassa.  Perchlorate  of  potassa  is  more  stable  than  the 
chlorate ;  it  deflagrates  with  redhot  charcoal,  but  not  so  powerfully  as  the  latter 
salt.  It  merely  evolves  perchloric  acid  when  heated  with  sulphuric  acid,  and 
does  not  turn  yellow  when  treated  with  concentrated  hydrochloric  acid. 

§  153.  HYPOCHLORITE  OF  POTASSA  (KO.C10),  in  the  pure  state,  is  known 
only  in  solution,  prepared  by  mixing  aqueous  solutions  of  hypochlorous  acid  and 
potassa  at  a  low  temperature. 

The  solution  known  as  Eau  deJavelley  contains  equivalent  proportions  of  chlo- 
ride of  potassium  and  hypochlorite  of  potassa,  and  is  prepared  by  passing  chlorine 
into  a  very  cold,  dilute  solution  of  potassa,  or  its  carbonate,  so  as  to  leave  the 
alkali  slightly  in  excess ;  or,  more  conveniently,  by  decomposing  the  solution  of 
the  corresponding  lime- com  pound  with  carbonate  of  potassa.  The  solution  evolves 
chlorine  when  treated  with  acids,  and  possesses  powerful  bleaching  properties; 
it  is  sometimes  used  as  a  bleaching  agent  and  disinfectant. 

If  a  deficiency  of  chlorine  be  passed  over  moist  carbonate  of  potassa,  a  mixture 
of  the  above  compound  with  bicarbonate  of  potassa  is  obtained. 

§  154.  BROMATE  OF  POTASSA  (KO.Br05)  is  prepared  by  a  process  similar  to 
that-. for  the  chlorate,  which  it  resembles  in  most  of  its  properties. 

IODATE  OF  POTASSA  (KO.I05)  is  prepared  by  a  somewhat  similar  process; 
when  heated,  this  salt  evolves  oxygen,  and  vapors  of  iodine,  leaving  a  residue 
containing  potassa,  and  iodide  of  potassium. 

There  are  two  acid  iodates  of  potassa,  the  formula  of  which  are,  respectively, 
K0.2I05,  and  K0.3I05. 

The  former  of  these  combines  with  chloride  of  potassium,  and  bisulphate  of 
potassa. 

PERIODATE  OF  POTASSA  (KO.I07)  resembles  the  perchlorate  in  properties, 
and  may  be  prepared  by  passing  chlorine  through  a  solution  of  iodate  of  potassa, 
mixed  with  caustic  potassa. 

SULPHATE  OF  POTASSA,  KO.S03. 

§  155.  This  salt  is  prepared  from  the  residue  (of  bisulphate)  left  after  the  pre- 
paration of  nitric  acid  ;  this  residue  is  dissolved  in  hot  water,  and  the  solution 
neutralized  with  carbonate  of  potassa;  the  sulphate  crystallizes  out  on  cooling. 
It  forms  hard,  colorless  prisms,  free  from  water.  When  heated,  these  crystals 
decrepitate,  and  fuse  at  a  red  heat,  but  are  not  decomposed.  Sulphate  of  potassa 
is  sparingly  soluble  in  water,  and  insoluble  in  alcohol.  Its  solubility  in  water 
increases  steadily  as  the  temperature  rises. 


250  CARBONATE   OP  POTASSA. 

BISULPHATE  or  POTASSA  (KO.S03,HO.S03)  constitutes  the  residue  obtained 
in  the  preparation  of  nitric  acid  from  equal  weights  of  nitrate  of  potassa  and  oil 
of  vitriol.  This  salt  crystallizes  in  rhombic  prisms,  which  deliquesce  in  air,  and 
are  very  soluble  in  water,  yielding  a  solution  which  has  a  very  acid  taste  and 
reaction. 

This  salt  is  sometimes  employed  as  a  flux  in  mineral  analysis,  and  is  also 
useful  for  cleaning  vessels  of  platinum.  It  fuses  at  a  low  temperature,  and  if 
strongly  heated,  is  converted  into  the  neutral  sulphate.  The  equivalent  of 
hydrated  acid  present  in  this  salt,  acts  very  much  as  if  it  existed  in  the  free 
state. 

Other  compounds  of  sulphate  of  potassa  and  sulphate  of  water  are  said 
to  exist.1 

The  phosphates  of  potassa  are  not  possessed  of  any  practical  interest. 

CARBONATE  or  POTASSA,  SALT  or  TARTAR,  POTASHES,  PEARLASHES. 
KO.COa.     Eq.  69. 

§  156.  Carbonate  of  potassa  exists  in  the  residue  left  on  incinerating  various 
inland  plants ;  these  contain  potassa  in  combination  with  various  organic  acids, 
forming  salts,  the  acid  of  which  is  decomposed  at  a  high  temperature,  leaving 
the  potassa  in  the  form  of  carbonate. 

Preparation. — From  the  ashes  of  land-plants,  the  carbonate  of  potassa  is  ex- 
tracted by  lixiviation  with  water  (see  Nitre) ;  the  lye  is  evaporated  to  dryness, 
and  the  residue  calcined  in  a  reverberatory-furnace  till  the  organic  matter  has 
burnt  off,  when  a  mass  is  left,  which  is  known  as  crude  potashes ;  it  contains 
about  60  per  cent,  of  alkaline  carbonate,  mixed  with  various  mechanical  and 
insoluble  impurities,  together  with  much  chloride  of  potassium,  sulphate  and 
silicate  of  potassa,  and  has  also,  generally,  a  greenish-blue  color,  due  to  manga- 
nate  of  potassa.  In  order  to  purify  this  substance,  it  is  exhausted  with  a  little 
water,  filtered,  evaporated,  the  sulphate  of  potassa  allowed  to  crystallize  out,  and 
the  liquid  evaporated  to  the  crystallizing  point  of  the  carbonate;  the  product 
thus  obtained  is  that  known  as  pearlash* 

Salt  of  tartar  is  a  purer  kind  of  carbonate  of  potassa,  obtained  by  calcining 
the  bitartrate. 

The  purest  carbonate  of  potassa,  for  chemical  purposes,  is  obtained  by  igniting 
the  binoxalate  of  potassa,  which  is  prepared  by  adding  an  excess  of  oxalic  -acid 
to  hydrate  of  potassa^  and  purifying  by  recrystallization. 

Properties. — Carbonate  of  potassa  may  be  crystallized,  on  cooling,  from  a  very 
concentrated  hot  solution,  in  indistinct  rhombic  octohedra,  of  the  formula 
KO.C02+2Aq.  When  heated,  these  lose  their  water,  and  the  dry  carbonate 
fuses,  unchanged,  at  a  bright  red  heat.  This  salt  deliquesces  when  exposed  to 
air,  and  dissolves  in  less  than  its  own  weight  of  water;  the  solution  is  powerfully 
alkaline  and  corrosive.  It  is  insoluble  in  alcohol. 

Uses. — Carbonate  of  potassa  is  very  largely  used  in  the  manufacture  of  soap 
and  glass;  it  is  also  employed  as  a  detergent,  and  as  the  source  of  most  of  the 
salts  of  potassa.  In  the  rectification  of  spirit  of  wine,  fused  carbonate  of  potassa 
is  sometimes  used  to  abstract  the  water.  The  chemist  employs  it  in  mineral 
analysis,  and  it  is  frequently  administered  medicinally. 

Since  carbonate  of  potassa  is  so  important  an  article  of  commerce,  it  is  neces- 

1  It  has  been  lately  found  that  sulphate  of  potassa  is  capable  of  forming  definite  com- 
pounds with  some  other  hydrated  acids,  especially  with  nitric  and  phosphoric  acids. 

2  The  carbonates  of  potassa  and  soda  may  be  readily  freed  from  silica  by  evaporating 
their  solutions  to  dryness,  with  addition  of  carbonate  of  ammonia ;  on  redissolving  the 
residue  in  water,  the  silica  is  left.     This  fact  is  of  importance  for  the  preparation  of  the 
pure  hydrated  alkalies. 


CHLORIDE  OP  POTASSIUM.  251 

sary  to  be  able  to  ascertain  the  real  value  of  any  particular  specimen,  which,  of 
course,  depends  upon  the  amount  of  pure  carbonate  of  potassa  which  it  contains. 
The  process  by  which  this  is  effected  is  termed  alkalimetry  (see  Special  Methods 
of  Analysis.) 

BICARBONATE  OF  POTASSA  (KO.COa,HO.C02)  is  prepared  by  passing  carbonic 
acid  through  a  cold  saturated  solution  of  carbonate  of  potassa,  when  the  less 
soluble  bicarbonate  is  deposited ;  or  by  passing  carbonic  acid  over  the  moistened 
carbonate. 

Properties. — Bicarbonate  of  potassa  crystallizes  from  a  warm  solution  in  color- 
less, rhomboidal  prisms,  of  the  formula  KO.C03,HO.COa;  when  heated,  they 
lose  water  and  carbonic  acid,  leaving  carbonate  of  potassa.  The  bicarbonate  re- 
quires 4  parts  of  cold  water  for  solution,  and  nearly  its  own  weight  of  hot  water ; 
it  is  insoluble  in  alcohol.  Its  aqueous  solution  is  not  nearly  so  alkaline  as  that 
of  carbonate  of  potassa,  into  which  it  is  gradually  converted  when  boiled. 

Bicarbonate  of  potassa  is  occasionally  used  in  medicine,  and  sometimes  as  a 
source  of  pure  carbonate  of  potassa. 

SILICATES  or  POTASSA. 

§  157.  Potassa  forms  several  combinations  with  silicic  acid,  which  may  be 
obtained  by  fusing  the  alkali  or  its  carbonate  with  different  proportions  of  silica. 
When  these  compounds  contain  a  large  excess  of  silica,  they  are  insoluble  in 
water ;  but  if  the  alkali  be  in  large  proportion,  the  combination  is  soluble.  The 
former  is  the  case  with  those  silicates  which  form  the  basis  of  the  ordinary 
potash-glass,  whilst  compounds  of  the  latter  order  constitute  the  soluble  glasses 
which  are  used  as  varnishes  to  protect  wood  from  decay  and  fire  (see  §  138). 

An  aqueous  solution  of  this  description,  prepared  from  a  fused  mixture  of 
1  part  of  quartz-sand  with  4  parts  of  carbonate  *of  potassa,  is  sometimes  also 
employed  as  a  reagent. 

Silicate  of  potassa  exhibits  a  remarkable  tendency  to  form  double  silicates. 

PEROXIDE  OF  POTASSIUM,  K03. 

§  158.  When  potassium  is  heated  in  a  current  of  dry  oxygen,  a  yellow  sub- 
stance is  produced,  which  is  the  peroxide.  This  compound  is  also  formed  when 
potassa  is  heated  in  oxygen,  and  is  left,  in  an  impure  state,  as  the  ultimate  pro- 
duct of  the  action  of  heat  upon  nitrate  of  potassa.  When  treated  with  water, 
this  substance  is  decomposed  with  evolution  of  heat ;  oxygen  is  disengaged  with 
effervescence,  and  hydrate  of  potassa  is  found  in  solution.  When  peroxide  of 
potassium  is  heated  with  organic  matter,  detonation  ensues.  It  is  deoxidized 
by  sulphurous  and  phosphorous  acids,  and  by  ammonia. 

CHLORIDE  OF  POTASSIUM,  KC1. 

§  159.  This  salt  occurs  in  sea-water,  and  in  the  water  of  many  mineral  springs  j 
it  is  formed  when  potassium  is  introduced  into  chlorine,  the  metal  taking  fire ;  it 
is  also  produced  when  chlorine,  or  hydrochloric  acid,  acts  upon  potassa  or  its 
carbonate,  the  chlorine  giving  rise,  at  the  same  time,  either  to  hypochlorite  or 
chlorate  of  potassa,  and  the  hydrochloric  acid  only  to  water.  Potassium  also 
decomposes  hydrochloric  acid,  combining  with  the  chlorine,  and  liberating 
hydrogen.  Chloride  of  potassium  is  obtained  as  a  by-product  in  various  pro- 
cesses, particularly  in  the  manufacture  of  soap  and  glass,  and  in  the  refining  of 
nitre. 

Properties. — Chloride  of  potassium  crystallizes  in  white  cubes,  which  are  an- 
hydrous and  unalterable  in  air ;  when  heated,  they  decrepitate.  This  salt  fuses 
at  a  red  heat,  and.  is  volatilized  at  a  higher  temperature.  It  dissolves  in  about 


252  IODIDE   OP  POTASSIUM. 

3  parts  of  water,  producing  considerable  cold  j1  it  is  more  soluble  in  hot  water, 
the  solubility  increasing  uniformly  with  the  temperature,  and  almost  insoluble  in 
alcohol.  Chloride  of  potassium  is  capable  of  combining  with  anhydrous  sulphuric 
acid,  forming  a  compound  of  the  formula  KC1.2S03.  It  also  unites  with  ter- 
chloride  of  iodine.  Chloride  of  potassium  is  sometimes  used  to  convert  into 
nitrate  of  potassa  the  nitrate  of  lime  obtained  in  artificial  nitrification  (§  145)  ; 
it  is  also  occasionally  employed  as  the  source  of  potassa  in  alum. 

BROMIDE  OF  POTASSIUM,  KBr. 

This  salt  is  formed  under  the  same  conditions  as  the  chloride  ;  it  is  usually 
prepared  by  dissolving  a  slight  excess  of  bromine  in  potassa,  separating  the  bro- 
mate  of  potassa  by  crystallization,  evaporating  the  mother-liquid,  and  decomposing 
any  bromate  of  potassa  by  igniting  the  residue,  which  may  then  be  dissolved  in 
water,  and  crystallized.  The  bromide  crystallizes  in  white  cubes,  which  are  an- 
hydrous, and  behave  like  the  chloride  when  heated.  It  is  readily  soluble  in 
water,  producing  cold,  and  nearly  insoluble  in  alcohol.  A  solution  of  bromide 
of  potassium  is  capable  of  dissolving  considerable  quantities  of  bromine. 

Bromide  of  potassium  is  used  in  photography. 

IODIDE  OF  POTASSIUM,  HYDRIODATE  OF  POTASSA,  KI. 

Preparation. — The  iodide  of  potassium  is  produced  under  similar  conditions 
to  those  which  yield  the  bromide,  and  may  be  prepared  by  the  same  process, 
substituting  iodine  for  bromine.  The  usual  method  of  preparing  iodide  of  potas- 
sium, however,  consists  in  digesting  2  parts  of  iodine  and  1  part  of  iron  filings 
in  10  parts  of  water,  till  they  have  combined  to  form  a  solution  of  a  pale  green 
color ;  the  solution  of  iodide  of  iron  thus  obtained  is  decomposed  with  exactly 
the  requisite  quantity  of  solution  of  carbonate  of  potassa  : — 

FeI+KO.C02=KI-fFeO.C08. 

The  solution  is  filtered  from  the  precipitated  carbonate  of  iron,  and  evaporated  to 
the  crystallizing  point. 

Properties. — Iodide  of  potassium  crystallizes  in  anhydrous  cubes,  sometimes 
opaque,  but  more  generally  transparent,  which  decrepitate  when  heated,  fuse 
easily,  and  volatilize  at  a  moderate  heat.  After  fusion,  it  has  an  alkaline  reac- 
tipn.  The  pure  salt  deliquesces  slightly,  and  dissolves  very  readily  in  less  than 
its  own  weight  of  water,  with  production  of  cold;  the  solution  has  a  very  slight 
alkaline  reaction;  but  if,  as  is  often  the  case,  the  salt  be  adulterated  with  carbo- 
nate of  potassa,  its  solution  will  be  strongly  alkaline,  and  the  solid  iodide  will 
deliquesce  rapidly  in  air.  Iodide  of  potassium  is  dissolved  by  alcohol.  The 
aqueous  solution  of  the  salt  is  capable  of  dissolving  a  large  quantity  of  iodine, 
which  gives  it  a  deep  brown  color.  This  property  is  turned  to  advantage  in  the 
compound  solution  of  iodine,  which  is  used  in  medicine.  Iodide  of  potassium  is 
an  important  medicinal  agent,  especially  in  scrofulous  diseases.  It  is  also  used 
in  photography. 

The  iodide  .of  potassium  of  commerce  often  contains,  in  addition  to  carbonate 
of  potassa,  caustic  potassa,  iodate  of  potassa,  bromide  and  chloride  of  potassium.2 

In  order  to  ascertain  the  degree  of  purity  of  any  specimen  of  iodide  of  potas- 
sium, we  may  employ  a  solution  of  chloride  of  mercury ;  1  equivalent  of  this  salt 

1  This  depression  of  temperature,  being  much  greater  than  that  caused  by  chloride  of 
sodium,  has  been  applied  by  Gay-Lussac  to  the  determination  of  the  amount  of  the  former 
in  mixtures  of  the  two  salts. 

2  The  iodate  of  potassa  may  be   detected  by  adding  solution   of  sulphurous   acid, 
which  will   liberate   a  quantity  of  iodine,  imparting   a   brown   color   to   the   solution. 
The  other  impurities  in  iodide  of  potassium  may  be  detected  by  the  ordinary  methods 
of  analysis. 


SULPHIDE   OF   POTASSIUM.  253 

completely  precipitates  1  equivalent  of  iodide  of  potassium,  in  the  form  of  the 
bright  red  iodide  of  mercury ;  thus  : — 

HgCl+KI=HgI-f-KCl; 

another  equivalent  of  iodide  of  potassium  redissolves  this  precipitate,  so  that  if 
1  equivalent  of  chloride  of  mercury  be  added  to  2  equivalents  of  iodide  of  potas- 
sium, no  precipitate  is  produced.  In  order  to  apply  this  principle,  1  equivalent 
(135.5  parts)  of  chloride  of  mercury  (HgCl,  corrosive  sublimate),  and  2  equiva- 
lents (166.1  parts)  of  the  iodide  of  potassium  to  be  tested,  are  dissolved  in  two 
equal  quantities  of  water.  The  solution  of  chloride  of  mercury  is  poured  from 
a  burette  into  that  of  iodide  of  potassium,  constantly  stirring,  till  a  permanent 
precipitate  begins  to  appear;  when  this  is  the  case,  of  course  a  little  more  than 
1  equivalent  of  chloride  of  mercury  must  have  been  added  for  every  2  equivalents 
of  iodide  of  potassium  present,  so  that  if  the  salt  tested  were  absolutely  pure,  the 
whole  of  the  mercury-solution  should  have  been  added,  whereas  an  impure  speci- 
men will  require  only  one-half,  two-thirds,  &c.,  of  the  solution,  according  to  the 
amount  of  impurity  present.  * 

FLUORIDE  OP  POTASSIUM,  KF. 

This  salt  is  formed  when  hydrofluoric  acid  is  decomposed  by  potassium,  hydro- 
gen being  evolved;  it  is  best  prepared  by  supersaturating  potassa,  or  carbonate 
of  potassa,  with  hydrofluoric  acid,  and  evaporating  in  a  platinum  dish.  It  crys- 
tallizes in  anhydrous  cubes,  which  deliquesce  in  air,  and  dissolve  readily  in 
water.  The  solution  has  an  alkaline  reaction,  and  acts  upon  glass. 

Hydrated  crystals  of  fluoride  of  potassium  may  be  produced  at  low  tempe- 
ratures.3 


POTASSIUM  AND  SULPHUR. 

§  160.  Potassium  combines  with  sulphur,  when  gently  heated  with  it,  with 
vivid  combustion,  producing  several  sulphides  of  potassium. 

SULPHIDE  OF  POTASSIUM,  KS. 

This  sulphide  is  formed  when  hydrogen  is  passed  over  sulphate  of  potassa  at  a 
red  heat,  and  also  when  sulphur  is  fused  with  excess  of  hydrate  of  potassa ; 
thus : — 

3(KO.HO)+S4=2KS+KO.S303+3HO. 

Preparation. — It  may  be  prepared  by  heating  to  bright  redness,  in  an  earthen 
crucible,  an  intimate  mixture  of  three  parts  of  sulphate  of  potassa  and  1  part  of 
charcoal : — 

KO.S03  +  C4=KS+4CO. 

The  sulphide  is  thus  obtained  as  a  light  red  mass,  containing  always  an  admix- 
ture of  a  higher  sulphide. 

1  A  new  method  recently  proposed  by  Penny  (Chem.  Gaz.  October,  1852),  consists  in 
ascertaining  the  amount  of  a  solution  containing  a  known  weight  of  the  iodide,  which  is 
required  to  decompose  a  given  quantity  of  bichromate  of  potassa  dissolved  in  water  acidu- 
lated with  hydrochloric  acid.     The  point  at  which  the  chromic  acid  is  completely  reduced 
is  indicated  by  dipping  a  glass  rod  into  the  solution,  and  touching  a  drop  of  a  solution  of 
protosulphate  of  iron  and  sulphocyanide  of  potassium  placed  upon  a  white  plate ;  when  a 
red  color  is  no  longer  produced,  the  decomposition  is  complete.     10  grs.  of  K0.2Cr03  cor- 
respond to  33.3  grs.  of  KL 

2  A  hydroftuate  of  fluoride  of  potassium,  KF.HF,  has  been  obtained. 


254  POTASSIUM  AND   SULPHUR. 

If  lampblack  be  substituted  for  charcoal  in  this  process,  the  resulting  sulphide 
of  potassium  is  pyrophoric.1 

It  may  be  obtained  in  a  pure  state  by  saturating  a  solution  of  potassa  with 
hydrosulphuric  acid,  and  afterwards  adding  a  volume  of  the  same  solution  of 
potassa,  equal  to  that  originally  employed  ;  the  first  operation  gives  rise  to  hydro- 
sulphate  of  sulphide  of  potassium,  KS.HS,  which  is  converted,  by  addition  of 
potassa,  into  sulphide  of  potassium.  The  solution  may  be  evaporated  to  dryness 
in  a  retort,  when  the  sulphide  of  potassium  remains  as  a  white  crystalline  mass. 

Properties. — Sulphide  of  potassium,  when  heated  in  air,  absorbs  oxygen,  and 
becomes  covered  with  a  coating  of  sulphate  of  potassa.  It  is  volatile  at  a  high 
temperature.  This  sulphide  deliquesces  in  air,  and  dissolves  rapidly  in  water 
with  rise  of  temperature,  giving  a  colorless  solution,  which  possesses  an  alkaline 
reaction  and  a  bitter  taste;  it  is  also  soluble  in  alcohol.  When  exposed  to  air, 
solution  of  sulphide  of  potassium  absorbs  oxygen,  and  becomes  gradually  con- 
verted into  a  mixture  of  potassa  with  a  higher  sulphide,  which  imparts  a  yellow 
color  to  the  solution.3  When  a  pure  solution  of  sulphide  of  potassium  is  mixed 
with  dilute  hydrochloric  acid,  hydrosulphuric  acid  is  evolved,  and  the  solution 
remains  clear : — 

KS+HC1=KC1+HS; 

but  if  a  higher  sulphide  be  present,  a  deposition  of  sulphur  will  take  place, 
rendering  the  solution  milky ;  thus  : — 

KS,+HC1=KC1+HS+S. 

Sulphide  of  potassium  is  a  powerful  sulphur-base  (see  p.  155);  it  combines  with 
those  metallic  sulphides  which  play  the  part  of  acids,  such  as  those  of  arsenic 
and  antimony,  to  form  sulphur-salts;  advantage  is  taken  of  this  property  in 
analysis,  where  sulphide  of  potassium  is  sometimes  used  to  dissolve  the  sulphur- 
acids,  and  thus  to  separate  them  from  other  metallic  sulphides. 

When  a  solution  of  potassa,  or  of  sulphide  of  potassium,  is  saturated  with 
hydrosulphuric  acid,  the  compound  KS.HS,  hydrosulphate  of  sulphide  of  potas- 
sium, is  produced,  and  if  the  solution  be  evaporated  to  a  syrup  in  an  atmosphere 
of  sulphuretted  hydrogen,  and  allowed  to  cool,  the  new  compound  may  be  ob- 
tained in  colorless  prisms,  which  are  exceedingly  deliquescent  and  soluble.3  The 
solution  of  this  substance  is  strongly  alkaline,  and  emits  an  odor  of  hydrosul- 
phuric acid,  due  to  the  action  of  the  atmospheric  carbonic  acid ;  if  evaporated  in 
an  open  vessel,  it  loses  hydrosulphuric  acid,  leaving  sulphide  of  potassium; 
when  exposed  to  air,  it  gradually  absorbs  oxygen,  and  becomes  first  yellow,  from 
the  formation  of  a  higher  sulphide  of  potassium,  and  is  ultimately  converted  into 
a  colorless  solution  of  hyposulphite  of  potassa. 

I.  KS.HS-f  0=KS3-f-HO. 
II.  KS3+ 03=KO.S303- 

A  pure  solution  of  hydrosulphate  of  sulphide  of  potassium,  when  mixed  with 
acids,  evolves  hydrosulphuric  acid,  and  remains  clear. 

When  sulphur  is  heated  in  a  solution  of  hydrosulphate  of  sulphide  of  potas- 
sium, hydrosulphuric  acid  is  expelled,  and  a  higher  sulphide  of  potassium 
formed. 

When  an  alcoholic  solution  of  sulphide  of  potassium  is  mixed  with  bisulphide 
of  carbon,  an  orange  crystalline  substance  is  deposited,  which  is  known  as  sulpho- 

1  It  has  been  noticed  in  another  place  that  the  flash  attendant  xipon  the  discharge  of 
fire-arms  is  due  to  the  combustion  of  the  vapor  of  sulphide  of  potassium  issuing  from  the 
muzzle. 

2  The  excess  of  sulphur  may  be  removed  by  means  of  finely-divided  copper  or  silver. 

3  This  compound  is  also  formed  when  potassium  is  gently  heated  in  a  current  of  dry 
hydrosulphuric  acid,  hydrogen  being  evolved. 


HEPAR   SULPHURIS.  255 

carbonate  of  sulphide  of  potassium  (KS.CSa),  and  may  be  viewed  as  carbonate 
of  potassa,  in  which  all  the  oxygen  is  replaced  by  sulphur. 
The  higher  sulphides  of  potassium,  namely  : — 

KSa,  KS8,  KS4,  and  KS5, 

may  be  prepared  by  fusing  sulphide  of  potassium  with  the  proper  proportion  of 
sulphur;  they  have  all  a  yellow  or  brown  color,  and  their  solutions  are  alkaline; 
these  yellow  solutions  become  colorless  when  exposed  to  the  air,  from  the  forma- 
tion of  hyposulphite  of  potassa,  and  sulphur  is  deposited  in  all  cases,  except  that 
of  bisulphide  of  potassium;  when  hydrochloric  acid  is  added  to  the  solutions  of 
the  higher  sulphides  of  potassium,  hydrosulphuric  acid  is  evolved,  and  the  excess 
of  sulphur  deposited,  but  if  a  solution  of  one  of  these  sulphides  be  very  gradually 
added  to  an  excess  of  hydrochloric  acid,  a  portion  of  persulphide  of  hydrogen  is 
formed  at  the  same  time,  since  the  excess  of  acid  gives  it  a  certain  degree  of 
stability. 

Bisulphide  of  potassium  (KS2)  is  produced  when  bisulphate  of  potassa  is 
reduced  by  charcoal. 

§  161.  Hepar  sulphuris,  or  liver  of  sulphur,  is  a  brown-red  mass,  which  is 
sometimes  used  in  medicine,  and  is  prepared  by  fusing  sulphur  with  carbonate 
of  potassa  in  closed  earthen  crucibles ;  it  varies  in  composition  according  to  the 
proportions  in  which  these  ingredients  are  employed ;  the  common  proportions 
are  two  parts  of  carbonate  of  potassa  to  one  of  sulphur ;  the  resulting  mass  is  a 
mixture  of  tersulphide  of  potassium,  hyposulphite  of  potassa,  and  sulphate  of 
potassa,  the  proportions  of  the  two  latter  varying  according  to  the  temperature 
employed. 

Thus,  at  a  low  temperature,  the  decomposition  will  be  represented  by  the 
equation : — 

3(KO.CO,)+S8=2KS8+KO.Sa09+3COa; 

whilst,  at  a  full  red  heat,  a  portion  of  the  hyposulphite  will  be  decomposed  with 
production  Qipentasulphi.de  of  potassium,  according  to  the  equation  : — 
4(KO.S303)=KS5+3(KO.S03). 

It  is  from  hepar  sulphuris,  or  some  similar  compound,  that  milk  of  sulphur  is 
always  obtained;  for  this  purpose,  the  mass  is  prepared  by  fusing  carbonate  of 
potassa  at  rather  a  low  temperature,  with  enough  sulphur  to  produce  the  penta- 
sulphide,  which  is,  of  course,  mixed  with  hyposulphite ;  when  an  acid  is  added  to 
this  solution,  it  acts  upon  both  these  salts,  precipitating  sulphur,  liberating 
hydrosulphuric  acid  from  the  pentasulphide,  and  evolving  hyposulphurous  acid 
from  the  hyposulphite;  but  the  hyposulphurous  acid  is  almost  immediately  re- 
solved into  sulphurous  acid  and  sulphur,  the  latter  being  precipitated ;  the  sul- 
phurous acid,  meeting  with  the  hydrosulphuric,  is  decomposed  according  to  the 
equation : — 

S03+2HS=S3-f-2HO, 
so  that  all  the  sulphur  is  precipitated. 

The  most  economical  method  of  preparing  milk  of  sulphur,  therefore,  consists 
in  fusing  together  equal  weights  of  carbonate  of  potassa  and  sulphur,  at  a  tem- 
perature of  about  500°  F.  (260°  C.),  when  the  following  decomposition  takes 
place : — 

3(KO.C03)-fS13=2KS5+KO.SaOa-f3COa; 
if  an  acid  be  now  added  to  the  aqueous  solution  of  this  mass  : — 
*KSs+KO.SaOa+3HCi=3KCi+Su  +  3HO. 

The  silico-fluoride  of  potassium,  3KF  2SiF3,  is  sparingly  soluble  in  water, 
whence  hydrotiuosilicic  acid  is  sometimes  employed  for  precipitating  potassa. 

The  description  of  the  compounds  of  potassium  with  cyanogen  and  the  cyano- 
gen-radicals, falls  strictly  within  the  province  of  organic  chemistry. 


256  SODIUM   AND   OXYGEN. 


SODIUM. 

Sym.  Na.    Eq.  23.    Sp.  Gr.  0.97. 

§  162.  Sodium  was  discovered  by  Sir  H.  Davy  in  soda,  in  the  year  1807. 

This  metal  occurs  in  great  quantity,  and  very  widely  diffused  in  nature, 
chiefly  in  combination  with  chlorine,  in  the  form  of  sea-salt,  which  is  found  not 
only  in  the  waters  of  the  ocean,  but  also  in  those  of  most  springs.  Sodium  also 
occurs  in  nature  in  combination  with  oxygen  and  certain  acids ;  the  silicate  of 
soda  is  a  constituent  of  many  minerals,  such  as  albite  (silicate  of  soda  and  alu- 
mina, Na0.3Si03,Ala03.Si03),  analcime  (silicate  of  soda  and  alumina,  NaO. 
Si03,Al303.3Si03-j-2Aq.),  labradorite  (silicate  of  soda,  alumina,  and  lime,  NaO. 
Si03,3(CaO.Si03),4(Al203.2Si03),  kryolite  (3NaF,Al2F3),  &c.  The  nitrate,  car- 
bonate, biborate,  and  sulphate  of  soda  are  found  in  nature.  Soda  is  likewise 
found  in  all  the  animal  fluids,  and  in  plants,  especially  such  as  grow  near  the  sea. 

Sodium  and  its  compounds  are  prepared  from  the  ashes  of  sea-plants,  and  from 
sea  or  rock  salt. 

Preparation. — Sodium  may  be  obtained  from  the  hydrate  of  soda,  by  the  same 
processes  as  potassium  from  hydrate  of  potassa.  The  process  which  is  employed 
in  practice,  consists  in  converting  the  acetate  of  soda  into  a  mixture  of  carbonate 
of  soda  and  charcoal  by  ignition,  and  distilling  this  with  an  additional  quantity 
of  carbon,  exactly  in  the  same  way  as  in  the  preparation  of  potassium ;  the  pre- 
paration of  sodium,  however,  is  far  easier,  since  it  is  more  readily  reduced,  and 
does  not  form  any  combination  with  the  carbonic  oxide,  and  there  is  hence  no 
fear  of  explosion  from  the  choking  of  the  tube.  By  a  careful  operator,  almost 
the  theoretical  quantity  of  sodium  may  be  obtained  in  this  manner.  Sodium 
may  be  purified  in  the  same  manner  as  potassium. 

Properties. — Sodium  is  a  yellowish-white  lustrous  metal,  more  nearly  resemb- 
ling silver  than  potassium,  to  which,  in  its  other  physical  properties,  it  is  very 
similar.  Its  surface  tarnishes  rapidly  in  air,  from  oxidation;  it  is  therefore 
preserved  under  petroleum.  Sodium  fuses  at  194°  F.  (90°  C.),  and  distils  at 
higher  temperatures;  its  vapor  is  said  to  be  colorless.  When  heated  in  air  or 
oxygen,  sodium  burns  with  a  bright  yellow  flame,  and  is  (entirely,  if  the  metallic 
surface  be  continually  renewed  by  scraping)  converted  into  soda.  The  specific 
gravity  of  sodium  is  about  0.97,  so  that,  like  potassium,  it  floats  upon  water, 
which  it  decomposes  with  great  energy,  producing  soda,  and  liberating  hydrogen ; 
the  heat  is  not  sufficient  to  kindle  this  gas,  unless  the  sodium  be  confined  to  one 
spot;  for  example,  upon  the  surface  of  water  thickened  with  gum,  or  upon  moist- 
ened filter-paper;  the  hydrogen  then  burns  with  a  fine  yellow  flame.  Sodium, 
being  little  inferior  to  potassium  in  its  affinity  for  oxygen,  may  often  be  substi- 
tuted for  this  metal  in  chemical  experiments,  and,  since  sodium  is  much  less 
costly  than  potassium,  it  should  always  replace  it  if  possible. 

SODIUM    AND   OXYGEN. 

Soda NaO. 

Teroxide  of  sodium1      .     .     .     Na03. 

§  163.  By  the  imperfect  oxidation  of  sodium,  a  grayish  brittle  substance  is 
produced,  which  is  believed  to  be  a  suboxide  of  sodium,  corresponding  to  the 
suboxide  of  potassium  : — 

1  Considered  by  some  chemists  to  be  a  sesquioxide,  Na203. 


NITRATE  OF  SODA.  257 

OXIDE  OF  SODIUM,  SODA. 
NaO.    Eq.  31. 

The  pure  oxide  may  be  prepared  by  processes  exactly  similar  to  those  em- 
ployed in  the  case  of  potassium;  it  forms  a  gray  mass,  much  resembling  anhy- 
drous potassa. 

The  affinity  of  soda  for  bases  is  less  powerful  than  that  of  potassa.  Its  salts 
are,  with  very  few  exceptions,  soluble  in  water ;  when  neutral  in  constitution, 
they  are  generally  neutral  in  reaction. 

HYDRATE  OF  SODA.    CAUSTIC  SODA. 
NaO.HO.   E%.  40. 

Preparation. — This  compound  may  be  prepared  in  exactly  the  same  way  as 
hydrate  of  potassa;  3  parts  of  crystallized  carbonate  of  soda  are  dissolved  in  15 
parts  of  water,  and  decomposed  by  milk  of  lime,  prepared  by  slaking  1  part  of 
lime  with  3  parts  of  hot  water;  the  decomposition  is  effected  more  easily  than 
in  the  case  of  potassa,  and  the  product  may  be  purified  in  a  similar  manner.1 

Properties. — The  hydrate  of  soda  forms  a  white,  brittle  mass,  which  fuses 
easily,  and  volatilizes  at  a  high  temperature  in  white  fumes ;  the  water  cannot 
be  expelled  by  heat.  When  exposed  to  air,  the  hydrate  first  deliquesces,  and  is 
afterwards  converted  into  a  white  mass  of  carbonate  of  soda.  Hydrate  of  soda 
dissolves  very  readily  in  water  and  alcohol,  with  evolution  of  heat.  The  solution 
of  soda  thus  obtained  may  be  prepared  in  the  same  way  as  solution  of  potassa, 
and  since  it  can  be  easily  made  much  purer  than  this  latter,  it  is  frequently 
substituted  for  it.  When  gases,  however,  are  passed  into  solution  of  soda,  it 
froths  up  very  much,  so  that  it  cannot  replace  hydrate  of  potassa  in  organic 
analysis. 

The  strength  of  this  solution,  like  that  of  solution  of  potassa,  may  be  inferred 
from  its  specific  gravity.  The  spec.  grav.  of  the  most  concentrated  solution  is 
about  2.00;  it  contains  77.8  per  cent,  of  alkali.  The  description  which 
we  have  given  of  the  properties  of  solution  of  potassa,  will  apply  to  those  of  solu- 
tion of  soda.  If  this  solution  be  preserved  in  stoppered  bottles,  a  slip  of  paper 
should  be  inserted  between  the  stopper  and  the  neck,  since  the  carbonate  of  soda, 
formed  on  exposure  to  the  air,  will  otherwise  cement  the  stopper  firmly  into  its 
place. 

Solution  of  hydrate  of  soda  is  largely  employed  by  soap-makers  for  making 
hard  soaps.  This  solution  may  be  readily  distinguished  from  solution  of  potassa 
by  diluting  with  water,  and  stirring  with  an  excess  of  tartaric  acid,  when  solution 
of  potassa  gives  a  crystalline  precipitate,  whilst  that  of  soda  remains  clear. 

A  strong  solution  of  hydrate  of  soda  when  exposed  to  a  low  temperature, 
yields  four- sided  very  fusible  crystals,  the  amount  of  water  in  which  has  not 
been  determined. 

NITRATE  OF  SODA,  CUBIC  NITRE,  CHILI  SALTPETRE. 
NaO.N05. 

§  164.  This  salt,  like  nitrate  of  potassa,  occurs  as  an  incrustation  on  the  earth 
in  certain  hot  districts  (especially  in  Chili  and  Peru,  where  it  is  found  in  layers 
of  considerable  thickness),  and  may  be  purified  from  foreign  matters  by  solution 
and  recrystallization.  It  may  be  prepared  in  the  laboratory  by  decomposing 
carbonate  of  soda  with  nitric  acid. 

1  For  soap-boiling,  the  lye  is  often  made  in  the  cold,  more  lime  being  employed ;  the 
soda  is  placed  upon  the  lime,  and  gradually  lixiviatfed  with  water. 

17 


258  HYPOSULPHITE   OF   SODA. 

Properties. — Nitrate  of  soda  crystallizes  in  anhydrous  rhombohedral  crystals 
(whence  the  name  cubic  nitre).  When  heated  it  behaves  like  nitrate  of  potassa. 
Exposed  to  air,  it  deliquesces,  and  hence  cannot  be  substituted  for  nitrate  of 
potassa  in  the  preparation  of  gunpowder.  It  dissolves  very  readily  in  about 
twice  its  weight  of  water,  with  depression  of  temperature.  In  its  oxidizing  pro- 
perties, nitrate  of  soda  resembles  the  corresponding  potassa-salt,  but  does  not 
form  such  powerful  detonating  mixtures. 

Uses. — Nitrate  of  soda  is  preferred  to  nitrate  of  potassa  for  the  preparation  of 
nitric  acid  on  a  large  scale,  since  it  is  cheaper,  and  yields  a  greater  percentage  of 
acid;  moreover,  the  residue  of  sulphate  of  soda  is  a  very  useful  salt. 

Nitrate  of  soda  is  also  sometimes  employed  for  the  preparation  of  nitrate  of 
potassa,  by  double  decomposition  with  carbonate  or  sulphate  of  potassa,  or  chlo- 
ride of  potassium.  It  is  also  occasionally  used  as  a  manure. 

§  165.  HYPOCHLORITE  OP  SODA  (NaO.CIO),  mixed  with  one  equivalent  of 
chloride  of  sodium,  and  a  little  bicarbonate  of  soda,  constitutes  the  bleaching 
liquid  of  Lalarraque,  or  chloride  of  soda. 

This  liquid  is  prepared  by  passing  chlorine  through  a  dilute  solution  of  soda 
or  its  carbonate,  until  about  as  much  chlorine  has  been  passed  as  corresponds  to 
rather  less  than  one  equivalent  for  each  equivalent  of  soda  : — 
2(NaO.C03)+Cl3=NaO.C10+NaCl  +  2COa. 

The  carbonic  acid  which  is  evolved  at  first  converts  the  carbonate  of  soda  into 
bicarbonate,  a  part  of  which  remains  undecomposed. 

The  solution  thus  obtained  has  a  pale  yellow  color,  smells  faintly  of  chlorine, 
and  has  an  alkaline  reaction  to  test-papers,  which  it  afterwards  bleaches.  "When 
mixed  with  acids,  it  evolves  chlorine ;  thus : — 

NaO.C10+NaCl+2(HO.S03)=2(NaO.S03)-f2HO  +  Cla. 

If  solution  of  chloride  of  soda  be  rapidly  boiled,  it  loses  its  bleaching  property, 

and  is  converted  into  a  solution  of  chlorate  of  soda  and  chloride  of  sodium,  for : — 

3(NaO.C10)==NaO.C105-f2NaCL 

Solution  of  chloride  of  soda  is  sometimes  employed  for  medicinal  purposes ;  it 
is  also  used  to  remove  ink-stains  from  linen. 

CHLORATE  OF  SODA,  NaO.ClO5. — This  salt  is  formed  under  the  same  condi- 
tions as  the  corresponding  salt  of  potassa.  Since,  however,  it  is  difficult  to  sepa- 
rate it  from  the  chloride  of  sodium  formed  at  the  same  time,  it  is  best  prepared 
by  decomposing  a  concentrated  hot  solution  of  chlorate  of  potassa  with  solution 
of  bitartrate  of  soda,  when  bitartrate  of  potassa  crystallizes  out  on  cooling,  and 
the  chlorate  of  soda  may  be  obtained  in  cubical  crystals  by  evaporation. 

The  properties  of  this  salt  are  very  similar  to  those  of  chlorate  of  potassa;  it 
is  readily  soluble  in  cold  water,  and  moderately  so  in  alcohol. 

§  166.  HYPOSULPHITE  OF  SODA,  NaO.S?Oa. — This  salt  is  formed  when  solu- 
tion of  a  sulphide  of  sodium  is  exposed  to  air,  or  when  sulphurous  acid  is  passed 
through  solution  of  pentasulphide  of  sodium,  until  the  color  of  the  latter  is 
destroyed. 

AVhen  an  aqueous  solution  of  sulphite  of  soda  is  digested  with  sulphur  for 
some  days,  in  a  closed  vessel,  at  a  moderate  heat,  and  the  filtered  liquid  then 
concentrated  by  slow  evaporation,  large  prismatic  crystals  of  hyposulphite  of 
soda  are  obtained.  These  crystals  have  the  formula  NaO.S302-f5Aq ;  they 
are  unaltered  by  exposure  to  air.  When  heated  gently,  this  salt  fuses,  water  is 
evolved,  and,  at  a  higher  temperature,  sulphur  escapes,  whilst  a  mixture  of  sul- 
phide of  sodium  and  sulphate  of  soda  remains : — 

4(NaO.SaOa)=3(NaO.S03)+NaS  +  S4. 

Hyposulphite  of  soda  is  readily  soluble  in  water,  but  not  in  alcohol ;  its  aqueous 
solution  is  neutral  to  test-papers,  and  gradually  decomposes  into  sulphur,  which 


SULPHATE   OF    SODA.  259 

deposits,  and  sulphite  of  soda,  which,  with  access  of  air,  passes  into  sulphate  of 
soda. 

The  use  of  this  salt  in  photographic  experiments  has  already  been  mentioned 
(§  104). 

SULPHITE  OF  SODA  (NaO.SOa)  is  prepared  by  passing  sulphurous  acid  to 
saturation  into  a  solution  of  carbonate  of  soda;1  half  the  carbonic  acid  which  is 
at  first  disengaged  converts  the  carbonate  of  soda  into  bicarbonate,  which  is  after- 
wards decomposed  by  the  sulphurous  acid  with  rapid  effervescence ;  the  mixture 
of  sulphurous  acid  and  carbonic  acid,  evolved  by  heating  oil  of  vitriol  with  char- 
coal, may  be  advantageously  employed  for  this  purpose.  By  evaporating  the 
solution,  the  sulphite  of  soda  may  be  obtained  in  crystals,  which  have  the 
formula  NaO.S03-f-8Aq. 

Properties. — Sulphite  of  soda  crystallizes  in  transparent  four  or  six-sided 
prisms,  which,  when  exposed  to  air,  become  covered  with  a  white  crust  of  sul- 
phate of  soda. 

When  heated,  this  salt  is  decomposed,  water  and  sulphur  are  evolved,  and  a 
mixture  of  soda  and  sulphate  of  soda  remains  : — 

3(NaO.SOa)=2(NaO.S03)+NaO-fS. 

The  sulphite  of  soda  dissolves  readily  in  4  parts  of  water,  yielding  an  alkaline 
solution;  it  is  most  soluble  at  91°.4  F.  (33°  C.) 

Uses. — This  salt  is  occasionally  employed  in  analysis  as  a  deoxidizing  agent ; 
it  has  lately  become  an  article  of  commerce,  being  used,  under  the  name  of 
antichlore,  to  neutralize  any  excess  of  chlorine  which  may  have  been  used  in 
bleaching  certain  fabrics.  The  action  of  chlorine,  in  presence  of  water,  upon 
sulphite  of  soda,  will  be  understood  from  the  following  equation  : — 
NaO.S02-fHO-fCl=NaO.S03+HCl. 

Sulphite  of  soda  has  also  been  recommended  for  the  preservation  of  wines,  and 
for  the  refining  of  beetroot  sugar.  ^-  . 

A  crystallizable  bisulphite  of  soda,  NaO.S03,  HO.S02,  has  been  obtained. 

SULPHATE  OF  SODA,  GLAUBER'S  SALT,  NaO.S03. 

§  167.  This  salt,  in  the  anhydrous  state,  sometimes  forms  an  incrustation 
upon  the  surface  of  the  soil;  it  is  then  called  Thtnardite;  it  also  occurs  in  sea- 
water  and  in  mineral  waters. 

Preparation. — Sulphate  of  soda  is  sometimes  prepared  from  the  mother- 
liquors  of  salt,  extracted  from  salt-springs;  these  mother-liquors  are  exposed  in 
the  winter,  when  the  decrease  of  temperature  causes  a  crystallization  of  sulphate 
of  soda. 

A  larger  quantity  of  this  salt,  however,  is  prepared  by  decomposing  chloride 
of  sodium  with  sulphuric  acid  (see  p.  264).  It  is  also  a  by-product  in  the 
preparation  of  nitric  acid  on  the  large  scale,  and  may  be  purified  by  dissolving  to 
saturation  in  tepid  water  and  crystallization. 

Properties. — Sulphate  of  soda  occurs  in  commerce  in  large  transparent  pris- 
matic crystals,  of  the  formula  NaO.S03-f- lOAq;  these  effloresce  in  moderately 
dry  air,  becoming  first  covered  with  a  white  pulverulent  crust,  and  afterwards 
falling  to  a  white  powder  of  anhydrous  sulphate  of  soda,  NaO.S03.  When 
heated  to  about  86°  F.  (30°  C.),  the  crystals  fuse  in  their  water  of  crystalliza- 
tion ;  at  a  higher  temperature,  all  the  water  is  expelled,  but  the  salt  undergoes 
no  further  alteration.  The  crystals  are  insoluble  in  alcohol. 

The  solubility  of  crystallized  sulphate  of  soda  in  water  presents  a  strange  ano- 

1  On  the  large  scale,  this  salt  is  prepared  by  passing  sulphurous  acid  over  moist  crys- 
tals of  carbonate  of  soda ;  the  sulphurous  acid  is  evolved  from  burning  sulphur,  and  the 
excess  is  sometimes  passed  into  the  ieaden  chambers  in  which  oil  of  vitriol  is  prepared. 


260  PHOSPHATES   OF    SODA. 

maly.  Water  at  91°. 5  F.  (33°  C.)  dissolves  a  larger  quantity  of  this  salt  than  at 
a  higher  or  lower  temperature ;  1  part  of  the  crystals  dissolves,  at  32°  F.  (0°  C.), 
in  8.22  parts  of  water,  at  77°  F.  (25°  C.),  in  1  part  of  water,  and  at  91°. 5  F. 
(33°  C.)  in  0.31  part.  A  solution  saturated  at  this  last  temperature,  when 
heated  to  212°  F.  (100°  C.),  deposits  rhombic  octohedra,  which  are  anhydrous. 
If  such  a  saturated  solution  be  allowed  to  cool,  it  deposits  four-sided  prisms  of 
the  formula  NaO.S03+ 8  Aq,  until  the  temperature  has  fallen  to  68°  F.  (20°  C.), 
after  which  crystals  of  the  ordinary  salt  make  their  appearance.  »' 

If  a  saturated  solution  of  sulphate  of  soda  be  covered  with  a  layer  of  oil,  and 
allowed  to  cool,  it  will  remain  without  crystallizing  until  it  is  agitated,  when  it 
at  once  crystallizes  throughout. 

The  crystals  of  anhydrous  sulphate  of  soda  absorb  water  from  the  air,  and  fall 
to  a  powder  containing  8  equivalents  of  water ;  the  anhydrous  salt  fuses  at  a 
red  heat. 

Uses. — Sulphate  of  soda  is  used  to  a  considerable  extent  in  medicine.  It  is 
very  largely  employed'  in  the  manufacture  of  carbonate  of  soda  (§  170).  The 
sulphate  of  soda,  in  conjunction  with  common  hydrochloric  acid,  is  also  used  as 
a  refrigerator  in  the  ice-making  machines,  since  such  a  mixture  produces  intense 
cold.  For  this  purpose,  5  parts  of  common  hydrochloric  acid  are  poured  upon  8 
parts  of  crystallized  sulphate  of  soda  in  coarse  powder. 

BISULPHATE  OF  SODA,  NaO.S03,HO.S03. — This  salt  may  be  obtained  by 
mixing  a  solution  of  sulphate  of  soda  with  1  equivalent  of  sulphuric  acid,  and 
evaporating  when  crystals  are  deposited  of  the  formula  NaO.S03,HO.S03-f  2Aq. 
When  heated,  these  undergo  the  aqueous  fusion,  and  are  converted  into  NaO.S03, 
HO.S03 ;  if  further  heated,  this  latter  loses  the  last  equivalent  of  water,  leaving 
Na0.2S03,  from  which,  at  a  higher  temperature,  one  equivalent  of  S03  may  be 
distilled,1  the  residue  consisting  of  anhydrous  sulphate  of  soda,  NaO.S03.  The 
crystallized  bisulphate  does  not  deliquesce,  but  is  very  soluble  in  water ;  its  solu- 
tion has  an  acid  reaction.  A  large  quantity  of  water  decomposes  it  into  neutral 
sulphate  of  soda  and  free  sulphuric  acid. 

If  half  an  equivalent  of  sulphuric  acid  be  added  to  one  equivalent  of  sulphate 
of  soda;  a  sesquimlpJiate  of  soda  is  said  to  be  produced. 


PHOSPHATES   OF   SODA. 

§  168.  Soda  forms  a  complete  series  of  salts  with  the  three  modifications  of 
phosphoric  acid,  viz : — 

With  the  tribasic  (common)  phosphoric  acid. 

Triphosphate  of  soda 3NaO.P05 

Common  phosphate 2NaO.HO.P05 

Acid  phosphate Na0.2HO.P05 

With  the  bibasic  (pyro-)  phosphoric  acid. 

Dipyrophosphate  of  soda 2NaO.P05 

Acid  pyrophosphate '  .     .     .     .     NaO.HO.P05 

With  the  monobasic  (meta-)  phosphoric  acid. 
Metaphosphate  of  soda .     NaO.P05 

TRIPHOSPHATE  (OR  SUBPHOSPHATE)  OF  SODA.    3NaO.P05. 

This  salt  may  be  obtained  by  adding  an  excess  of  soda  to  a  solution  of  the 
common  phosphate,  2NaO.HO.P05,  and  evaporating  to  crystallization.     Six-sided 

1  Bisulphate  of  soda  may  Tbe  employed  for  the  preparation  of  fuming  sulphuric  acid. 


PHOSPHATES    OF    SODA.  261 

prisms  are  obtained,  of  the  formula  8NaO.P05+24Aq.  The  crystals  are  unal- 
tered in  air,  they  undergo  aqueous  fusion  below  212°  F.  (100°  C.),  and  lose  'all 
their  water  at  a  red  heat.1  They  are  soluble  in  5  parts  of  cold  water,  yielding 
an  alkaline  solution  ;  an  equivalent  of  soda  is  easily  withdrawn  from  this  solution, 
even  by  feeble  acids ;  thus,  if  exposed  to  air,  it  absorbs  carbonic  acid,  yielding 
carbonate  and  common  phosphate  of  soda  (2NaO.HO.P05). 

With  solution  of  nitrate  of  silver,  triphosphate  of  soda  gives  a  yellow  precipi- 
tate of  triphosphate  of  silver,  3AgO.P05,  the  supernatant  liquid  becoming  neutral 
if  an  excess  of  nitrate  of  silver  be  added : — 

3NaO.P05+3(AgO.N05)=3AgO.P05+3(NaO.N05). 

COMMON  PHOSPHATE  or  SODA. 
2NaO.HO.PO5. 

The  common  phosphate  of  soda  occurs  in  the  urine. 

Preparation. — The  solution  of  acid  phosphate  of  lime  which  is  obtained  on 
decomposing  bone-earth  with  sulphuric  acid,  as  in  the  preparation  of  phosphorus, 
is  mixed  with  solution  of  carbonate  of  soda,  as  long  as  any  precipitate  is  produced; 
the  lime  is  precipitated  as  a  basic  phosphate,  together  with  phosphate  of  magne- 
sia ;  the  fijfrered  liquid  containing  the  phosphate  of  soda  is  evaporated,  allowed 
to  crystallize,  and  the  salt  subsequently  purified  by  recrystallization. 

Properties. — The  ordinary  phosphate  of  soda  is  thus  obtained  in  transparent 
oblique  rhombic  prisms,  of  the  formula  2NaO.HO.P05+24Aq.  These  effloresce 
rapidly  in  air.  When  moderately  heated,  they  undergo  the  aqueous  fusion,  and 
lose  24  eqs.  of  water,  leaving  a  white  mass  of  2NaO.HO.P05,  and  if  this  be 
redissolved  in  water,  crystals  of  the  original  salt  may  be  obtained  from  the  solu- 
tion ;  at  a  red  heat,  the  equivalent  of  basic  water  is  expelled,  and  2NaO.P05 
(pyrophosphate  of  soda)  left ;  if  the  mass  be  now  dissolved  in  water,  the  solu- 
tion deposits  no  longer  crystals  of  the  original  salt,  but  those  of  pyrophosphate 
of  soda. 

The  crystals  of  common  phosphate  of  soda  dissolve  in  4  parts  of  cold  and  2  of 
hot  water ;  the  solution  has  an  alkaline  reaction,  and  is  capable  of  absorbing  car- 
bonic acid  (probably  giving  rise  to  NaO.C03,  and  Na0.2HO.P05) ;  when  the 
solution  is  kept  in  bottles  of  ordinary  lead-glass,  the  latter  is  attacked,  and  white 
scales  (phosphate  of  lead?)  separate  from  it;  the  solution  should  therefore  be 
preserved  in  German  glass  bottles,  which  are  not  corroded  by  it.  When  the 
solution  of  common  phosphate  of  soda  is  evaporated  at  91°. 5  F.  (33°  C.)>  and 
left  to  crystallize,  crystals  are  obtained  of  the  formula  2NaO.HO.P05-f  14Aq ; 
these  do  not  effloresce  in  air,  and  behave  like  the  ordinary  crystals  when  heated. 
Nitrate  of  silver  produces,  in  solution  of  common  phosphate  of  soda,  a  yellow 
precipitate  of  triphosphate  of  silver  (3AgO.P03),  the  supernatant  liquid  being 
acid : — 

2NaO.HO.P05+3(AgO.N05)=3AgO.P05+2(NaO.N05)+HO.N05. 

Hydrochloric  acid  removes  half  the  soda  from  the  common  phosphate,  convert- 
ing it  into  acid  phosphate  of  soda. 

Uses. — Common  phosphate  of  soda  is  administered  medicinally  as  a  purgative ; 
it  is  employed  in  analysis  (see  Reagents),  and  is  the  source  from  which  the  other 
phosphates  of  soda  are  generally  prepared. 

ACID  PHOSPHATE  OF  SODA,  NaO.2HO.PO-,  is  obtained  by  adding  tribasic 
phosphoric  acid  to  solution  of  common  phosphate  of  soda  until  it  ceases  to  pre- 
cipitate chloride  of  barium;  the  solution  is  then  evaporated  and  left  to  crystal- 

1  Gerhardt  states  that  this  salt,  dried  at  212°  F.  (100°  C.),  has  the  formula  3NaO. 
P05-|-HO.  After  the  salt  has  been  ignited,  it  absorbs  1  equivalent  of  water  with  re- 
markable avidity. 


262  PHOSPHATES    OF    SODA. 

lize,  when  prismatic  crystals1  are  obtained,  of  the  formula  Na0.2HO.P05-f  2Aq; 
when  these  are  heated  to  212°  F.  (100°  C.)  the  2  eqs.  of  water  of  crystallization 
are  expelled,  and  at  about  392°  F.  (200°  C.)  a  third  equivalent  of  water  is  ex- 
pelled, leaving  NaO.HO.P05  (acid  pyrophosphate  of  soda),  which  is  converted 
into  the  metaphosphate  (NaO.P05)  below  482°  F.  (250°  C.)  The  acid  phos- 
phate of  soda  is  easily  soluble  in  water,  and  insoluble  in  alcohol  ;  the  aqueous 
solution  is  of  course  acid,  and  gives,  with  nitrate  of  silver,  a  yellow  precipitate 
of  triphosphate,  the  supernatant  liquid  being  strongly  acid : — 

Na0.2HO.P05+3(AgO.N05)=3AgO.P05+NaO.N05+2(HO.N05). 

DlPYROPHOSPHATE,  OR  PYROPHOSPHATE  OF  SODA,  2NaO.P05. 

This  salt  is  obtained  by  heating  the  common  phosphate  of  soda  to  redness, 
when  it  is  left  as  a  transparent  glass.  If  this  glass  is  dissolved  in  hot  water, 
and  the  solution  cooled,  prismatic  crystals  are  deposited,  of  the  formula  2NaO. 
P05+10Aq;  they  do  not  effloresce  in  air.  The  aqueous  solution  of  this  salt 
has  an  alkaline  reaction;  when  boiled,  it  is  scarcely  altered,  but  if  previously 
acidulated,  even-with  acetic  acid,  the  salt  2NaO.HO.P05  is  obtained  on  boiling. 
A  solution  of  pyrophosphate  of  soda  is  capable  of  dissolving  several  insoluble 
pyrophosphates,  such  as  pyrophosphate  of  silver.  The  solution  of  pyrophosphate 
of  soda  gives  a  white  precipitate  with  nitrate  of  silver,  the  supernatant  liquid 
being  neutral : — 

2NaO.P05+2(AgO.N05)=2AgO.P05+2(NaO.N05). 

ACID  .PYROPHOSPHATE  OF  SODA,  NaO.HO.P05,  may  be  obtained,  as  already 
stated,  by  heating  the  salt  Na0.2HO.P05  to  about  392°  F.  (200°  C.)  It  can 
be  prepared  also  by  dissolving  pyrophosphate  of  soda  (2NaO.P05)  in  acetic  acid, 
and  adding  alcohol,  when  the  salt  in  question  is  precipitated,  and  acetate  of  soda 
remains  in  solution. 

The  acid  pyrophosphate  is  obtained  as  a  white  crystalline  powder,  which, 
when  heated,  is  converted  into  metaphosphate  (NaO.P05).  The  acid  salt  dissolves 
easily  in  water,  and  gives  an  acid  solution,  from  which  nitrate  of  silver  throws 
down  white  pyrophosphate  of  silver  (2AgO.P05),  the  supernatant  liquid  being 
acid : — 

NaO.HO.P05+2(AgO.N05)=NaO.N05+2AgO.P05+HO.N05. 

The  salt  cannot  be  crystallized  by  evaporating  its  aqueous  solution,  but  regular 
crystals  have  been  obtained  by  pouring  a  layer  of  alcohol  upon  its  surface,  and 
allowing  it  to  stand.2 

METAPHOSPHATE  OF  SODA,  NaO.P05. 

This  compound  may  be  easily  prepared  by  expelling  the  water  either  from 
the  acid  tribasic  phosphate,  Na0.2HO.P05,  or  from  the  acid  pyrophosphate, 
NaO.HO.P05,  or,  more  readily,  by  igniting  microcosmic  salt,  NaO  NH4O.HO. 
P05.  It  is  left,  after  ignition,  as  a  clear  glass,  which,  if  slowly  cooled,  is  crys- 
talline; it  deliquesces  in  air,  and  dissolves  very  readily  in  water,  but  is  insoluble 
in  alcohol;  its  solution  is  almost  neutral,  and,  if  evaporated  in- a  shallow  vessel, 
at  about  86°  F.  (30°  C.),  deposits,  according  to  Fleitmann  "and  Heuneberg, 
oblique  rhombic  prisms,  containing  4  eqs.  of  water.  The  aqueous  solution  gives, 
with  nitrate  of  silver,  a  white  precipitate  of  metaphosphate  of  silver  (AgO.P03), 
the  supernatant  liquid  being  neutral : — 

NaO.P05+AgO.N05=AgO.P05+NaO.N05. 

1  This  salt  may  also  be  obtained  in  octoliedra. 

2  A  double  pyrophosphate  of  potassa  and  soda  (KO.NaO.P05-{-12Aq)  is  obtained  by 
neutralizing  the  acid  pyrophosphate  of  soda  with  carbonate  of  potassa,  and  evaporating 
to  crystallization. 


CARBONATE   OF    SODA.  263 

If  the  ignited  metaphosphate  of  soda  be  rapidly  cooled,  its  aqueous  solution 
will  not  crystallize  on  evaporation.  If  the  salt  NaO.HO.PO5  be  heated  until  it 
has  lost  all  its  water,  but  has  not  fused,  it  dissolves  with  difficulty  in  water. 

All  the  phosphates  of  soda,  when  fused  with  excess  of  hydrate  or  carbonate 
of  soda,  are  converted  into  SNaO.PO.. 

Fleitmann  and  Henneberg,  who  have  recently  studied  the  phosphates  of  soda, 
are  disposed  to  consider  the  metaphosphate  as  6Na0.6POs,  and  observed  that  if 
the  composition  of  the  other  phosphates  be  referred  to  the  same  quantity  of 
base,  viz.  6  eqs.,  a  series  will  be  obtained  in  which  certain  hiatus  exist,  which 
these  chemists  have  endeavored  to  fill  up;  thus: — 

NaO.P05  will  become  6Na0.6P05 

NaO.HO.P05  "          3Na0.3H0.3POs 

2NaO.P05  "          6Na0.3P05 

Na0.2HO.P05  "          2Na0.4H0.2P05 

2NaO.HO.P05  «         4Na0.2H0.2P05 

3NaO.P05  "          6Na0.2P05 

Of  the  members  required  to  complete  this  series,  Fleitmann  and  Henneberg 
believe  that  they  have  discovered  three,  viz  : — 

6Na0.5P05, 

6Na0.4P05, 

4Na0.2H0.4P05; 

the  two  former  having  been  obtained  by  fusing  different  mixtures  of  metaphos- 
phate and  pyrophosphate  of  soda,  and  the  last  compound  by  drying  the  acid 
pyrophosphate  of  soda  (NaO.HO.P05)  at  220°  F. 

CARBONATE  OF  SODA,  commonly  called  SODA. 
NaO.C03. 

§  169.  Carbonate  of  soda  occurs  as  a  natural  product  in  the  soda-lakes  of 
Egypt  and  Hungary;  it  also  sometimes  forms  an  incrustation  on  the  soil  in 
those  countries ;  the  walls  of  houses  built  with  limestone  containing  much  soda- 
salt  are  occasionally  covered  with  an  incrustation  composed  of  carbonate  mixed 
with  sulphate  of  soda.  This  carbonate  also  exists  in  large  quantity  in  the  ashes 
of  marine  plants,  being  produced  by  the  decomposition  of  salts  of  soda  with 
organic  acids,  during  incineration. 

Preparation. — The  old  process  for  obtaining  carbonate  of  soda,  which  is  very 
little  practised  at  the  present  day,  consists  in  the  incineration  of  various  plants 
growing  on  the  sea-shore,  especially  of  the  sahola  soda  and  salicornia  Europcea ; 
the  plants  are  collected,  and  burnt  in  trenches,  when  a  grayish  semi-fused  as  his 
obtained,  which  contains  carbonate  of  soda  mixed  with  various  impurities,  espe- 
cially sand,  carbon,  salts  of  lime,  sulphate,  and  hyposulphite  of  soda,  sulphide 
and  chloride  of  sodium.  This  product  is  introduced  into  commerce  under  the 
names  Barilla,  Blanquttte,  tSalicor,  and  Kelp.  Of  these,  the  barilla,  or  Alicant 
soda,  is  said  to  be  the  richest,  and  the  kelp,  or  Scotch  soda,  the  poorest  in  car- 
bonate of  soda.1  This  product  may  be  purified  by  lixiviation  and  crystallization 
(see  Manufacture  of  Nitre,  §  145). 

Previously  to  the  French  Revolution,  in  the  latter  part  of  the  last  century,  a 
large  quantity  of  the  carbonate  of  soda  consumed  in  France  was  imported  from 
Spain ;  but  during  the  war,  the  price  of  the  barilla  having  risen  very  consider- 
ably, a  premium  was  offered  by  the  government  for  the  discovery  of  a  process 

1  Barilla  contains  from  25  to  30  per  cent,  of  carbonate  of  soda,  salicor,  about  14  or 
15  ;  blanquette,  3  to  8 ;  and  kelp,  only  2  per  cent. 


264  SODA-MANUFACTURE. 

for  the  artificial  production  of  carbonate  of  soda  from  some  native  source;  such  a 
process  was  discovered  by  Leblanc,  and  has  been  employed  ever  since  without 
any  essential  alteration.  This  process  for  the  artificial  production  of  carbonate 
of  soda  merits  a  considerable  share  of  our  attention,  since  it  has  not  only  exerted 
a  very  important  influence  upon  the  various  manufactures  in  which  this  salt  is 
employed,  e.  g.  those  of  soap  and  glass — and  upon  others  which  are  called  into 
play  by  the  process  itself,  e.  g.  that  of  sulphuric  acid — but  has  also  very  materially 
contributed  to  the  general  advancement  of  chemical  science. 

MANUFACTURE  OF  CARBONATE  OF  SODA  FROM  COMMON  SALT. 

§  170.  Leblanc's  process  for  the  preparation  of  carbonate  of  soda  from  chlo- 
ride of  sodium  consists  : — 

1.  In  the  conversion  of  chloride  of  sodium  into  sulphate  of  soda; 

2.  In  the  reduction  of  the  sulphate  of  soda  to  sulphide  of  sodium  by  roasting 

with  carbon;  and 

3.  In  the  conversion  of  the  sulphide  thus  obtained  into  carbonate  of  soda,  by 

roasting  with  coal  and  limestone. 

A  charge  of  about  6  cwts.  of  chloride  of  sodium  (ordinary  sea-salt,  or  powdered 
rock-salt)  is  spread  out  on  the  floor  of  a  reverberatory  furnace,1  and  well  mixed 
with  an  equal  weight  of  oil  of  vitriol  (spec.  grav.  1.6),  just  as  it  is  derived  from 
the  leaden  chambers  of  the  vitriol  factory,  which  is  usually  in  connection  with 
the  alkali  works;  these  proportions  leave  the  chloride  of  sodium  slightly  in  ex- 
cess. The  mixture  is  then  strongly  heated  by  the  coal-flame  which  plays  over  its 
surface,until  it  is  converted  into  a  perfectly  dry  mass  of  sulphate  of  soda,  accord- 
ing to  the  equation : — 

NaCl  +  HO.SO,=NaO.SOs  +  HCl. 

Very  large  quantities  of  hydrochloric  acid,  therefore,  pass  off  in  this  operation ; 
this  acid,  in  most  cases,  is  said  not  to  repay  the  manufacturer  for  collecting  it, 
and  yet  must  not  be  allowed  to  contaminate  the  air  in  the  neighborhood,  since 
its  eifects  upon  vegetation  are  highly  injurious.  It  is  generally  either  carried 
into  the  upper  strata  of  the  atmosphere  by  a  high  chimney,  or  conducted  through 
towers  filled  with  lumps  of  coke  or  with  flints,  over  which  water  is  allowed  to 
trickle  in  a  contrary  direction  to  the  stream  of  gas;  a  solution  of  hydrochloric 
acid  is  thus  obtained.3 

In  some  works,  binoxide  of  manganese  is  added  to  the  mixture  of  chloride  of 
sodium  and  oil  of  vitriol,  so  that,  instead  of  hydrochloric  acid,  chlorine  is  evolved, 
which  is  devoted  to  the  manufacture  of  bleaching- powder ;  the  mass  is  very 
strongly  heated,  and  then  exhausted  with  water,  when  the  sulphate  of  soda  alone 
is  dissolved. 

The  reduction  of  the  sulphate  of  soda  to  sulphide  of  sodium,  and  conversion  of 

1  The  floor  or  sole  of  the  furnace  is  commonly  lined  with  lead  for  this  process ;  the 
bricks  used  in  constructing  the  furnace  are  such  as  are  not  easily  acted  upon  by  acid 
vapors.     The  hearth  is  usually  divided  by  a  partition  of  bricks,  into  two  compartments, 
in  one  of  which  (lined  with  lead),  more  remote  from  the  grate,   the  decomposition  is 
effected,  while  in  that  nearest  to  the  grate  (lined  with  fire-brick)  the  whole  of  the  hydro- 
chloric acid  is  expelled,  and  the  sulphate  of  soda  fused. 

2  Limestone  (carbonate  of  lime)  has  also  been  employed  to  absorb  the  hydrochloric 
acid,  carbonic  acid  being  then  evolved.     It  has  also  been  proposed  to  decompose  the 
chloride  of  sodium  with  sulphuric  acid  in  the  presence  of  zinc,  when  sulphate  of  soda 
and  chloride  of  zinc  are  produced,  with  evolution  of  hydrogen:  — 

NaCl-fHO.S03-fZn=NaO.S034-ZnCl+H. 

The  products  of  the  operation  might  be  separated  by  crystallization,  and  the  chloride 
of  zinc  afterwards  decomposed  by  lime,  when  oxide  of  zinc  would  be  obtained,  which 
could  be  employed  again  to  retain  the  hydrochloric  acid. 


SODA-MANUFACTURE. 

this  latter  into  carbonate  of  soda,  are  effected  in  one  process,  termed  tho  lotting- 
process1 : — 

100  parts  of  sulphate  of  soda, 

108  parts  of  limestone,2  and 
62  parts  of  small  coal,3 

are  well-ground,  sifted,  and  very  intimately  mixed.  This  mixture,  in  charges  of 
8  or  4  cwts.,  is  subjected  to  a  gradually-increasing  heat  in  a  reverberatory  fur- 
nace,4 and  constantly  stirred ;  during  this  operation,  a  blue  flame  of  carbonic 
oxide  is  seen  playing  over  tho  surface  of  the  mass ;  as  soon  as  the  latter  is  in  a 
state  of  tranquil  fusion,  the  operation  is  completed;  in  practice,  however,  it  is 
found  advantageous  to  arrest  the  operation  when  there  is  still  a  lively  disengage- 
ment of  gas.  The  product  thus  obtained  is  termed  Hack  a*h}  and  consists  chiefly 
of  a  mixture  of  carbonate  of  soda  with  an  insoluble  oxysulphido  of  calcium,  or 
of  a  combination  of  lime  with  sulphide  of  calcium.* 

The  <lrc<;iiijM>sitioM  whic.h  is  cd'ccJcd  in  tlm  balling-procoss  will  bo  readily 
understood  from  the  following  equations,  the  first  representing  the  reduction  of 
the  sulphate  of  soda,  the  second  the  conversion  of  the  sulphide  of  sodium  into 
carbonate  of  soda: — 

I.  NaO.S03+C4=NaS-f  400. 
II.  3NaS+4(CaO.COa)  +  C=3(NaO.COa)-f-Ca0.3CaS-f2CO. 

Tho  proper  regulation  of  tho  draught  is  of  the  greatest  importance  in  tho  ball- 
ing-process, so  that  a  sufficiently  high  temperature  may  be  obtained  without 
introducing  much  free  oxygen,  which  would  oxidize  the  sulphides. 

Some  experiments  of  Unger's  have  recently  shown  that  tho  presence  of  aqueous 
vapor  must  have  a  considerable  influence  upon  the  balling-process ;  for  it  was 
found  that,  when  a  mixture  of  gypsum  and  charcoal  was  exposed  to  the  action  of 
steam  at  a  red  heat,  oxysulphide  of  calcium  was  formed,  and  hydrosulphuric  acid 
evolved  :— 

4(CaO.S08)+C8+HO=3CaS.CaO+HS+8COfl. 

Black  ash,  or  crude  soda,  as  it  is  sometimes  termed,  is  used  for  some  purposes 
in  the  arts.  In  this  case  it  is  prepared  from  sulphate  of  soda  containing  about 
•j*j  of  common  salt,  which  causes  tho  resulting  soda-ash  to  crumble  down  in  moist 
air,  and  renders  grinding  unnecessary.  For  the  chief  application  of  this  product, 
viz.  in  soap-boiling,  tho  presence  of  common  salt  is  advantageous. 

The  black  ash  is  now  lixiviated  with  warm  water,"  which  dissolves  out  tho 
carbonate  of  soda,  forming  a  solution  of  a  green  color  (apparently  duo  to  a  little 
sulphide  of  iron),  and  leaves  a  residue  consisting  chiefly  of  the  oxysulphide  of 

1  So  called  because  the  ingredients  accumulate  into  little  round  masses. 

2  The  chalk  or  limestone  should  not  contain  much  alumina.     Deposits  from  carbonated 
waters  are  sometimes  employed. 

:1  'I' ho  coal  must  not  leave  too  much  ash. 

4  This  furnace  has  a  double  hearth ;  a  molting  hearth  nearer  to  the  grate,  and  some- 
what lower  than  the  more  remote  hearth,  from  which  the  dried  materials  are  raked  into 

Mir  lornicr  In-arlh.      Sunn-  furnaces  have  three  hearths. 

6  The  composition  of  this  compound,  according  to  Dumas,  is  Ca0.2CaS,  according  to 
Un-er,  (':.().:',( ':iS. 

(i  In  OI-.IIT  l<>  (lii-inte^rate  the  Mack  nsli,  previously  to  lixivialion,  it  is  sprinkled  with 
water  while  hot,  when  it  soon  crumbles  down.  It  is  then  inclosed  in  perforated  boxes  of 
sheet-iron,  arid  suspended  just  below  the  surface  of  water,  at  a  temperature  of  about  104° 
F.  (40°  C.),  in  the  lixiviating  cisterns,  which  are  so  arranged  that  tin-  water  .shall  cum.' 
in  contact,  first  with  the  nearly  exhausted  ash,  afterwards  with  that,  which  has  lust  suine 
of  its  alkali  to  a  former  portion  of  water,  and  lastly,  wi.th  the  fresh  ash  ;  this  is  effected 
by  placing  the  iron  cases  in  each  cistern  in  succession,  beginning  at  tho  hint,  while  the, 
water  is  allowed  to  enter  at  tho  first  cistern  and  to  flow  through  to  the  last;  the*object 
be-in;:;  ID  crmiomi/.c  both  water  (and  cunsiMjncntly  fuel)  and  alkali. 


264  SODA-MANUFACTURE. 

for  the  artificial  production  of  carbonate  of  soda  from  some  native  source;  such  a 
process  was  discovered  by  Leblanc,  and  has  been  employed  ever  since  without 
any  essential  alteration.  This  process  for  the  artificial  production  of  carbonate 
of  soda  merits  a  considerable  share  of  our  attention,  since  it  has  not  only  exerted 
a  very  important  influence  upon  the  various  manufactures  in  which  this  salt  is 
employed,  e.  g.  those  of  soap  and  glass — and  upon  others  which  are  called  into 
play  by  the  process  itself,  e.  g.  that  of  sulphuric  acid — but  has  also  very  materially 
contributed  to  the  general  advancement  of  chemical  science. 

MANUFACTURE  OF  CARBONATE  OF  SODA  FROM  COMMON  SALT. 

§  170.  Leblanc's  process  for  the  preparation  of  carbonate  of  soda  from  chlo- 
ride of  sodium  consists  : — 

1.  In  the  conversion  of  chloride  of  sodium  into  sulphate  of  soda; 

2.  In  the  reduction  of  the  sulphate  of  soda  to  sulphide  of  sodium  by  roasting 

with  carbon;  and 

3.  In  the  conversion  of  the  sulphide  thus  obtained  into  carbonate  of  soda,  by 

roasting  with  coal  and  limestone. 

A  charge  of  about  6  cwts.  of  chloride  of  sodium  (ordinary  sea-salt,  or  powdered 
rock-salt)  is  spread  out  on  the  floor  of  a  reverberatory  furnace,1  and  well  mixed 
with  an  equal  weight  of  oil  of  vitriol  (spec.  grav.  1.6),  just  as  it  is  derived  from 
the  leaden  chambers  of  the  vitriol  factory,  which  is  usually  in  connection  with 
the  alkali  works ;  these  proportions  leave  the  chloride  of  sodium  slightly  in  ex- 
cess. The  mixture  is  then  strongly  heated  by  the  coal-flame  which  plays  over  its 
surface,until  it  is  converted  into  a  perfectly  dry  mass  of  sulphate  of  soda,  accord- 
ing to  the  equation : — 

NaCl-fHO.S03=NaO.S03  +  HCl. 

Very  large  quantities  of  hydrochloric  acid,  therefore,  pass  off  in  this  operation ; 
this  acid,  in  most  cases,  is  said  not  to  repay  the  manufacturer  for  collecting  it, 
and  yet  must  not  be  allowed  to  contaminate  the  air  in  the  neighborhood,  since 
its  effects  upon  vegetation  are  highly  injurious.  It  is  generally  either  carried 
into  the  upper  strata  of  the  atmosphere  by  a  high  chimney,  or  conducted  through 
towers  filled  with  lumps  of  coke  or  with  flints,  over  which  water  is  allowed  to 
trickle  in  a  contrary  direction  to  the  stream  of  gas;  a  solution  of  hydrochloric 
acid  is  thus  obtained.3 

In  some  works,  binoxide  of  manganese  is  added  to  the  mixture  of  chloride  of 
sodium  and  oil  of  vitriol,  so  that,  instead  of  hydrochloric  acid,  chlorine  is  evolved, 
which  is  devoted  to  the  manufacture  of  bleaching- powder ;  the  mass  is  very 
strongly  heated,  and  then  exhausted  with  water,  when  the  sulphate  of  soda  alone 
is  dissolved. 

The  reduction  of  the  sulphate  of  soda  to  sulphide  of  sodium,  and  conversion  of 

1  The  floor  or  sole  of  the  furnace  is  commonly  lined  with  lead  for  this  process ;  the 
bricks  used  in  constructing  the  furnace  are  such  as  are  not  easily  acted  upon  by  acid 
vapors.     The  hearth  is  usually  divided  by  a  partition  of  bricks,  into  two  compartments, 
in  one  of  -which  (lined  with  lead),  more  remote  from  the  grate,    the  decomposition  is 
effected,  while  in  that  nearest  to  the  grate  (lined  with  fire-brick)  the  whole  of  the  hydro- 
chloric acid  is  expelled,  and  the  sulphate  of  soda  fused. 

2  Limestone  (carbonate  of  lime)  has  also  been  employed  to  absorb  the  hydrochloric 
acid,  carbonic  acid  being  then  evolved.     It  has   also  been  proposed  to  decompose  the 
chloride  of  sodium  with  sulphuric  acid  in  the  presence  of  zinc,  when  sulphate  of  soda 
and  chloride  of  zinc  are  produced,  with  evolution  of  hydrogen: — 

NaCl+HO.S034-Zn==NaO.S03-fZnCl-f-H. 

The  products  of  the  operation  might  be  separated  by  crystallization,  and  the  chloride 
of  zinc  afterwards  decomposed  by  lime,  when  oxide  of  zinc  would  be  obtained,  which 
could  be  employed  again  to  retain  the  hydrochloric  acid. 


SODA-MANUFACTURE.  265 

this  latter  into  carbonate  of  soda,  are  effected  in  one  process,  termed  the  lallmy- 
process1 : — 

100  parts  of  sulphate  of  soda, 

103  parts  of  limestone,2  and 
62  parts  of  small  coal,3 

are  well-ground,  sifted,  and  very  intimately  mixed.  This  mixture,  in  charges  of 
3  or  4  cwts.,  is  subjected  to  a  gradually -increasing  heat  in  a  reverberatory  fur- 
nace,* and  constantly  stirred ;  during  this  operation,  a  blue  flame  of  carbonic 
oxide  is  seen  playing  over  the  surface  of  the  mass ;  as  soon  as  the  latter  is  in  a 
state  of  tranquil  fusion,  the  operation  is  completed;  in  practice,  however,  it  is 
found  advantageous  to  arrest  the  operation  when  there  is  still  a  lively  disengage- 
ment of  gas.  The  product  thus  obtained  is  termed  black  ash,  and  consists  chiefly 
of  a  mixture  of  carbonate  of  soda  with  an  insoluble  oxysulphide  of  calcium,  or 
of  a  combination  of  lime  with  sulphide  of  calcium.5 

The  decomposition  which  is  effected  in  the  balling- process  will  be  readily 
understood  from  the  following  equations,  the  first  representing  the  reduction  of 
the  sulphate  of  soda,  the  second  the  conversion  of  the  sulphide  of  sodium  into 
carbonate  of  soda: — 

I.  NaO.S08+C4=NaS+4CO. 

II.  3NaS+4(CaO.C03)  +  C=3(NaO.C02)-fCa0.3CaS-f2CO. 

The  proper  regulation  of  the  draught  is  of  the  greatest  importance  in  the  ball- 
ing-process, so  that  a  sufficiently  high  temperature  may  be  obtained  without 
introducing  much  free  oxygen,  which  would  oxidize  the  sulphides. 

Some  experiments  of  Unger's  have  recently  shown  that  the  presence  of  aqueous 
vapor  must  have  a  considerable  influence  upon  the  balling-process ;  for  it  was 
found  that,  when  a  mixture  of  gypsum  and  charcoal  was  exposed  to  the  action  of 
steam  at  a  red  heat,  oxysulphide  of  calcium  was  formed,  and  hydrosulphuric  acid 
evolved : — 

4(CaO.S03)  +  C8+HO=3CaS.CaO+HS+8C03. 

Black  ash,  or  crude  soda,  as  it  is  sometimes  termed,  is  used  for  some  purposes 
in  the  arts.  In  this  case  it  is  prepared  from  sulphate  of  soda  containing  about 
T\  of  common  salt,  which  causes  the  resulting  soda-ash  to  crumble  down  in  moist 
air,  and  renders  grinding  unnecessary.  For  the  chief  application  of  this  product, 
viz.  in  soap-boiling,  the  presence  of  common  salt  is  advantageous. 

The  black  ash  is  now  lixiviated  with  warm  water,6  which  dissolves  out  the 
carbonate  of  soda,  forming  a  solution  of  a  green  color  (apparently  due  to  a  little 
sulphide  of  iron),  and  leaves  a  residue  consisting  chiefly  of  the  oxysulphide  of 

1  So  called  because  the  ingredients  accumulate  into  little  round  masses. 

2  The  chalk  or  limestone  should  not  contain  much  alumina.     Deposits  from  carbonated 
waters  are  sometimes  employed. 

3  The  coal  must  not  leave  too  much  ash. 

4  This  furnace  has  a  double  hearth ;  a  melting  hearth  nearer  to  the  grate,  and  some- 
what lower  than  the  more  remote  hearth,  from  which  the  dried  materials  are  raked  into 
the  former  hearth.     Some  furnaces  have  three  hearths. 

5  The  composition  of  this  compound,  according  to  Dumas,  is  Ca0.2CaS,  according  to 
Unger,  CaO.SCaS. 

6  In  order  to  disintegrate  the  black  ash,  previously  to  lixiviation,  it  is  sprinkled  with 
water  while  hot,  when  it  soon  crumbles  down.     It  is  then  inclosed  in  perforated  boxes  of 
sheet-iron,  and  suspended  just  below  the  surface  of  water,  at  a  temperature  of  about  104° 
F.  (40°  C.),  in  the  lixiviating  cisterns,  which  are  so  arranged  that  the  water  shall  come 
in  contact,  first  with  the  nearly  exhausted  ash,  afterwards  with  that  which  has  lost  some 
of  its  alkali  to  a  former  portion  of  water,  and  lastly,  with  the  fresh  ash  ;  this  is  effected 
by  placing  the  iron  cases  in  each  cistern  in  succession,  beginning  at  the  last,  while  the 
water  is  allowed  to  enter  at  the  first  cistern  and  to  flow  through  to  the  last;  the*object 
being  to  economize  both  w  ater  (and  consequently  fuel)  and  alkali. 


266  CARBONATE   OF   SODA. 

calcium  and  carbonate  of  lime.1  This  residue  is  known  as  soda-waste,  and  is 
occasionally  used  as  a  cement  for  rough  building  purposes.  The  lye  containing 
the  carbonate  of  soda  is  evaporated  to  dryness  in  iron  pans,  and  the  residue,  which 
is  termed  crude  soda-ash,  is  mixed  with  small  coal  or  sawdust,  and  heated  in  a 
reverberatory  furnace,  when  the  sulphate  and  hydrate  of  soda  which  it  contains 
are  converted  into  carbonate ;  the  salt  is  now  redissolved  in  water,  and  the  solu- 
tion evaporated  to  crystallization,  when  large  crystals  of  ordinary  washing-soda 
are  obtained. 

The  following  analysis  of  the  products  of  the  soda-manufacture  have  been  made 
by  Unger  : —  • 

Black  ash.        Soda-waste. 

Sulphate  of  soda 1.99 

Carbonate     "        .     .     .* 23.57 

Hydrate        "        .     .     • 11.12 

Chloride  of  sodium 2.54 

Sulphide       "             1.78 

Carbonate  of  lime 12.90         19.56 

Sulphate        "            3.69 

Hyposulphite  of  lime 4.12 

Hydrate               "            10.69 

Sulphide  of  calcium 34.76           3.25 

Bisulphide     "            4.67 

Oxysulphide"         (3CaS.CaO)     .     .     .  32.80 

Silicate  of  magnesia 4.74           6.91 

Sulphide  of  iron 2.45 

Oxide  of  iron 3.70 

Charcoal 1.59           2.60 

Sand 2.02           3.09 

Water  2.10           3.45 


99.78       100.31 

100  parts  of  sulphate  of  soda  have  been  found  to  yield  153  to  168  parts  of 
black  ash,  containing  from  50  to  55  parts  of  carbonate  of  soda;  theoretically,  75 
parts  of  carbonate  should  be  obtained. 

In  order  to  prepare  perfectly  pure  carbonate  of  soda  for  chemical  purposes,  it 
may  be  converted  into  the  bicarbonate  (as  described  hereafter),  the  latter  washed 
with  cold  water  till  the  washings  are  free  from  chlorine  and  sulphuric  acid,  and 
then  ignited,  to  reconvert  it  into  carbonate. 

According  to  a  process  recently  patented,  chloride  of  sodium  is  converted  into 
sulphate  of  soda  by  roasting  with  iron-pyrites  (FeSa)  in  a  reverberatory  furnace, 
when  it  appears  that  the  following  decomposition  takes  place  : — 

FeS2+2NaCl+Og  (from  the  air)  =2(NaO.S03)+FeO+Cl2. 

The  chlorine  of  course  escapes,  and  the  oxide  of  iron  is  converted,  by  further 
absorption  of  oxygen,  into  sesquioxide. 

The  sulphate  of  soda  is  extracted  from  the  mass  by  water,  or  the  mass  may  be 
subjected,  at  once,  to  the  balling-process. 

[Various  other  methods  have  been  proposed  for  converting  the  common  salt 
into  sulphate  of  soda  without  the  use  of  sulphuric  acid;  on  boiling  a  solution 
containing  chloride  of  sodium  and  sulphate  of  magnesia,  a  double  decomposition 
ensues,  resulting  in  the  production  of  sulphate  of  soda  and  chloride  of  magnesium, 
which  may  be  separated  by  crystallization ;  the  latter  salt  may  afterwards  be  pre- 

1  If  only  1  eq.  of  limestone  were  used  for  each  eq.  of  sulphate  of  soda,  it  would  be  found 
that,  on  treating  the  black  ash  with  water,  the  decomposition  would  be  reversed,  sulphide 
of  sodium  and  carbonate  of  lime  being  reproduced. 


CARBONATE   OF    SODA.  267 

cipitated  as  carbonate,  and  reconverted  into  sulphate  by  means  of  sulphate  of 
lime.  Common  salt  may  also  be  decomposed  by  sulphate  of  ammonia  (obtained 
from  gas  or  bone-black  factories)  or  by  sulphate  of  iron. 

Dyer  and  Hemming  have  proposed  to  convert  common  salt  directly  into  car- 
bonate of  soda  by  means  of  sesquicarbonate  of  ammonia.  Tilghman's  process 
consists  in  passing  steam  into  an  iron  retort,  in  which  chloride  of  sodium  is  main- 
tained in  a  state  of  fusion;  the  steam  thus  takes  up  a  considerable  amount  of 
vapor  of  chloride  of  sodium,  and  is  then  passed  over  lumps  of  alumina  (prepared 
by  igniting  the  sulphate)  heated  to  redness  in  a  cylinder  of  fire  clay,  aluminate 
of  soda  and  hydrochloric  acid  are  thus  produced;  the  former  is  extracted  by  water 
and  decomposed  by  carbonic  acid,  when  carbonate  of  soda  is  obtained.  This  pro- 
cess, however,  requires  a  very  high  temperature.  The  same  author  has  described 
another  method  in  which  sulphate  of  soda  is  produced  by  the  action  of  steam,  at 
a  high  temperature,  upon  a  mixture  of  common  salt  and  gypsum  (hydrochloric 
acid  being  evolved).  The  sulphate  of  soda  is  afterwards  decomposed  by  the 
united  agencies  of  alumina  and  steam,  at  a  high  temperature.] 

The  above  brief  description  of  Leblanc's  process  will  suffice  to  show  the  great 
influence  which  it  must  have  exerted  upon  various  manufactures.  When  it  is 
remembered  that  we  have  in  this  country  practically  inexhaustible  supplies  of 
chloride  of  sodium,  of  coal,  and  of  limestone,  and  that  the  alkali  produced  from 
these  ingredients  may  be  converted,  almost  on  the  spot,  into  soap  and  glass,  two 
materials  for  which  there  must  be  constantly  a  great  demand,  it  will  excite  iittle 
surprise  that  this  process  should  be  looked  upon  as  contributing,  in  no  small 
degree,  to  the  prosperity  of  the  country,  and  the  well-being  of  the  community, 
especially  since  it  will  be  seen  to  stand  in  intimate  connection  with  the  manufac- 
ture of  bleaching-powder,  with  that  of  sulphuric  acid,  and  through  the  latter,  to 
produce  an  effect  upon  the  numerous  processes  in  which  that  acid  is  largely  em- 
ployed. It  is,  probably,  no  exaggeration  to  say,  that  the  discovery  of  the  artifi- 
cial production  of  soda  forms  the  most  important  epoch  in  the  annals  of  chemical 
manufactures,  and  that  it  has  given  a  greater  impulse  to  the  science  of  chemistry 
than  any  other  of  the  numerous  discoveries  of  recent  times. 

§  171.  PROPERTIES  OF  CARBONATE  OF  SODA. — This  salt  occurs  in  commerce 
in  oblique  rhombic  prisms  of  the  formula  NaO.COa-flOAq;  the  water  amounts 
to  62.9  percent.  These  crystals  effloresce  rapidly  in  air;  when  heated,  they 
fuse  readily  in  their  water  of  crystallization,  and,  if  the  heat  be  continued  for  a 
sufficient  period,  are  converted  into  anhydrous  carbonate  of  soda.  The  latter 
fuses  at  a  moderate  red  heat,  into  a  clear  liquid,  which  is  not  affected  by  a  higher 
temperature,  and  becomes  crystalline  on  cooling. 

The  ordinary  crystals  dissolve  in  2  parts  of  cold  water,  and  in  less  than  their 
own  weight  of  boiling  water,  the  solution  is  strongly  alkaline,  but  not  so  caustic 
as  that  of  carbonate  of  potassa.  Tables  will  be  found  in  larger  chemical  works 
for  deducing  the  strength  of  a  given  solution  from  its  specific  gravity.  If  a  hot 
saturated  solution  of  this  salt  be  allowed  to  cool,  it  deposits  rectangular  prisms 
of  the  formula  NaO.C03-f  8Aq.  Rhombic  octohedra  containing  5  eqs.  of  water 
of  crystallization  are  formed,  when  the  ordinary  crystals  effloresce  in  air  at  54°. 5 
F.  (12°.'5  C.),  and  are  deposited  at  a  temperature  above  91°.5  F.  (33°  C.)  from 
the  ordinary  salt  when  fused  in  its  water  of  crystallization.  If  a  saturated  aque- 
ous solution  of  carbonate  of  soda  be  evaporated  between  77°  and  99°  F.  (25° 
and  37°  C.),  four-sided  tables  are  obtained,  of  the  formula  NaO.C02+ Aq.  These 
crystals  do  not  fuse  when  gently  heated,  and  lose  all  their  water  at  a  temperature 
below  the  boiling-point.  When  exposed  to  air  they  absorb  four  more  equivalents 
of  water. 

Carbonate  of  soda  is  sparingly  soluble  in  alcohol. 

When  steam  is  passed  over  carbonate  of  soda  at  a  bright  red  heat,  hydrate  of 
soda  is  formed,  and  carbonic  acid  disengaged. 


268  CARBONATES   OF   SODA. 

Phosphorus  at  a  high  temperature  reduces  the  carbonate,  carbon  being  sepa- 
rated, and  phosphate  of  soda  formed. 

Uses. — The  uses  of  carbonate  of  soda  are  very  numerous ;  we  have  already 
more  than  once  alluded  to  its  application  in  glass  and  soap-making ;  it  is  also 
constantly  used  in  manufactures,  merely  as  an  alkali,  for  neutralizing  acids,  and 
is  very  largely  employed  for  cleansing  various  fabrics.  The  chemist  finds,  in 
carbonate  of  soda,  a  source  of  many  other  soda-salts,  especially  of  the  bicarbonate, 
and  makes  use  of  it  for  precipitating  the  insoluble  carbonates,  for  example,  that 
of  magnesia. 

The  specimens  of  carbonate  of  soda  found  in  commerce  differ  very  considerably 
in  value,  from  the  different  amount  of  impurity  which  they  contain ;  the  chief  of 
these  impurities  are  hydrate  of  soda  (produced  by  the  decarbonation  of  the  car- 
bonate by  the  lime  formed  by  the  action  of  a  high  temperature  upon  the  lime- 
stone), sulphate  of  soda,  hyposulphite  of  soda,  sulphide  of  sodium,  sulphate  of 
lime,  carbonate  of  lime,  alumina,  and  silica  (for  the  method  of  detecting  these 
see  Analysis,  Reagents). 

For  the  method  of  ascertaining  the  amount  of  available  alkali  in  carbonate  of 
soda,  we  refer  to-  Quantitative  Analysis,  Special  Methods. 

A  double  carbonate  of  potassa  and  soda,  of  the  formula  2(NaO.C03)-}-KO.C03 
+  18 Aq,  has  been  crystallized  from  a  mixture  of  solutions  of  these  salts;  it 
appears  to  be  owing  to  the  formation  of  a  double  carbonate,  that  a  mixture  of 
single  equivalents  of  these  two  salts  fuses  much  more  readily  than  either  of  the 
salts  separately. 

§  172.  SESQUICARBONATE  OF  SODA,  2Na0.3C02,  occurs  in  the  mineral  king- 
dom as  Trona  and  Urao,  both  which  have  the  formula  2Na0.3C03+4Aq.  It 
may  be  prepared  by  rapidly  boiling  an  aqueous  solution  of  the  bicarbonate,  when 
the  salt  crystallizes  out,  on  cooling,  in  prismatic  crystals  of  the  above  formula. 
It  is  less  soluble  in  water  than  the  carbonate,  but  more  so  than  the  bicarbonate. 

BICARBONATE  OF  SODA,  NaO.C03,HO.C03. 

This  salt  occurs  in  certain  alkaline  mineral  waters. 

Preparation. — It  may  be  prepared  by  passing  carbonic  acid  to  saturation 
through  a  concentrated  solution  of  the  carbonate,  when  crystals  of  the  bicarbonate 
are  deposited ;  the  same  salt  is  obtained  on  the  large  scale  by  exposing  the  crys- 
tallized carbonate,  in  wooden  boxes,  to  a  current  of  carbonic  acid,  which  is  some- 
times evolved  from  chalk  by  the  hydrochloric  acid  flowing  out  of  the  condensers 
in  the  soda-manufacture. 

The  box  containing  the  crystals  is  provided  with  a  small  pipe,  through  which 
the  separated  water  of  crystallization^  escapes.  The  absorption  of  the  carbonic 
acid  is  attended  with  considerable  evolution  of  heat.  The  bicarbonate  is  dried  at 
a  very  gentle  heat,  and  ground  between  stones,  -care  being  taken  that  the  friction 
does  not  evolve  sufficient  heat  to  expel  any  carbonic  acid. 

It  may  also  be  prepared  by  stirring  up  3  or  4  parts  of  crystallized  carbonate 
of  soda  with  1  part  of  sesquicarbonate  of  ammonia,  and  exposing  the  mixture  to 
the  air  till  the  ammonia  has  escaped.  Again,  if  chloride  of  sodium  be  dissolved 
in  three  parts  of  water,  and  an  equal  weight  of  powdered  sesquicarbonate  of 
ammonia  be  added,  crystals  of  bicarbonate  of  soda  are  deposited  after  some  hours; 
in  this  case,  the  bicarbonate  contained  in  the  salt  of  ammonia  is  decomposed  by 
the  chloride  of  sodium. 

Properties. — Bicarbonate  of  soda  crystallizes  in  prisms  of  the  formula  NaO. 
C02,HO.C03.  It  occurs  in  commerce  as  a  white  crystalline  powder.  When 
exposed  to  air,  it  is  gradually  converted  into  sesquicarbonate,  a  change  which 
may  also  be  effected  by  gently  heating;  if  a  strong  heat  be  applied,  carbonate  of 
soda  alone  remains. 


BIBORATE   OF   SODA.  269 

Bicarbonate  of  soda  is  sparingly  soluble  in  cold  water,  yielding  a  solution 
which  is  alkaline  to  litmus,  but  not  to  turmeric;  if  the  solution  be  boiled,  car- 
bonic acid  is  expelled,  sesquicarbonate  of  soda  being  produced  at  first,  and  ulti- 
mately the  carbonate.  The  bicarbonate  of  soda  is  frequently  employed  in 
medicine,  since  its  taste  is  far  less  unpleasant  than  that  of  the  neutral  salt. 

Bicarbonate  of  soda  is  distinguished  from  the  carbonate  and  sesquicarbonate, 
by  its  giving  no  precipitate  with  solutions  of  magnesia-salts. 

§  173.  BORATE  OF  SODA,  NaO.B03,  is  obtained  by  fusing  a  mixture  of  sin- 
gle equivalents  of  biborate  and  carbonate  of  soda;  if  the  fused  mass  be  dissolved 
in  water,  it  may  be  crystallized  with  8  equivalents  of  water ;  this  salt  absorbs 
carbonic  acid  from  the  air,  and  is  converted  into  a  mixture  of  carbonate  and 
biborate  of  soda. 

BIBORATE  OF  SODA,  BORAX,  Na0.2B03. 

This  salt  is  found  in  certain  lakes  in  Thibet,  and  occurs  native  in  some  parts 
of  the  East  Indies,  also  in  China,  Persia,  and  Peru,  whence  it  is  imported  under 
the  name  of  tincal,  which  contains  borax  mixed  with  various  saponaceous  and 
other  impurities.  In  order  to  refine  tincal,  it  is  repeatedly  treated  with  lime- 
water,  which  removes  a  great  portion  of  the  soapy  matter  with  which  it  is 
incrusted;  the  salt  is  then  dissolved  in  hot  water,  and  the  solution  mixed  with  a 
little  chloride  of  calcium,  when  chloride  of  sodium  is  formed,  together  with  an 
insoluble  lime-soap;  the  clear  liquid  filtered  from  the  latter,  is  evaporated  to  the 
proper  extent,  and  set  aside  to  crystallize  in  conical  vessels  of  wood,  lined  with 
lead,  the  shape  of  which  allows  any  insoluble  matter  to  separate  readily. 

Another  process  consists  in  washing  the  tincal  with  a  weak  solution  of  soda, 
until  the  latter  runs  off  colorless,  when  the  soap  is  known  to  be  washed  away; 
the  crystals  are  drained,  dissolved  in  water,  and  a  small  quantity  of  soda  added 
to  the  solution,  to  precipitate  any  earthy  matters ;  the  filtered  liquid  is  afterwards 
evaporated  to  crystallization. 

The  larger  quantity  of  the  borax  of  commerce  is  prepared  by  dissolving  12 
parts  of  crystallized  carbonate  of  soda  in  20  parts  of  water,  and  adding,  in  small 
portions,  10  parts  of  boracic  acid;1  the  liquor  is  boiled,  allowed  to  subside,  and 
the  clear  portion  decanted  into  leaden  pans,  where  it  is  left  to  crystallize.  The 
crystals  which  are  then  deposited  are  drained,  redissolved  in  hot  water,  and 
allowed  to  crystallize  by  very  slow  cooling,  since  none  but  large  crystals  are 
marketable. 

On  this  account,  the  liquor  is  allowed  to  crystallize  in  closed  wooden  cisterns, 
lined  with  lead,  and  inclosed  in  a  wooden  box,  so  that  a  space  is  left  between 
the  walls  of  the  cistern  and  box,  which  is  filled  with  some  non-conducting  sub- 
stance (small  coal,  or  woollen  cloth),  to  prevent  rapid  cooling.  The  crystalliza- 
tion requires  25  to  30  hours.  As  much  as  possible  of  the  mother-liquor  is  then 
rapidly  drawn  off  with  a  siphon ;  and  the  rest  is  soaked  up  with  sponges,  so  that 
no  small  crystals  may  be  deposited;  the  case  is  then  covered  up,  and  the  crystals 
allowed  to  cool  slowly,  so  that  they  may  not  crack,  after  which  they  are  sorted 
and  packed.3 

Two  kinds  of  borax  are  found  in  commerce,  common  borax,  Na0.2B03  +  10Aq, 
and  octahedral  borax,  Na0.2B03  +  5Aq. 

Octohedral  borax  is  obtained  by  crystallization  from  a  solution  of  spec.  grav. 

1  If,  as  is  sometimes  the  case,  crude  boracic  acid  (which,  contains  about  8  per  cent,  of 
sulphate  of  ammonia)  is  employed  for  this  purpose,  the  liquid  is  boiled,  by  the  aid  of 
steam,  in  a  closed  vessel,  so  that  the  carbonate  of  ammonia,  which  would  otherwise  be 
lost,  may  be  conducted,  by  a  tube,  into  sulphuric  acid,  and  reconverted  into  sulphate. 

2  A  process  has  been  proposed  for  preparing  borax  in  the  dry  way,  by  exposing,  in 
thin  layers,  to  a  moderate  heat  (100°  F.),  a  mixture  of  38  parts  of  dry  boracic  acid,  and 
45  parts  of  crystallized  carbonate  of  soda,  when  the  carbonic  acid  is  expelled. 


270  BIBORATE   OP   SODA. 

1.166,  which  has  been  evaporated  at  212°  F.  (100°  C.).  The  deposition  of  octo- 
hedral  borax  begins  at  174°  F.  (79°  C.),  and  terminates  at  133°  F.  (56°  C.), 
when  the  mother-liquor  must  be  rapidly  removed,  since  ordinary  borax  begins 
to  form.  The  octohedral  borax  forms  very  hard,  compact  plates  of  crystals.  On 
account  of  a  curious  prejudice  in  the  trade,  the  manufacturers  are  obliged  to 
remove  all  projecting  angles  of  the  crystals  before  sending  the  octohedral  borax 
into  the  market,  since  the  appearance  of  such  angles  is  supposed  by  the  buyers 
to  distinguish  the  ordinary  borax.1  The  borax  obtained  from  tincal  does  not 
decrepitate  when  heated,  which  causes  it  to  be  preferred,  for  soldering,  to  artifi- 
cial borax.  It  is  said,  however,  that  by  adding  to  the  latter,  previously  to 
recrystallization,  a  small  quantity  of  tincal,  the  disadvantage  alluded  to  may  be 
prevented. 

Properties. — Common  borax  forms  large  transparent  prisms,  which  effloresce 
when  exposed  to  air;  when  heated,  the  crystals  first  decrepitate  slightly,  and 
undergo  the  aqueous  fusion ;  they  then  lose  their  water,  with  very  great  intu- 
mescence, and  form  a  white,  spongy  mass,  which  fuses  at  a  red  heat  to  a  clear 
glass,  unaltered  at  higher  temperatures.  The  crystals  of  common  borax  dissolve 
in  12  parts  of  cold,  and  in  2  parts  of  boiling  water;  the  solution  has  a  feeble 
alkaline  reaction.3 

The  crystals  of  octohedral  borax  become  opaque  in  moist  air,  from  absorption 
of  water  ;  they  do  not  intumesce  so  violently  when  heated  as  those  of  ordinary 
borax. 

The  glass  of  borax,  or  vitrified  borax,  obtained,  as  above  described,  by  heating 
the  crystals,  absorbs  water  from  the  air,  and  becomes  opaque;  in  the  fused  state, 
it  is  capable  of  dissolving  many  metallic  oxides,  and  is  hence  much  used  in  blow- 
pipe experiments,  and  in  assaying. 

Uses. — Borax  is  extensively  employed  in  the  manufacture  of  some  kinds  of 
glass,  in  glazing  stoneware,  in  smelting  operations,  and  in  soldering.  In  the  last 
case,  it  serves  to  cleanse  the  surfaces  of  metal  to  be  united  from  all  oxide;  the 
powdered  crystals  are  sprinkled  over  the  two  surfaces,  when  they  fuse  on  the 
application  of  the  solder,  and  the  fused  borax  is  pressed  out  upon  bringing  the 
surfaces  together.  The  octohedral  borax  is  preferred  for  this  purpose,  because  it 
intumesces  less  than  the  ordinary  crystals. 

The  value  of  specimens  of  tincal  is  determined  in  the  same  way  as  that  of 
carbonate  of  potassa,  by  adding  the  standard  sulphuric  acid  to  a  solution  of  the 
salt,  until  the  bright  red  color  is  produced  in  litmus;  boracic  acid,  like  carbonic, 
is  capable  of  producing  only  a  wine-red  tint. 

Another  method  (proposed  by  Schweitzer)  consists  in  dissolving  a  weighed 
amount  of  the  specimen  in  water,  adding  excess  of  hydrochloric  acid,  evaporating 
the  solution  to  dryness,  in  order  to  Wpel  the  excess  of  hydrochloric  acid,  and 
determining  the  amount  of  chlorine  existing  in  the  residue  (in  the  form  of  chlo- 
ride of  sodium),  by  precipitation,  as  chloride  of  silver  (see  Quantitative  Analysis). 
One  eq.  (35. 5  parts)  of  chlorine  corresponds  to  1  eq.  (100.8  parts)  of  anhydrous 
borax. 

Other  acid  borates  of  soda  appear  to  exist,  but  are  of  no  practical  importance. 

§  174.  We  possess  but  little  definite  knowledge  respecting  the  compounds  of 
silicic  acid  with  soda,  which  appear  to  be  rather  numerous;  they  may  be  obtained 
by  fusing  silica  with  different  proportions  of  hydrate  or  carbonate  of  soda.  Sili- 
cate of  soda  enters  into  the  composition  of  most  varieties  of  glass.  The  relations 
of  soda  to  silicic  acid  are  quite  similar  to  those  of  potassa. 

1  A  strange  example  of  the  inconvenience  arising  from  a  want  of  acquaintance  with 
the  first  principles  of  chemistry. 

2  Schweitzer  has  shown,  that  when  carbonic  acid  and  sulphuretted  hydrogen  are  passed, 
to  saturation,  into  a  strong  aqueous  solution  of  borax,  the  salt  is  completely  decomposed. 


CHLORIDE   OP   SODIUM.  271 

PEROXIDE  OF  SODIUM,  Na.03  (?) 

The  composition  of  this  oxide  is  uncertain;  it  is  a  greenish-yellow  solid, 
which  is  obtained  in  the  same  way,  and  possesses  the  same  properties  in  most 
respects,  as  the  peroxide  of  potassium. 

CHLORIDE  OF  SODIUM,  COMMON  OR  CULINARY  SALT,  ROCK  SALT,  SEA  SALT. 

NaCl. 

§  175.  The  conditions  under  which  this  salt  is  formed  are  exactly  the  same  as 
those  which  furnish  chloride  of  potassium;  if  sodium  be  heated  to  fusion  in  air, 
and  then  introduced  into  chlorine,  it  bursts  out,  after  a  few  seconds,  into  a  very 
vivid  yellow  flame,  the^jar  becoming  filled  with  thick  white  fumes  of  chloride  of 
sodium. 

Chloride  of  sodium  is  the  most  important  salt  contained  in  sea-water,  in  which 
it  amounts  to  nearly  3  per  cent. ;  various  salt-springs  are  also  very  rich  in  this 
substance.  Very  extensive  beds  of  rock  salt  are  found  in  certain  geological  strata 
posterior  to  the  coal  formation,  as  may  be  seen  at  Northwich,  in  Cheshire,  and 
in  various  parts  of  Spain  and  Poland.  Large  salt  mines  also  exist  in  Mexico. 

Preparation. — The  rock  salt  of  commerce  is  simply  extracted  from  the  salt- 
mines. It  is  then  sometimes  purified  by  dissolving  in  water,  allowing  the  im- 
purities to  subside,  and  evaporating  till  crystals  are  deposited. 

In  warm  situations  (near  Marseilles,  for  example),  salt  is  obtained  by  the 
spontaneous  evaporation  of  sea  water  in  shallow  pits  dug  in  the  sea-shore,  and 
lined  with  clay;  the  salt  forms  a  crust  upon  the  surface,  which  is  removed  from 
time  to  time.  The  salt  thus  obtained  is  made  into  heaps  and  covered  with  straw, 
so  as  to  protect  it  from  the  rain ;  the  moisture  of  the  atmosphere  then  causes 
the  chloride  of  magnesium  to  deliquesce  and  drain  off. 

In  Russia,  the  sea- water  is  allowed  to  remain  in  shallow  pits  till  partly  con- 
gealed ;  the  ice,  which  retains  very  little  salt,  is  removed,  and  the  remaining 
brine  evaporated. 

Salt  is  also  separated  as  a  by-product  in  the  evaporation  of  sea-water  by  artifi- 
cial heat,  on  some  parts  of  the  coast  of  Britain,  in  order  to  obtain  the  sulphate 
of  magnesia  from  the  mother-liquor. 

In  some  places,  a  reservoir  of  brine  is  made  in  the  salt-beds  by  boring  a  hole, 
and  introducing  a  quantity  of  water,  which,  when  saturated  with  salt,  is  drawn 
off  and  evaporated. 

At  Droitwich,  in  Worcestershire,  large  quantities  of  salt  are  annually  obtained 
from  the  salt-springs,  the  water  of  which  is  pumped  up  by  steam-engines  into 
iron  pans,  and  evaporated  by  artificial  heat. 

In  some  parts  of  France  and  Germany,  the  water  obtained  from  the  salt- 
springs  is  not  sufficiently  concentrated  to  pay  for  evaporation  by  artificial  heat. 
It  is  then  partly  evaporated,  in  the  graduating  works,  by  pumping  it  to  the  top 
of  a  wooden  scaffolding,  and  allowing  it  to  descend  in  the  form  of  rain  through 
a  quantity  of  brush-wood  and  branches  of  trees,  through  which  there  is  a  strong 
current  of  air;  in  this  way,  a  great  part  of  the  water  is  evaporated,  and  the 
brine  becomes  sufficiently  strong  for  the  salt  pans.  A  brine  containing  only  1£ 
per  cent,  of  salt,  may  thus  be  concentrated  to  18  per  cent.1 

1  These  graduation-houses  are  erected  in  airy  situations,  and  built  at  right  angles  to 
the  direction  of  the  prevailing  wind.  The  operation  proceeds  best,  of  course,  under  the 
influence  of  a  moderately  warm,  dry  wind.  Rain  and  frost  are  disadvantageous ;  the 
former  for  obvious  reasons  ;  the  latter,  because  at  temperatures  below  27°  F.  (  — 3°  C.), 
the  sulphate  of  magnesia  present  in  the  brine  decomposes  the  chloride  of  sodium,  yielding 
sulphate  of  soda  and  chloride  of  magnesium,  which  interferes  greatly  with  the  subsequent 
crystallization. 

After  a  little  time,  the  brushwood  and  twigs  become  coated  with  an  incrustation  com- 


272  CHLORIDE   OF   SODIUM. 

The  process  by  which  the  salt  is  extracted  from  the  brines,  is  divided  into  two 
operations;  the  sclilotage,  or  evaporation,  and  ihesoccage,  or  crystallization.  The 
brine  is  rapidly  heated  to  violent  ebullition,  and  fresh  liquid  continually  added 
to  replace  the  evaporated  water.  A  considerable  deposit  is  then  formed,  which 
consists  chiefly  of  a  double  sulphate  of  soda  and  lime,  and  is  removed  from  time 
to  time.  After  about  twenty-four  hours,  when  a  scum  of  crystallized  salt  begins 
to  form  on  the  surface,  the  temperature  is  allowed  to  fall  considerably  below  the 
boiling-point  of  water,  and  maintained  at  that  point  for  several  days,  while  the 
crystallization  is  proceeding.  The  higher  the  temperature  at  which  the  crystals 
are  deposited,  the  finer  the  grain  of  the  salt.  It  is  found  that  when  chloride  of 
magnesium  is  present  in  considerable  quantity,  a  film  of  crystals  of  salt  is  con- 
tinually formed  upon  the  surface  of  the  bricffe,  and  much  retards  the  evaporation ; 
this  evil  has  been  obviated  by  the  addition  of  sulphate  of  soda,  which  converts 
the  chloride  of  magnesium  into  sulphate  of  magnesia.1 

The  crystals  of  salt  are  afterwards  drained,  dried  by  exposure  to  air,  and 
packed. 

The  mother-liquors  of  the  salt-works  are  employed  for  the  preparation  of  sul- 
phates of  soda  and  magnesia,  bromine  and  iodine. 

Properties. — The  ordinary  rock-salt  is  usually  contaminated  with  sesquioxide 
of  iron,  to  which  its  peculiar  rusty  color  is  due.  Perfectly  pure  rock-salt  is 
transparent  and  colorless.3  Its  cleavage  always  exhibits  the  form  of  the  cube. 
Common  crystallized  salt  contains  various  impurities,  consisting  chiefly  of  sul- 
phate of  soda,  chloride  of  calcium,  sulphate  of  lime,  chloride  of  magnesium,  and 
sulphate  of  magnesia;  the  chlorides  of  calcium  and  magnesium  confer  upon  it 
the  property  of  becoming  moist  when  exposed  to  air;  which  is  not  exhibited  by 
pure  salt. 

Chloride  of  sodium  crystallizes  in  cubes  which  are  sometimes  aggregated 
together  in  the  form  of  hollow,  four-sided  pyramids;  occasionally,  it  is  deposited 
from  urine  in  octohedra ;  the  crystals  contain  no  water  of  crystallization,  and  are 
generally  transparent ;  they  are  unalterable  in  moderately  dry  air. 

When  heated,  the  crystals  decrepitate,  from  the  expansion  of  a  little  water 
mechanically  inclosed :  if  heated  to  redness,  they  fuse  to  a  clear  liquid,  which 
becomes  crystalline  on  cooling ;  at  a  bright  red  heat,  the  salt  volatilizes,  un- 
changed, in  thick  white  fumes.  1  part  of  chloride  of  sodium  dissolves  in  about 
2.7  parts  of  water;  its  solubility  is  very  slightly  increased  by  elevation  of  tem- 
perature. A  saturated  solution  has  a  specific  gravity  of  1.205,  and  boils,  accord- 
ing to  Gray-Lussac,  at  229°. 5  F.  (110°  C.);  if  such  a  solution  be  exposed  to  a 
temperature  of  14°  F.  ( — 10°  C.),  large  transparent  prisms  are  formed,  of  the 
composition  NaCl+4Aq.  These  crystals  effloresce  in  the  air  at  low  tempera- 
tures, and  are  easily  converted  into  the  anhydrous  cubical  crystals.  When  a 
saturated  solution  of  chloride  of  sodium  is  boiled  in  an  open  vessel,  the  ordinary 
cubical  crystals  are  deposited.  Chloride  of  sodium  is  almost  insoluble  in  alcohol. 

Uses  of  Chloride  of  Sodium. — Its  use  as  a  condiment  suggests  itself  at  once; 
again,  its  great  antiseptic  properties  render  it  peculiarly  applicable  to  the  preser- 
vation of  meat  and  other  articles  of  food.  The  enormous  consumption  of  chloride 
of  sodium  for  the  manufacture  of  carbonate  of  soda  has  already  been  mentioned. 

posed  chiefly  of  earthy  carbonates,  deposited  in  consequence  of  the  escape  of  carbonic 
acid  ;  this  fills  up  the  interstices  in  the  heap,  which  is  therefore  changed  every  five  or  six 
years. 

1  Berthier  has  recommended  hydrate  of  lime  for  the  decomposition  of  the  chloride  of 
magnesium,  when  hydrate  of  magnesia  is  precipitated,  and  chloride  of  calcium  remains  in 
solution ;  on  continuing  the  evaporation,  the  latter  salt  decomposes  the  sulphate  of  soda, 
yielding  chloride  of  sodium,  and  sulphate  of  lime,  which  is  deposited. 

2  Rose  found,  in  the  crystals  of  rock-salt  from  Wieliczka,  a  peculiar  hydrocarbon  (C^Hg), 
which  is  confined  in  cavities  in  the  salt,  and  escapes  with  a  crackling  noise  on  dissolving 
the  crystals  in  water. 


SULPHIDES   OF   SODIUM.  273 

Chloride  of  sodium  is  also  employed  in  glazing  the  coarser  kinds  of  earthenware  ; 
for  this  purpose,  it  is  'thrown  into  the  kiln  in  which  such  ware  is  baked,  at  a  full 
red  heat,  when  it  is  converted  into  vapor,  which  acts  upon  the  surface  of  the  clay 
in  such  a  manner  as  to  produce  a  silicate  of  soda,  forming  a  true  glass.  Since 
the  clay  from  which  earthenware  is  fabricated  almost  invariably  contains  sesqui- 
oxide  of  iron,  the  decomposition  may  be  represented  by  the  following  equation, 
where  the  clay  is  regarded  as  neutral  silicate  of  alumina,  containing  sesquioxide 
of  iron  :  — 


The  sesquichloride  of  iron  is  expelled  in  the  state  of  vapor.  If  no  sesquioxide 
of  iron  be  present,  nevertheless  silicate  of  soda  is  formed,  the  aqueous  vapor  which 
is  found  amongst  the  products  of  combustion  in  the  kiln  taking  part  in  the  reac- 
tion, thus  :  — 

Al303.3Si03  +  3HO  +  3NaCl=Ala03-f3(NaO.Si03)+3HCl. 

The  bromide  and  iodide  of  sodium  crystallize  in  cubes  which  are  very  soluble 
in  water  ;  they  are  prepared  in  the  same  manner  as  the  corresponding  compounds 
of  potassium,  which  they  very  much  resemble.  The  iodide  of  sodium  occurs,  it 
will  be  remembered,  in  the  mother-liquors  of  salt-works,  &c. 

The  fluoride  of  sodium  crystallizes  in  anhydrous  cubes,  which  require  25  parts 
of  water  for  solution. 

SULPHIDES  OF  SODIUM. 

§  176.  The  sulphides  of  sodium  are  probably  as  numerous  as  those  of  potas- 
sium, but  only  the  first  of  the  series,  NaS,  appears  to  be  well-known.  This  sul- 
phide is  obtained  by  methods  exactly  similar  to  those  employed  for  the  prepara- 
tion of  the  sulphide  of  potassium,  and  crystallizes  in  large  prismatic  crystals, 
containing  9  eqs.  of  water.  This  compound  resembles  sulphide  of  potassium  in 
all  its  properties;  it  is  oxidized  in  the  same  manner  when  exposed  to  air,  and 
also  combines  with  the  sulphur-acids. 

By  fusing  together  equal  weights  of  carbonate  of  soda  and  sulphur,  a  liver  of 
sulphur  may  be  prepared,  exactly  similar  to  that  obtained  with  carbonate  of 
potassa,  and  sometimes  used  in  medicine. 

A  hydrosulphate  of  sulphide  of  sodium,  NaS.HS,  is  prepared  by  the  same 
methods  as  the  corresponding  .compound  of  potassium. 

A  sulphide  of  sodium  appears  to  be  an  essential  constituent  of  the  color  known 
as  ultramarine.  The  natural  ultramarine  is  extracted  from  the  mineral1  known 
as  lapis  lazuli;  it  consists  chiefly  of  silica,  sulphuric  aeid,  sulphut,  alumina, 
soda,  lime,  and  oxide  of  iron.1 

This  pigment  was  first  artificially  prepared  by  Guimet,  in  1827.  The  process 
by  which  it  is  obtained  requires  very  great  precaution  to  insure  success,  since  the 
conditions  necessary  for  the  production  of  a  perfect  color  are  not  thoroughly 
understood  ;  every  manufacturer  has  his  own  prescription  for  its  preparation,  but 

1  The  following  are  the  results  of  an  analysis  of  lapis  lazuli  :  — 

Silica       ...........  45.40 

Alumina          V       V       '.         .......  31.67 

Soda                 .    ~   ........         ;  9.09 

Sulphuric  acid         ......  •        .         .         .5.89 

Sulphur  ........       '  .         .         .  6.95 

Iroa        .         .     ..'.    '    .         ......         .  0.86 

Lime       .........   ...  3.52 

Chlorine          .'       .        >       ',         .         .         .                  .         .  0.42 

Water     .;,,>..        .        .        .        .        .,/>,.  0.12- 

97.92 
This  mineral  is  usually  accompanied  by  iron-pyrites. 

18 


274  LITHIUM. 

the  essential  part  of  the  process  appears  to  be  the  fusion,  at  a  high  temperature, 
of  a  mixture  of  soda,  or  carbonate  of  soda,  sulphur,  silica,  and  clay  containing  a 
little  iron,  and  the  subsequent  roasting  of  the  mass  thus  obtained.  The  product 
is  washed  with  water,  and  dried.  It  is  yet  doubtful  whether  the  presence  of  iron 
is  essential  (as  is  generally  asserted)  to  the  production  of  a  blue  color. 

Ultramarine  is  very  stable  in  the  air;  it  resists  the  action  of  alkalies,  and  of 
a  high  temperature;  acids,  however,  bleach  it  immediately,  with  evolution  of 
sulphuretted  hydrogen,  showing  that  the  sulphide  which  is  present  is  essential  to 
the  color.  If  carbonate  of  potassa  be  substituted  for  carbonate  of  soda  in  the 
preparation  of  artificial  ultramarine,  a  white  compound  is  obtained,  so  that  sodium 
would  appear  to  be  a  necessary  constituent. 

Green  ultramarine  is  said  to  consist  of  blue  ultramarine  which  has  not  been 
roasted. 


LITHIUM. 

Sym.  Li.     Eq.  6.5. 

§  177.  This  somewhat  rare  metal  was  discovered  in  1818,  by  Arfwedson. 
Its  name  is  derived  from  ?u'0£ioj,  stony,  because  it  was  first  obtained  from  a 
mineral.1 

Davy  prepared  lithium  from  the  oxide,  lithia,  by  means  of  the  galvanic 
battery.  Hitherto  this  metal  has  been  obtained  only  in  small  quantity,  but  it  is 
probable  that  larger  quantities  of  it  might  be  prepared  by  methods  similar  to 
those  in  use  for  extracting  potassium  and  sodium  from  their  oxides. 

Lithium  is  very  similar  to  potassium  and  sodium,  and,  like  these  metals,  de- 
composes water  at  the  ordinary  temperature. 

The  OXIDE  OF  LITHIUM,  LITHIA  (LiO),  occurs  in  certain  minerals,  particu- 
larly in  spodumene,  petalite,  and  lepidolite.  The  last  is  generally  employed  for 
the  preparation  of  lithia;  the  powdered  mineral  is  mixed  with  two  parts  of  quick- 
lime, and  strongly  heated ;  the  mass  is  reduced  to  powder,  and  boiled  with  milk 
of  lime,  when  alumina,  sesquioxide  of  iron,  and  silica,  are  left  undissolved,  whilst 
the  filtered  solution  contains  potassa,  soda,  lithia,  and  a  little  lime ;  this  solution 
is  acidulated  with  hydrochloric  acid,  and  concentrated,  in  order  that  most  of  the 
chloride  of  potassium  may  crystallize  out;  the  lime  is  precipitated  from  the  solu- 
tion by  carbonate  of  ammonia,  the  filtered  liquid  evaporated  to  dryness,  and  the 
residue  ignited,  to  expel  ammoniacal  salts ;  this  residue,  consisting  of  the  chlorides 
of  potassium,  sodium,  and  lithium,  is  digested  with  alcohol,  which  dissolves  the 
chloride  of  lithium  ;  this  latter,  after  the  evaporation  of  the  alcohol,  is  decom- 
posed by  sulphuric  acid,  and  the  sulphate  of  lithia  thus  obtained  subsequently 
converted  into  acetate  by  double  decomposition  with  acetate  of  baryta ;  the  solu- 
tion of  acetate  of  lithia,  filtered  from  the  sulphate  of  baryta,  is  evaporated  to 
dryness,  and  the  residue  ignited,  when  it  is  converted  into  carbonate  of  lithia, 
from  which  hydrate  of  lithia  may  be  obtained  by  decomposition  with  hydrate 
of  lime. 

Properties. — Hydrate  of  Lithia  (LiO. HO)  resembles  in  its  properties  the 
hydrates  of  potassa  and  soda,  but  is  less  soluble  in  water,  and  does  not  deliquesce 
in  air. 

Its  solution  has  a  strongly  alkaline  reaction,  and  its  basic  properties  are  very 

1  The  chief  minerals  from  which  lithium  is  obtained  are  litkion-spodumene  (3(LiO.Si03), 
4  (Al203.3Si03)  ) ;  petalite  (silicate  of  soda,  lithia,  and  alumina),  and  lepidolite  or  lithia-mica 
(containing  silicates  of  alumina  and  lithia  and  silicofluoride  of  potassium). 


SALTS    OF   AMMONIA.  275 

powerful.  Hydrate  of  lithia  possesses  the  peculiar  property  of  readily  attacking 
platinum  at  a  high  temperature. 

The  Salts  of  Lithia  are  colorless,  and  much  resemble  those  of  potassa  and 
soda ;  the  nitrate  is  very  soluble  and  deliquescent  j  the  sulphate  is  soluble,  and 
may  be  obtained  in  fine  crystals }  the  carbonate  is  rather  sparingly  soluble  ;  its 
solution  has  an  alkaline  reaction. 

Phosphate  of  Lithia  is  sparingly  soluble  in  water,  and  the  double  phosphate  of 
lithia  and  soda  is  almost  insoluble,  so  that  we  may  test  for  lithia  by  mixing  its 
solution  with  phosphate  of  soda,  evaporating  to  dry  ness,  and  extracting  with 
water,  when  the  double  phosphate  of  lithia  and  soda  remains  undissolved. 

Chloride  of  Lithium  crystallizes  in  cubes  of  the  formula  LiCl+4Aq;  it  is 
deliquescent,  and  very  soluble  in  water ;  it  also  dissolves  readily  in  alcohol,  therein 
differing  from  the  chlorides  of  potassium  and  sodium. 

The  salts  of  lithia,  when  exposed  on  platinum  wire  to  the  inner  blowpipe-flame 
impart  a  red  color  to  the  outer  flame. 

From  the  foregoing  brief  description  of  the  characters  of  the  salts  of  lithia, 
it  will  be  seen  that  this  oxide  forms  a  sort  of  connecting  link  between  the  alkalies 
and  alkaline  earths. 


AMMONIUM. 

NH4=Am.     Eq.  18. 

§178.  This  metal  has  never  yet  been  obtained  in  the  separate  state;  it  is 
strictly  hypothetical,  and  the  grounds  upon  which  its  existence  is  assumed  have 
been  stated  in  the  description  of  the  compounds  of  nitrogen  and  hydrogen.  The 
method  by  which  the  so-called  amalgam  of  ammonium  is  prepared,  together 
with  the  properties  of  this  amalgam,  have  been  detailed  in  the  same  place  (§91). 

Since  the  com  pounds  produced  by  the  combination  of  ammonium  with  the  elec- 
tro-negative elements,  and  of  oxide  of  ammonium  with  the  oxygen-acids,  are  very 
analogous  to  those  formed  by  potassium  and  sodium,  we  have  deferred  the  history 
of  these  compounds  till  the  present  occasion. 

OXIDE  OF  AMMONIUM,  NH40=AmO.     Eq.  26. 

A  very  good  reason  for  supposing  this  compound  to  exist,  although  it  has  not 
been  isolated,  is  found  in  the  complete  analogy  between  the  salts,  which  are  formed 
when  ammonia  (NH3)  is  brought  into  contact  with  hydrated  acids,  and  the  cor- 
responding salts  of  potassa  and  soda.  When  liberated  from  its  compounds,  oxide 
of  ammonium  is  decomposed  into  ammonia  and  water. 

NITRITE  OF  OXIDE  OF  AMMONIUM,  NITRITE  OF  AMMONIA. 

NH4O.N03=AmO.N03. 

§  179.  This  salt  is  prepared  by  decomposing  nitrite  of  silver  with  chloride  of 
ammonium,  filtering  from  the  precipitated  chloride  of  silver,  and  evaporating  the 
filtrate  in  vacito ;  it  may  likewise  be  obtained  by  passing  nitrous  acid  into  excess 
of  ammonia,  and  evaporating  over  lime.  It  forms  a  mass  of  confused  crystals, 
which  are  easily  decomposed  by  heat ;  they  are  very  soluble  in  water,  and  the 
solution,  like  the  solid,  evolves  nitrogen  when  heated,  according  to  the  equa- 
tion : — 

NII4O.N03=4HO-fN2. 

According  to  Millon,  if  the  solution  be  rendered  slightly  alkaline  by  ammonia, 
this  decomposition  will  be  gradual,  but  if  a  slight  excess  of  a  mineral  acid  be 


276  SALTS   OP    AMMONIA. 

added,  it  will  take  place  very  rapidly.  Concentrated  sulphuric  acid  effects  the 
same  decomposition. 

This  salt  is  sometimes  employed  for  the  preparation  of  nitrogen  (§  80). 

NITRATE  OF  OXIDE  OF  AMMONIUM,  NITRATE  OF  AMMONIA. 
NH4O.N05=AmO.NO5. 

Tbe  nitrate  is  prepared  by  dissolving  ordinary  sesquicarbonate  of  ammonia  in 
moderately  dilute  nitric  acid,  perfectly  free  from  hydrochloric  acid,  till  the  car- 
bonate is  slightly  in  excess;  the  solution  is  then  evaporated  down,  till  a  drop 
placed  upon  a  watch-glass  solidifies  on  cooling,  when  the  whole  is  poured  out 
upon  a  clean  stone  slab,  broken  up,  and  preserved  in  a  stoppered  bottle. 

If  the  evaporation  be  arrested  at  an  earlier  period,  distinct  crystals  may  be 
obtained  on  cooling,  which  are  six-sided  prisms,  of  the  formula  NH4O.N05-fAq. 

Properties. — Nitrate  of  ammonia  deliquesces  on  exposure  to  air,  and  is  very 
soluble  in  water,  with  great  reduction  of  temperature.  When  heated,  it  fuses  at 
about  226°  F.  (108°  C.),  and  at  482°  F.  (250°  C.)  is  rapidly  decomposed  into 
water  and  oxide  of  nitrogen  : — 

NH4O.N05=4HO+2NO. 

If  the  temperature  be  raised  so  high  that  the  vessel  becomes  filled  with  white 
fumes,  there  are  produced,  beside  the  oxides  of  nitrogen,  a  quantity  of  nitric 
oxide,  free  ammonia,  and  nitrite  of  ammonia.  In  the  presence  of  spongy  plati- 
num, the  salt  is  decomposed  at  320°  F.  (160°  C.),  yielding  water,  nitric  acid, 
and  nitrogen : — 

5(NH4O.N05)=2(HO.N05)-fl8HO+N8. 

This  salt  deflagrates  violently  with  carbon,  and  other  combustible  bodies,  at  a 
high  temperature.  When  thrown  into  a  redhot  crucible,  it  deflagrates,  emitting 
a  pale  yellow  light,  probably  due  to  a  combustion  of  the  ammonia  at  the  expense 
of  the  nitric  acid.  When  heated  with  an  excess  »of  concentrated  sulphuric  acid, 
nitrate  of  ammonia  is  decomposed  in  the  same  manner  as  when  heated  alone. 

Nitrate  of  ammonia  is  employed  as  a  source  of  nitrous  oxide,  and  is  also  occa- 
sionally used  to  facilitate  the  incineration  of  organic  substances,  and  in  the  pre- 
paration of  refrigerating  mixtures. 

§  180.  SULPHITE  OF  OXIDE  OF  AMMONIUM,  SULPHITE  OF  AMMONIA,  NH40. 
SOa=AinO.S03. — When  sulphurous  acid  is  passed  through  an  aqueous  solution 
of  ammonia,  combination  takes  place,  with  disengagement  of  heat.  The  sulphite 
may  be  crystallized  from  this  solution.  It  is  very  soluble  in  water ;  the  solution 
evolves  ammonia  when  boiled  ;  the  crystals,  when  heated,  evolve  ammonia  and 
water,  whilst  a  bisulphite  sublimes.  '  The  solution  of  sulphite  of  ammonia,  pre- 
pared by  passing  sulphurous  acid  into  solution  of  ammonia,  is  sometimes  em- 
ployed in  analysis. 

SULPHATE  OF  OXIDE  OF  AMMONIUM,  SULPHATE  OF  AMMONIA. 

NH4O.S03=AmO  .SO,.1 

Sulphate  of  ammonia  occurs  native  as  mascaynine,  which  is  an  efflorescence 
upon  recent  lavas. 

1  A  class  of  substances  exists,  composed  of  ammonia  (NIT3)  in  combination  with  certain 
anhydrous  acids.  Thus  with  sulphurous  acid,  the  compound  NHg.S02  (sulphite  of  ammon) ; 
with  sulphuric  acid  NH3.S03  (sulphate  of  ammon),  sometimes  improperly  termed  sulpha- 
mide).  These  compounds  are  converted  into  the  corresponding  ammoniacal  salts,  when 
boiled  with  water.  The  amides,  properly  so  called,  are  compounds  of  amidogen  (NH2) 
with  an  acid,  minus  1  equivalent  of  its  oxygen,  and  may  often  be  produced  by  the  elimina- 
tion of  2  equivalents  of  water  from  the  ammoniacal  salt.  They  are  converted  into  salts 
of  oxide  of  ammonium  by  boiling  with  water.  Sulphamide  (NH2.S02)  is  a  white  deliques- 


CARBONATE   OF  AMMONIA.  277 

Preparation. — This  salt  is  prepared  on  a  large  scale  from  the  ammoniacal 
liquors  obtained  in  the  destructive  distillation  of  coal  and  bones ;  these  contain 
ammonia  chiefly  in  the  form  of  carbonate ;  they  are  decomposed  either  by  sul- 
phuric acid  or  by  sulphate  of  lime,  in  the  former  case,  with  evolution  of  carbonic 
acid,  in  the  latter,  with  precipitation  of  carbonate  of  lime;  the  liquid  containing 
the  sulphate  of  ammonia  is  then  evaporated  to  crystallization;  the  crystals  thus 
obtained  are  gently  heated,  to  destroy  various  organic  matters  with  which  they 
are  contaminated,  and  are  then  recrystallized. 

Properties. — Sulphate  of  ammonia  is  isomorphous  with  sulphate  of  potassa, 
crystallizing  in  flattened  six-sided  prisms,  which  contain  no  water  of  crystalliza- 
tion; it  becomes  slightly  moist  when  exposed  to  air.  When  heated,  the  crystals 
decrepitate,  afterwards  fuse,  and  finally  disappear  entirely,  sulphite  of  ammonia 
subliming,  and  water,  ammonia,  nitrogen,  and  sulphurous  ,acid,  passing  off. 

Sulphate  of  ammonia  dissolves  in  2  parts  of ,  cold  and  1  part  of  boiling  water. 
It  has  lately  been  proposed  to  employ  this  ^altiin  order  to  render  certain  fabrics 
less  combustible;  it  is  also  employed  in  rtbe  manufacture  of  artificial  manures, 
and  for  the  preparation  of  ammonia,  alum,  and  other  ammoniacal  salts. 

JBtsulphate  of  Ammonia  (NH4Q.S03,HQ.S03)  may  be  obtained  by  the  addi- 
tion of  sulphuric  acid  torthe  neutral  salt. 

§  181.  The  Phosphates  of  Oxides  of  Ammonium  possess  but  little  practical 
interest;  when  heated,  they  disengage  ammonia  and  water,  leaving  phosphoric 
acid.  Gay-Lussac  has  proposed  the  use  of  phosphate  of  ammonia  for  rendering 
stuffs  incombustible. 

PHOSPHATE  OF  SODA  AND  AMMONIA,  ^PHOSPHORUS  SALT,  MICROCOSMIC  SALT. 

NaO.NH4O.HO.PQ5=NaO.AmO.HO.P05. 

This  salt  occurs  in  the  urine.  It  is  prepared  by  dissolving  6  or  7  parts  of 
phosphate  of  soda  (2NaO.HO.P05)  and  1  part  of  chloride  of  ammonium  in  hpt 
water,  and  allowing  the  solution  to  crystallize.  It  forms  large  jtransparent 
prisms,  of  the  formula  NaO.NH4O.HO.P05+8Aq.  The  crystals  effloresce 
slightly  in  air,  and  evolve  a  little  ammonia.  When  gently  heated,  they  fuse 
easily,  and  lose,  at  first,  water  and  ammonia,  being  converted  into  NaO.HO.P05; 
if  this  last  be  further  heated,  it  is,  of  course,  converted  into  NaO.P05.  Micro- 
cosmic  salt  is  easily  soluble  in  water;  the  solution  evolves  ammonia  when 
evaporated.  This  salt  is  much  used  as  a  flux  in  blowpipe  experiments. 

SESQUICARBONATE  or  AMMONIA,  SAL  VOLATILE,  COMMERCIAL  CARBONATE 
OF  AMMONIA,  2NH40.3C02. 

§  182.  This  compound  has  been  alluded  to  above,  as  produced  in  the  destruc- 
tive distillation  of  coal  and  bones ;  when  obtained  from  these  sources,  it  is  gene- 
rally purified  by  one  or  two  sublimations  with  animal  charcoal,  which  retains 
the  empyreumatic  matters ;  the  ordinary  process,  however,  by  which  the  sesqui- 
carbonate  of  commerce  is  prepared,  consists  in  subliming  a  mixture  of  sulphate 
of  ammonia  (or  chloride  of  ammonium)  and  2  parts  of  chalk,  in  an  earthen  or 
iron  retort,  furnished  with  a  receiver  of  earthenware  or  lead;  the  salt  distils  over 
in  the  liquid  form,  and  solidifies  in  the  receiver,  which  is  broken  up  when  the 
mass  is  removed.  The  decomposition  is  represented  by  the  following  equation :  — 

3NH4Cl+3(CaO.C03)=3CaCl+2NH40.3C03  +  NH3+HO;  or, 
3(NH4O.S03)+3(CaO.C02)=3(CaO.S03)-f2NH40.3COa+NH3+HO. 

cent  solid,  produced  by  the  action  of  dry  ammonia  uponchlorosulphuric  aceW(S02Cl),  which 
is  obtained  when  a  mixture  of  chlorine  and  sulphurous  acid  is  exposed  to  the  action  of 
solar  light.  Phosphamide,  see  §116.  Carbamide  (NHg.CO)  is  obtained  when  ammonia  acts 
upon  chlorocarbonic  acid  gas. 


2<«  SALTS   OF   AMMONIA. 

The  salt  obtained  by  this  process,  however,  is  a  mixture  consisting  chiefly  of 
the  sesquicarbonate  with  varying  proportions  of  other  carbonates. 

Properties. — When  freshly  prepared,  sesquicarbonate  of  ammonia  forms  a 
transparent  fibrous  mass,  which,  when  exposed  to  air,  soon  becomes  covered  with 
an  opaque,  friable  crust,  into  which  the  whole  mass  is  gradually  converted,  the 
salt,  meanwhile,  exhaling  a  powerful  odor  of  ammonia.  This  white  crust  con- 
sists of  the  bicarbonate  of  ammonia,  and  appears  to  be  formed  from  the  sesqui- 
carbonate by  the  abstraction  of  ammonia  and  carbonic  acid: — 

2NH40.3C03=NH4O.C03HO.C03+NH3+C02. 

This  change  takes  place  much  more  rapidly  if  the  salt  be  powdered ;  when  it  is 
completed,  the  residue  has  lost  its  pungent  odor.  When  sesquicarbonate  of 
ammonia  is  heated,  carbonic  acid  is  evolved  at  first,  and  part  of  the  sesquicar- 
bonate of  ammonia  sublimes  unchanged,  whilst  the  remainder  enters  into  fusion, 
and  is  decomposed  into  compounds  containing  different  proportions  of  ammonia 
and  carbonic  acid.  The  sesquicarbonate  of  ammonia  dissolves  in  about  3  parts 
of  cold  water;  if  the  salt  be  treated  with  a  small  quantity  of  water,  it  appears  to 
suffer  a  partial  decomposition,  the  solution  containing  chiefly  the  neutral  carbon- 
ate, NH4O.C03,  and  the  residue  the  bicarbonate.  If  a  warm  saturated  solution 
be  allowed  to  cool,  large  crystals  of  bicarbonate  of  ammonia  are  deposited.  The 
latter  salt  also  appears  to  be  precipitated  when  the  aqueous  solution  of  the  ses- 
quicarbonate is  mixed  with  alcohol. 

The  aqueous  solution  has  an  alkaline  reaction,  and  an  ammoniacal  odor;1  if 
exposed  to  the  air,  it  is  gradually  converted  into  solution  of  the  bicarbonate; 
when  the  solution  is  boiled,  carbonic  acid,  and  traces  of  ammonia,  are  disengaged 
with  effervescence,  and  the  neutral  carbonate  remains  in  solution;  if  this  be 
further  evaporated,  the  latter  salt  is  also  volatilized. 

The  Bicarbonate  of  Ammonia*  may  be  obtained  by  passing  carbonic  acid 
through  a  concentrated  solution  of  the  sesquicarbonate;  it  is  deposited  in  crystals 
of  the  formula  NH4O.COa,HO.COs,  which  have  the  same  form  as  those  of  bicar- 
bonate of  potassa.  They  are  inodorous,  permanent  in  the  air,  and  volatilize 
when  heated;  this  salt  is  much  less  soluble  in  water  than  the  neutral  carbonate. 
When  the  solution  is  boiled,  it  disengages  carbonic  acid,  and  neutral  carbonate 
of  ammonia  (NH^O.CO^)  remains  in  solution. 

When  sesquicarbonate  of  ammonia  is  dissolved  in  boiling  water,  in  a  flask, 
which  is  afterwards  closed  to  prevent  the  escape  of  carbonic  acid,  the  solution 
deposits,  on  cooling,  large  prismatic  crystals  of  the  formula  2(NH4O.H0.2C00)-j- 
Aq. 

Sesquicarbonate  of  ammonia  is  employed  as  a  smelling-salt,  and,  to  a  consider- 
able extent,  medicinally. 

In  the  laboratory  it  is  very  useful  as  a  reagent,  and  as  a  source  of  many  other 
ammoniacal  salts. 

Other  carbonates  of  ammonia,  of  more  complicated  composition,  have  been 
obtained,  but  present  no  points  of  interest. 

The  jborates  of  Ammonia  are  devoid  of  practical  interest. 

CHLORIDE  OF  AMMONIUM,  HYDROCHLORATE  OF  AMMONIA,  SAL-AMMONIAC. 

NH4Cl=AmCl. 

§  183.  This  salt  is  formed,  in  thick  white  fumes,  when  hydrochloric  acid  gas 
and  ammoniacal  gas  are  brought  into  contact ;  it  is  sometimes  found  in  the 
neighborhood  of  volcanoes. 

1  If  an  aqueous  solution  of  sesquicarbonate  of  ammonia  be  exposed  to  a  temperature 
approaching  the  freezing  point,  it  deposits  crystals  of  the  formula  2NH40.3C02-j-3Aq. 
'    2  Bicarbonate  of  ammonia  has  been  found  in  considerable  quantity,  forming  crystalline 
masses,  in  a  bed  of  guano  on  the  western  coast  of  Patagonia. 


CHLORIDE   OF   AMMONIUM.  279 

Preparation. — Chloride  of  ammonium  was  formerly  prepared  chiefly  in  Egypt, 
•where  the  inhabitants  collected  the  soot  arising  from  the  imperfect  combustion 
of  the  dung  of  camels ;  this  soot  was  afterwards  heated  in  large  glass  flasks, 
when  the  chloride  of  ammonium  sublimed  in  the  upper  part,  and  was  extracted 
by  breaking  the  flask.1 

A  large  quantity  of  sal-ammoniac  is"  now  prepared  from  the  ammoniacal  liquors 
obtained  in  the  distillation  of  bones  for  the  preparation  of  animal  charcoal,  and 
of  coal  in  the  gas-works.  These  ammoniacal  liquors  are  neutralized  with  hydro- 
chloric acid  (which  decomposes  the  carbonate  of  ammonia  and  sulphide  of  ammo- 
nium, with  evolution  of  carbonic  and  hydrosulphuric  acids),  evaporated,  and 
allowed  to  crystallize ;  the  salt  is  then  gently  heated  to  destroy  the  tarry  matter 
which  it  contains,  dissolved  in  water,  and  purified  by  animal  charcoal  j  the  pure 
crystals  are  afterwards  sublimed  in  large  earthen  bottles,  or  in  iron  vessels,  lined 
with  clay,  and  provided  with  leaden  domes. 

Chloride  of  ammonium  is  also  prepared  by  subliming  a  mixture  of  sulphate 
of  ammonia  and  chloride  of  sodium,  when 

NH4O.S08+NaCl=NaO.SO,+NH4Cl. 

The  sulphate  of  ammonia  is  obtained  from  the  ammoniacal  liquor  of  the  gas- 
works, or  of  the  bone-black  factories,  either  by  neutralizing  them  with  sulphuric 
acid,  or  by  double  decomposition  with  a  sulphate  (of  lime  or  oxide  of  iron). 

The  chloride  of  ammonium  is  also  sometimes  prepared  from  mixed  solutions 
of  sulphate  of  ammonia  and  chloride  of  sodium  ;  on  evaporation,  the  chloride  of 
ammonium  crystallizes  out,  and  sulphate  of  soda  remains  in  the  mother-liquor. 

Properties. — The  sublimed  chloride  of  ammonium  of  commerce  forms  a  very 
tough,  translucent,  fibrous  mass,  generally  retaining  the  shape  of  the  vessel  into 
which  it  was  sublimed,  and  often  of  a  brown  color  where  it  has  been  in  contact 
with  this  vessel.  It  is  not  altered  by  exposure  to  air.  At  a  red-heat  it  vola- 
tilizes in  thick  white  clouds,  without  previously  fusing.  It  may,  however,  be 
fused  in  a  tube,  which  is  hermetically  sealed. 

Chloride  of  ammonium  dissolves  in  2.7  parts  of  cold  water,  and  in  an  equal 
weight  of  boiling  water.  The  solution,  on  cooling,  deposits  anhydrous  crystals 
of  a  peculiar  feathery  appearance  and  consisting  of  an  assemblage  of  minute 
octohedra. 

When  an  aqueous  solution  of  chloride  of  ammonium  is  evaporated,  a  little  of 
the  salt  passes  off  with  the  vapor. 

The  solution  of  chloride  of  ammonium  is  capable  of  dissolving  many  metallic 
oxides  and  salts  insoluble  in  water.  Chloride  of  ammonium  is  sparingly  soluble 
in  alcohol. 

Many  metals,  at  somewhat  elevated  temperatures,  decompose  chloride  of 
ammonium,  metallic  chlorides  being  formed,  while  ammonia  and  hydrogen  are 
evolved. 

Uses  of  Chloride  of  Ammonium. — This  salt  is  the  source  from  which  ammonia 
is  always  prepared  in  the  laboratory,  and  is  also  very  useful  in  analysis. 

It  is  employed  occasionally  in  soldering,  to  cleanse  the  metallic  surfaces  to  be 
united;  its  action  in  this  case  appears  to  depend  upon  the  principle  which  Hose 
has  recently  turned  to  account  in  analytical  operations. 

Rose  found  that  when  the  arseniates,  arsenites,  antimoniates,  and  stannates  of 
the  alkalies  were  heated  with  several  times  their  weight  of  chloride  of  ammonium, 
the  arsenic,  antimony  and  tin  were  volatilized  in  the  form  of  chlorides.  The 
alkaline  phosphates  were  entirely  converted  into  chlorides  by  the  same  treatment. 
Alumina  was  partly,  and  sulphate  of  alumina  entirely,  volatilized  when  heated 

1  At  Liege,  sal-ammoniac  is  prepared  by  burning,  in  peculiarly  constructed  ovens,  a 
mixture  of  coal,  common  salt,  clay,  and  animal  matter,  collecting  the  soot,  and  separating 
the  chloride  of  ammonium  from  it  by  sublimation. 


280  SALTS    OP  AMMONIUM. 

with  sal-ammoniac.  Sesquioxide  of  iron  was  also  partly  volatilized.  The  oxides 
of  nickel,  cobalt,  and  bismuth,  were  reduced  to  the  metallic  state.  Oxide  of 
zinc,  oxide  of  lead,  sulphide  of  lead,  and  sulphate  of  zinc,  were  completely  vola- 
tilized. These  reactions  have  been  applied  by  their  discoverer  to  facilitate  the 
quantitative  analysis  of  various  substances. 

Chloride  of  ammonium  is  also  employed  in  medicine. 

The  bromide  (NH4Br)  and  the  iodide  (NH4l)  of  ammonium,  much  resemble 
the  chloride. 

SULPHIDE  OP  AMMONIUM,  HYDROSULPHATE  OP  AMMONIA. 
NH4S=AmS. 

§  184.  This  compound  is  obtained  when  hydrosulphuric  acid  gas  is  mixed 
with  excess  of  ammoniacal  gas  in  a  vessel  which  is  cooled  down  to  0°  F.  (-  18° 
C.1)  ',  it  may  also  be  obtained  by  distilling  a  mixture  of  single  equivalents  of 
chloride  of  ammonium  and  sulphide  of  potassium,  the  receiver  being  cooled  to 
the  above  temperature. 

When  thus  prepared,  it  forms  colorless  crystals,  which  decompose  at  the 
ordinary  temperature,  into  ammonia  and  bydrosulphate  of  sulphide  of  ammo- 
nium :  — 

2NH4S=NH3+NH4S.HS. 

A  solution  of  sulphide  of  ammonium  is  prepared  by  saturating  a  solution  of 
ammonia  with  hydrosulphuric  acid,  and  afterwards  adding  a  quantity  of  the  same 
solution  equal  to  that  originally  employed  ;  hydrosulphate  of  sulphide  of  ammo- 
nium (NH4S.HS)  is  first  produced,  and  is  converted  into  sulphide  of  ammonium 
(NH4S)  by  the  additional  equivalent  of  ammonia. 

Properties.  —  The  solution  thus  obtained,  which  is  frequently  employed  in  ana- 
lysis, is  colorless,  possesses  a  strongly  alkaline  reaction,  and  a  disagreeable  odor 
of  ammonia  and  hydrosulphuric  acid.  When  exposed  to  air,  it  soon  becomes 
yellow,  from  the  formation  of  the  bisulphide  :  — 

2NHJ3  +  0  (from  the  a7>)=NH4S9+HO  +  NH3; 
a  small  quantity  of  hyposulphite  of  ammonia  is  also  formed  :  — 


A  solution  of  pure  sulphide  of  ammonium  remains  clear  when  mixed  with 
excess  of  acid,  whilst,  if  one  of  the  higher  sulphides  be  present,  sulphur  is  de- 


Sulphide  of  ammonium  is  a  sulphur-base,  like  the  sulphides  of  potassium 
and  sodium ;  it  hence  dissolves  the -sulphides  of  arsenic,  antimony,  and  other 
sulphur-acids. 

The  Hydrosulphate  of  Sulphide  of  Ammonium  (NH4S.HS),  may  be  obtained, 
by  passing  equal  volumes  of  ammonia  and  hydrosulphuric  acid  into  a  vessel 
surrounded  with  ice ;  it  forms  colorless  needles,  which  are  very  volatile  and  soon 
decomposed  in  the  air.  Its  solution  is  alkaline  to  test-papers. 

Bisulphide  of  ammonium  (NH4Sa)  is  obtained  in  yellow  crystals  when  vapors 
of  sulphur  and  sal-ammoniac  are  passed  through  a  porcelain  tube,  heated  to  red- 
ness, and  connected  with  a  cooled  receiver. 

It  is  very  deliquescent,  and  is  readily  decomposed  by  acids,  sulphuretted 
hydrogen  being  evolved,  and  sulphur  deposited. 

The  compounds  NH4S3,NH4S4,NH4S5  and  NH4Sy  have  been  obtained. 

The  solution  known  as  Liquor  fumans  Boylii,  is  obtained  by  distilling  a  mix- 
ture of  1  part  of  sulphur  with  2  parts  of  chloride  of  ammonium,  and  2  or  3 

1  At  ordinary  temperatures,  or  when  an  excess  of  hydrosulphuric  acid  is  employed,  the 
compound  NH4S.HS  is  obtained. 


SULPHIDE   OF  AMMONIUM.  281 

parts  of  lime;  it  appears  to  be  a  mixture  of  different  sulphides  of  ammonium, 
especially  of  NH4S  and  NH4S5,  with  water.  The  reaction  by  which  it  is  pro- 
duced may  probably  be  thus  expressed  :  — 


The  liquid  is  obtained,  even  when  the  ingredients  are  anhydrous,  in  which 
case,  water  must  be  formed  by  a  secondary  decomposition  between  the  lime  and 
chloride  of  ammonium. 

It  is  of  a  yellow  color  and  disagreeable  odor  ;  it  fumes  in  the  air.  Liquor 
fumans  Boylii  is  sometimes,  though  rarely,  used  in  medicine. 


282  BARIUM   AND   OXYGEN 


METALS  OF  THE  SECOND  GROUP. 

(Metals  of  the  Alkaline  Earths.'} 


BARIUM. 

Sym.  Ba.     Eq.  68.5. 

§  185.  THIS  metal  was  first  obtained  by  Davy,  in  1808.  Its  name  is  de- 
rived from  j3ap£j,  heavy,  because  of  the  great  density  of  its  compounds.  Barium 
occurs  in  considerable  quantities  in  the  mineral  kingdom,  in  combination  with 
oxygen  and  acids.  Carbonate  of  baryta  constitutes  the  mineral  witherite,  the 
sulphate  is  known  as  heavy  spar. 

Preparation. — Barium  may  be  obtained  by  decomposing  hydrate,  carbonate, 
or  nitrate  of  baryta,  or  chloride  of  barium,  in  a  moist  state,  by  the  galvanic 
battery,  in  contact  with  mercury,  into  which  the  negative  pole  dips ;  an  amalgam 
of  barium  is  thus  obtained,  from  which  the  mercury  may  be  separated  by  distil- 
lation in  an  atmosphere  free  from  oxygen. 

Another  method. of  preparing  barium  consists  in  passing  the  vapor  of  potassium 
over  redhot  baryta,  in  an  iron  tube,  and  extracting  the  barium  from  the  result- 
ing mixture  of  this  metal  with  potassa,  by  means  of  mercury. 

Small  quantities  of  this  metal  may  also  be  obtained  by  the  reduction  of  baryta, 
supported  on  a  piece  of  charcoal  or  slate,  by  a  jet  of  a  mixture  of  three  volumes 
of  hydrogen  and  one  volume  of  oxygen,  when  globules  of  barium  are  obtained. 

Properties. — Barium  is  a  white  malleable  metal,  not  very  lustrous.  Its  spe- 
cific gravity  is  about  4.  It  fuses  below  a  red  heat,  and  volatilizes  at  a  much 
higher  temperature.  When  exposed  to  air,  it  becomes  covered  with  a  white 
coating  of  baryta;  if  heated  in  air,  this  oxidation  is  attended  with  combustion. 
Barium  decomposes  water  energetically  at  common  temperatures,  hydrogen  being 
evolved  and  baryta  dissolved  in  the  water. 


BARIUM   AND   OXYGEN. 

Baryta BaO. 

Bin  oxide  of  barium Ba02. 

OXIDE  OF  BARIUM,  BARYTA. 

BaO.     Eq.  76.5. 

§  186.  Baryta  is  prepared  by  heating  the  nitrate  of  baryta  to  bright  redness 
in  a  covered  porcelain  crucible  or  retort  until  no  more  fumes  are  evolved : — 

BaO.N05=BaO+N04+0. 

It  may  also  be  obtained  by  reducing  the  carbonate  of  baryta,  by  means  of 
charcoal,  at  a  high  temperature. 


BARYTA.  283 

Baryta  which  has  been  prepared  by  igniting  the  nitrate  in  a  porcelain  or 
earthen  vessel,  generally  contains  certain  earthy  impurities;  it  is  therefore  better 
to  heat  the  nitrate  in  a  clean  iron  vessel  ;  platinum  should  not  be  used,  since  it 
is  easily  attacked  by  baryta  at  a  high  temperature. 

The  crucible  or  retort  employed  in  preparing  baryta  should  be  rather  capa- 
cious, since  the  nitrate  swells  up  very  much  when  heated;  for  the  same  reason, 
the  heat  should  be  applied  gradually. 

Properties.  —  Baryta,  thus  obtained,  is  a  gray,  porous  mass,  which  fuses  only 
at  a  very  high  temperature;  it  is  very  heavy,  having  a  specific  gravity  between 
4  and  5.  When  exposed  to  air,  it  absorbs  water,  and  falls  to  a  white  powder  of 
hydrate  of  baryta;  the  same  combination  takes  place,  with  great  evolution  of 
heat,  when  baryta  is  moistened  with  water. 

HYDRATE  OF  BARYTA,  BaO.HO. 

In  order  to  prepare  the  hydrate  of  baryta,  a  solution  of  sulphide  of  barium 
may  be  boiled  with  oxide  of  copper  till  it  gives  a  white  precipitate  with  acetate 
of  lead;  the  solution  is  then  rapidly  filtered,  evaporated,  and  the  hydrate  of 
baryta  allowed  to  crystallize  out;  the  following  equation  expresses  the  decom- 
position :  — 


Properties.  —  The  crystals  are  transparent  four  or  six-sided  prisms,  of  the 
formula  BaO.IIO-f  9Aq.  When  exposed  to  air,  they  absorb  carbonic  acid,  and 
are  converted  into  carbonate  of  baryta;  at  a  gentle  heat,  they  lose  the  9Aq, 
leaving  pure  hydrate  of  baryta,  from  which  the  water  cannot  be  expelled  by 
heat. 

Hydrate  of  baryta  fuses  somewhat  below  redness,  and  becomes  crystalline  on 
cooling. 

It  is  soluble  in  2  parts  of  boiling,  and  20  parts  of  cold  water;  the  solution  is 
strongly  alkaline,  and,  if  exposed  to  air,  rapidly  absorbs  carbonic  acid,  and 
deposits  carbonate  of  baryta.  A  cold  saturated  solution  is  known  as  laryta- 
iwtfer. 

The  hydrate,  and  all  the  soluble  salts  of  baryta,  are  powerful  poisons. 

Hydrate  of  baryta  is  much  employed  in  analysis. 

The  salts  of  baryta  are,  for  the  most  part,  neutral  to  test-papers. 

NITRATE  OF  BARYTA,  BaO.N05. 

§  187.  This  salt  is  prepared  by  dissolving  carbonate  of  baryta  in  very  dilute 
nitric  acid,  or  by  decomposing  a  dilute  solution  of  sulphide  of  barium  with  this 
acid,  evaporating  and  crystallizing. 

Properties.  —  The  nitrate  forms  white  translucent  octohedra,  which  are  anhy- 
drous, and  unalterable  in  the  air.  When  heated,  they  decrepitate,  fuse  easily, 
and  are  decomposed  at  a  red  heat,  evolving  peroxide  of  nitrogen  (N04)  and 
oxygen,  and  leaving  a  mass  of  baryta,  which  is  much  swollen  from  the  escape  of 
gas  during  the  decomposition.  If  the  heat  be  cautiously  applied,  nitrite  of 
baryta  is  at  first  formed.  The  nitrate  detonates,  but  not  very  violently,  with 
combustible  matters.  It  is  soluble  in  8  parts  of  cold,  and  3  parts  of  boiling 
water;  it  is  much  less  soluble  in  dilute  nitric  acid,  so  that  the  latter  generally 
produces  a  precipitate  in  an  aqueous  solution  of  this  salt;  it  is  for  this  reason, 
also,  that  moderately  concentrated  nitric  acid  will  not  act  upon  carbonate  of 
baryta.  Nitrate  of  baryta  is  insoluble  in  alcohol.  This  salt  is  sometimes  em- 
ployed for  the  detection  of  acids  in  analysis,  and  is  the  source  from  which  we 
prepare  baryta. 

Chlorate  of  Baryta  (BaO.C105)  may  be  prepared  by  decomposing  a  hot  solu- 
tion of  chlorate  of  potassa  with  a  slight  excess  of  hydrofluosilicic  acid,  filtering, 


284  SALTS    OF   BARYTA. 

and  saturating  the  solution  with  carbonate  of  baryta;  the  filtered  liquid,  when 
evaporated,  yields  crystals  of  the  chlorate. 

Another  process  consists  in  decomposing  the  chlorate  of  ammonia  with  car- 
bonate of  baryta,  and  allowing  the  filtrate  to  crystallize.  For  this  purpose, 
122.6  parts  of  chlorate  of  potassa,  and  167  parts  of  bitartrate  of  ammonia  are 
dissolved  in  the  smallest  possible  quantity  of  boiling  water,  and  the  bitartrate  of 
potassa  allowed  to  crystallize  out.  The  solution  is  then  mixed  with  an  equal 
volume  of  alcohol,  to  precipitate  the  remainder  of  the  bitartrate  of  potassa, 
filtered,  and  digested  with  freshly  precipitated  carbonate  of  baryta. 

Sulphite  of  Baryta,  BaO.S02,  is  precipitated  in  fine  needles  when  sulphite 
of  soda  is  added  to  chloride  of  barium. 


SULPHATE  or  BARYTA,  BaO.S03. 

§  188.  We  have  already  mentioned  this  salt,  as  found  native  in  the  form  of 
heavy-spar.  It  may  be  prepared  very  readily  by  precipitating  a  hot  solution  of 
chloride  of  barium  with  dilute  sulphuric  acid  in  excess,  heating  the  solution  to 
ebullition,  collecting  the  precipitate  on  a  filter,  and  washing  with  hot  water  till 
the  washings  are  no  longer  acid. 

Properties.  —  The  crystals  of  heavy-spar  belong  to  the  right  prismatic  system  ; 
their  specific  gravity  is  4.4.  The  precipitated  sulphate  of  baryta  is  a  white 
powder. 

Sulphate  of  baryta  fuses  at  a  very  high  temperature  to  a  white  enamel  ;  when 
mixed  with  carbon  and  heated  to  redness,  it  is  reduced  to  sulphide  of  barium  :  — 

BaO.S03-fC4=BaS+4CO. 

When  boiled  with  a  solution  of  carbonate  of  potassa  or  of  soda,  or  better,  if 
fused  with  these  salts,  it  is  decomposed  into  carbonate  of  baryta  and  sulphate  of 
potassa  or  soda  ;  if  sulphate  of  baryta  be  fused  with  hydrate  of  potassa,  sulphate 
of  potassa  is  formed,  together  with  hydrate  of  baryta.  It  is  almost  perfectly 
insoluble  in  water  and  dilute  acids;  it  is  soluble  in  concentrated  sulphuric  acid 
to  some  extent,  but  is  reprecipitated  by  water.1 

When  sulphate  of  baryta  is  precipitated  from  a  solution  containing  other  salts, 
especially  nitrate  of  baryta,  a  portion  of  the  latter  is  carried  down  with  the  sul- 
phate, and  can  only  be  separated  from  it  by  long  washing  with  hot  water.  Ni- 
trate of  soda  may  also  be  carried  down  in  this  way,  in  considerable  quantity. 

When  sulphate  of  baryta  is  fused  with  chloride  of  calcium,  chloride  of  barium 
is  produced,  together  with  sulphate  of  lime,  whereas,  if  a  solution  of  the  latter 
salt  be  added  to  solution  of  chloride  of  barium,  the  decomposition  is  reversed, 
sulphate  of  baryta  and  chloride  of  calcium  being  formed. 

Sulphate  of  baryta  is  the  source  from  which  all  baryta-compounds  are  usually 
prepared.  It  is  sometimes  used  instead  of  white  lead  as  a  pigment,  but  is  more 
frequently  employed  to  adulterate  that  substance  (see  White  Lead).  This  salt 
also  receives  application  as  a  flux  in  copper  smelting. 

Seleniate  of  Baryta,  BaO.Se03,  is  precipitated  when  chloride  of  barium  is 
added  to  solution  of  selenic  acid  or  a  seleniate  ;  it  resembles  the  sulphate  in  its 
insolubility  in  water  and  in  dilute  acids  ;  when  boiled  with  hydrochloric  acid, 
however,  it  dissolves,  being  converted  into  chloride  of  barium,  with  liberation  of 
selenious  acid  and  chlorine  :  — 


BaO.Se08+2HCl=BaCl+2HO  +  SeO, 

The  Phosphates  of  Baryta  are  precipitated  by  chloride  of  barium  from  the 

1  A  boiling  solution  of  sulphate  of  baryta  in  concentrated  sulphuric  acid  deposits,  on 
cooling,  needles  of  the  formula  BaO.S03,HO.S03,  bisulphate  of  baryta;  this  salt  is  decom- 
posed by  water  into  sulphate  of  baryta  and  free  sulphuric  acid. 


BINOXIDE    OF   BARIUM.  285 

corresponding  soda-salts.     They  are  sparingly  soluble  in  water,  but  soluble  in 
hydrochloric  or  nitric  acid. 

CARBONATE  OF  BARYTA,  BaO.COa. 

§  189.  This  compound  occurs  in  nature  as  the  mineral  witlierite.  When,  as 
is  often  the  case,  the  pure  freshly  precipitated  carbonate  is  required,  it  is  pre- 
pared by  precipitating  solution  of  chloride  of  barium  with  a  slight  excess  of 
carbonate  of  ammonia,  and  washing,  by  decantation,  with  hot  water,  till  the 
washings  are  not  rendered  turbid  by  excess  of  nitric  acid  and  nitrate  of  silver. 

Properties. — Witherite  is  found  crystallized  in  rhombohedra,  of  spec.  grav.  4.3. 

The  precipitated  carbonate  of  baryta  is  a  soft,  white  powder;  when  very 
strongly  heated,  it  fuses,  and  loses  its  carbonic  acid  at  a  very  high  temperature  ; 
when  very  finely  divided  and  suspended  in  water,  it  has  an  alkaline  reaction. 
Carbonate  of  baryta  is  poisonous  ;  it  is  nearly  insoluble  in  water,  but  dissolves 
in  solution  of  carbonic  acid,  and  very  readily  in  dilute  hydrochloric  or  nitric 
acid ;  it  is  also  slightly  soluble  in  solution  of  chloride  of  ammonium  in  the  cold, 
but  if  long  boiled  with  this  reagent,  it  dissolves  with  decomposition  : — 

NH4Cl-fBaO.C02=BaCl+NH4O.COa, 
the  carbonate  of  ammonia  being  carried  off  with  the  steam. 

Carbonate  of  baryta  is  decomposed  by  steam  at  a  bright  red  heat,  hydrate  of 
baryta  being  formed. 

If  carbonate  of  baryta  be  suspended  in  a  solution  of  an  equal  weight  of  sul- 
phate of  potassa  or  of  soda,  in  the  cold,  and  frequently  agitated,  sulphate  of 
baryta  will  be  formed,  and  an  alkaline  carbonate  found  in  solution,  but  if  the 
mixture  be  boiled,  the  decomposition  will  be  reversed. 

Native  carbonate  of  baryta  is  used  for  the  preparation  of  other  salts  of  baryta; 
the  freshly  precipitated  carbonate  is  sometimes  employed  in  the  preparation  of 
organic  substances,  for  removing  free  sulphuric  acid,  or  for  decomposing  the  solu- 
ble sulphates  of  organic  bases.  . 

Carbonate  of  baryta  is  dissolved  by  a  solution  of  carbonic  acid,  bicarbonate  of 
baryta  being  produced,  which  has  not  been  obtained  in  a  solid  state. 

Scsquicarbonate  of  Baryta,  2Ba0.3CO3,  is  precipitated  when  chloride  of 
barium  is  decomposed  by  sesquicarbonate  of  soda. 

A  Borate  and  a  Blborate  of  Baryta  may  be  precipitated  by  adding  chloride  of 
barium  to  the  corresponding  salts  of  soda.  They  are  sparingly  soluble  in  water, 
but  easily  in  hydrochloric  or  nitric  acid. 

BINOXIDE  OF  BARIUM,  Ba03. 

§  190.  This  substance  is  precipitated  in  the  form  of  a  crystalline  hydrate, 
when  an  excess  of  baryta-water  is  added  to  binoxide  of  hydrogen. 

Preparation. — Fragments  of  anhydrous  baryta  are  heated  to  low  redness  in  a 
green  glass  retort,  and  a  current  of  dry  oxygen  passed  over  them ;  the  appear- 
ance of  the  fragments  is  scarcely  altered. 

The  binoxide  may  also  be  prepared  by  gradually  adding  about  1  part  of  chlo- 
rate of  potassa  to  4  parts  of  baryta,  heated  to  low  redness  in  a  porcelain  crucible. 
The  mass,  which  contains  binoxide  of  barium  and  chloride  of  potassium,  is  washed 
with  cold  water,  when  the  binoxide  is  left  as  a  hydrate. 

Properties. — Binoxide  of  barium  combines  with  water,  without  evolution  of 
heat,  to  form  a  hydrate  (Ba03.6HO),  which  is  a  white,  very  slightly  soluble 
powder ;  when  this  is  boiled  with  water,  oxygen  escapes,  and  baryta  is  found  in 
solution.1 

1  Binoxide  of  barium  also  loses  half  its  oxygen,  when  heated  alone  to  a  very  high 
temperature ;  but,  iu  an  atmosphere  of  steam,  this  decomposition  may  be  effected,  as 
Boussingault  has  recently  shown,  at  a  much  lower  temperature. 


286  SULPHIDE   OF   BARIUM. 

It  is  very  easily  decomposed  by  deoxidizing  agents;  when  heated  in  hydro- 
gen, it  yields  hydrate  of  baryta,  and  gives  up  its  second  equivalent  of  oxygen 
to  carbon,  phosphorus,  sulphur,  boron,  and  the  metals  at  elevated  temperatures; 
when  dissolved  in  hydrated  acids,  a  salt  of  baryta  is  formed,  together  with  bin- 
oxide  of  hydrogen  : — 

Ba03-fHO.S03=BaO.S03-fH03; 

this  decomposition  is  taken  advantage  of  for  the  preparation  of  the  latter  com- 
pound. 

Biuoxide  of  barium  is  also  used  in  the  preparation  of  certain  of  the  rarer 
metallic  peroxides,  and  has  lately  been  proposed  as  an  oxidizing  agent  in  analysis. 

It  has  also  been  recently  employed  by  Boussingault  for  the  extraction  of  oxy- 
gen from  atmospheric  air  (§  69). 

CHLORIDE  OF  BARIUM,  MURIATE  OF  BARYTES,  Bad. 

§  191.  This  salt  is  formed  when  chlorine  is  passed  over  baryta  at  a  high  tem- 
perature, oxygen  being  expelled. 

Preparation. — Native  carbonate  of  baryta  may  be  dissolved  in  dilute  hydro- 
chloric acid,  to  "saturation,  and  the  solution  evaporated  to  the  crystallizing  point. 
Another  method  consists  in  decomposing  solution  of  sulphide  of  barium  with  a 
slight  excess  of  hydrochloric  acid,  boiling,  filtering  to  separate  a  little  precipi- 
tated sulphur,  and  crystallizing. 

On  the  large  scale,  chloride  of  barium  is  prepared  by  calcining  a  mixture  of 
powdered  heavy-spar  (sulphate  of  baryta)  with  half  its  weight  of  chloride  of  cal- 
cium (the  residue  from  the  preparation  of  ammonia)  in  a  reverberatory  furnace ; 
the  mass  is  exhausted,  as  rapidly  as  possible,  with  hot  water,  which  leaves  the 
sulphate  of  lime  undissolved,  and  the  clear  solution  of  chloride  of  barium  decanted 
and  evaporated.1 

The  salt  prepared  by  any  of  the  above  processes  should  be  purified  by  recrys- 
tallization. 

Properties — Chloride  of  barium  forms  colorless  tabular  crystals,  of  the  for- 
mula BaCl-f  2  Aq  ;  these  are  unaltered  in  air;  when  heated,  they  decrepitate, 
and  lose  their  water;  the  anhydrous  salt  thus  obtained  fuses  at  a  red  heat,  and 
when  strongly  heated,  in  the  presence  of  aqueous  vapor,  it  is  partly  converted 
into  baryta.  The  fused  salt  absorbs  2  eqs.  of  water  from  the  air.  1  part  of  the 
crystals  dissolves  in  about  2.3  parts  of  cold  and  1.3  of  boiling  water.  This  chlo- 
ride is  much  less  soluble  in  dilute  hydrochloric  acid,  so  that  an  addition  of  this 
acid  causes  a  precipitate  in  the  aqueous  solution.  Chloride  of  barium  is  almost 
insoluble  in  absolute  alcohol. 

This  salt  is  constantly  used  as  a  teagent  for  the  detection  of  various  acids. 

Wurtz  has  also  recently  employed  it  in  the  analysis  of  certain  siliceous  minerals, 
since  he  found  that  many  insoluble  silicates,  when  fused  with  anhydrous  chloride 
of  barium,  were  converted  into  masses  which  were  decomposed  by  hydrochloric 
acid. 

Fluoride  of  Barium  (BaF)  is  precipitated  when  chloride  of  barium  is  added 
to  solution  of  fluoride  of  potassium. 

SULPHIDE  OF  BARIUM,  SULPHURET  OF  BARIUM,  BaS. 

§  192.  Sulphide  of  barium  is  formed  when  hydrosulphuric  acid  acts  on  baryta, 
or  when  hydrogen  is  passed  over  sulphate  of  baryta  at  a  red  heat. 

Preparation. — It  is  best  prepared  by  mixing  powdered  heavy-spar  with  about 
\  of  its  weight  of  charcoal,  and  enough  oil  to  form  a  paste ;  this  is  thoroughly 

1  Another  method  consists  in  fusing  heavy-spar  with  chloride  of  calcium,  iron-filings. 
and  charcoal,  when  chloride  of  barium,  sulphide  of  iron,  and  (insoluble)  oxysulpi. 
calcium  are  produced ;  the  mass  is  then  treated  with  boiling  water. 


STRONTIUM.  287 

incorporated,  and  maintained  at  a  red  heat,  in  an  earthen  crucible,  till  no  more 
carbonic  oxide  escapes  :  — 


The  sulphate  of  baryta  is  sometimes  mixed  with  $  lampblack,  J  resin,  and  £ 
starch,  made  up  into  balls  with  a  little  water,  and  these  carbonized  in  a  coal 
fire.1 

The  black  mass  is  powdered,  boiled  with  a  small  quantity  of  water,  and  filtered 
while  hot  ;  on  cooling,  the  sulphide  of  barium  crystallizes  out  in  thin,  nearly 
colorless  plates.  If  the  sulphide  be  required  for  the  preparation  of  some  other 
salt  of  barium,  the  crude  mass  obtained  as  above  may  be  boiled  with  a  larger 
quantity  of  water,  so  that  the  solution  shall  not  crystallize  on  cooling.3 

Properties.  —  The  crystals  appear  to  contain  6  eqs.  of  water.  When  exposed 
to  the  air,  sulphide  of  barium  is  decomposed  by  the  atmospheric  water  and  car- 
bonic acid,  evolving  sulphuretted  hydrogen  :  — 

BaS  +  HO  +  COa=BaO  CO.+  HS. 

Sulphide  of  barium  is  oxidized  by  steam,  at  a  red  heat,  hydrogen  being  evolved, 
and  sulphate  of  baryta  produced. 

When  sulphide  of  barium  is  dissolved  in  water,  it  appears  to  undergo  partial 
decomposition,3  hydrate  of  baryta  and  hydrosulphate  of  sulphide  of  barium  being 
formed;  double  compounds  of  baryta  with  sulphide  of  barium  (crystallizing  with 
water)  are  also  produced  under  these  circumstances. 

The  aqueous  solution  of  sulphide  of  barium,  when  exposed  to  the  air,  absorbs 
oxygen,  first  becoming  yellow  from  the  production  of  a  higher  sulphide,  and 
afterwards  depositing  crystals  of  hyposulphite  of  baryta  (13aO.S302). 

Sulphide  of  barium  is  a  sulphur-base.  Ilydrosulpliate  of  sulphide  of  barium 
(BaS.IIS)  may  be  prepared  like  the  corresponding  compound  of  potassium. 

Barium  forms  also  a  tersulphide  (BaS3),  and  a  penta&ulphide  (BaS5). 

Silicoftuoride  of  Barium,  8BaF.2SiF3,  is  thrown  down  as  a  crystalline  preci- 
pitate, wrhen  hydrofluosilicic  acid  is  added  to  chloride  of  barium  ;  this  compound 
is  very  sparingly  soluble  in  water  and  acids,  and  is  decomposed  by  heat  into 
fluoride  of  barium  and  terfluoride  of  silicon,  which  escapes. 


STRONTIUM. 

Sym.  Sr.    Eq.  43.8. 

§  193.  This  metal  was  first  obtained  by  Sir  H.  Davy,  in  1808.  It  is  named 
from  Strontian,  in  Argyleshire,  where  it  was  first  discovered. 

Strontium  is  by  no  means  so  abundant  in  nature  as  barium ;  it  occurs  chiefly 
in  the  forms  of  sulphate  and  carbonate,  and  is  found  in  small  quantity  in  certain 
mineral  waters.  It  may  be  prepared  by  the  same  methods  as  barium,  which  it 

1  When  sulphate  of  baryta,  free  from  iron,  is  ignited  with  a  small  quantity  of  carbona- 
ceous matter,  a  mass  possessed  of  phosphorescent  properties  is  obtained,  which  is  termed 
Bologna  phosphorus. 

2  \Vhen  the  sulphide  of  barium  is  prepared  below  a  bright  red  heat,  the  aqueous  solu- 
tion obtained  from  the  ignited  mass  contains  much  hydrate  of  baryta  and  a  higher  sulphide 
of  barium. 

3  When  the  mass  obtained  in  the  preparation  of  sulphide  of  barium  .is  treated  with 
successive  small  portions  of  water,  the  first  two  solutions  are  yellow,  and  contain  con- 
siderable quantities  of  hydrosulphate  of  sulphide  of  barium  and  the  higher  sulphides  of 
barium  ;   the  third  is  a  solution  of  nearly  pure  sulphide  of  barium,  while  the  succeeding 
solutions  contain  gradually  increasing  quantities  of  baryta,  the  last  being  nearly  pure 
baryta- water. 


288  STRONTIUM  AND   OXYGEN. 

much  resembles  in  its  appearance,  properties,  and  combinations.     It  is  heavier 
than  oil  of  vitriol,  and  less  fusible  than  barium. 


STRONTIUM   AND   OXYGEN. 

Strontia .     .     .     SrO 

Binoxide  of  Strontium SrOa. 

OXIDE  OF  STRONTIUM,  STRONTIA. 

SrO.    #2.51.8. 

The  oxide  of  strontium  is  prepared  from  the  native  carbonate  or  sulphate,  in 
exactly  the  same  way  as  baryta.  It  is  similar  to  that  oxide  in  its  properties, 
and  combines  with  water  very  energetically,  to  form  hydrate  of  strontia. 

Crystallized  hydrate  of  strontia  has  the  formula  SrO.HO-f9Aq,  and  is  easily 
converted  into  carbonate  by  exposure  to  air.  At  212°  F.  (100°  0.)  it  loses  the 
whole  of  its  water  of  crystallization,  becoming  converted  into  SrO. HO,  which  is 
not  decomposed^  at  a  red  heat. 

NITRATE  OF  STRONTIA,  SrO.N05. 

This  salt  is  prepared  in  the  same  manner  as  nitrate  of  baryta. 

The  ordinary  crystals  are  anhydrous,  colorless  octohedra,  which  decrepitate 
•when  heated,  and  are  ultimately  decomposed,  leaving  anhydrous  strontia.  They 
are  soluble  in  five  parts  of  cold,  and  in  considerably  less  of  boiling  water,  and 
insoluble  in  absolute  alcohol.  At  a  low  temperature,  the  solution  deposits 
prismatic  crystals,  of  the  formula  SrO.N05+Aq,  which  effloresce  in  air. 

Nitrate  of  strontia  is  employed  in  the  preparation  of  the  red  fires  used  upon 
the  stage,  and  in  fireworks;  a  common  mixture  for  these  purposes  consists  of  40 
parts  of  nitrate  or  strontia,  13  of  flowers  of  sulphur,  10  of  chlorate  of  potassa,  and 
4  of  tersulphide  of  antimony. 

SULPHATE  OF  STRONTIA  (SrO.S03)  is  found  in  nature  in  the  form  of  cehstine, 
crystallized  in  rhomboidal  prisms,  and  in  considerable  quantity,  associated  with 
sulphur,  in  the  neighborhood  of  volcanoes;  it  is  the  commonest  mineral  of 
strontia. 

The  sulphate  may  be  prepared  artificially  by  precipitating  a  solution  of  nitrate 
of  strontia  with  sulphuric  acid.  Its  properties  exactly  resemble  those  of  sulphate 
of  baryta;  it  is  somewhat  more  soluble  in  water  and  acids.  It  may  be  com- 
pletely dissolved  by  a  solution  of  common  salt. 

Carbonate  of  strontia  (SrO.COa)  constitutes  the  mineral  known  as  stronthnite  ;* 
its  crystals  belong  to  the  right  prismatic  system;  it  may  be  prepared  in  the  same 
manner  as  carbonate  of  baryta.  Its  properties  resemble  those  of  the  latter,  but 
its  carbonic  acid  is  more  easily  expelled. 

The  Binoxide  of  Strontium  (Sr02)  is  deposited  as  a  hydrate,  in  crystalline 
scales,  when  a  solution  of  binoxide  of  hydrogen  is  added  to  a  solution  of  stroutia. 
This  substance  cannot  be  formed,  like  the  binoxide  of  barium,  by  passing  oxygen 
over  heated  baryta. 

Chloride  of  Strontium  (SrCl)  is  obtained  by  decomposing  the  carbonate  or 
sulphide  with  hydrochloric  acid;  it  forms  deliquescent  needles  of  the  formula 
SrCl  +  6Aq,  which  lose  all  their  water  when  gently  ignited;  they  are  very  solu- 
ble in  water,  and  moderately  so  in  alcohol.  This  salt  is  almost  insoluble  in  con- 
centrated hydrochloric  acid. 

The  Sulphide  of  Strontium  exactly  resemble  those  of.  barium  in  preparation 
and  properties. 

1  Carbonate  of  strontia  is  also  found  in  some  mineral  waters. 


CALCIUM   AND   OXYGEN.  289 


CALCIUM. 

Sym.  Ca.    Eq.  20. 

§  194.  We  are  indebted  for  the  discovery  of  calcium  to  Sir  H.  Davy,  who  first 
obtained  it,  in  1808. 

The  natural  sources  of  this  metal  are  very  numerous ;  it  occurs  chiefly  in  the 
forms  of  carbonate  of  lime,  which  constitute  the  different  varieties  of  limestone, 
chalk,  and  marble,  found  in  all  parts  of  the  world.  Gypsum,  the  sulphate  of 
lime,  is  another  form  in  which  this  metal  occurs.  Phosphate  of  lime  is  also 
found  in  the  mineral  kingdom.  Fluoride  of  calcium  constitutes  the  mineral 
known  as  fluor-spar. 

This  metal  is  obtained  in  the  same  way  as  barium,  and  is  very  similar  to  it. 
It  combines  with  oxygen  to  form  an  oxide,  CaO,  and  a  binoxide,  CaOa. 


CALCIUM    AND   OXYGEN. 

Lime    .  CaO 


Binoxide  of  calcium CaO 


OXIDE  OF  CALCIUM,  LIME,  QUICKLIME. 
CaO.   Eq.ZS. 

Preparation. — This  very  usefiil  substance  is  prepared  by  the  decomposition  of 
carbonate  of  lime  by  heat.  The  operation  is  carried  out  on  a  very  large  scale  in 
kilns  or  furnaces,  so  constructed  that  the  products  of  combustion  of  the  fuel 
(wood,  turf,  or,  sometimes,  coal),  shall  pass  through  the  carbonate;  for  it  is 
found  that  the  carbonic  acid  is  much  more  easily  expelled  when  the  carbonate 
is  heated  in  a  stream  of  another  gasr  than  in  a  crucible. 

The  various  forms  of  carbonate  of  lime  do  not  give  up  their  carbonic  acid 
with  the  same  facility,  in  consequence  of  the* difference  in  their  texture;  chalk 
or  limestone  is  much  more  easily  decomposed  than  marble,  and,  being  much  more 
abundant,  is  always  employed  on  the  large  scale.  Moist  limestone  is  much  mo-re 
easily  caustified  than  that  which  is  perfectly  dry. 

The  lime-kilns  are  of  two  kinds,  in  one  of  which  the  process  is  interrupted 
after  every  operation,  whilst  in  the  other  it  is  continuous. 

The  simplest  form  of  lime-kiln  is  a  tall  conical  furnace,  over  the  hearth  of 
which  the  lime-burner  constructs  an  arch  with  large  lumps  of  the  limestone  to  be 
burnt;  upon  this  arch  the  rest  of  the  limestone  is  heaped,  so  as  to  fill  up  the 
furnace;  the  fire  is  then  kindled,  and  the  operation  allowed  to  continue  (for 
about  three  days  and  nights),  until  the  whole  of  the  lime  is  thoroughly  burnt. 
The  heat  is  raised  gradually,  so  that  the  stones  forming  the  arch  may  not  crack. 

The  continuous  lime-kiln  is  an  inverted  cone  of  brick-work,  with  an  aperture 
at  the  lower  part,  through  which  the  burnt  lime  is  withdrawn.  A  layer  of 
brushwood  is  placed  at  the  bottom,  upon  this  a  layer  of  coal,  then  a  layer  of 
limestone,  the  coal  and  limestone  being  arranged  in  alternate  layers,  until  the 
kiln  is  filled.  The  fire  is  then  lighted,  and  as  soon  as  the  upper  layers  have 
sunk  in  the  mouth  of  the  kiln,  fresh  charges  of  coal  and  limestone  are  intro- 
duced. The  lime  is  raked  out  from  the  bottom  at  intervals  of  about  half  an 
hour. 

The  lime  thus  obtained  is  by  no  means  pure;  it  usually  contains  silica, 
alumina,  and  sesquioxide  of  iron,  derived  from  the  limestone,  together  with  alka- 
line sulphates  and  chlorides  from  the  ashes  of  the  fuel.  For  many  purposes  the 

.ty 


290  CALCIUM   AND   OXYGEN. 

presence  of  the  three  former  impurities  is  of  no  consequence,  and  the  lime  may 
be  freed  from  the  two  latter  by  slaking  it,  throwing  the  hydrate  upon  a  filter, 
washing  with  water  till  the  washings  are  no  longer  rendered  turbid  by  nitrate 
of  silver  (after  acidulating  with  nitric  acid),  and  igniting  the  purified  hydrate  in 
an  earthen  crucible. 

Very  nearly  pure  lime  may  also  be  obtained  by  heating  oyster-shells,  or  frag- 
ments of  Carrara  marble,  to  bright  redness,  either  in  an  open  fire,  or  in  an 
earthen  crucible  with  a  hole  in  the  bottom. 

Lime  of  absolute  purity  may  be  prepared  by  saturating  dilute  nitric  acid  with 
powdered  marble,  evaporating  to  dryness,  and  igniting  the  residual  nitrate. 

Properties  of  Lime. — Anhydrous  lime,  or  quicklime,  is  a  soft,  white,  amor- 
phous solid,  of  specific  gravity  varying  between  2.5  and  3.  It  preserves  the 
external  appearance  which  the  carbonate  presented  before  ignition.  Ordinary 
quicklime  has  usually  a  gray  color,  probably  due  to  a  trace  of  carbon.  Lime  is 
one  of  the  most  infusible  bodies  which  we  possess;  it  resists  the  highest  heat  of 
our  furnaces.  A  mass  of  lime  heated  in  the  flame  of  the  oxyhydrogen  blow- 
pipe emits  a  most  dazzling  white  light,  and  fuses  at  the  edges. 

When  exposed  to  air,  quicklime  very  soon  absorbs  water,  the  lumps  crumbling 
to  a  bulky  powder,  which  is  hydrate  of  lime,  or  slaked  lime ;  when  a  mass  of 
lime  is  moistened  with  water,  very  energetic  combination  takes  place,  and  occa- 
sionally a  slight  explosion,  due  to  the  sudden  evolution  of  steam  ;  the  mass  splits 
in  all  directions,  and  finally  crumbles  to  a  dry  powder  of  hydrate;  the  slaking 
takes  place  more  rapidly,  and  a  more  finely-divided  hydrate  is  obtained  when 
hot  water  is  employed.1  Ordinary  quicklime  frequently  contains  fragments  which 
•will  not  slake,  but  are  left  as  cinder-like  masses  in  the  midst  of  the  hydrate; 
these  masses  appear  to  consist  of  semi-fused  silicate  of  lime,  and  are  most  fre- 
quently found  in  lime  which  has  been  over-lurnt,  i.  e.  calcined  at  too  high  a 
temperature.3 

Besides  silicic  acid,  quicklime  often  contains  magnesia,  alumina,  &c.  When 
it  contains  large  quantities  of  these  impurities  it  slakes  very  feebly,  and  is  called 
poor  lime,  but  if  it  be  pretty  pure  and  slakes  easily,  it  is  termed  fat  lime. 

Uses. — Quicklime  is  used  chiefly  for  the  preparation  of  mortar,  and  for  agri- 
cultural purposes.  It  is  very  useful  in  the  laboratory  for  drying  certain  gases, 
for  abstracting  the  water  from  alcohol,  and  for  decomposing  various  organic 
substances. 

HYDRATE  OF  LIME,  SLAKED  LIME,  CaO.HO. 

The  hydrate  is  always  prepared  by  slaking  quicklime. 

Properties. — It  forms  a  fine  white  powder,  which  loses  its  water  at  a  red  heat, 
but  does  not  fuse.  When  exposed  to  air,  it  absorbs  carbonic  acid,  and  is  con- 
verted into  a  mixture  of  carbonate  of  lime  and  hydrate  of  lime;  after  long  ex- 
posure it  ceases  to  absorb  carbonic  acid,  and  is  then  found  to  contain  single 
equivalents  of  hydrate  and  carbonate. 

Hydrate  of  lime  is  very  sparingly  soluble  in  water,  1  part  requiring  about 
1000  parts  of  water;  it  is  less  soluble  in  hot  water  than  in  cold,  so  that  a  cold 
saturated  solution  becomes  turbid  when  heated  to  the  boiling  point.3  Lime  water 
should  therefore  always  be  prepared  with  cold  water;  the  best  plan  is  to  place  a 
considerable  quantity  of  freshly-slaked  lime,  previously  washed  with  water  to 
remove  alkaline  salts,  in  a  large  bottle,  which  is  then  filled  up  with  cold  distilled 

1  The  hydrate  is  also  more  finely  divided  when  a  larger  quantity  of  water  has  been 
used  than  the  lime  is  capable  of  absorbing. 

2  Imperfectly  burnt  limestone  will  not  slake,  but,  when  immersed  in  water,  forms  a 
hard  mass  which  is  a  compound  of  hydrate  and  carbonate  of  lime. 

3  The  hydrate  of  lime  deposited  upon  boiling  lime-water  is  not  redissolved  to  any  per- 
ceptible extent  when  the  water  is  allowed  to  cool. 


MORTARS   AND    CEMENTS.  291 

water,  and  shaken  from  time  to  time;  it  is  then  allowed  to  stand,  in  order  that 
the  excess  of  lime  may  subside;  the  bottle  should  always  be  kept  filled  with 
water.  If  a  saturated  solution  of  hydrate  of  lime  be  evaporated  in  vacua  over 
oil  of  vitriol,  it  deposits  the  crystallized  hydrate  in  six-sided  tables. 

Lime-water  has  a  distinct  alkaline  reaction,  and  a  feebly  alkaline  taste.  When 
lime-water  is  exposed  to  air,  a  pellicle  of  carbonate  forms  upon  its  surface,  and 
if  this  be  broken,  a  fresh  pellicle  forms  until  all  the  lime  is  precipitated;  hence, 
lime-water  must  be  kept  in  well-closed  bottles. 

A  mixture  of  finely  divided  hydrate  of  lime  with  water,  is  termed  milk  or 
cream  of  lime,  according  to  its  consistence.  Hydrate  of  lime  is  much  more  solu- 
ble in  solution  of  sugar  than  in  pure  water;  the  solution  is  usually  known  as 
sugar-lime,  and  is  useful  in  the  laboratory. 

§  195*  USES  OF  HYDRATE  OF  LIME. — This  substance  is  applied  to  numerous 
purposes  in  the  arts  and  manufactures.  It  is  chiefly  employed  in  the  prepara- 
tion of  mortar  for  building  purposes;  this  is  usually  composed  of  1  part  of 
freshly-slaked  lime,  and  2  or  3  parts  (or  even  more,  according  to  the  quality  of 
the  lime)  of  sand,  mixed  with  water  to  a  paste,  which  is  spread  in  a  thin  layer 
between  the  stones  to  be  cemented. 

The  hardening  of  mortar  is  explained  partly  on  mechanical,  partly  on  chemi- 
cal principles.  The  chief  chemical  alteration  which  mortar  undergoes,  consists 
in  the  conversion  of  a  part  of  the  lime  into  carbonate,  which  is  capable  of  com- 
bining with  unaltered  hydrate  of  lime,  to  form  a  solid  mass.  It  also  appears 
that  the  deposition  of  minute  crystals  of  carbonate  of  lime  helps  materially  to 
bind  the  particles  together.  These  reasons  may  aiford  a  satisfactory  explanation 
of  the  rapid  setting  of  the  mortar ;  but  direct  experiments  and  analyses  of  very 
old  mortars  have  shown  that  its  ultimate  conversion  into  a  hard  stone-like  mass, 
must  be  attributed  in  great  measure  to  the  formation  of  a  silicate  of  lime,  by 
the  action  of  lime  upon  the  sand,  in  the  presence  of  moisture.  The  sand  has, 
moreover,  a  most  important  mechanical  effect  in  preventing  the  mass  from  shrink- 
ing too  much  when  dried,  and  in  forming  a  number  of  nuclei  around  which  the 
lime  adheres. 

The  nature  of  the  sand  is  not  without  influence  upon  the  quality  of  the  mortar; 
rough  irregular  grains  are  preferable  to  those  which  are  quite  smooth ;  the  sand 
should  also  be  as  pure  as  possible.  Mortar  does  not  set  firmly  when  dried  too 
quickly ;  hence  it  sets  better  in  temperate  seasons  than  in  hot  summers. 

Water  containing  much  alkaline  chloride  should  not  be  employed  for  the  pre- 
paration of  mortar,  since  its  action  upon  lime  would  give  rise  to  the  production 
of  chloride  of  calcium,  which  would  prevent  the  drying  of  the  mortar. 

Hydraulic,  mortars  and  cements  are  such  as  set  under  water,  and  are  not  dis- 
integrated by  its  action.  These  are  usually  prepared  either  from  natural  or 
artificial  mixtures  of  carbonate  of  lime  with  silica,  or  silicate  of  alumina  or  of 
magnesia. 

They  are  prepared  from  limestones  containing  certain  proportions  of  the  three 
latter  ingredients.  When  a  limestone  of  this  description  is  calcined,  a  double 
silicate  of  alumina  (or  magnesia)  and  lime  is  formed,  which  is  capable  of  com- 
bining with  water  to  produce  a  compact  hydrate  which  resists  the  action  of  that 
solvent. 

Even  dolomite  (carbonate  of  lime  and  magnesia)  calcined  at  a  moderate  heat, 
exhibits  the  property  of  a  hydraulic  lime ;  and  half-burnt  lime  (containing  still 
a  certain  quantity  of  carbonate)  will  also  set  under  water. 

In  order  that  a  limestone  containing  silica  may  be  employed  for  the  produc- 
tion of  hydraulic  lime,  it  is  necessary  that  this  ingredient  be  present  in  a  state 
in  which  it  is  capable  of  entering  readily  into  combination  with  the  lime,  which 
is  the  case  with  the  silica  contained  in  clay.  If  carbonate  of  lime  be  mixed  with 
gelatinous  silica,  a  good  cement  is  obtained  on  calcination,  but  if  sand  or  rock- 


292  MORTARS   AND   CEMENTS. 

crystal  be  employed,  the  resulting  product  is  valueless.  Those  clays  are  best 
fitted  for  the  production  of  cements  which  yield  a  portion  of  their  silica  to  a 
solution  of  potassa. 

If  an  hydraulic  lime  be  calcined  at  too  high  a  temperature,  the  silicates  undergo 
a  partial  fusion,  and  will  not  set  afterwards  under  water.  The  heat  employed 
should  be  only  just  high  enough  to  expel  the  water  from  the  clay,  and  the  greater 
part  of  the  carbonic  acid  from  the  carbonate  of  lime. 

Neither  clay  (silicate  of  alumina)  nor  lime,  alone,  will  set  under  water,  but 
if  an  intimate  mixture  of  clay  and  chalk  be  calcined  at  a  moderate  heat,  and 
afterwards  mixed  with  water,  a  hydrated  double  silicate  of  alumina  and  lime  is 
formed  as  a  hard  mass,  which  yields  gelatinous  silica  when  treated  with  acids, 
although  no  silica  can  be  separated  in  this  manner  from  ordinary  clay.  If  the 
clay  or  limestone  should  contain  a  little  alkali,  it  appears  to  promote  the  solidifi- 
cation of  the  cement  by  carrying  the  silica  to  the  lime. 

When  clay  which  has  been  dried  at  a  moderately  high  temperature  is  immersed 
in  lime-water,  it  slowly  extracts  the  lime,  depriving  the  solution  of  its  alkaline 
reaction.  Hydrated  alumina  and  gelatinous  silica  act  in  a  similar  manner,  but 
more  slowly.  -Hence  it  appears  that  clay,  and,  to  some  extent  also,  alumina  and 
silica,  are  capable  of  forming  insoluble  compounds  with  lime,  even  at  ordinary 
temperatures. 

One  variety  of  hydraulic  lime  is  simply  a  poor  lime,  containing  10  or  15  per 
cent,  of  clay;  when  such  lime  is  slaked  and  made  into  a  paste  with  water,  it  is 
found  to  set,  even  under  water,  after  some  time,  in  consequence  of  a  combination 
between  the  silicate  of  alumina  (clay)  and  the  lime.  Cements  similar  to  this, 
prepared  by  the  judicious  calcination  of  certain  argillaceous  limestones,  are  known 
as  Roman  cement,  Portland  cement,  &c. ;  they  contain  from  10  to  35  per  cent,  of 
clay;  those  which  contain  most  of  this  ingredient  solidify  most  rapidly.  Lime- 
stones containing  8  to  12  per  cent,  of  clay  furnish  a  hydraulic  lime,  which  hardens 
under  water  in  15  or  20  days.  When  they  contain  15  to  18  per  cent,  of  clay, 
the  hardening  takes  place  in  8  days.  If  the  clay  amount  to  25  per  cent,  the 
resulting  cement  will  set  in  3  or  4  days. 

Roman  cement  contains  about  35  per  cent,  of  clay,  and  hardens  even  within 
an  hour,  if  of  good  quality. 

The  amount  of  clay  contained  in  any  specimen  of  limestone  may  be  readily 
determined  by  treating  it  with  dilute  hydrochloric  acid,  when  the  clay  is  left  un- 
dissolved,  and  may  be  collected  on  a  filter,  well  washed,  dried,  ignited,  and 
weighed. 

The  Roman  cement  was  originally  made  by  calcining  a  mixture  of  slaked 
lime  and  puzzolano1  (a  rock  of  volcanic  origin  found  near  Naples),  but  is  now 
prepared  from  masses  of  argillaceous  limestone  (containing  30  per  cent,  of  clay) 
procured  from  the  bed  of  the  Thames,  and  other  parts  of  the  London  clay.  Lime- 
stones which  contain  more  than  35  per  cent,  of  clay  do  not  furnish  a  cement 
when  burnt.  Hydraulic  limes  are  sometimes  made  artificially,  by  mixing  lime 
and  clay  in  proper  proportions.9 

Hydraulic  mortar  of  good  quality  may  be  known  by  its  not  showing  any  tend- 

1  This  mineral  is  remarkable  for  the  readiness  with  which  it  combines  with  lime,  being 
capable  even  of  extracting  it  from  its  solution  in  water.     Most  of  the  tufas  of  volcanic 
origin  present  the  properties  of  puzzolano,  and  are  found  in  various  localities;  "puzzolano 
may  also  be  replaced  by  many  varieties  of  common  clay  calcined  at  a  moderate  heat. 

A  variety  of  puzzolano,  not  of  volcanic  origin,  has  lately  been  discovered  by  Sauvage 
in  the  Dep.  des  Ardennes.  It  contains  56  per  cent,  of  soluble  silica  (see  §  137). 

2  An  excellent  Cement  is  made  in  the  neighborhood  of  Paris,  and  used  for  many  public 
works  in  that  city,  from  1  part  of  clay  and  4  parts  of  chalk;  these  are  intimately  mixed 
with  water,  afterwards  allowed  to  settle,  and  the  deposit  thus  obtained  is  moulded  into 
bricks,  which  are  dried  and  calcined  at  a  gentle  heat.     This  hydraulic  lime,  like  the  best 
obtained  from  natural  sources,  is  entirely  dissolved  by  acids. 


NITRATE   OP  LIME.  293 

ency  to  crack  when  hardened  under  water,  by  its  acquiring  a  very  considerable 
degree  of  hardness  in  a  short  time,  and  afterwards  resisting  the  action  of  water. 
The  surfaces  of  the  stones  should  always  be  moistened  before  the  mortar  is  applied. 
A  certain  quantity  of  sand  is  always  added  to  hydraulic  mortar,  to  prevent 
excessive  shrinking. 

Hydraulic  lime  will  not  harden  if  it  be  immediately  placed  in  water,  without 
having  acquired  a  certain  consistence.  Care  should  be  taken  to  prevent  it  from 
attracting  moisture  to  any  extent  from  the  atmosphere,  as  its  quality  is  then 
much  deteriorated. 

The  solidification  of  hydraulic  lime  is  much  promoted  by  a  high  temperature 
and  increased  pressure. 

Ransome's  vitrified  cement  is  prepared  by  boiling  flints,  under  pressure,  with 
caustic  soda  or  potassa,  when  a  solution  of  alkaline  silicate  is  obtained,  which 
is  intimately  mixed  with  1  part  of  pipe-clay,  1  part  of  powdered  flint,  and  10 
parts  of  sand ;  the  mixture  is  pressed  into  moulds,  dried,  and  carefully  annealed. 

Alum-shale,  ashes  of  coal,  &c.,  are  sometimes  used  instead  of  clay  for  the 
manufacture  of  cement. 

The  hydraulic  mortar  of  Tournay  is  prepared  from  the  refuse  of  the  lime- 
kilns (containing  lime  and  coal-ashes  in  the  proportion  of  about  1  :  3),  which  is 
slaked  with  water  and  well  mixed. 

Certain  iron  and  copper  slags  have  also  been  found  to  afford  excellent  cements 
when  mixed  with  burnt  lime. 

In  order  to  ascertain  whether  a  slag  is  fitted  for  this  purpose,  it  is  digested,  in 
the  state  of  fine  powder,  with  a  little  hydrochloric  acid ;  if  much  gelatinous  silica 
be  separated,  the  slag  may  be  used  for  preparing  a  cement. 

Liine  is  also  employed  as  a  manure ;  its  action  in  this  capacity  can  scarcely  be 
said  to  be  thoroughly  understood,  but  it  appears  to  depend,  to  a  slight  extent, 
upon  its  furnishing  an  adequate  supply  of  lime  for  the  crops,  and  in  a  much 
greater  degree,  upon  its  promoting  the  decay  of  the  organic  matters  contained 
in  the  soil,  hastening  their  conversion  into  carbonic  acid  and  ammonia,  from 
which  the  plants  appear  to  derive  their  food.  The  lime  may  also  be  useful  in 
decomposing  minerals  containing  potassa,  and  converting  this  base  into  a  soluble 
form.  In  some  cases,  lime  containing  magnesia  has  been  found  injurious  to 
plants. 

Large  quantities  of  hydrate  of  lime  are  employed  in  the  preparation  of  am- 
monia and  of  bleaching-powder,  and  in  the  purification  of  gas ;  it  is  also  exten- 
sively employed  by  the  candle-maker,  the  soap-boiler,  the  cotton-printer,  the 
tanner,  and  the  sugar-refiner.  In  medicine,  lime-water  is  used  as  an  antacid. 

The  chemist  devotes  hydrate  of  lime  to  a  variety  of  uses ;  it  serves  him  to 
prepare  the  caustic  alkalies,  and  to  absorb  carbonic  acid ;  it  is  also  used  as  a 
reagent. 

Nearly  all  those  salts  of  lime  which  are  neutral  in  constitution  are  neutral  to 
test-papers. 

NITRATE  OP  LIME,  CaO.N05. 

§  196.  This  salt  sometimes  effloresces  on  the  walls  of  cloacae,  &c.,  being  formed 
by  nitrification  (see  §  144).  It  is  also  produced  in  the  nitre- beds  by  the  same 
process. 

Nitrate  of  lime  is  prepared  by  saturating  dilute  nitric  acid  with  carbonate  of 
lime,  and  evaporating  to  crystallization.  It  crystallizes  in  six-sided  prisms,  of 
the  formula  CaO.N05-f  4Aq  ;  they  are  very  deliquescent,  and  soluble  in  water ; 
concentrated  nitric  acid,  added  to  the  aqueous  solution,  produces  a  crystalline 
precipitate  of  the  nitrate.  When  heated,  the  crystals  fuse,  lose  their  water 
easily,  and  are  finally  decomposed  into  lime,  peroxide  of  nitrogen,  and  oxygen. 
Nitrate  of  lime  sometimes  finds  an  application  in  consequence  of  its  great 


294  SALTS   OF   LIME. 

attraction  for  water  ;  this  salt  is  also  an  intermediate  product  of  the  nitre  manu- 
facture. 

Nitrate  of  lime  is  capable  of  combining  with  lime  to  form  two  basic  salts. 

HYPOCHLORITE  OF  LIME,  CaO.ClO. 

§  197.  This  salt  is  prepared  by  adding  solution  of  hypochlorous  acid  to  milk 
of  lime,  so  that  the  latter  may  remain  in  excess;  it  is  only  known  in  solution, 
which  bleaches  test-papers,  and  is  easily  decomposed  into  chlorate  of  lime  and 
chloride  of  calcium.  In  mixture  (or  combination  ?)  with  1  equivalent  of  chloride 
of  calcium,  it  forms  the  well  known  chloride  of  lime. 

HYPOCHLORITE  OF  LIME  WITH  CHLORIDE  OF  CALCIUM.     CHLORIDE  OF  LIME. 
BLEACH.    CaO.ClO  +  CaCl. 

This  compound,  which  is  so  important  in  the  arts,  is  obtained  by  the  action  of 
chlorine  upon  an  excess  of  hydrate  of  lime. 

If  an  excess  of  chlorine  be  brought  in  contact  with  hydrate  of  lime,  chloride 
of  calcium  and  chlorate  of  lime  are  formed  :  — 


6(CaO.HO)+Cl6=5CaCl+CaO.C105 
but  if  the  hydrate  of  lime  be  in  excess,  the  decomposition  is  as  follows  :  — 
2(CaO.HO)+Cl2=CaO.C10-fCaCl+2HO. 

This  process  is  carried  out  on  a  very  large  scale  ;  the  chlorine  is  slowly  gene- 
rated, in  a  leaden  or  stone  retort  heated  by  steam,  from  a  mixture  of  binoxide  of 
manganese,  chloride  of  sodium,  and  oil  of  vitriol,  or  from  binoxide  of  manganese 
and  the  hydrochloric  acid  obtained  from  the  alkali-works  (with  which  the  bleach- 
factory  is  often  in  connection),  and  is  passed  into  chambers  of  brickwork,  in 
which  hydrate  of  lime  is  spread  out  upon  trays  placed  one  above  the  other.1  In 
this  process,  the  temperature  should  not  rise  above  62°  F.  (16°.  5  C.),  or  much 
chlorate  of  lime  will  be  produced.  When  the  chloride  of  lime  is  to  be  used  in 
solution,  it  is  often  made  on  the  spot  by  passing  chlorine  into  an  excess  of  milk 
of  lime  kept  in  continual  agitation. 

Properties.  —  The  substance  termed  chloride  of  lime  is  a  white,  somewhat 
moist  powder,  the  formula  of  which,  if  pure,  would  be  CaO.C10-f-CaCl+2  Aq  ; 
it  contains,  however,  besides  these,  an  excess  of  hydrate  of  lime,  and  a  certain 
amount  of  carbonate.  When  exposed  to  air,  it  continually  evolves  hypochlorous 
acid,  in  consequence  of  the  action  of  the  carbonic  acid  upon  the  hypochlorite  of 
lime  ;  it  also  deliquesces  rapidly.  When  heated,  it  loses  water,  and  is  converted 
into  a  mixture  of  chloride  of  calcium  and  chlorate  of  lime  :  — 

3(CaO.C10+CaCl)=CaO.C105+5CaCl  ; 

the  chlorate  of  lime  is  afterwards  decomposed  by  the  heat,  with  evolution  of 
oxygen.  When  chloride  of  lime  is  shaken  with  about  10  parts  of  cold  water, 
the  chloride  of  calcium  and  hypochlorite  of  lime  are  dissolved  out  together  with 
a  little  hydrate  of  lime,  leaving  the  remainder  of  the  hydrate,  and  the  carbonate 
of  lime.  The  solution  has  an  alkaline  reaction  to  test-papers,  which  it  after- 
wards bleaches,  by  reason  of  its  oxidizing  action  upon  the  coloring  matter  ;  if 
the  solution  be  boiled,  it  loses  its  bleaching  properties,  and  is  found  to  contain 
chlorate  of  lime  and  chloride  of  calcium. 

When  exposed  to  air,  solution  of  chloride  of  lime  evolves  hypochlorous  acid, 

1  The  chlorine  is  generally  passed  through  a  little  water,  to  remove  hydrochloric  acid, 
&c.,  and  afterwards  over  coke  through  which  oil  of  vitriol  is  continually  trickling,  to 
remove  the  water. 


BLEACHING-POWDER.  295 

and  deposits  carbonate  of  lime.     When  the  solid  chloride  of  lime,  or  its  solution, 
is  kept  for  any  length  of  time,  it  decomposes  according  to  the  equation  : — 

9(CaO.C10  +  CaCl)==CaO.C105+  17CaCl  +  0M ; 
so  that  it  is  advantageous  to  use  it  freshly  prepared. 

If  chloride  of  lime  be  treated  with  an  excess  of  acid,  even  of  carbonic  acid,  it 
evolves  chlorine  : — 

CaO.ClO-f  CaCl-f  2(HO.S03)=2HO+2  (CaO.SO,)  +  Cla ; 
and,  by  means  of  the  nascent  chlorine,  a  mixture  of  chloride  of  lime  and  free 
acid  bleaches  much   more  powerfully  than  the  chloride  alone.     If  the  acid  be 
added  in  small  quantity,  hypochlorous  acid  is  evolved. 

Uses  of  Chloride  of  Lime. — This  substance  is  the  chief  bleaching  agent  em- 
ployed for  cotton  and  linen ;  it  is  generally  used  in  conjunction  with  an  acid. 
The  stuff  is  first  soured,  as  it  is  termed,  in  a  bath  of  very  dilute  (sulphuric)  acid, 
then  steeped  in  the  bath  of  chloride  of  lime,  afterwards  soured  again,  and  finally 
washed  in  an  alkaline  lye. 

The  superior  bleaching  power  of  a  mixture  of  chloride  of  lime  with  an  acid 
is  taken  advantage  of  in  cotton  printing,  for  the  production  of  white  patterns 
upon  a  colored  ground.  The  pattern  is  printed  upon  a  madder-red  ground,  for 
example,  with  solution  of  tartaric  acid  thickened  with  gum  ;  it  is  then  immersed 
for  a  very  short  time  in  the  bleaching  liquor,  when  the  color  is  discharged  in 
those  parts  only  which  were  impregnated  with  the  acid. 

Chloride  of  lime  is  also  employed  to  destroy  the  gaseous  poisons  with  which 
the  atmosphere  of  sick-rooms,  and  other  localities,  is  contaminated }  the  hypo- 
chlorous  acid  evolved  from  the  compound  by  the  action  of  the  carbonic  acid  of 
the  air,  oxidizes  and  destroys  the  miasmata;  in  this  application,  the  solution  of 
chloride  of  lime  is  sometimes  sprinkled  over  the  floor  of  the  room;  sometimes 
a  cloth  is  saturated  with  it,  and  hung  up  in  the  air,  or,  in  extreme  cases,  as 
where  large  quantities  of  sulphuretted  hydrogen,  emanating  from  cloacae,  &c., 
are  to  be  destroyed,  the  powder  itself  is  mixed  with  dilute  sulphuric  acid,  added 
by  small  portions  at  a  time,  in  a  shallow  vessel.  A  mixture  of  bleaching  powder 
and  alum  is  particularly  well  suited  for  this  purpose. 

Chloride  of  lime  is  occasionally  used  in  the  laboratory  as  an  oxidizing  agent. 

When  we  remember  the  circumstances  which  may  alter  the  composition  of 
chloride  of  lime — viz  :  the  extent  to  which  the  lime  was  saturated  with  chlorine, 
the  degree  of  humidity  of  the  lime,  and  the  length  of  time  for  which  the  bleach, 
when  prepared,  has  been  kept  in  store,  as  well  as  the  nature  of  the  place  in  which 
it  has  been  kept,  we  shall  not  wonder  that  various  samples  of  bleaching  powder 
contain  very  different  quantities  of  available  chlorine. 

Good,  freshly  prepared  bleach  cdn tains  30  per  cent,  of  available  chlorine,  but 
specimens  are  sometimes  met  with  which  contain  only  10  per  cent. 

Several  methods  are  in  use  for  the  determination  of  the  value  of  specimens  of 
bleach,  which  operation  is  usually  termed  chlorimetry  (see  Quantitative  Analysis, 
Special  Methods). 

SULPHITE  OP  LIME,  CaO.S03-f  2Aq. 

§  198.  This  salt  may  be  prepared  in  a  similar  manner  to  sulphite  of  soda, 
substituting  the  hydrate,  or  carbonate  of  lime,  in  a  fine  state  of  division,  for  the 
solution  of  soda. 

Sulphite  of  lime  is  very  sparingly  soluble  in  water ;  when  exposed  to  air,  it 
becomes  covered  with  an  incrustation  of  sulphate.     When  heated,  sulphite  of 
lime  is  decomposed  into  sulphate  of  lime  and  sulphide  of  calcium : — 
4(CaO.S02)=3(CaO.S03)-fCaS. 

The  sulphite  of  lime  dissolves  in  solution  of  sulphurous  acid,  forming,  proba- 


298  SALTS   OF   LIME. 

Stucco  consists  of  plaster  which  has  been  mixed  with  water  containing  gela- 
tin (size)  or  gum  in  solution;  it  is  capable  of  receiving  a  high  polish,  and  may  be 
variously  colored. 

A  composition  containing  plaster  of  Paris  and  alum  has  been  lately  introduced 
for  taking  casts,  and  is  not  only  harder  than  ordinary  plaster,  but  possesses  some- 
what the  appearance  of  marble,  and  is  capable  of  resisting  the  action  of  moisture 
in  a  higher  degree  than  common  plaster.  In  order  to  prepare  this  material,  the 
gypsum,  having  been  burnt  in  the  ordinary  manner,  is  soaked  in  a  saturated 
solution  of  alum  for  some  hours,  and  then  again  burnt  at  a  dull  red  heat.  This 
plaster  takes  longer  to  set  than  the  ordinary  kind.  When  mixed  with  an  equal 
quantity  of  sand,  it  gives  a  very  hard  cement.  By  impregnating  plaster-casts 
with  solution  of  soluble  glass,  and  exposing  them  to  air,  they  acquire  a  high 
degree  of  hardness. 

Gypsum  is  occasionally  used  for  agricultural  purposes ;  its  operation  as  a 
manure  seems  to  be  due  chiefly  to  its  direct  necessity  to  the  composition  of  the 
plant,  for  nearly  all  plant-ashes  contain  this  substance.  It  has  been  found  advant- 
ageous to  mix  gypsum  with  dung  or  stable-manure,  since  it  fixes  the  carbonate 
of  ammonia,  converting  it,  by  double  decomposition,  into  sulphate. 

PHOSPHATES  OF  LIME. 

§  199.  Only  the  tribasic  phosphates  of  this  base  have  received  any  consider- 
able share  of  attention. 

TRIPHOSPHATE  OF  LIME  (3CaO.P05)  is  precipitated  when  chloride  of  calcium 
is  added  to  triphosphate  of  soda  (3NaO-P05).  It  is  likewise  obtained  when 
chloride  of  calcium  is  added  to  common  phosphate  of  soda  (2NaO.HO.P05), 
mixed  with  a  little  ammonia,  or  when  an  excess  of  phosphoric  acid  (3HO.P05) 
is  added  to  chloride  of  calcium,  and  followed  by  excess  of  ammonia. 

The  composition  of  these  precipitates  is  expressed  by  the  formula  3CaO.P05 
-f-2Aq;  they  are  white,  gelatinous,  and  easily  soluble  in  acids. 

The  mineral  apatite  is  a  compound  of  triphosphate  of  lime  with  chloride  or 
fluoride  of  calcium  (3(3CaO.P05),CaF). 

COMMON  PHOSPHATE  OF  LIME  (2CaO.HO.P05). — When  common  phosphate 
of  soda  (2NaO.HO.P05  is  added  to  chloride  of  calcium,  a  white  gelatinous  pre- 
cipitate is  obtained,  of  the  formula  2CaO.HO.P05-f  4Aq.  This  precipitate  is 
easily  soluble  in  acids;  when  digested  with  ammonia,  it  is  converted  into  the 
triphosphate  (30aO.P05),  whilst  phosphate  of  ammonia  is  found  in  solution. 

ACID  PHOSPHATE  OF  LIME  (Ca0.2HO.P05)  is  formed  when  bone-earth  is 
treated  with  sulphuric  acid;  if  the  former  be  digested  for  some  time  with  oil  of 
vitriol,  water  then  added,  and  the  sblution  filtered  from  the  insoluble  sulphate  of 
lime,  it  yields,  on  evaporation,  crystals  of  the  formula  Ca0.2HO.P05;  these  are 
deliquescent,  and  very  soluble  in  water.  When  a  large  excess  of  sulphuric  acid 
is  added  to  triphosphate  of  lime,  the  whole  of  the  phosphoric  acid  is  liberated. 

It  will  be  remembered  that  the  acid  phosphate  of  lime  is  employed  for  the 
preparation  of  phosphorus. 

BONE-EARTH,  BONE- ASH. 

The  residue  obtained  by  the  incineration  of  bones,  contains  about  |-  of  phos- 
phate of  lime;  the  formula  of  this  phosphate  was  formerly  written  8Ca0.3P05, 
being  viewed  as  a  combination  of  2(3CaO.P05)  with  2CaO.P05.  The  recent 
investigations  of  Kaewsky,  however,  have  shown  this  to  be  merely  triphosphate 
of  lime,  3CaO.P05. 

Ground  bones  are  frequently  employed  as  a  manure,  their  action  depending 
partly  upon  the  readily  decomposable  animal  matter  (gelatin)  which  they  con- 
tain;  and  partly  upon  the  supply  of  the  phosphoric  acid  so  necessary  to  the  com- 


CARBONATE   OF   LIME.  299 

position  of  plants.  When  ground  bones  alone  are  employed,  the  triphosphate  of 
lime  which  they  contain,  being  insoluble  in  water,  can  only  be  taken  up  by  the 
roots  of  the  plants  in  minute  quantities,  dissolved  by  the  saline  solutions  which 
it  meets  with  in  the  soil;1  where  an  abundant  supply  of  phosphoric  acid  is 
needed,  as  for  turnip-crops,  it  is  found  more  advantageous  to  convert  the  triphos- 
phate into  the  acid  phosphate  of  lime,  which  is  soluble  in  water.  This  is  effected 
by  gradually  mixing  the  bone-dust  with  £  of  its  weight  of  oil  of  vitriol,  and 
adding  an  equal  quantity  of  water  after  each  portion  of  oil  of  vitriol;  the  mass 
is  allowed  to  remain  in  a  heap  till  quite  dry,  and  is  then  used  under  the  name 
of  fuperpJtospJifite ;  it  consists  of  a  mixture  of  the  animal  portion  of  the  bones 
with  acid  phosphate  and  sulphate  of  lime. 

Hose  has  recently  examined  certain  double  phosphates  of  lime  and  the  alka- 
lies. By  igniting  mixtures  of  pyrophosphate  of  lime  with  the  proper  propor- 
tions of  alkaline  carbonates,  insoluble  compounds  were  obtained,  having  the 
composition  corresponding  approximately  to  the  formula  M0.2CaO.P05.  Simi- 
lar compounds  were  obtained  by  igniting  mixtures  of  pyrophosphate  of  lime 
•with  the  alkaline  chlorides.  These  compounds,  however,  could  only  be  produced 
in  the  dry  way. 

Hose  also  thinks  it  probable  that  a  class  of  soluble  double  phosphates  exists, 
having  the  general  formula  2MO.CaO.P05  (M  representing,  as  before,  an  alkali- 
metal.)  The  experiments  were  extended  to  baryta  and  strontia,  with  similar 
results. 

CARBONATE  OF  LIME,  CHALK,  CaO.COa. 

§  200.  This  substance  is  found  in  great  abundance,  and  in  numerous  forms, 
in  the  mineral  world.  Calcareous  spar,  Iceland  spar,  arrogonite,  limestone, 
chalk,  and  marble,  all  consist  of  pure  carbonate  of  lime. 

Shells  are  composed  chiefly  of  this  substance;  the  bones  of  animals  likewise 
contain  a  considerable  quantity.  It  is  also  found  in  spring  and  river  waters. 

Carbonate  of  lime  may  be  prepared  artificially  by  precipitating  a  solution  of 
chloride  of  calcium  with  carbonate  of  soda,  and  washing;  the  precipitated  chalk 
of  the  Pharmacopoeia  is  prepared  in  this  manner. 

Iceland  spar  is  found  in  transparent  colorless  rhombohedra,  of  spec.  grav.  2.7; 
these  crystals  exhibit  the  property  of  double  refraction,  and  are  therefore  in 
much  request  for  optical  experiments.  Other  kinds  of  calcareous  spar  crystallize 
in  the  same  system. 

Arragonite  forms  rectangular  prisms,  which  are  sometimes  colorless,  and  occa- 
sionally colored  yellow  and  blue  by  metallic  oxides.  Its  spec.  grav.  is  3.75. 
When  heated,  a  crystal  of  arragonite  is  reduced  to  a  number  of  small  crystals, 
of  the  same  form  as  those  of  Iceland  spar.2 

The  different  varieties  of  marble  owe  their  various  colors  chiefly  to  organic 
(bituminous)  matters,  and  the  oxides  of  iron.  The  white  Carrara  marble  is  the 
purest. 

Properties. — It  will  be  seen  from  the  above  statements  respecting  Iceland 
spar  and  arragonite,  that  carbonate  of  lime  is  a  dimorphous  substance.  When 
an  alkaline  carbonate  is  added  to  a  cold  solution  of  a  lime-salt,  a  bulky  precipi- 
tate is  obtained,  which  shortly  becomes  crystalline,  and  when  examined  under 
the  microscope,  exhibits  the  rhombohedra  of  Iceland  spar.  If,  however,  a  hot 
solution  of  a  lime-salt  be  added  to  a  hot  solution  of  carbonate  of  ammonia,  a 

1  Phosphate  of  lime  may  also  be  taken  up  by  the  plants,  in  a  state  of  solution  in  water 
containing  carbonic  acid. 

2  When  waters  containing  bicarbonate  of  lime  in  solution  are  exposed  to  a  high  tem- 
perature, the  carbonate  of  lime  is  deposited  in  the  same  crystalline  form  as  arragonite, 
whilst  that  which  is  deposited  at  the  ordinary  temperature,  presents  the  same  form  as 
Iceland  spar. 


300  CARBONATE   OF   LIME. 

powder  is  precipitated,  which  is  composed  of  minute  crystals  similar  to  those  of 
arragouite ;  if  this  powder  be  gently  heated,  it  is  resolved  into  a  collection  of 
minute  rhombohedra. 

When  heated  to  redness,  carbonate  of  lime  loses  its  carbonic  acid,  and  is  con- 
verted into  quicklime  ;  this  decomposition  is  more  easily  effected  in  a  current 
of  steam  or  atmospheric  air.  If  carbonate  of  lime  (chalk)  be  sealed  in  an  iron 
tube,  and  heated,  it  is  not  decomposed,  but  may  be  fused  into  a  mass  which, 
when  cool,  has  a  crystalline  structure,  and  much  resembles  marble. 

Carbonate  of  lime  is  insoluble  in  water,  but  dissolves  in  a  solution  of  carbonic 
acid,  forming,  probably,  a  bicarbonate  of  lime.  If  a  stream  of  carbonic  acid  be 
passed  through  lime-water,  the  white  precipitate  produced  at  first,  gradually  dis- 
appears, and  a  solution  of  bicarbonate  of  lime  is  produced.  This  solution  readily 
parts  with  carbonic  acid,  and  deposits  carbonate  of  lime.  This  change  takes 
place  even  on  exposure  to  air,  and  hence,  cisterns  which  contain  water  rich  in 
bicarbonate  of  lime,  are  often  coated  with  a  compact  incrustation  of  the  carbonate. 

The  so-called  petrifying  springs  in  Tuscany  and  Auvergne,  owe  their  curious 
properties  to  the  presence  of  bicarbonate  of  lime.  When  any  object  is  exposed 
to  the  action  of -these  waters,  it  becomes  incrusted  with  carbonate  of  lime. 

Stalactites,  found  in  certain  caverns,  are  composed  of  carbonate  of  lime,  which 
is  deposited  in  a  crystalline  state  from  every  drop  of  water,  holding  bicarbonate 
of  lime  in  solution,  which  drips  through  the  roof;  from  the  spot  upon  which 
the  drops  of  water  fall,  a  stalagmite  often  rises  to  meet  the  stalactite  depending 
from  above. 

The  solution  of  bicarbonate  of  lime  also  deposits  the  carbonate  when  boiled, 
thus  giving  rise  to  an  incrustation  of  this  salt  upon  the  interior  of  boilers  in 
which  highly  calcareous  waters  are  employed  (page  121).  Carbonate  of  lime 
dissolves  in  all  acids  which  form  soluble  salts  with  its  base  (excepting  in  hydrocy- 
anic), with  evolution  of  carbonic  acid. 

When  a  solution  of  lime  in  sugar-water  is  exposed  to  the  air  at  a  temperature 
of  about  32°F.  (0°C.),  colorless  rhombohedral  crystals  are  deposited,  of  the 
formula  CaO.COa+5Aq;  these  lose  their  water  at  a  comparatively  low  tem- 
perature (80°  to  100°  F.) 

Uses  of  Carbonate  of  Lime. — These  are  very  various.  Most  kinds  of  stone 
employed  for  building  purposes  are  varieties  of  limestone ;  marble  is  also  used 
to  a  great  extent  in  building  and  for  statuary.  Lithographic  stones  are  composed 
of  carbonate  of  lime. 

It  will  be  remembered  that  limestone  is  the  source  of  quicklime  ;  it  is  burnt 
in  considerable  quantities  for  agricultural  purposes,  and  is  sometimes  employed, 
unburnt,  for  the  mechanical  amelioration  of  soils. 

Limestone  is  also  very  much  used  as  a  flux.  Of  late  years,  burnt  lime  has 
been  substituted,  in  some  furnaces,  apparently  with  considerable  advantage. 

Chalk  is  occasionally  used  in  medicine  as  an  antacid ;  for  this  purpose,  it  is 
prepared  by  careful  levigation.  Testae  preparatae  (levigated  shells),  are  merely 
another  form  of  carbonate  of  lime. 

From  what  we  have  said  above  respecting  the  uses  of  quicklime  in  the  pre- 
paration of  mortars  and  cements,  and  the  influence  which  the  presence  of  other 
substances  has  upon  their  quality,  it  becomes  matter  of  importance  that  we 
should  be  acquainted  with  the  composition  of  a  specimen  of  limestone  before 
employing  it  for  the  preparation  of  quicklime.  For  the  analysis  of  limestones, 
see  Quantitative  Analysis,  Special  Methods. 

A  double  carbonate  of  lime  and  soda  is  found  in  nature,  as  the  mineral  gay- 
lussite,  the  formula  of  which  is  CaO.C02,NaO.C03-f  5Aq.  This  mineral  is  in- 
soluble in  water,  but  if  its  water  of  crystallization  be  expelled  by  a  gentle  heat, 
water  afterwards  decomposes  it  into  carbonate  of  lime  and  carbonate  of  soda. 

BINOXIDE  or  CALCIUM,  Ca(X,  is  obtained  as  a  white  hydrate,  when  binoxide 


CHLORIDE   OP   CALCIUM.  801 

of  hydrogen  is  added  to  lime-water ;  the  binoxide  is  very  unstable,  easily  parting 
with  the  second  equivalent  of  oxygen. 

CHLORIDE  OF  CALCIUM,  CaCl. 

§  201.  This  compound  is  found  in  most  natural  waters.  It  may  be  obtained 
by  dissolving  lime  or  its  carbonate  in  hydrochloric  acid. 

Preparation  and  Properties. — Chloride  of  calcium  is  generally  prepared  from 
the  residue  in  the  retort  after  the  preparation  of  ammonia;  this  residue  contains 
chloride  of  calcium  mixed  with  a  slight  excess  of  lime;  it  is  treated  with  water, 
filtered,  mixed  with  a  slight  excess  of  hydrochloric  acid,  and  evaporated.  The 
concentrated  solution,  on  cooling,  deposits  large  crystals  of  the  formula  CaCl+ 
6  Aq. 

These  crystals  are  colorless  and  highly  deliquescent  six-sided  prisms.  When 
exposed  in  vacuo,  they  lose  4  equivalents  of  water,  and  become  opaque.  They 
fuse  very  easily  in  their  water  of  crystallization,  and  lose  4  equivalents  below 
392  F.  (200°C.),  leaving  a  white  porous  mass,  which  readily  absorbs  water,  and 
is  advantageously  employed  for  drying  gases.  When  further  heated,  all  the 
water  is  expelled,  and  the  chloride  undergoes  the  igneous  fusion.  If  the 
fused  mass  be  strongly  ignited,  with  access  of  air,  chloride  is  evolved,  and  the 
residue  becomes  alkaline,  from  the  presence  of  lime.  Fused  chloride  of  calcium 
after  exposure  to  light,  is  phosphorescent  in  the  dark.  Anhydrous  chloride  of 
calcium  combines  with  water,  with  evolution  of  heat,  but  the  hydrated  salt  gives 
rise  to  considerable  depression  of  temperature  when  dissolved  in  water.  A  mix- 
ture of  crystallized  chloride  of  calcium  and  snow,  or  powdered  ice,  is  capable  of 
lowering  the  temperature  to  the  extent  of  82°  F.  At  the  ordinary  temperature, 
water  dissolves  15  parts  of  the  crystals.  A  saturated  solution  boils  at  336°  F. 
(169°C.),  and  is  sometimes  employed  in  operations  where  a  bath  of  this  tempera- 
ture is  required. 

Anhydrous  chloride  of  calcium  dissolves  readily  in  alcohol ;  if  the  solution 
be  evaporated,  tabular  crystals  are  obtained,  containing  59  per  cent,  of  alcohol. 

Chloride  of  calcium  is  capable  of  absorbing  ammoniacal  gas  to  a  very  con- 
siderable extent,  producing,  it  is  said,  a  compound  of  the  formula  CaCl,4NHf. 

Uses. — Crystallized  chloride  of  calcium  is  employed  for  preparing  the  solution 
used  as  a  reagent. 

The  dried  porous  mass,  obtained  by  expelling  4  equivalents  of  water  from  the 
crystals,  is  used  for  drying  gases,  and  for  absorbing  the  water  in  the  direct  de- 
termination of  this  substance,  or  of  hydrogen,  in  organic  analysis.1 

Anhydrous  (fused)  chloride  of  calcium  is  useful  for  abstracting  water  from 
liquid  organic  substances;  thus,  in  purifying  oil  of  turpentine,  it  is  digested  for 
a  day  or  two  with  fragments  of  fused  chloride  of  calcium,  and  then  distilled  from 
them. 

Oxyclilori.de  of  Calcium  (CaCl,3CaO)  may  be  prepared  by  boiling  hydrate  of 
lime  for  some  time  in  a  concentrated  solution  of  chloride  of  calcium ;  the  filtered 
solution,  on  cooling,  deposits  prismatic  crystals  of  the  formula  CaC1.3CaO  +  15Aq ; 
these  crystals  are  decomposed  by  alcohol,  or  by  pure  water,  into  lime  and  chloride 
of  calcium. 

FLUORIDE  OF  CALCIUM,  FLUOR  SPAR,  CaF. 

This  substance  is  pretty  abundant  in  the  mineral  kingdom,  where  it  constitutes 
all  the  varieties  of  fluor-spar. 

1  Care  should  be  taken  that  the  chloride  employed  for  this  latter  purpose  be  not  al- 
kaline (as  it  sometimes  is,  from  neglecting  to  add  excess  of  hydrochloric  acid  in  preparing 
it  from  ammonia  residues),  or  it  will,  by  absorbing  part  of  the  carbonic  acid,  cause  an 
excess  in  the  hydrogen,  and  a  deficiency  of  carbon. 


302  SULPHIDES    OF  CALCIUM. 

Fluor-spar  is  generally  found  in  veins  associated  with  ores  of  tin,  lead,  cop- 
per, and  zinc. 

It  will  be  remembered  that  fluoride  of  calcium  occurs,  associated  with  phosphate 
of  lime,  in  apatite. 

Fluoride  of  calcium,  in  small  quantity,  enters  into  the  composition  of  the  bones 
of  animals,  and  is  found  in  some  mineral  waters. 

It  is  precipitated  when  a  soluble  lime-salt  is  mixed  with  an  alkaline  fluoride. 

The  precipitate  is  gelatinous,  and  very  transparent,  nearly  insoluble  in  acetic 
acid,  and  sparingly  soluble  in  hydrochloric. 

Properties. — Fluor-spar  is  found  in  crystals,  the  primitive  form  of  which  is 
the  cube;  these  are  generally  of  a  yellow  or  purple  color,  due  to  the  presence  of 
organic  matter ;  they  are  sometimes  pale  green,  or  even  colorless.  The  specific 
gravity  of  fluor-spar  is  3.1.  When  heated,  the  crystals  decrepitate,  at  the  same 
time  emitting  a  peculiar  blue  or  green  light,  which  resembles  a  flame  playing 
over  the  surface.  When  the  decrepitation  has  ceased,  the  phosphorescence  is 
no  longer  perceived,  perhaps  it  is  an  electric  phenomenon.  At  a  high  tempe- 
rature (in  the  blowpipe-flame)  fluor-spar  fuses,  and  becomes  crystalline  on  cooling. 

Fluoride  of  calcium  is  very  sparingly  soluble  in  water;  it  dissolves  to  some 
extent  in  hydrochloric  and  nitric  acids,  with  evolution  of  a  little  hydrofluoric 
acid;  ammonia  precipitates  part  of  the  fluoride  unchanged  from  these  solutions. 

Concentrated  sulphuric  acid  converts  it  into  sulphate  of  lime,  with  expulsion 
of  hydrofluoric  acid. 

Fluoride  of  calcium  is  decomposed  when  fused  with  alkaline  carbonates,  yield- 
ing carbonate  of  lime  and  an  alkaline  fluoride.  It  has  lately  been  asserted  that 
this  decomposition  is  not  complete  unless  silica  be  mixed  with  the  fluor-spar, 
when  an  alkaline  silicofluoride  is  formed.  4 

Uses. — Fluor-spar  is  employed  in  the  laboratory  as  the  source  of  all  other 
fluorine-compounds.  It  is  used  as  a  flux  in  smelting  certain  ores,  especially  those 
of  copper. 

Moreover,  considerable  quantities  of  it  are  employed  for  the  fabrication  of 
ornamental  vases,  &c.  Derbyshire  spar,  so  much  used  for  this  purpose,  is  a 
variety  of  fluoride  of  calcium. 

SULPHIDES  or  CALCIUM. 

§  202.  Three  sulphides  of  calcium  are  known. 

Sulphide  of  Calcium  (CaS)  is  formed  when  hydrosulphuric  acid  comes  in  con- 
tact with  lime ;  it  may  also  be  obtained  by  calcining  a  mixture  of  sulphate  of 
lime  with  charcoal. 

Sulphide  of  calcium  is  a  white  amorphous  substance,  which  is  luminous  in  the 
dark;1  it  is  very  sparingly  soluble  in  water.  The  solution  has  an  alkaline  reac- 
tion. When  boiled  with  water,  it  yields  hydrate  of  lime,  and  hydrosulphate  of 
sulphide  of  calcium  : — 

2CaS+2HO=CaO.HO+CaS.HS. 

Suspended  in  water,  and  subjected  to  a  current  of  carbonic  acid,  it  yields  car- 
bonate of  lime  and  sulphuretted  hydrogen. 

An  insoluble  ovy  sulphide  of  calcium  is  formed  in  the  balling  process,  in  making 
carbonate  of  soda. 

Bisulphide  of  Calcium  (CaS2)  may  be  obtained  by  boiling  for  a  few  instants  a 
mixture  of  milk  of  lime  and  flowers  of  sulphur;  the  liquid  filtered  while  hot, 
deposits,  on  cooling,  orange-yellow  needles  of  the  bisulphide,  which  are  almost 
insoluble  in  cold  water;  their  formula  is  CaS34-3Aq. 

Pentasulphide  of  Calcium  (CaS5)  is  obtained  in  solution  when  milk  of  limo  is 

1  Sulphide  of  calcium  is  hence  sometimes  termed  Canton' 's  phosphorus. 


MAGNESIUM.  303 

boiled  for  a  considerable  time  with  a  large  excess  of  sulphur.  It  is  needless  to 
say  that  the  formation  of  the  bisulphide  and  pentasulphide  of  calcium  is  attended 
by  that  of  hyposulphite  of  lime  :  — 

2CaSa+CaO.S2Oa- 


PHOSPHIDE  OF  CALCIUM,  Ca2P. 

Preparation.  —  To  prepare  phosphide  of  calcium,  vapor  of  phosphorus  is  passed 
over  quicklime  heated  to  redness. 

An  earthen  crucible  of  about  a  pint  capacity  is  taken,  and  a  round  hole  drilled 
into  the  centre  of  the  bottom  ;  into  this  hole  the  neck  of  a  Florence  flask  is  luted 
(with  a  lute  composed  of  8  or  10  parts  of  brick-dust,  1  part  of  litharge,  and  lin- 
seed oil),  so  that  it  may  project  about  half  an  inch  in  the  interior  of  the  crucible; 
the  apparatus  should  be  allowed  to  remain  for  a  day  or  two,  that  the  lute  may 
dry  ;  a  small  quantity  of  dry  phosphorus  is  then  introduced  into  the  flask,  the 
crucible  is  filled  with  fragments  of  quicklime,  and  so  placed  in  a  furnace  that  it 
may  be  surrounded  with  redhot  coke  or  charcoal,  without  heating  the  phos- 
phorus. When  the  crucible  is  heated  to  redness,  a  few  pieces  of  redhot  charcoal 
may  be  placed  beneath  the  Florence  flask,  and  the  phosphorus  converted  into 
vapor. 

The  reaction  which  takes  place  when  vapor  of  phosphorus  is  passed  over  red- 
hot  lime  may  be  expressed  by  the  equation  :  — 

14CaO+P7==2(2CaO.P05)-|-5Ca2P. 

The  product  of  the  operation  is  brown  and  amorphous.  When  treated  with 
water,  it  is  decomposed,  with  evolution  of  the  spontaneously  inflammable  liquid 
phosphuretted  hydrogen,  PH3,  which  resolves  itself  at  once  into  solid  and  gaseous 
phosphuretted  hydrogen  (see  page  181). 

The  alliaceous  odor  exhaled  by  the  brown  mass  is  due  to  the  phosphuretted 
hydrogen  produced  by  the  action  of  atmospheric  moisture. 


MAGNESIUM. 

Sym.  Mg.     E%.  12.     Sp.  Gr.  1.743. 

§  203.  This  metal,  in  combination,  is  found  pretty  abundantly  in  nature.  It 
enters  into  the  composition  of  many  minerals,  and  exists  in  most  natural  waters. 

Magnesium  was  first  prepared  by  Bussy,  who  obtained  it  by  decomposing 
chloride  of  magnesium  with  potassium  at  a  high  temperature. 

Preparation. — A  few  pellets  of  potassium  or  sodium  are  placed  at  the  bottom 
of  a  platinum  crucible,  and  covered  with  fragments  of  anhydrous  chloride  of 
magnesium ;  the  cover  of  the  crucible  is  then  secured  with  iron  wire,  and  the 
heat  of  a  spirit-lamp  applied.  A  violent  reaction  takes  place,  the  result  of 
which  is  expressed  by  the  following  equation : — 

MgCl+K=KCl  +  Mg. 

The  crucible  is  then  allowed  to  cool,  and  the  mass  treated  with  very  cold 
water,  which  dissolves  the  chloride  of  potassium  and  the  excess  of  chloride  of 
magnesium,  and  leaves  the  metal  in  the  form  of  globules. 

This  metal  has  recently  been  prepared  in  large  quantities  by  Bunsen,  by 
decomposing  fused  chloride  of  magnesium  by  the  galvanic  current. 

Properties. — Magnesium  is  a  white  malleable1  metal  resembling  silver. 

1  According  to  Bunsen,  the  magnesium  obtained  by  electrolysis  is  scarcely  more  duc- 
tile than  zinc  at  ordinary  temperatures,  whilst  that  reduced  by  potassium  may  be  ham- 


304  MAGNESIA. 

It  is  not  altered  by  dry  air  at  the  ordinary  temperature,  but  is  tarnished 
when  exposed  to  moist  air.  When  heated  to  dull  redness  in  air  or  oxygen,  it 
burns  with  a  vivid  light,  and  is  converted  into  magnesia. 

This  metal  fuses  at  a  moderate  red  heat.  It  is  scarcely  affected  by  pure  water 
at  the  ordinary  temperature,  but  it  decomposes  it  at  the  boiling  point,  evolving 
hydrogen.  Dilute  acids  readily  dissolve  this  metal,  evolving  hydrogen,  and  pro- 
ducing a  salt  of  magnesia. 

Nitric  acid  is  entirely  deoxidized  by  magnesium,  nitrogen  being  evolved ;  the 
metal  takes  fire  when  thrown  into  dilute  nitric  acid.  Concentrated  sulphuric 
acid  dissolves  it,  with  evolution  of  sulphurous  acid. 

Magnesium  forms  only  one  oxide — magnesia. 

OXIDE  OF  MAGNESIUM,  MAGNESIA,  MAGNESIA  USTA,  CALCINED  MAGNESIA. 

MgO.     Eq.  20. 

Preparation. — This  oxide  is  generally  prepared  by  calcining  the  substance 
termed  in  pharmacy  magnesia  alba  until  it  ceases  to  effervesce  with  acids.  Mag- 
nesia alba  is  a  compound  of  hydrate  and  carbonate  of  magnesia,  from  which  the 
water  and  carbonic  acid  may  be  expelled  at  a  moderately  high  temperature. 

The  magnesia  prepared  in  this  way  is  a  very  light  bulky  powder ;  when  a 
denser  kind  is  required,  it  is  prepared  by  calcining  the  heavy  carbonate  of  mag- 
nesia, as  it  is  termed;  the  magnesia  thus  obtained  is  known  as  heavy  calcined 
magnesia. 

It  may  also  be  obtained  in  a  state  of  perfect  purity,  by  igniting  the  nitrate  of 
magnesia. 

Properties. — Magnesia  is  a  white  powder,  varying,  as  already  mentioned,  in 
density.  It  is  unaltered  by  heat,  having  never  yet  been  fused.  Magnesia 
slowly  absorbs  water  and  carbonic  acid  from  the  air.  When  moistened  with 
water,  it  combines  with  it,  without  appreciable  elevation  of  temperature,  to  form 

hydrate  of  magnesia. 

.  '  A 

HYDRATE  OP  MAGNESIA,  MgO. HO. 

Crystallized  hydrate  of  magnesia  composes  the  mineral  brucite. 

It  may  be  prepared  directly  from  anhydrous  magnesia,  or  by  decomposing  a 
solution  of  a  salt  (sulphate)  of  magnesia,  with  potassa. 

Properties. — Hydrate  of  magnesia  forms  a  white  powder,  which  slowly  absorbs 
carbonic  acid  from  the  air.  Its  water  is  easily  expelled  by  heat.  This  hydrate 
is  very  sparingly  soluble  in  water,  but  sufficiently  so  to  exhibit  an  alkaline  reac- 
tion. 1  part  of  anhydrous  magnesia  requires  about  5,000  parts  of  water  at  the 
ordinary  temperature j  it  is  even  less  soluble  in  hot  water,  1  part  requiring 
36,000  parts. 

Magnesia  is  chiefly  employed  in  medicine  as  an  antacid ;  it  is  especially  useful 
as  an  antidote  to  the  mineral  acids  in  cases  of  poisoning.  Magnesia  is  sometimes 
administered  as  an  antidote  to  arsenious  acid. 

The  magnesia-salts  are  generally  neutral  to  test-papers. 

NITRATE  OF  MAGNESIA,  MgO.N03. 

§  204.  This  salt  is  found  in  the  mother-liquors  of  the  saltpetre  refinery. 
It  may  be  prepared  by  dissolving  magnesia  or.  its  carbonate  in  dilute  nitric 
acid,  and  evaporating  to  crystallization. 

Properties. — The  nitrate  crystallizes  in  deliquescent  prisms,  of  the  formula 

mered  out  into  thin  plates ;  he  attributes  this  difference  to  the  circumstance  that  the 
magnesium  reduced  by  potassium  retains  a  little  of  that  metal ;  that  obtained  by  electro- 
lysis nearly  always  contains  a  little  aluminum  and  silicon. 


SULPHATE  OF   MAGNESIA.  305 

MgO.N05-f  6Aq.  It  is  very  soluble  in  water  and  alcohol.  Nitrate  of  magnesia 
is  easily  decomposed  by  heat ;  when  exposed  for  some  time  to  a  temperature  of 
482°  F.  (250°  C.),  it  is  converted  into  a  basic  salt,  of  the  formula  2MgO.N05-f 
4Aq  j  all  the  nitric  acid  is  expelled  below  a  red  heat. 

The  Hypochlorite  of  Magnesia,  or  rather,  a  mixture  of  this  substance  with 
chloride  of  magnesium,  has  lately  been  applied  to  the  bleaching  of  flax  by  Claus- 
son,  who  prepares  it  by  mixing  equivalent  quantities  of  sulphate  of  magnesia 
and  bleach,  in  solution,  when  sulphate  of  lime  is  deposited,  and  the  clear  liquor 
is  drawn  off  for  use. 

SULPHATE  OF  MAGNESIA,  EPSOM  SALTS,  MgO.S03. 

§  205.  This  salt  is  sometimes  found  as  an  efflorescence  on  the  surface  of  rocks. 
It  occurs  native  as  the  mineral  hair-salt  (Haar  salz),  found  as  an  efflorescence, 
in  some  parts  of  Spain. 

Sulphate  of  magnesia  exists  in  sea-water  and  in  many  spring-waters  in  con- 
siderable quantity.  In  England,  the  springs  at  Epsom  and  Cheltenham  are  noted 
for  the  amount  of  this  salt  which  they  contain.  The  waters  of  Sedlitz  and  Pullna, 
in  Bohemia,  also  contain  considerable  quantities  of  this  salt. 

Preparation. — Much  of  the  sulphate  of  magnesia  found  in  commerce  is  pre- 
pared from  the  mother-liquor  (bittern)  in  the  separation  of  salt  from  sea- water; 
this  mother-liquor  is  concentrated  by  evaporation,  the  crystals  of  common  salt 
being  removed  as  they  are  deposited,  and  the  solution  allowed  to  crystallize. 
The  rough  crystals  thus  obtained  are  called  single  Epsom  salts;  when  purified  by 
another  crystallization,  they  are  termed  double  Epsom  salts. 

Sulphate  of  magnesia  is  also  sometimes  prepared  by  saturating  dilute  sulphuric 
acid  with  powdered  magnesian  limestone  (dolomite,  carbonate  of  lime  and  mag- 
nesia), when  the  lime  is  separated  as  sulphate,  and  the  sulphate  of  magnesia 
may  be  crystallized  from  the  solution.1  The  carbonic  acid  evolved  in  the  decom- 
position of  the  dolomite  is  employed  in  the  preparation  of  bicarbonate  of  soda. 

Near  Genoa,  sulphate  of  magnesia  is  obtained  from  a  magnesian  shale,  con- 
taining sulphides  of  copper  and  iron.  When  the  shale  is  roasted  and  exposed 
to  the  action  of  air  and  moisture,  the  sulphur  is  in  great  measure  converted  into 
sulphuric  acid,  part  of  which  enters  into  combination  with  the  magnesia,  forming 
sulphate  of  magnesia,  while  the  remainder  is  converted  into  the  sulphates  of  iron 
and  copper.  The  mixture  is  then  treated  with  water,  and  the  liquid  is  digested 
with  scraps  of  iron,  which  precipitate  the  copper  in  the  metallic  state.  On  add- 
ing to  the  solution  a  certain  quantity  of  lime,  the  whole  of  the  iron  is  precipi- 
tated, and  sulphate  of  magnesia  (containing  traces  of  iron  and  copper)  may  be 
crystallized  from  the  clear  liquor. 

Refuse  alum-liquors  are  also  employed  for  the  preparation  of  sulphate  of  mag- 
nesia. These  contain,  besides  sulphate  of  magnesia,  compounds  of  sulphuric  acid 
with  potassa,  alumina,  and  the  oxides  of  nickel,  cobalt,  and  iron ;  the  impure 
sulphate  of  magnesia  is  separated  from  them  by  crystallization,  and  the  sulphates 
of  alumina,  nickel,  cobalt,  and  iron,  contained  in  this  product,  are  precipitated 
by  a  suitable  addition  of  magnesian  limestone ;  the  mixture  is  then  dried  and 
roasted,  to  peroxidize  the  iron,  after  which  it  is  ground  to  powder,  treated  with 
water,  the  solution  filtered  and  evaporated  to  crystallization. 

Properties. — Ordinary  sulphate  of  magnesia  occurs  in  the  form  of  fine  needle- 
like  crystals,  which  are  rectangular  four-sided  prisms;  the  formula  of  these  crystals 
is  MgO.S03.HO-f-  6Aq.  These  effloresce  slightly  in  dry  air.3  When  heated,  the 

1  The  magnesian-limestone  is  sometimes  calcined  previously  to  the  treatment  with  sul- 
phuric acid,  and  the  lime  removed,  as  far  as  possible,  by  washing  with  water. 

2  Some  specimens  of  the  commercial  sulphate  deliquesce  slightly,  from  the  presence  of 
a  little  chloride  of  magnesium. 

20 


306 

crystals  undergo  the  aqueous  fusion,  and  lose  5  eqs.  of  water  below  212°  F. 
(100°  C.);  at  270°  F.  (132°  C.)  they  lose  another  equivalent  of  water,  but  the 
last  equivalent  (water  of  constitution)  is  not  expelled  till  the  temperature  rises 
to  460°  F.  (238°  C.);  if  further  heated,  the  salt  undergoes  the  igneous  fusion, 
and,  at  a  very  high  temperature,  is  decomposed. 

Sulphate  of  magnesia  is  very  soluble  in  water;  at  the  ordinary  temperature, 
100  parts  of  water  dissolve  68  parts,  and,  at  the  boiling-point,  150  parts  of  the 
common  crystals.  If  a  hot  saturated  solution  be  allowed  to  cool  the  crystals 
which  deposit  between  77°  and  86°  F.  (25°  and  30°  C.)  have  the  formula 
MgO.S03.HO-{-5Aq,  and  have  not  the  same  crystalline  form  as  those  with  6Aq; 
below  77°  F.,  the  ordinary  crystals  are  deposited,  until  the  temperature  falls 
below  32°  F.  (0°  C.),  when  the  crystals  have  the  composition  MgO.S03.HO-f- 
11  Aq.  The  reaction  of  solution  of  sulphate  of  magnesia  is  neutral;  and  its  taste 
bitter.  Sulphate  of  magnesia  is  very  sparingly  soluble  in  alcohol. 

When  anhydrous  sulphate  of  magnesia  is  mixed  with  carbon  and  ignited,  it 
leaves  a  residue  of  magnesia,  not  of  sulphide  of  magnesium. 

Sulphate  of  magnesia  is  decomposed  by  chloride  of  sodium ;  when  solutions 
of  these  salts  are  mixed,  and  exposed  to  a  low  temperature,  crystals  of  sulphate 
of  soda  are  obtained. 

The  occurrence  of  sulphate  of  magnesia  in  waters  may  be  explained  by  the 
action  of  the  sulphate  of  lime,  which  these  formerly  contained,  upon  the  mag- 
nesian  limestone  with  which  they  have  come  in  contact.  It  is  found  that  if  a 
solution  of  sulphate  of  lime  is  filtered  several  times  through  a  layer  of  magnesian 
limestone,  all  the  lime  is  replaced  by  magnesia  : — 

MgO.CQ3+CaO.S03=MgO.S03+CaO.C02. 

This  reaction  may,  however,  be  reversed,  for  it  is  found  that  if  carbonate  of  lime 
be  heated  with  solution  of  sulphate  of  magnesia,  to  a  temperature  of  392°  F. 
(200°  C.)>  in  a  stout  sealed  glass  tube,  carbonate  of  magnesia  and  sulphate  of 
lime  are  formed. 

Sulphate  of  magnesia  is  used  extensively  in  medicine.  It  is  employed  to  the 
laboratory  as  a  reagent,  and  is  the  source  of  most  other  compounds  of  magnesia. 

The  sulphate  of  magnesia  of  commerce  is  sometimes  adulterated  with  sulphate 
of  soda. 

The  water  of  constitution  in  sulphate  of  magnesia  is  capable  of  being  replaced 
by  an  alkaline  sulphate,  a  double  salt  being  thus  formed. 

The  double  sulphate  of  magnesia  and  potassa,  MgO.S03,KO.S03  +  6  Aq,  is 
deposited  during  the  evaporation  of  the  mother-liquor  from  the  salt-works. 

The  formula  of   the  corresponding  ammonia-salt  is  MgO.S03,NH4O.S03 
6Aq;  it  has  the  same  form  as  the  preceding. 

PHOSPHATES  OF  MAGNESIA. 

§  206.  COMMON  PHOSPHATE  OF  MAGNESIA  (2MgO.HO.P05)  may  be  ob- 
tained by  dissolving  basic  carbonate  of  magnesia  (magnesia  alba)  in  common 
phosphoric  acid,  or  by  mixing  hot  concentrated  solutions  of  sulphate  of  magnesia 
and  phosphate  of  soda,  when  the  new  salt  is  deposited  on  cooling.  It  crystallizes 
in  hexagonal  needles  of  the  formula  2MgO.HO.P05-f-14Aq.  These  crystals 
lose  8  equivalents  of  water  at  the  boiling-point,  and  14  equivalents  at  347°  F. 
(175°  C.)  ',  at  a  higher  temperature  the  last  equivalent  of  water  is  expelled,  and 
pyrophosphate  of  magnesia,  2MgO.P05,  remains. 

Common  phosphate  of  magnesia  is  sparingly  soluble  in  water,  but  dissolves 
easily  in  acids.  If  it  be  long  boiled  with  water,  it  is  decomposed  into  free  phos- 
phoric acid,  and  a  basic  salt,  of  the  formula  3MgO.P05+7Aq. 

Phosphate  of  magnesia  enters  into  the  composition  of  the  bones  of  animals. 
This  phosphate  is  said  to  be  3MgO.POs. 


CARBONATE  OF  MAGNESIA.  307 

PHOSPHATES  OF  MAGNESIA  AND  AMMONIA. 

TRIPLE  PHOSPHATE  (MgO.NH4O.HO.POs)  is  sometimes  a  constituent  of  uri- 
nary calculi. 

It  may  be  prepared  by  adding  phosphite  of  ammonia  (2NH4O.HO.P05)  to  a 
hot  solution  of  sulphate  of  magnesia,  when  prismatic  crystals  are  deposited  on 
cooling,  of  the  formula  MgO.NH4O.HO.P05-f  3Aq.  When  ignited,  this  salt 
yields  metaphosphate  of  magnesia  (MgO.PO.). 

AMMONIACO-MAGNESIAN  PHOSPHATE  (2MgO.NH4O.P05)  occurs  in  the  seeds 
of  some  of  the  cereals,  and  sometimes  in  the  form  of  calculi.  It  is  also  occasion- 
ally deposited  from  urine.  The  minerals  guanite&ud  struvite  consist  of  this  salt. 
Ammoniaco-magnesian  phosphate  is  precipitated  by  adding  a  solution  of  phos- 
phate of  soda  to  a  mixture  of  sulphate  of  magnesia  with  chloride  of  ammonium 
and  ammonia ;  it  is  thus  obtained  as  a  white  crystalline  precipitate  (minute  four- 
sided  prisms),  which  is  slightly  soluble  in  water,  but  insoluble  in  dilute  ammonia. 
Its  formula  is  2MgO.NH4O.P05+12Aq.  By  ignition,  this  salt  is  converted 
into  pyrophosphate,  2MgO.P05.  When  heated  to  212°  F.  (100°  C.)  it  loses 
10  equivalents  of  water.  The  ammoniaco-magnesian  phosphate  dissolves  readily 
in  acids. 

Hose  has  obtained  an  insoluble  double  phosphate  of  magnesia  and  potassa 
(2MgO.KO.P05)  by  igniting  phosphate  of  magnesia  with  carbonate  of  potassa. 

CARBONATE  OF  MAGNESIA,  MgO.C02. 

§  207.  This  salt  is  found  in  nature  in  the  pure  state  as  the  mineral  magnesite 
(MgO.COa+3Aq). 

Preparation. — The  anhydrous  carbonate  maybe  prepared  artificially,  by  placing 
a  tube  containing  solution  of  carbonate  of  soda  in  a  strong  tube  containing  solu- 
tion of  sulphate  of  magnesia,  sealing  the  outer  tube  hermetically,  heating  it  to 
320°  F.  (160°  C.),  and  inverting  it  so  that  the  solutions  may  mix;  crystalline 
grain*  of  the  anhydrous  carbonate  are  deposited. 

This  carbonate  is  also  deposited  in  crystals,  when  a  solution  of  bicarbonate  of 
magnesia  is  evaporated  in  a  current  of  carbonic  acid  gas. 

Properties. — The  native  carbonate  is  occasionally  met  with  in  rhombohedral 
crystals.  Magnesite  is  a  white  amorphous  mineral,  very  hard,  of  specific  gravity 
about  2.6.  When  heated,  carbonate  of  magnesia  is  easily  converted  into  mag- 
nesia. It  is  insoluble  in  water,  but  dissolves  in  acids,  with  evolution  of  carbonic 
acid. 

Carbonate  of  magnesia  dissolves  in  solution  of  carbonic  acid,  probably  forming 
a  "bicarbonate;  the  solution  deposits  carbonate  of  magnesia  when  boiled.  When 
a  solution  of  bicarbonate  of  magnesia  is  exposed  to  air,  a  portion  of  the  carbonic 
acid  passes  off,  and  transparent  hexahedral  crystals  are  deposited,  of  the  formula 
MgO.C03-f3Aq.  At  a  very  low  temperature,  crystals  containing  5  eqs.  water 
are  deposited.  These  are  very  unstable,  easily  parting  with  a  portion  of  their 
carbonic  acid,  and  passing  into  basic  carbonates. 

BASIC  CARBONATE  OF  MAGNESIA,  SUBCARBONATE  OF  MAGNESIA.  MAGNESIA 
ALBA,  3(MgO.C02),MgO.HO+3Aq. 

This  important  compound  is  prepared  by  boiling  a  solution  of  sulphate  of  mag- 
nesia1 with  a  slight  excess  of  solution  of  carbonate  of  potassa  or  of  soda  for  a 
short  time  : — 

4(MgO.S03)+4(KO.C02)+4HO=(3(MgO.C02).MgO.HO-f3Aq) 
+4(KO.S03)+C02, 

1  The  mother-liquors  of  the  salt-works  are  sometimes  employed  for  this  purpose. 


308  SALTS   OP   MAGNESIA. 

the  excess  of  carbonic  acid  being  expelled  as  gas;  if  the  mixture  were  not  boiled, 
the  free  carbonic  acid  would  retain  some  carbonate  of  magnesia  in  solution.  The 
white  precipitate  is  thrown  upon  a  cloth  filter,  well  washed  with  boiling  water, 
till  the  washings  give  no  precipitate  with  chloride  of  barium,  and  dried. 

The  product  thus  obtained  is  a  very  bulky  white  powder ;  it  is  usually  met 
with  in  rectangular  masses  produced  by  drying  it  in  moulds.  It  is  converted,  by 
a  moderate  heat,  into  magnesia. 

This  substance  is  very  sparingly  soluble  in  cold  water,  and  even  less  soluble 
in  hot  water.  It  dissolves  readily  in  acids,  carbonic  acid  being  disengaged. 

The  substance  known  as  heavy  carbonate  of  magnesia,  has  the  same  composi- 
tion as  the  above,  and  is  prepared  by  mixing  hot  solutions  of  carbonate  of  soda 
and  sulphate  of  magnesia,  evaporating  to  dryness,  and  washing  the  residue;  the 
product  is  much  less  bulky  than  the  preceding. 

When  solution  of  carbonate  of  soda  is  added  to  solution  of  sulphate  of  mag- 
nesia in  the  cold,  a  precipitate  of  the  formula  4(MgO.C02),MgO.HO-|-9Aq  is 
produced  ;*  when  this  is  boiled  in  the  solution,  it  is  converted  into  magnesia  alba. 
This  latter  is  used  in  medicine  for  the  same  purposes  as  calcined  magnesia.  Car- 
bonate of  magnesia  is  capable  of  combining  with  other  carbonates  to  form  double- 
salts.  Thus,  we  have  double  carbonates  of  magnesia  and  potassa,  soda  and 
ammonia. 

When  a  concentrated  solution  of  a  magnesia-salt  is  mixed  with  an  excess  of 
solution  of  bicarbonate  of  potassa,  and  allowed  to  stand  for  some  days,  crystals 
are  deposited  of  the  formula  (KO.C02,HO.C03),2(MgO.C03)-f8Aq. 

Dolomite  is  a  double  carbonate  of  lime  and  magnesia,  and  contains  generally 
single  equivalents  of  these  salts,  but  is  often  mixed  with  an  excess  of  carbonate 
of  lime.  Since  the  carbonates  of  lime  and  magnesia  are  isomorphous,  the  car- 
bonate of  magnesia  does  not  alter  the  crystalline  form  of  the  calcareous  mineral.2 

The  borates  of  magnesia  possess  no  practical  importance.  The  mineral  boracite 
is  found  crystallized  in  cubes,  of  the  formula  3Mg0.2B03.  A  double  borate  of 
magnesia  and  soda  exists.  The  mineral  hydroboracite  has  the  formula  3(MgO. 
CaO).2B03+9  Aq. 

SILICATES  OF  MAGNESIA. 

Combinations  of  silicic  acid  with  magnesia  are  abundant  in  the  mineral  king- 
dom. Meerschaum  is  a  silicate  of  the  formula  MgO.Si03 +2  Aq ;  Steatite 
(soap-stone  or  French  chalk)  is  represented  by  5(MgO.Si03)-f-2Aq.  Chrysolite 
and  olivine  have  the  formula  2MgO.Si03.  The  formula  of  peridote  is  3MgO.Si 
03 ;  some  specimens  are  green,  from  the  substitution  of  oxide  of  iron  for  part  of 
the  magnesia.  Talc  is  a  hydrated  silicate  of  magnesia.  Serpentine  is  a  com- 
pound of  silicate  of  magnesia  with  hydrate  of  magnesia;  it  is  much  used  for 
ornamental  purposes,  and  often  possesses  beautiful  colors  due  to  metallic  oxides. 
Augite  and  amphibole  are  double  silicates  of  lime  and  magnesia,  often  colored 
black  or  green,  from  the  replacement  of  the  latter  by  oxide  of  iron.  Asbestos  or 
amianthj  and  hornblende,  are  also  silicates  of  lime  and  magnesia  (sometimes 
containing  oxide  of  iron). 

11  According  to  Fritzsche,  when  a  very  large  excess  of  carbonate  of  soda  is  added  to 
sulphate  of  magnesia,  and  the  mixture  boiled,  a  precipitate  is  obtained,  which  has  the 
composition  2  (Mgp.C02)MgO.HO-f  2 Aq. 

2  In  some  experiments  respecting  the  formation  of  dolomite,  it  was  found  that  when  a 
mixture  of  1  eq.  of  crystallized  sulphate  of  magnesia  and  2  eqs.  of  powdered  calcareous 
spar  was  exposed,  in  a  sealed  tube,  to  a  temperature  of  392°  F.  (200°  C.),  a  double  salt  of 
carbonate  of  lime  and  carbonate  of  magnesia  was  formed,  the  sulphate  of  magnesia  being 
entirely  converted  into  sulphate  of  lime. 


CHLORIDE   OF   MAGNESIUM.  309 

CHLORIDE  OF  MAGNESIUM,  HYDROCHLORATE  OF  MAGNESIA,  MgCl. 

§  208.  This  salt  exists  in  considerable  quantity  in  the  mother-liquors  of  the 
salt-works,  and  is  formed  when  magnesia  or  its  carbonate  is  dissolved  in  hydro- 
chloric acid.  It  is  also  produced  when  chlorine  is  passed  over  a  mixture  of 
magnesia  with  charcoal. 

In  order  to  prepare  pure  anhydrous  chloride  of  magnesium,  moderately  con- 
centrated hydrochloric  acid  is  saturated  with  magnesia  alba,  a  considerable  excess 
of  chloride  of  ammonium  (in  solution)  added,  and  the  whole  evaporated  to 
dryness,  when  the  residue  consists  of  a  double  salt  of  chloride  of  magnesium 
and  chloride  of  ammonium  ;  this  residue  is  heated  in  a  platinum  dish,  when  all 
chloride  of  ammonium  is  expelled,  and  anhydrous  chloride  of  magnesium  remains. 

The  hydrated  chloride  may  be  obtained  by  evaporating  the  solution  of  magnesia 
in  hydrochloric  acid,  and  allowing  it  to  crystallize. 

Properties.  —  Anhydrous  chloride  of  magnesium  forms  white  fused  masses 
which  deliquesce  when  exposed  to  air  ;  it  is  very  soluble  in  water  and  alcohol. 

The  crystallized  chloride  forms  colorless  deliquescent  needles  of  the  formula 
MgCl+6Aq  ;  when  heated,  these  evolve  water  and  hydrochloric  acid,  leaving  a 
residue  of  chloride  of  magnesium  mixed  with  a  considerable  quantity  of  mag- 
nesia :  — 


so  that  waters  rich  in  this  salt  should  not  be  employed  for  making  distilled  water, 
unless  lime  be  added  to  retain  the  hydrochloric  acid. 

Chloride  of  magnesium  forms  double  salts  with  the  chlorides  of  the  alkali- 
metals.1 

Sulphide  of  Magnesium,  MgS.  —  This  compound  has  been  but  little  studied. 
It  cannot  be  produced  by  boiling  or  fusing  sulphur  together  with  magnesia.  It 
may  be  obtained  in  solution  by  precipitating  sulphate  of  magnesia  with  sulphide 
of  barium.  When  magnesia  is  suspended  in  water  and  saturated  with  sulphu- 
retted hydrogen,  a  solution  is  obtained  containing,  according  to  Berzelius,  the 
hydrosulphate  of  sulphide  of  magnesium,  and  which,  on  boiling,  deposits  a  white 
gelatinous  precipitate  of  sulphide  of  magnesium. 

This  sulphide  appears  to  be  a  sulphur-base. 

The  properties  of  magnesia  and  its  compounds  show  that  this  base  stands  be- 
tween the  alkaline  earths  and  the  earths  proper,  much  as  lithia  does  between  the 
alkalies  and  the  alkaline  earths. 

In  its  alkaline  reaction  and  its  relations  to  carbonic  acid,  it  resembles  the  alka- 
line earths  (lime,  &c.),  whilst  its  behavior  with  sulphur  and  the  instability  of 
its  chloride,  give  it  a  similarity  to  the  earths  proper  (alumina,  &c.). 

1  It  was  found  by  Clark  that  when  chloride  of  magnesium  was  strongly  heated  in  dry 
ammoniacal  gas,  it  was  almost  entirely  volatilized,  a  white  powder  subliming,  which  had 
the  composition  MgCl+2NHa. 


310  ALUMINUM. 


METALS  OF  THE  THIRD  GROUP. 


ALUMINUM. 

Sym.  Al.     Eq.  13.7. 

§  209.  THIS  metal,  in  an  oxidized  state,  is  very  abundant  in  nature,  a  fact 
which  will  at  once  appear  when  we  say  that  all  clays  are  combinations  of  alumina 
with  silicic  acid. 

Wb'hler  first  isolated  aluminum  by  a  process  exactly  similar  to  that  employed 
for  preparing  magnesium. 

The  preparation  of  this  metal  is  best  conducted  as  follows :  A  quantity  of 
anhydrous  chloride  of  aluminum  is  placed  in  a  pretty  large  platinum  crucible, 
within  which  is  inclosed  a  smaller  crucible  containing  fragments  of  potassium; 
the  outer  crucible  is  covered,  the  lid  being  secured  with  wire,  and  a  moderate 
heat  applied;  the  potassium  is  thus  converted  into  vapor,  which  decomposes  the 
chloride  of  aluminum.  The  mass  is  washed  with  cold  water,  which  leaves  only 
the  aluminum. 

Care  should  be  taken  not  to  employ  an  excess  of  potassium,  since  solution 
of  potassa  (produced  by  the  decomposition  of  water)  is  capable  of  dissolving 
aluminum. 

Properties. — The  metal  is  thus  obtained  as  a  gray  powder,  which  assumes  a 
white  lustre  when  burnished ;  its  spec.  grav.  is  2.6.  It  requires  a  high  tem- 
perature for  fusion,  and  is  afterwards  malleable. 

Aluminum  is  unaltered  by  exposure  to  air  at  the  ordinary  temperature,  but 
when  heated  in  air  or  oxygen,  is  rapidly  oxidized  and  converted  into  alumina. 
Water  is  not  decomposed  by  this  metal  at  the  ordinary  temperature,  and  is 
slowly  acted  on  even  at  the  boiling  point. 

Aluminum  decomposes  water  with  facility  in  presence  of  free  acids  or  alkalies, 
hydrogen  being  evolved,  and  a  compound  of  alumina  formed. 

Only  one  combination  of  this  metal  with  oxygen  is  known. 

SESQUIOXIDE  OF  ALUMINUM,  ALUMINA. 
Ala03.     Eq.  51.4. 

This  oxide,  as  we  have  before  remarked,  is  abundant  in  nature;  it  not  only 
exists  in  combination  with  silicic  acid,  in  clay,  feldspar,  mica,  &c.,  but  is  often 
found  in  the  pure  state.  The  mineral  corundum  consists  of  nearly  pure 
alumina. 

Crystallized  alumina,  colored  with  metallic  oxides,  forms  different  varieties  of 
precious  stones.  The  ruby,  emerald,  amethyst,  and  sapphire  consist  of  nearly 
pure  alumina.  The  topaz  is  chiefly  fluoride  of  aluminum  combined  with 
alumina. 

Preparation. — Anhydrous  alumina  may  be  prepared  by  calcining  ammonia- 
alum  (sulphate  of  alumina  and  ammonia)  at  a  very  high  temperature;  the 
alumina  thus  prepared  retains  generally  a  little  sulphuric  acid. 


HYDRATES  OF  ALUMINA.  311 

Properties. — Alumina  in  its  native  state,  as  corundum,  is  a  very  hard  mineral 
(standing  next  to  the  diamond,  in  this  respect),  of  spec.  grav.  about  4.  An 
opaque  variety  of  this  mineral,  containing  a  considerable  amount  of  iron,  is 
known  as  emery,  which,  when  ground  and  separated  by  levigation  into  different 
degrees  of  fineness,  is  much  used  for  polishing.1 

Alumina  is  obtained  artificially  as  a  perfectly  white  substance,  which  is  not 
altered  by  exposure  to  the  highest  temperature  of  a  furnace ;  it  may,  however, 
be  fused,  and  become  very  liquid,  in  the  flame  of  the  oxyhydrogen  blowpipe, 
and  this  circumstance  has  been  taken  advantage  of  for  the  preparation  of  artificial 
gems  by  fusing  the  alumina  with  traces  of  metallic  oxides. 

When  exposed  to  air,  alumina  is  capable  of  absorbing  a  considerable  quantity 
of  water,  but  it  does  not  form  a  hydrate  even  when  moistened.  It  is  quite  inso- 
luble in  water,  and  dissolves  with  difficulty  in  the  strong  mineral  acids  and  in 
caustic  alkalies ;  if  it  be  fused  with  hydrate  of  potassa  or  of  soda,  the  fused  mass 
dissolves  entirely  in  water.  Anhydrous  alumina  adheres  very  tenaciously  to  the 
tongue. 

The  relations  which  alumina  exhibits  to  acids  and  to  other  bases  are  some- 
what remarkable :  it  appears  to  be  a  weak  base,  for  it  does  not  combine  with 
very  weak  acids,  and  is  not  capable  of  completely  neutralizing  the  stronger  acids; 
on  the  other  hand,  it  combines  with  very  strong  bases,  as  will  be  presently  seen, 
to  form  crystallizable  compounds  presenting  the  characters  of  salts ;  hence  it 
would  appear  that  alumina  stands  on  the  limit  between  the  two  classes,  comport- 
ing itself  as  an  acid  towards  strong  bases,  and  as  a  base  with  strong  acids. 

HYDRATES  OP  ALUMINA. 

There  are  several  hydrates  of  alumina.  The  mineral  known  as  diaspore  is  a 
crystallized  hydrate  of  alumina,  having  the  formula  A1203.2HO. 

Hydrate  of  Alumina  (A12O3.3HO)  is  prepared  by  adding  an  excess  of  car- 
bonate of  ammonia  to  a  solution  of  alum  (sulphate  of  alumina  and  potassa), 
heating  for  a  few  minutes,  collecting  the  precipitate  on  a  filter,  and  well  washing 
with  hot  water;  this  precipitate,  however,  still  retains  some  sulphuric  acid;  in 
order  to  obtain  it  perfectly  pure,  it  should  be  redissolved,  as  far  as  possible,  in 
hot  hydrochloric  acid,  and  the  solution  reprecipitated  with  excess  of  ammonia; 
the  precipitate  is  washed  till  free  from  chlorine,  and  dried  by  a  gentle  heat. 

Properties. — Hydrate  of  alumina  is  a  very  bulky  gelatinous  precipitate,  which 
shrinks  very  much  on  drying  to  a  mass  resembling  gum.  Its  water  is  not  en- 
tirely expelled  below  a  red  heat.  It  does  not  affect  test-papers.  The  freshly 
precipitated  hydrate  is  sensibly  dissolved  by  water  or  by  solution  of  ammonia; 
indeed,  if  a  considerable  excess  of  the  latter  be  added  to  a  dilute  solution  of 
alumina,  no  precipitate  is  obtained;  but  this  solubility  is  much  diminished  by 
the  presence  of  chloride  of  ammonium,  so  that,  by  adding  a  considerable  amount 
of  this  salt  before  adding  ammonia,  we  may  insure  the  complete  precipitation  of 
the  hydrate.  The  precipitate  is  easily  redissolved  by  acids  and  fixed  alkalies; 
but  if  the  precipitate  produced  by  ammonia  in  solution  of  alum  be  collected  on 
a  filter  and  washed,  it  cannot  be  entirely  redissolved  in  hydrochloric  acid. 

Hydrate  of  alumina  has  a  great  affinity  for  most  coloring  matters,  forming 
compounds  which  are  termed  lakes.  Thus,  if  a  solution  of  alum  be  mixed  with 
an  infusion  of  logwood,  and  an  excess  of  carbonate  of  potassa  be  then  added,  the 
hydrate  of  alumina  will  form,  with  the  coloring  matter,  a  purplish-red  lake, 

1  J.  Lawrence  Smith  has  recently  determined  the  effective  hardness  of  different  varie- 
ties of  emery;  he  found  that,  aeteris  paribus,  those  emeries  which  contained  the  least 
water  were  the  hardest.  In  addition  to  alumina,  oxide  of  iron,  and  a  little  water,  the 
specimens  were  found  to  contain  silica,  lime,  and  sometimes  small  quantities  of  iron- 
pyrites,  titanic  acid,  and  the  oxides  of  zirconium  and  manganese. 


312  SALTS   OP  ALUMINA. 

which  leaves  the  solution  colorless.  This  property  is  turned  to  advantage  in 
calico-printing,  where  the  compounds  of  alumina  are  largely  used  as  mordants. 
The  chief  aluminous  mordant  is  the  acetate,  which  is  decomposed  by  a  boiling 
heat,  with  precipitation  of  a  basic  acetate,  capable  of  combining  with  coloring 
matters;  hence,  if  a  pattern  be  printed  in  acetate  of  alumina,  and  the  stuff  be 
then  steeped  in  a  hot  color-bath,  the  basic  acetate  will  be  precipitated  in  the 
fibres,  and  will  fix  the  color  there. 

Aluminate  of  Potassa,  KO.A1203. — This  compound  may  be  obtained  in  white 
granular  crystals,  by  slowly  evaporating  a  solution  of  alumina  in  potassa.  The 
crystals  have  a  sweet  taste,  and  a  strongly  alkaline  reaction. 

A  solution  of  alumina  in  potassa  is  sometimes  used  as  a  mordant. 

The  Aluminate  of  Maynesia,  MgO.Al303,  is  found  as  a  very  hard  mineral, 
termed  spindle;  it  crystallizes  in  octohedra. 

Nitrate  of  Alumina  (Ala03.3N05)  is  prepared  by  dissolving  alumina  in  nitric 
acid;  it  may  be  obtained  from  an  acid  solution  in  colorless  oblique  rhombic 
prisms,  containing  eighteen  eqs.  of  water.  The  crystals  are  very  deliquescent 
and  soluble. 

SULPHATE  OP  ALUMINA,  A1303.3S03. 

§  210.  This  salt -is  occasionally  found  native,  when  it  is  sometimes  termed 
hair-salt. 

Preparation. — It  is  usually  prepared  from  clay,  as  free  from  iron  as  possible. 
The  clay  is  calcined  at  a  dull  red  heat,  reduced  to  a  fine  powder,  and  mixed  with 
half  its  weight  of  sulphuric  acid  of  spec.  gr.  1.45.  The  mixture  is  heated  till 
the  acid  begins  to  go  off,  then  left  to  itself  for  a  day  or  two ;  after  this  time  it  is 
extracted  with  water,  when  a  solution  is  obtained,  containing  sulphate  of  alumina 
and  sulphate  of  sesquioxide  of  iron.  The  solution  is  now  mixed  with  a  solution 
of  ferrocyanide  of  potassium1  (yellow  prussiate  of  potassa),  as  long  as  any  blue 
precipitate  (sesquiferrocyanide  of  iron,  Prussian  blue)  is  obtained,  and  the  filtered 
liquid,  which  is  now  free  from  iron,  evaporated  to  a  syrupy  consistence,  and  al- 
lowed to  solidify  in  shallow  leaden  pans. 

Properties. — The  sulphate  thus  obtained  is  a  white  mass,  which  resists  a  high 
temperature  without  decomposition.  It  is  very  soluble  in  water,  requiring  only 
twice  its  weight  for  complete  solution,  but  very  sparingly  soluble  in  aleohoi. 
The  aqueous  solution  has  a  sweet  astringent  taste,  and  an  acid  reaction;  a  hot 
saturated  solution,  on  cooling,  deposits  small  tabular  crystals,  of  the  formula 
Al3033S03+18Aq. 

These  crystals  fuse  when  heated,  intumesce  greatly,  and  are  ultimately  decom- 
posed, losing  the  greater  part  of  their  acid.  Sulphate  of  alumina  is  extensively 
used  as  a  mordant. 

A  basic  Sulphate  of  Alumina,  of  the  formula  2A1303.3S03,  may  be  obtained 
by  digesting  a  solution  of  the  neutral  sulphate  with  hydrate  of  alumina.  It  has 
not  been  crystallized.  Another  basic  sulphate  occurs  in  nature,  in  the  mineral 
aluminite  (A1203.3S03,2A1303,9HO).  It  may  be  prepared  by  adding  a  little 
ammonia  to  a  solution  of  the  neutral  sulphate,  when  it  falls  down  as  a  crystalline 
precipitate. 

Sulphate  of  alumina  is  capable  of  combining  with  the  sulphates  of  the  alkalies, 
giving  rise  to  certain  double  salts,  which  may  be  taken  as  the  types  of  the  class 
of  salts  termed  alums. 

AN  ALUM  is  a  double-salt,  composed  of  a  sulphate  of  a  protoxide  combined 

1  On  the  large  scale,  ferrocyanide  of  sodium  is  commonly  employed ;  the  precipitated 
Prussian  blue  is  afterwards  decomposed  with  solution  of  caustic  soda,  in  order  to  repro- 
duce the  ferrocyanide  of  sodium,  which  is  used  to  precipitate  a  fresh  portion  of  iron. 


ALUM.  313 

with  the  neutral  sulphate  of  a  sesquioxide,  thus  the  general  formula  of  an  alum 
may  be  written : — 

MO.S03,M203.3S03; 

where  MO  represents  the  basic  protoxide,  and  M203  the  basic  sesquioxide. 
The  alums  all  crystallize  in  cubes  or  octohedra  containing  24  eqs.  of  water. 
In  order  to  render  the  above  definition  more  intelligible,  we  subjoin  the  form- 
ulae of  some  of  the  principal  alums : — 

Potash-alum KO.SOa,Ala08.3SO,  +  24Aq 

Soda-alum NaO.S03,Ala03.3S03+24Aq 

Ammonia-alum  .  .  .  NH4O.S03,Ala03.3S03+24Aq 
Potash-iron-aluin  ....  KO.S08,Fe9Oa.3S08+24Aq 
Soda-manganese-alum  .  .  NaO.S03,Mna03.3S03+24Aq 
Ammonia-chrome-alum  .  NH4O.S03,  Cra08.3SOa+24Aq 

SULPHATE  OF  ALUMINA  AND  POTASSA,  POTASSA-ALUMINA-ALUM,  COMMON 
ALUM,  Ala08.3S08,KO.SOa  +  24  Aq.1 

§  211.  This  salt  exists  native  in  the  neighborhood  of  Naples,  where  it  is 
extracted  by  simply  treating  the  rock  with  water.3 

It  may  be  prepared  by  mixing  together  hot  concentrated  solutions  of  sulphate 
of  alumina  and  sulphate  of  potassa,  when  crystals  of  alum  are  deposited  as  the 
solution  cools. 

In  Italy,  alum  is  prepared  from  alum-stone,  which  is  found  at  Tolfa,  near 
Civita-Vecchia.  The  composition  of  this  mineral  is  KO  S03,3(Ala03.S03)-f-9Aq; 
when  this  mineral  is  calcined,  a  portion  of  the  alumina  is  converted  into  the  insolu- 
ble form;  and  when  the  mineral  is  afterwards  treated  with  water,  a  quantity  of 
alum  is  dissolved  out;3  the  washings  are  evaporated,  when  they  yield  cubical  crystals 
of  alum ;  these  crystals  have  a  reddish  color,  from  the  presence  of  a  little  sesqui- 
oxide of  iron  in  the  insoluble  state  ('/).  This  variety  of  alum  is  known  as  Roman 
alum,  or  Rock  alum,  and  is  preferred  by  dyers,  since  its  aqueous  solution  is  always 
free  from  iron.  It  is  at  present  prepared  artificially,  by  mixing  solution  of  alum 
with  a  small  quantity  of  carbonate  of  potassa,  which  precipitates  any  sesquioxide 
of  iron  which  may  be  present,  evaporating  to  crystallization,  and  coloring  the 
crystals  thus  obtained  with  brick-dust,  or  Armenian  bole,  to  make  them  appear 
like  true  Roman  alum. 

Alum  is,  however,  most  extensively  prepared  from  alum  slafe,  or  shale,  which 
is  a  mineral  of  very  common  occurrence.  Alum  slate  contains  silicate  of  alu- 
mina, together  with  finely-divided  iron-pyrites,  and  more  or  less  bituminous  mat- 
ter.4 The  mineral  is  coarsely  broken  up,  and  subjected  to  a  process  of  oxidation, 
which  generally  consists  either  in  exposing  it  to  the  continued  action  of  air  and 
moisture,  or  in  throwing  it  into  pyramidal  heaps,  with  or  without  an  additional 
quantity  of  combustible,  and  setting  fire  to  these  in  different  parts,  letting  them 
smoulder  away  till  all  the  pyrites  are  oxidized.  The  produce  is  better,  the  more 
slowly  and  uniformly  this  operation  is  conducted.  The  roasted  heaps  are  then 
allowed  to  remain  exposed  to  the  air  till  they  are  in  a  fit  state  for  extraction. 

1  According  to  Jacquelain,  22Aq. 

2  The  natural  formation  of  alum  may  "be  easily  explained,  where  iron-pyrites  occurs 
associated  with  feldspathic  rocks;  the  oxidation  of  the  iron-pyrites  (FeS2)  gives  rise  to 
sulphate  of  iron  and  free  sulphuric  acid,  which  combines  with  the  alumina  and  potassa 
contained  in  the  feldspar. 

3  The  calcination  of  the  mineral  continues  until  sulphurous  vapors  begin  to  pass  off; 
the  mineral  is  then  transferred  to  cisterns,  and  repeatedly  moistened  with  water  during  3 
or  4  months,  when  it  crumbles  down  to  a  sort  of  mud. 

4  Alum-earth  differs  from  alum-slate  more  in  its  texture,  which  is  soft  and  friable,  than 
in  its  composition. 


314  SALTS    OP  ALUMINA. 

Sometimes  the  heaps  take  fire  spontaneously  from  the  heat  evolved  by  the 
oxidation  of  the  pyrites;  the  workmen  then  smother  the  fire,  to  prevent  loss  of 
sulphur  in  the  form  of  sulphurous  acid.1 

The  alum-shale  is  often  associated  with  so  much  coal,  that  any  further  addi- 
tion of  fuel  to  the  heaps  is  found  unnecessary ;  indeed,  in  some  cases,  it  is  re- 
quisite to  add  a  certain  quantity  of  shale  which  is  poor  in  coal,  in  order  to 
economize  the  fuel. 

The  change  which  takes  place  during  the  oxidation  is  easily  intelligible. 

The  iron-pyrites  is  converted  into  sulphate  of  iron,  whilst  the  excess  of  sulphur 
yields  a  quantity  of  free  sulphuric  acid  :3 — 

FeS2+07=FeO.S03+S03. 

The  latter,  acting  upon  the  silicate  of  alumina,  gives  rise  to  sulphate  of  alumina. 
The  sulphate  of  alumina  and  sulphate  of  iron  are  then  extracted  by  water,3  and 
the  solution  evaporated  to  the  requisite  degree  of  concentration. 

The  principal  substances  contained  in  the  crude  alum-liquor  are,  sulphates  of 
alumina,  iron,  magnesia,  and  soda,  together  with  small  quantities  of  the  sulph- 
ates of  manganese,  potassa,  and  lime,  the  chlorides  of  magnesium  and  aluminum, 
sesquichloride  of  iron,  and  free  sulphuric  and  hydrochloric  acids.  The  liquor 
always  contains  a  certain  amount  of  potassa-alum  (the  potassa  being  derived 
from  the  shale  itself,  or  from  the  wood  employed  as  fuel)  and  of  ammonia- alum 
(unless  too  high  a  temperature  has  been  employed  in  the  process  of  oxidation, 
the  ammonia  being  derived  from  the  destructive  distillation  of  the  coal). 

The  crude  alum-liquor  generally  contains  a  sufficient  amount  of  green  vitriol 
(sulphate  of  iron)  to  pay  for  extraction,  hence  the  manufacture  of  this  salt  is 
usually  carried  on  simultaneously  with  that  of  alum.  Any  persalt  of  iron  which 
the  liquor  may  contain  is  reduced  by  metallic  iron,  and  the  solution  is  then 
boiled  down  to  the  point  at  which  the  green  vitriol  crystallizes  out.  In  this 
manner  a  mother-liquor  is  obtained,  which  is  saturated  with  sulphate  of  alumina. 
The  green  vitriol  is  purified  by  recrystallization. 

The  liquor  is  now  mixed  with  a  strong  solution  of  chloride  of  potassium,4 
which  converts  the  sulphates  (with  the  exception  of  sulphate  of  alumina)  into 
chlorides,  which,  being  much  more  soluble,  are  more  easily  removed  from  the 
resulting  alum  than  the  sulphates  could  be.  The  due  regulation  of  the  amount 
of  chloride  of  potassium  added,  is  of  considerable  importance,  since  an  excess  of 
that  salt  would  give  rise  to  the  production  of  chloride  of  aluminum. 

The  solution  of  the  chloride  is  gradually  added  to  the  liquor,  with  constant 
agitation,  and  the  alum-flour  thus  produced  is  then  allowed  to  subside;  it  is 
afterwards  drained,  and  washed  with  a  little  cold  water.  It  is  then  redissolved, 
by  exposing  it,  in  a  perforated  leaden  funnel,  to  the  action  of  steam,  and  the 
saturated  solution  thus  obtained  is  allowed  to  flow  into  wooden  casks,  or  roach- 
iny-tuns,  where  it  crystallizes. 

1  It  would  appear  that  the  sulphurous  acid  which  is  produced  in  those  parts  of  the 
heap  where  the  temperature  is  very  high,  is  absorbed  by  the  alumina,  and  subsequently 
converted  into  sulphuric  acid,  by  the  sulphate  of  sesquioxide  of  iron  formed  on  exposing 
the  protosulphate  to  the  air. 

A  certain  quantity  of  sulphuric  acid  is  also  liberated,  in  consequence  of  the  formation 
of  a  basic  sulphate  of  sesquioxide  of  iron  when  the  protosulphate  is  oxidized  by  exposure. 

It  is  found  advantageous  to  cover  the  heaps  with  exhausted  ore,  which  retains  a  quan- 
tity of  sulphuric  acid  that  would  otherwise  be  lost. 

The  oxidation  of  the  heap  requires  from  10  to  24  months,  according  to  the  nature  of 
the  ore. 

2  Part  of  the  sulphur  also  sublimes  upon  the  outer  and  cooler  portion  of  the  heap. 

3  The  lixiviation  of  the  alum-earth  is  carried  out  upon  the  same  principles  as  those 
already  explained  in  the  manufactures  of  nitre  and  borax  ($$  145  and  173). 

4  This  salt  is  obtained  as  soap-boilers'  waste,  also  from  the  saltpetre  refineries  and 
glass-houses. 


ALUM.  315 

The  mother-liquor  from  the  alum-crystals  receives  different  applications,  de- 
pending upon  its  composition.  If  it  contain  much  sulphate  of  iron,  it  is  digested 
with  metallic  iron,  to  neutralize  any  free  sulphuric  acid,  and  to  deoxidize  any 
persulphate  of  iron,  and  green  vitriol  is  then  crystallized  from  it.  If  much 
chloride  of  iron  be  present,  the  liquor  is  evaporated  to  dryness,  and  heated  to 
redness,  when  sesquioxide  of  iron  is  left,  which  is  employed  as  a  pigment.  The 
mother-liquors  are  also  sometimes  employed  for  the  preparation  of  sulphate  of 
ammonia,  from  the  ammoniacal  liquor  of  the  gas-works,  or,  when  they  contain 
much  magnesia,  for  the  manufacture  of  Epsom  salts. 

[In  some  places,  alum  is  manufactured  by  allowing  the  sulphurous  acid,  pro- 
duced in  metallurgic  operations,  to  act  upon  rocks  containing  alumina,  in  the 
presence  of  air  and  moisture,  thus  giving  rise  to  sulphate  of  alumiria,  from  which 
alum  may  be  manufactured,  in  the  manner  above  detailed.  Alum  is  also  made 
from  clay,  which  is  converted  into  sulphate  of  alumina  by  a  process  which  has 
already  been  described  (§  210).  It  has  been  proposed  to  manufacture  alum 
from  feldspar,  by  fusing  it  first  with  sulphate,  arid  afterwards  with  carbonate  of 
potassa;  when  the  resulting  mass  is  boiled  with  water,  an  insoluble  silicate  of 
alumina  and  potassa  is  left,  which  is  converted  into  alum  by  treatment  with 
sulphuric  acid.] 

Properties. — Alum  is  found  in  commerce  in  large  octohedral  crystals,  the 
angles  of  which  are  sometimes  truncated  by  the  faces  of  a  cube;  these  crystals 
are  frequently  aggregated  in  large  masses,  which  retain  the  form  of  the  casks  in 
which  the  crystallization  has  taken  place. 

The  crystals  of  ordinary  alum  are  colorless,  but  those  of  Koch  alum  have  (as 
before  mentioned)  a  brownish-red  color.  They  are  somewhat  efflorescent  in  dry 
air.1  When  heated  to  198°  F.  (92°  C.),  they  undergo  the  aqueous  fusion,  and 
when  further  heated,  lose  their  water  with  very  considerable  intumescence,  yield- 
'  ing  a  spongy  mass,  which  is  known  as  burnt  alum  (alumen  exsiccatum  velustum). 
A  high  temperature  is  required  to  expel  the  whole  of  the  water;  even  at  392° 
F.  (200°  C.)  a  small  quantity  of  water  remains.  Alum,  which  has  been  heated 
to  this  temperature,  redissolves  with  difficulty  in  water.  At  a  much  higher  tem- 
perature, the  salt  itself  is  decomposed,  sulphurous  acid  and  oxygen  are  disengaged, 
and  a  mixture  of  alumina  and  sulphate  of  potassa  remains.3 

The  crystals  dissolve  in  about  ten  parts  of  water  at  50°  F.  (10°  C.),  and  in 
less  than  one-third  of  their  weight  at  the  boiling-point,  so  that  a  hot  saturated 
solution  of  alum  deposits  the  greater  part  in  crystals,  on  cooling. 

The  solution  of  alum  has  an  acid  reaction  and  a  sweetish  astringent  taste. 

If  alum  be  dissolved  in  hot  concentrated  sulphuric  acid,  crystals  are  deposited 
on  cooling,  of  the  formula  A1303  3S03,  KO.S03+3Aq. 

When  potassa  or  its  carbonate  is  gradually  added  to  a  solution  of  alum,  until 
the  precipitate  which  is  formed  is  no  longer  dissolved  on  stirring,  the  liquid, 
when  evaporated,  gives  cubical  crystals,  which  have  been  noticed  above  as  artifi- 
cial Roman  alum.  These  crystals  are  generally  supposed  to  have  the  same  com- 
position as  those  of  ordinary  octohedral  alum,  but  it  has  been  asserted  that  they 
consist  of  a  basic  alum,  which  is  very  probable,  since,  when  their  solution  is 
boiled,  it  deposits  a  white  precipitate,  and  the  filtered  liquid,  on  evaporation, 
deposits  octohedra  of  common  alum. 

If  an  intimate  mixture  of  alum  with  carbon  or  sugar  be  calcined  in  a  close 
vessel  as  long  as  any  inflammable  gas  (carbonic  oxide)  is  evolved,  the  residue 
will  consist  of  a  mixture  of  alumina,  charcoal,  and  sulphide  of  potassium  in  a 
very  finely-divided  state.  In  consequence  of  the  rapid  oxidation  of  the  last- 

1  According  to  Hertwig,  alum  loses  10  eqs.  of  water  at  212°  F.  (100°  C.). 

2  If  a  very  intense  heat  be  employed,  a  compound  of  alumina  and  potassa  is  left. 


316  SILICATES   OF  ALUMINA. 

mentioned  substance,  the  mixture  takes  fire  when  thrown  into  the  air,  and  has 
hence  received  the  name  of  Homberg's  pyroplwrus. 

Uses  of  Alum. — This  salt  is  very  largely  employed  in  dyeing  and  calico- 
printing,  in  paper-making,  in  the  manufacture  of  colors,  in  rendering  wood  and 
paper  incombustible,  and  in  medicine. 

For  the  first  three  of  these  uses,  the  presence  of  iron  in  a  soluble  form  in  the 
alum  would  be  very  injurious.  Iron  may  be  easily  detected  by  mixing  the 
solution  of  alum  with  ferrocyanide  of  potassium,  which  would  produce  a  blue 
precipitate. 

A  sulphate  of  alumina  and  potassa  having  the  same  composition  as  the  mine- 
ral alum-stone,  viz.,  KO.S03,  3(Al2O3-S03)-f9Aq,  may  be  obtained  as  a  crys- 
talline precipitate  by  boiling  a  solution  of  alum  with  freshly-precipitated  hydrate 
of  alumina. 

Soda-alum  is  much  more  soluble  in  water  than  potassa-alum.  Like  this  salt, 
it  is  sometimes  found  native. 

Ammonia-alum,  which  also  occurs  native,  may  be  prepared  by  the  direct  com- 
bination of  sulphate  of  alumina  with  sulphate  of  ammonia.  On  the  large 
scale,  ammonia-alum  is  prepared  by  processes  similar  to  those  employed  in  the 
manufacture  of  potassa-alum.  It  is  very  similar  in  its  properties  to  potassa- 
alum  ;  when  ignited,  it  leaves  a  residue  of  alumina. 

Phosphate  of  Alumina  occurs  in  nature  as  the  mineral  wavellite,  the  formula 
of  which  is  3Al203.2P05+12Aq.  Hermann  has  recently  shown  that  the  mine- 
ral gibbsite,  formerly  supposed  to  be  a  hydrate  of  alumina,  is  really  a  phosphate, 
the  presence  of  the  phosphoric  acid  having  been  overlooked  by  other  analysts,  in 
this  mineral,  as,  at  an  earlier  period,  it  was  overlooked  in  wavellite.  The  formula 
of  gibbsite  is  Al203.P05-f8Aq. 

The  precipitate  produced  by  common  phosphate  of  soda  in  solution  of  alum, 
formerly  supposed  to  be  Ala03.P05,  has  been  found  by  Ludwig  to  contain 
8A1203.9P05..  On  dissolving  this  precipitate  in  hydrochloric  acid,  reprecipi- 
tating  by  ammonia,  and  igniting  the  washed  precipitate,  the  compound  A1303.P05, 
was  obtained. 

The  existence  of  a  carbonate  of  alumina  is  not  certainly  established.  The 
precipitate  produced  by  alkaline  carbonates  in  solutions  of  alumina  is  generally 
considered  as  a  hydrate,  since  its  formation  is  attended  with  disengagement  of 
carbonic  acid.1 


SILICATES  OF  ALUMINA. 

§  212.  Combinations  of  alumina  with  silicic  acid  are  very  abundant  in  nature. 
The  minerals  known  as  andalusite,  cyanite  (disthene)  and  sillimanite,  are  silicates 
of  alumina  of  the  formula  3Ala03.2Si03.  AUophane  is  the  hydrate  of  this 
silicate. 

The  feldspars  form  a  most  important  class  of  minerals,  of  which  the  neutral 
silicate  of  alumina  Ala03.3Si03  is  always  a  constituent;  indeed,  the  feldspars 
occupy  much  the  same  position  among  the  silicates  as  the  anhydrous  alumina- 
alums  occupy  among  the  sulphates;  for  they  consist  of  silicate  of  alumina 
combined  with  an  alkaline  silicate,  or  with  silicate  of  lime  or  magnesia. 

Potash-feldspar  (orthoclase,  adularia)  is  represented  by  the  formula 

KO.Si03,Al303.3Si03. 
This  is  the  most  common  of  the  feldspars;  it  is  found  in  very  hard  oblique 

1  According  to  Muspratt,  the  formula  of  the  precipitate  produced  by  carbonate  of 
ammonia  in  a  solution  of  alum  is  3Al203.2C02-|-16Aq. 


SILICATES   OF  ALUMINA.  317 

prisms,  of  spec.  gray,  about  2.5;  it  fuses  to  a  milky  glass  at  a  very  high  tempe- 
rature. 

Soda -feldspar  is  usually  called  albite ;  lithia-feldspar,  petalite  (tripliane, 
spoditmene),  and  lime-feldspar,  labradorite  (anorthite). 

A  feldspar  exists  containing  both  soda  and  potassa  (potash-albite,  pericline). 

Garnet  and  stilbite  are  double  silicates  of  alumina  and  lime. 

Pumice-stone  consists  almost  entirely  of  silicate  of  alumina. 

Mica  is  a  double  silicate  of  alumina  and  potassa,  the  latter  being  often 
replaced  by  lime  or  oxide  of  iron. 

Hornblende  contains  silicate  of  alumina  combined  with  silicates  of  lime,  mag- 
nesia, and  oxide  of  iron. 

Basalt  is  composed  of  pyroxene  (silicate  of  lime,  magnesia,  and  oxide  of  iron,) 
and  labradorite  (silicate  of  alumina,  lime,  and  soda). 

Granite  is  made  up  of  three  minerals,  quartz,  feldspar,  and  mica. 

Gneiss  contains  the  same  constituents  as  granite,  but  differs  from  it  in  struc- 
ture. 

The  clays,  which  are  also  very  important  members  of  the  mineral  kingdom, 
consist  of  hydrated  silicates  of  alumina. 

Kaolin,  which  is  the  purest  kind  of  clay,  and  serves  for  the  fabrication  of  fine 
porcelain,  consists  chiefly  of  a  silicate  having  the  formula  Al303,Si03,2Aq. 
This  substance  is  formed  by  the  disintegration  of  feldspathic  rocks  (granite,  for 
example)  under  the  influence  of  moisture,  when  the  feldspar  is  decomposed  into 
basic  silicate  of  alumina  (kaolin),  and  alkaline  silicates,  which  are  dissolved  by 
the  water.1 

Kaolin  is  found  in  white  amorphous  masses,  sometimes  containing  crystals  of 
unaltered  feldspar.  A  considerable  quantity  of  this  clay  is  found  at  Saint- 
Yrieix,  near  Limoges,  and  at  St.  Austle,  in  Cornwall. 

The  best  china-clay  used  in  England  is  prepared  in  Cornwall,  by  washing 
decomposed  granite  with  a  stream  of  water,  which  is  then  run  into  reservoirs, 
where  it  deposits  a  sediment,  which  is  afterwards  exposed  to  the  air  for  several 
months  before  being  used  for  the  manufacture  of  porcelain. 

The  composition  of  common  clays  is  very  similar  to  that  of  kaolin,  but  they 
are  generally  mixed  with  more  or  less  sand,  feldspar,  sesquioxide  of  iron,  car- 
bonates of  iron  and  lime,  and  organic  matter. 

When  these  impurities  are  present  only  in  small  quantity,  the  clay  is  termed 
fat  clay,  from  its  superior  plasticity.  Some  clays  contain  as  much  as  4  per  cent, 
of  potassa. 

Perfectly  pure  silicate  of  alumina  is  infusible  at  the  highest  temperature  of 
our  furnaces,  but  clays  containing  carbonate  of  lime  and  oxides  of  iron  are  more 
or  less  easily  fusible,  according  to  the  proportions  in  which  these  substances  are 
present. 

On  the  application  of  a  moderate  heat,  clay  loses  its  water,  and  shrinks  to  a 
dense  hard  mass.  When  exposed  to  a  very  high  temperature,  it  is  converted 
into  a  hard  sonorous  mass,  which  is  still  so  porous  as  to  absorb  water  with 
avidity.  The  density  of  the  mass  is  greatest  at  a  low  red  heat,  and  is  diminished 
by  the  application  of  a  higher  temperature. 

Dilute  acids  have  scarcely  any  action  upon  clay.  Even  concentrated  nitric 
and  hydrochloric  acids  decompose  it  slowly,  dissolving  the  alumina.  Concen- 
trated sulphuric  acid,  however,  attacks  it  readily,  at  a  high  temperature.  Clays 
are  generally  more  readily  acted  upon  by  acids  when  they  have  been  exposed  to 
a  moderate  heat,  but  if  strongly  calcined,  they  are  rendered  more  refractory. 

Solutions  of  the  alkalies  scarcely  act  upon  clay,  but  if  it  be  fused  with  the 
alkalies  or  their  carbonates,  it  is  converted  into  soluble  silicates  and  aluminates. 

1  Brongniart  and  Malaguti  have  succeeded  in  decomposing  feldspar  by  electricity. 


318  EARTHENWARE   AND   PORCELAIN. 

Pipe-clay  is  nearly  pure  silicate  of  alumina. 

Potter's-day  contains  a  considerable  amount  of  iron. 

Fire-clay,  when  burnt,  yields  a  very  porous  mass,  which  is  particularly  adapted 
to  resist  high  temperatures. 

Loam  is  a  very  impure  variety  of  clay,  employed  for  brick-making. 

Ochres  are  merely  clays  colored  with  the  oxides  of  iron  and  manganese. 

Yellow-ochre  contains  the  hydrated  sesquioxide  of  iron,  and  probably  the  car- 
bonate of  protoxide,  both  which  (the  latter  with  absorption  of  oxygen  and  ex- 
pulsion of  carbonic  acid)  are  converted  by  calcination  into  anhydrous  sesquioxide 
of  iron,  thus  yielding  red  ochre. 

The  colors  known  as  umber  and  sienna  are  merely  clays  colored  by  the  perox- 
ides of  iron  and  manganese. 

Bole  is  also  a  variety  of  ochre. 

Fuller's  earth  is  a  clay  of  a  particular  kind,  which,  when  dried,  is  highly 
capable  of  absorbing  grease  from  woollen  fabrics,  and  is  employed  for  this  purpose. 

Marl  is  a  term  applied  to  clay  which  contains  a  considerable  quantity  of  car- 
bonate of  lime.1 

The  method  to  be  followed  in  the  analysis  of  clays  is  quite  the  same  as  that 
recommended  in  the  case  of  the  insoluble  residue  of  a  limestone  (see  Quantita- 
tive Analysis,  Special  Methods). 

EARTHENWARE  AND  PORCELAIN. 

§  213.  We  need  not  say  that  the  chief  use  of  clay  is  in  the  manufacture  of 
pottery;  and  though  a  complete  description  of  the  processes  which  this  art 
involves  is  exceedingly  interesting,  it  would  be  beside  our  purpose  to  do  more 
than  enter  into  its  leading  chemical  features. 

Though  perfectly  pure  clay  possesses  a  high  degree  of  plasticity,  it  is  never- 
theless not  well  fitted  for  the  manufacture  of  porcelain,  since  it  shrinks  very 
much,  and  often  cracks  in  baking;  it  is  therefore  necessary  to  mix  it  with  some 
substance  which  shall  prevent  these  effects  from  becoming  apparent;  the  mate- 
rials generally  employed  for  this  purpose  are  silica  in  various  forms,  feldspar, 
chalk,  bone-ash,  and  heavy-spar  (sulphate  of  baryta). 

It  has  been  already  stated  that  perfectly  pure  clay  is  infusible  in  the  kiln, 
whilst  lime,  magnesia,  and  the  oxides  of  iron  render  it  fusible  with  difficulty, 
and  potassa  and  soda  give  it  a  high  degree  of  fusibility.  An  excess  of  iron  or 
lime  in  the  clay  may  be  corrected  by  an  addition  of  sand. 

Clays  containing  iron  (which  is  usually  present  as  carbonate  of  the  (prot-)ox- 
ide)  become  yellow  or  red  when  burnt,  the  iron  being  converted  into  sesquioxide. 
If  the  clay  have  a  blue  or  gray  color,  due  to  the  presence  of  organic  matter,  the 
color  will  be  destroyed  by  burning.  When  fragments  of  vegetable  matter 
(wood,  roots,  &c.)  are  present  in  the  clay,  they  are  very  carefully  picked  out 
before  it  is  employed  for  the  manufacture  of  earthenware,  since  they  leave  a 
space  when  the  clay  is  burnt.  Vessels  made  of  ordinary  clay  are  porous,  and 
allow  of  the  passage  of  liquids;  in  order  to  prevent  this,  they  are  covered  with 
a  glaze,  which  fuses  at  the  temperature  of  the  kiln,  and  renders  the  ware  im- 
permeable. 

In  the  finer  kinds  of  porcelain  and  earthenware,  the  glaze  is  of  a  nature  to  be 
absorbed  by  the  ware,  which  is  thus  rendered  translucent ;  whilst,  in  the  com- 
moner kinds  of  pottery,  the  glaze  is  only  spread  over  the  surface,  as  can  be  easily 
seen  by  examining  the  fracture  of  such  ware. 

In  determining  upon  the  glaze  to  be  applied  to  any  particular  ware,  care  is 
always  taken  that  its  expansion  under  the  influence  of  heat  shall  not  be  very  dif- 
ferent from  that  of  the  ware  itself,  which  would  otherwise  present  numerous 

1  Marl  is  employed  in  agriculture  for  the  mechanical  amelioration  of  soils. 


EARTHENWARE   AND   PORCELAIN.  319 

cracks,  due  to  unequal  contraction  in  cooling.  The  glaze  may  be  either  transpa- 
rent or  opaque,  the  latter  being  generally  the  case  with  coarser  wares,  the  imper- 
fections of  color  being  thus  concealed. 

The  chief  transparent  glazes  are  feldspar,  common  salt,  the  alkalies,  boracic 
acid,  silicate  of  lead,  &c.;  whilst  binoxide  of  tin  and  phosphate  of  lime  furnish 
opaque  glazes. 

The  glaze  is  sometimes  colored  with  a  metallic  oxide.  The  number  of  colors 
which  can  be  applied  in  this  way  is  very  limited,  since  few  are  capable  of  resist- 
ing the  high  temperature  to  which  the  ware  is  exposed. 

A  blu%  color  is  usually  imparted  by  cobalt ;  a  green  by  chromium ;  brown  is  ob- 
tained with  iron  and  manganese;  the  yellow  with  titanium ;  and  Hark  with  uranium. 

The  finer  colors  are  actually  painted  on  the  baked  ware,  and  are  of  such  a 
nature  that  they  may  be  burnt  in,  at  a  moderately  high  temperature,  in  a  muffle. 

These  colors  consist  of  certain  fluxes  (fusible  glasses)  colored  with  metallic 
oxides,  and  are  generally  ground  up  with  volatile  oils,  and  laid  on  with  a  brush. 
The  chief  ingredients  of  the  fluxes  are  sand,  feldspar,  borax  and  boracic  acid, 
nitre,  alkaline  carbonates,  litharge  and  red  lead,  and  teroxide  of  bismuth.  (See 
p.  225.) 

A  blue  color  is  obtained  with  cobalt;  green  with  sesquioxide  of  chromium  or 
oxide  of  copper;  yellow  with  sesquioxide  of  uranium,  chromate  of  lead,  sesqui- 
oxide of  iron,  antimonic  acid,  and  silver.  Red  is  imparted  by  suboxide  of  copper 
or  sesquioxide  of  iron. 

Violet  and  rose  tints  are  produced  by  purple  of  Cassius ;  Hack  by  uranium,  or 
a  mixture  of  oxides  of  cobalt  and  manganese. 

The  white  enamel  is  given  by  binoxide  of  tin,  phosphate  of  lime,  or  a  mixture 
of  oxides  of  antimony  (p.  226.) 

A  golden  lustre  is  imparted  by  fulminating  gold,  painted  on  with  turpentine, 
and  burnt  in  the  muffle ;  the  lustre  of  the  metallic  gold  thus  obtained  is  improved 
by  burnishing. 

We  shall  now  proceed  to  notice  a  few  of  the  chief  points  of  interest  in  the 
chemical  history  of  the  different  results  of  the  ceramic  art. 

Refractory  bricks,  which  are  employed  for  lining  thg  interior  of  furnaces,  are 
composed  of  plastic  clay  containing  no  gypsum,  carbonate  of  lime,  nor  oxides  of 
iron ;  hence  good  refractory  bricks  are  nearly  white. 

Crucibles  are,  of  necessity,  made  of  a  material  which  is  capable  of  resisting  a 
very  high  temperature ;  the  most  refractory  crucibles  are  termed  black-lead  cru- 
cibles, and  are  made  from  a  mixture  of  clay  and  graphite.  Hessian  crucibles  are 
made  of  a  mixture  of  clay  and  sand ;  their  porosity  is  a  great  disadvantage. 

The  materials  employed  in  the  manufacture  of  English  porcelain,  in  addition 
to  clay,  are  bone-ash,  flints,  Cornish  stone,  carbonate  of  soda,  borax,  and  binoxide 
of  tin.  The  use  of  the  bone-ash  and  flints  must  obviously  be  explained  for 
mechanical  reasons,  while  the  carbonate  of  soda  and  borax  act  as  fluxes  to  give 
greater  coherence  to  the  ware,  and  the  binoxide  of  tin  improves  its  color  and 
appearance. 

Afrit  is  generally  prepared  by  moderately  heating  a  mixture  of  Cornish  stone 
(composed  chiefly  of  quartz  and  feldspar),  flint,  soda,  borax,  and  binoxide  of  tin  ; 
this  frit  is  then  intimately  mixed  with  the  mass,  composed  of  plastic  clay,  kaolin, 
Cornish  stone,  flint,  and  bone-ash,  and  the  whole  is  ground  with  water  to  a  homo- 
geneous paste,  from  which  the  goods  are  made.  These  are  then  fired  in  a  kiln 
or  oven,  during  about  forty-eight  hours,  at  a  gradually  increasing  heat,  after  which 
they  are  allowed  to  cool  slowly,  and  glazed.  The  glaze  is  composed  of  flint, 
chalk,  Cornish  stone,  borax  (and  sometimes  white-lead);  it  is  applied  to  the  bis- 
cuit (or  baked  ware)  in  a  state  of  uniform  mixture  with  water ;  the  ware  is  then 
fired  for  a  shorter  time,  and  at  a  lower  temperature  than  before,  in  order  to  fuse 
the  glaze. 


320  PORCELAIN. 

Fine  porcelain,  or  china,  is  made  from  a  paste  of  the  purest  materials;  this 
paste  consists  of  kaolin,  or  pure  plastic  clay,  and  of  feldspar,  sand,  chalk,  or  gyp- 
sum, and  sometimes  of  a  mixture  of  these  substances.  The  paste  which  is  em- 
ployed at  Sevres  consists  of 

Silica    ....     58.5 

Alumina    .     .     .     34.5 

Lime     ....       4.0 

Potassa  3.0 


100.0  V 

This  porcelain  may  be  said  to  consist  of  two  parts,  the  plastic  material  (kaolin), 
and  the  vitreous  flux  (feldspar,  chalk,  quartz,  and  gypsum).  The  former,  which 
by  itself  would  yield  a  porous  opaque  mass,  becomes  impregnated  with  the  flux, 
which  at  once  renders  it  impermeable  and  translucent. 

Since  the  materials  employed  are  somewhat  variable  in  their  composition,  an 
analysis  of  each  is  usually  made,  and  the  mixture  is  then  proportioned,  so  that 
its  composition  may  be  expressed  by  the  numbers  given  above. 

The  glaze  consists  chiefly  of  feldspar,  or  sometimes  of  a  mixture  of  feldspar 
with  gypsum,  or  with  some  of  the  dried  paste  which  forms  the  material  itself. 
This  glaze,  being  very  similar  in  composition  to  the  flux,  contracts  a  very  firm 
adhesion  with  the  ware,  and  is  not  liable  to  crack  or  scale  off.  Since  this  glaze 
contains  no  lead  (see  Glass),  it  is  very  hard,  and  is  not  easily  scratched  by  a 
knife.  Much  depends  upon  the  degree  of  fusibility  of  the  glass ;  if  it  be  not 
sufficiently  fusible,  it  does  not  acquire  an  even  surface;  and  if,  on  the  other 
hand,  its  fusibility  be  too  great,  it  will  be  entirely  sucked  into  the  ware,  leaving 
the  surface  rough. 

When  the  ingredients  (kaolin  and  flux)  have  been  prepared  by  levigation  and 
intimately  mixed,  the  paste  has  to  be  reduced  to  the  consistence  proper  for  work- 
ing, for  which  purpose,  a  great  part  of  the  water  must  be  expelled.  If  this  were 
effected  by  heat,  the  plasticity  of  the  material  would  be  much  impaired,  to  avoid 
which,  the  paste  is  either  run  into  boxes,  the  bottoms  of  which  are  composed  of 
gypsum,  to  absorb  the  water,  or  it  is  pressed  in  linen  bags,  or  thrown  upon  a 
filter  made  of  felt,  placed  upon  a  funnel  from  which  the  air  may  be  exhausted, 
when  the  superfluous  water  is  forced  through  by  atmospheric  pressure.  The 
mass  is  next  kneaded,  to  render  it  perfectly  uniform,  and  stored  away  for  a  year 
or  so  in  a  moist  place ;  it  then  evolves  an  odor  of  sulphuretted  hydrogen,  due  to 
the  action  of  the  traces  of  organic  matter  upon  the  sulphate  of  lime,  and  its 
plasticity  becomes  greatly  improved,  probably  from  the  alteration  of  texture  which 
must  result  from  the  evolution  of  gaseous  products  of  the  putrefaction  of  the 
organic  matter.  The  paste  is  then  fit  for  working.  The  moulds  employed  to 
assist  in  forming  the  vessels  are  usually  made  of  gypsum,  which  absorbs  the 
water.  The  goods  are  dried  by  mere  exposure  to  the  air,  since  rapid  drying 
would  distort  them. 

The  vessels  are  fired  once,  as  mentioned  above,  before  glazing.  The  glaze  is 
usually  mixed  to  a  thin  slip  with  water  containing  vinegar,  which  prevents  the 
rapid  subsidence  of  the  glaze.  The  goods,  when  dipped  into  the  slip,  absorb  the 
water,  leaving  a  thin  film  of  glaze  on  their  outer  surface.  They  are  then  inclosed 
in  clay  vessels,  or  seggars,  which  are  exposed  in  a  furnace,  to  the  very  highest 
temperature  which  can  be  obtained  by  artificial  means.1 

1  The  Berlin  porcelain,  so  much  prized  by  chemists  for  its  power  of  resisting  the  action 
of  acids  and  alkalies,  and  of  a  high  temperature,  has  been  analyzed  by  Wilson,  -who  found 
it  to  contain 


Silicic  acid 71.340 

Alumina 23.763 

Protoxide  of  iron 1.743 


Lime 0.569 

Magnesia 0.192 

Potassa    .    .    ,  .     2.001 


GLUCINUM.  321 

The  translucent  variety  of  French  porcelain  (porcelalne  tendre)  is  made  of  a 
more  fusible  paste  than  ordinary  porcelain,  that  is,  of  a  paste  containing  a  larger 
quantity  of  alkali,  either  in  the  form  of  feldspar,  or  as  carbonate  or  nitrate.  The 
glaze  for  this  porcelain  contains  oxide  of  lead  to  render  it  more  fusible. 

The  coarser  kinds  of  earthenware  are  generally  glazed  with  salt  (see  p.  273), 
but  sometimes  with  a  sort  of  glass  containing  lead,  and  occasionally  colored  with 
oxides  of  iron,  &c.  Pans  glazed  with  lead  are  somewhat  dangerous  for  culinary 
purposes. 

SESQUICHLORIUE  OF  ALUMINUM,  A13C18. 

§  214.  Preparation.  —  When  alumina  is  dissolved  in  hydrochloric  acid,  a  solu- 
tion of  the  sesquichloride  is  obtained,  which,  when  evaporated  in  vacuo,  yields 
crystals  of  the  formula  AlaCl3  +  12Aq. 

In  order  to  prepare  the  anhydrous  salt,  recourse  is  had  to  a  method  often  em- 
ployed in  preparing  chlorides  from  oxides,  which  consists  in  passing  dry  chlorine 
gas  over  a  mixture  of  the  oxide  with  charcoal,  at  a  red  heat.  A  quantity  of  per- 
fectly dry  alumina  is  mixed  with  lampblack  and  a  little  oil,  to  a  thick  paste, 
which  is  moulded  into  small  pellets  ;  these  are  strongly  heated  in  a  closed  crucible, 
then  introduced  into  a  porcelain  tube  or  retort,  connected  at  one  end  with  an 
apparatus  for  evolving  dry  chlorine,  and  at  the  other  with  an  adapter  passing  into 
a  flask  surrounded  with  cold  water  ;  the  tube  01  retort  having  been  raised  to  a 
high  temperature,  a  stream  of  chlorine  is  passed,  when  the  sesquichloride  of 
aluminum  sublimes  into  the  receiver,  and  carbonic  oxide  escapes  :  — 


Properties.  —  Anhydrous  sesquichloride  of  aluminum  is  a  white,  volatile  crys- 
talline solid  which  fumes  in  contact  with  air.  When  thrown  into  water,  it  com- 
bines with  it  energetically,  with  a  hissing  sound  ;  the  solution  of  sesquichloride 
of  aluminum  is  decomposed  like  that  of  chloride  of  magnesium  when  evaporated 
to  dryness  ;  water  suffers  decomposition,  hydrochloric  acid  passes  off,  and  alumina 
is  left  :  — 

Al2Cl3-f3HO=Ala08+3HCl. 

The  crystallized  hydrate  is  decomposed  in  the  same  manner  by  heat.  It  is 
very  deliquescent,  and  soluble  in  water  and  alcohol.  Sesquichloride  of  aluminum 
is  capable  of  combining  with  ammoniacal  gas. 

The  Sesquiflaoride  of  Aluminum,  associated  with  fluoride  of  sodium,  occurs 
in  nature  as  the  mineral  kryolite. 

When  aluminum  is  heated  in  the  vapor  of  sulphur,  combination  takes  place, 
and  a  dark  gray  mass  is  formed,  which  assumes  a  feeble  metallic  lustre  when 
burnished.  When  exposed  to  air,  it  absorbs  moisture,  and  evolves  hydrosulphuric 
acid.  Water  resolves  it  into  hydrosulphuric  acid  and  alumina. 

No  compound  of  these  elements  has  yet  been  prepared  in  the  moist  way;  when 
an  alkaline  sulphide  is  added  to  a  solution  of  alumina,  the  latter  is  precipitated 
as  hydrate,  with  evolution  of  sulphuretted  hydrogen  \  thus  :  — 

„  Al203.3S03-f3NH4S4-6HO=Al303.3HO+3(NH4O.S03)+3HS.; 


GLUCINUM   (BERYLLIUM). 

Sym.  Gl  (or  Be).     Eq.  6.9. 

§  215.  This  metal  is  of  comparatively  rare  occurrence  in  nature,  where  it 
exists  generally  in  combination  with  silicic  acid. 

The  emerald  is  a  double  silicate  of  alumina  and  glucina,  colored  with  gesqui- 
21 


322  GLUCINUM. 

oxide  of  chromium.  Its  composition  may  be  expressed  by  the  formula  Gl3Og.Si03, 
Al203.Si03. 

The  beryl  is  a  pale  green  variety  of  emerald. 

JEuclase  is  another  mineral  containing  glucinum  ;  its  formula  is  2GL03.Si03, 
2Al303.Si03. 

Chrysoberyl  has  the  composition  A1303.G1208. 

Glucinum  may  be  prepared  by  decomposing  the  sesquichloride  with  potassium, 
in  exactly  the  same  way  as  aluminum  was  obtained.  Glucinum  is  very  similar 
to  aluminum;  it  is  not  oxidized  by  dry  air,  and  does  not  decompose  water  at  the 
ordinary  temperature.  When  heated  in  air  or  oxygen,  it  is  converted  into  glucina 

(G1A)- 
This  metal  decomposes  water  in  presence  of  acids  or  alkalies. 

Only  one  oxide  of  glucinum  is  known. 

GLUCINA,  G1203. 

Preparation. — This  oxide  is  generally  prepared  from  the  mineral  termed 
emerald  of  Limoges,  which  contains  silicates  of  alumina  and  glucina,  together 
with  lime  and  sesquioxide  of  iron. 

The  mineral,  in  a  state  of  fine  powder,  is  mixed  with  about  three  times  its 
weight  of  carbonate  of  potassa  and  fused  in  a  platinum  crucible;  the  fused 
mass  is  digested  with  dilute  sulphuric  acid,  which  leaves  a  quantity  of  silica 
undissolved ;  the  filtered  solution  is  evaporated  to  a  small  bulk,  and  allowed  to 
cool,  when  crystals  of  alum  are  deposited ;  the  liquor  separated  from  the  crystals 
is  now  mixed  with  excess  of  ammonia,  which  precipitates  the  sesquioxide  of  iron 
and  the  glucina,  together  with  a  little  alumina ;  this  precipitate  is  digested  with 
a  saturated  solution  of  carbonate  of  ammonia,  which  dissolves  only  the  glucina, 
and  deposits  the  carbonate  of  this  base  on  ebullition ;  the  precipitated  carbonate 
is  washed,  dried,  and  ignited,  when  pure  glucina  is  left. 

Properties. — Glucina  much  resembles  alumina,  being  white,  infusible,  and 
insoluble  in  water.  Unlike  that  base,  however,  it  absorbs  carbonic  acid  when 
exposed  to  air,  and  expels  ammonia  from  its  salts.  Glucina  is  soluble  in  acids  ; 
the  salts  thus  produced  have  a  sweet  astringent  taste  (hence  its  name,  from 
yxvxvj) ;  they  are  acid  to  test-papers.  It  is  also  soluble  in  solutions  of  potassa 
and  soda,  and  is  reprecipitated  when  these  solutions  are  diluted  with  water  and 
boiled. 

Glucina  is  considered  by  some  chemists  as  a  protoxide,  but  its  analogy  with 
alumina  favors  the  view  which  we  have  taken  above,  that  it  is  a  sesquioxide. 

Glucina  is  precipitated  from  its  solutions  in  the  form  of  hydrate. 

The  Neutral  Sulphate  of  Glucina,  crystallizes  in  octohedra  of  the  formula 
Gl303.3S03+12Aq.  It  is  very  soluble  in  water. 

Other  sulphates  of  glucina  exist,  but  it  does  not  form  an  alum. 

A  basic  Carbonate  of  Glucina,  Gl203.C03+5Aq,  is  obtained  by  precipitation ; 
it  is  soluble  in  alkaline  carbonates. 

Sesquichloride  of  Glucinum,  G13C13,  may  be  prepared  in  the  same  way  as  the 
corresponding  aluminum-compound,  which  it  much  resembles. 

Sesquisulphide  of  Glucinum,  G12S3,  may  be  obtained  by  the  direct  combination 
of  glucinum  with  sulphur;  it  is  precipitated  as  a  white  gelatinous  hydrate,  on 
adding  a  hydrosulphate  of  an  alkaline  sulphide  to  a  solution  of  glucinum. 

The  compounds  of  glucinum  have  at  present  received  no  practical  application. 

REACTIONS  OF  GLUCINA. — Potassa,  soda,  and  their  carbonates  produce,  in 
solutions  of  glucina,  white  precipitates  soluble  in  excess. 

Ammonia  and  Sulphide  of  Ammonium  also  give  a  gelatinous  precipitate, 
insoluble  in  excess,  but  soluble  in  carbonate  of  ammonia,  and  reprecipitated  by 
boiling. 


YTTRIUM,  ERBIUM,  TERBIUM.  32o 

Phosphate  of  soda  precipitates  phosphate  of  glucina. 

When  a  hot  solution  of  fluoride  of  potassium  is  added  to  a  hot  solution  of 
glucina  until  a  precipitate  begins  to  appear,  and  the  solution  then  cooled,  a  crys- 
talline precipitate  of  a  double  fluoride  is  produced. 

Fixed  organic  matters  interfere  with  the  precipitation  of  glucina.  Glucina 
does  not  yield  a  blue  compound  with  nitrate  of  cobalt  before  the  blowpipe. 


THORINUM  OR  THORIUM. 

Sym.  Th.     Eq.  59.6. 

§  216.  This  is  a  very  rare  metal,  found  in  the  minerals  thorite  and  pyroclilo- 
rite.  The  former  contains  about  57  per  cent,  of  thorina.  The  metal  itself  may 
be  prepared  by  the  same  process  as  aluminum,  which  it  resembles  in  most  of 
its  properties. 

It  is  not  easily  dissolved  by  acids,  with  the  exception  of  hydrofluoric  acid ; 
alkalies  are  said  to  have  no  action  upon  it. 

We  are  acquainted  with  only  one  oxide  of  thorinum. 

OXIDE  OF  THORINUM,  THORINA,  ThO. 

Preparation. — This  oxide  is  prepared  from  thorite,  in  which  it  is  associated 
with  silica,  lime,  magnesia,  and  the  oxides  of  iron,  manganese,  uranium,  lead, 
and  tin.  The  mineral  is  boiled  with  hydrochloric  acid,  the  solution  evaporated 
to  dryness,  the  residue  extracted  with  water,  the  lead  and  tin  precipitated  by- 
sulphuretted  hydrogen,  and  the  solution  mixed  with  excess  of  ammonia,  which 
throws  down  the  thorina,  together  with  the  oxides  of  iron  and  uranium ;  the 
precipitate  is  dissolved  in  sulphuric  acid,  and  the  solution  rapidly  boiled  down, 
when  sulphate  of  thorina,  being  sparingly  soluble  in  hot  water,  is  precipitated; 
this  is  collected  on  a  filter,  washed  with  boiling  water,  and  ignited,  when  pure 
thorina  is  obtained  as  a  white  powder. 

Properties. — This  earth  is  remarkable  for  its  great  density  (sp.  gr.  9.4). 
It  combines  with  water,  forming  a  hydrate  (ThO. HO),  which  is  insoluble  in  the 
alkalies,  soluble  in  the  acids  and  in  alkaline  carbonates.  After  ignition,  however, 
thorina  is  soluble  only  in  sulphuric  acid. 

»  REACTIONS  OP  THORINA. — Potassa,  soda,  ammonia,  and  sulphide  of  ammo- 
nium produce,  in  solutions  of  thorina,  gelatinous  precipitates,  insoluble  in  ex- 
cess. The  carbonates  of  potassa  and  of  ammonia  produce  a  precipitate  soluble 
in  excess. 

Phosphate  of  soda  precipitates  phosphate  of  thorina. 

Soluble  salts  of  thorina  are  decomposed  at  a  red  heat. 

Solutions  of  some  of  these,  e.  g.  the  sulphate,  yield  precipitates  upon  boiling, 
which  redissolve  very  slowly  as  the  solution  cools.  This  peculiar  reaction  does 
not  take  place  when  the  solution  contains  any  base  capable  of  forming  a  double- 
salt  with  thorina. 


YTTRIUM,    ERBIUM,   AND   TERBIUM. 

Sym.  Y.     Sym.  E.     Sym.  Tb. 

§  217.  These  metals  are  exceedingly  rare,  and  possess  no  practical  interest. 
They  are  found  in  the  minerals  aadolinite,  orthite,  and  yttrotantalite. 


324  CERIUM,    LANTHANIUM,    DIDYMIUM. 

Yttrium  is  obtained  by  decomposing  its  chloride  with  potassium ;  it  is  very 
similar  to  aluminum. 

The  oxides  of  these  metals,  viz.  yttria  (YO),  erbia  (EO),  and  terlia  (TbO) 
are  obtained  together  from  the  mineral  gadolinite. 

By  digesting  the  mixed  precipitate  in  very  dilute  sulphuric  acid,  the  yttria  is 
dissolved,  and  may  be  reprecipitated  /rom  the  solution  by  potassa.  The  residue 
of  erbia  and  terbia  is  dissolved  in  nitric  acid,  and  the  solution  saturated  with 
sulphate  of  potassa,  which  yields  a  sparingly  soluble  double-salt  with  the  sulphate 
of  erbia.  The  solution  yields  terbia  upon  addition  of  potassa. 

Pure  Yttria  is  a  white  powder  of  great  density ;  it  dissolves  more  easily  in 
dilute  than  in  concentrated  acids.  The  hydrate,  obtained  by  precipitation,  re- 
sembles hydrate  of  alumina. 

The  solutions  of  salts  of  yttria  are  sweet  and  astringent ;  they  have  an  acid 
reaction. — Nitrate  of  Yttria  is  white,  crystallizable,  and  deliquescent. — The  sul- 
phate forms  colorless  crystals,  which  are  sparingly  soluble. —  Chloride  of  Yttrium 
is  volatile,  crystalline,  and  deliquescent. 

Erbia  has  a  dark  yellow  color,  which  it  loses  when  ignited  in  a  current  of 
hydrogen,  and  regains  when  gently  heated  in  air.  It  dissolves  in  acids,  forming 
colorless  salts. 

The  sulphate  is  crystallizable,  and  does  not  effloresce  on  exposure  to  air  at  176° 
F.  (80°  C.) — Nitrate  of  Erbia  is  not  deliquescent;  its  solution  is  colorless,  even 
when  concentrated. 

The  Salts  of  Terbia  acquire  a  reddish  color  upon  desiccation. — The  sulphate 
is  efflorescent  at  122°  F.  (50°  C.) 

REACTIONS  OF  YTTRIA,  ERBIA,  AND  TERBIA. — Potassa,  soda,  ammonia,  and 
sulphide  of  ammonium,  yield  bulky  precipitates  of  the  hydrates,  insoluble  in 
excess. 

Alkaline  carbonates;  a  white  precipitate,  soluble,  though  with  difficulty,  in  a 
large  excess. 

Phosphate  of  Soda;  a  white  precipitate,  soluble  in  hydrochloric  acid,  repre- 
cipitated by  boiling. 


CERIUM,    LANTHANIUM,   DIDYMIUM. 

Sym.  Ce.    Eq.  47.    Sym.  La.    Eq.  47.    Sym.  D.    Eq.  50. 

§  218.  Gerite  is  the  chief  mineral  from  which  these  metals  are  extracted;  they 
exist  in  it  as  silicates.  They  are  also  contained  in  gadolinite,  orthite,  and  yttro- 
cerite.  Cerium  forms  two  basic  oxides,  the  oxide  (CeO)  and  sesquioxide  (Ce2O3). 

In  order  to  extract  the  oxides  of  cerium,  lanthanium,  and  didymium,  the  pow- 
dered cerite  is  ignited  and  extracted  with  aqua  regia;  the  solution  is  evaporated 
to  dryness,  and  the  residue  treated  with  dilute  hydrochloric  acid,  which  leaves 
the  silica  undissolved ;  the  filtered  liquid  is  precipitated  by  ammonia,  and  the 
precipitate  boiled  with  an  excess  of  oxalic  acid,  which  dissolves  the  sesquioxide 
of  iron,  and  leaves  the  three  oxides  in  the  form  of  oxalates;  this  residue  is  ignited, 
and  the  oxides  thus  obtained  are  dissolved  in  concentrated  nitric  acid  ;  the  solu- 
tion is  evaporated  to  dryness,  and  the  residue  ignited,  when  the  oxides  are  left 
in  a  very  finely  divided  state.  By  boiling  these  with  a  large  quantity  of  very 
dilute  nitric  acid,  the  oxide  of  lanthanium  is  then  dissolved,  and  may  be  precipi- 
tated, as  carbonate,  by  carbonate  of  ammonia.  To  separate  the  didymium  and 
cerium,  the  residue  left  by  nitric  acid  is  boiled  with  hydrochloric  acid,  which 
dissolves  the  oxide  of  didymium,  and  leaves  sesquioxide  of  cerium. 


CERIUM,   LANTHANIUM,   DIDYMIUM.  325 

Cerium,  Lanthanium,  and  Diclymium  are  obtained  by  reducing  their  chlorides 
with  potassium  ;  they  form  gray  powders,  which  become  lustrous  when  burnished; 
they  are  very  infusible,  and  non-volatile.  These  metals  oxidize  rapidly  when 
exposed  to  air ;  they  readily  decompose  water  at  the  boiling-point. 

Oxide  of  Cerium  (CeO)  is  obtained  by  heating  the  carbonate  in  a  current  of 
hydrogen.  The  hydrate,  obtained  by  precipitation,  is  white  at  first,  and  becomes 
yellow  when  exposed  to  air,  or  when  treated  with  chlorine  (oxide  of  lanthanium 
is  not  turned  yellow  by  chlorine). 

The  Salts  of  Oxide  of  Cerium  are  colorless,  and  have  an  acid  reaction.  The 
nitrate  is  soluble  and  crystallizable. — The  sulphate  crystallizes  in  hydrated  prisms ; 
it  forms  a  nearly  insoluble  double  salt  with  sulphate  of  potassa. — The  carbonate 
is  insoluble  in  water. 

Sesquioxide  of  Cerium  (Ce203)  is  obtained  by  heating  the  metal  in  air  or 
oxygen.  It  has  a  yellow  color,  which  is  darkened  by  ignition.  The  sesquioxide 
is  slowly  acted  upon  by  hydrochloric  acid,  which  forms  chloride  of  cerium,  with 
evolution  of  chlorine.  Sulphuric  acid  (cone.)  dissolves  it  easily  with  the  aid  of 
heat. 

The  hydrated  sesquioxide  forms  a  yellow  gelatinous  precipitate. — The  neutral 
sulphate  forms  a  yellow  double  salt  with  sulphate  of  potassa,  which  is  sparingly 
soluble  in  water.  , 

Chloride  of  Cerium  (CeCl)  is  white ;  soluble  in  water  and  alcohol ;  its  solu- 
tion in  the  latter  burns  with  a  green  flame. — Sulphide  of  Cerium  has  a  yellow 
or  red  color,  and  is  easily  dissolved  by  acids. 

Only  one  Oxide  of  Lanthanium  (LaO)  is  known;  it  is  a  white  powder,  soluble 
in  acids,  and  in  ammoniacal  salts,  from  which  it  expels  the  ammonia.  The 
hydrate,  obtained  by  precipitation,  rapidly  absorbs  carbonic  acid  from  the  air. 
The  salts  of  oxide  of  lanthanium  have  a  sweet  astringent  taste.  The  nitrate 
crystallizes  in  deliquescent  prisms. — Sulphate  of  lanthanium  forms  six-sided 
prisms  of  the  formula  LaO.S03-j-3Aq,  which  are  soluble  in  6  parts  of  cold  water 
and  in  120  of  boiling  water.  A  solution  of  this  salt,  saturated  at  a  low  tempera- 
ture, deposits  the  greater  part  of  the  sulphate  when  heated  to  ebullition. —  Car- 
bonate of  lanthanium  has  been  found  native.  The  chloride  is  very  soluble. 

The  Oxide  of  Didymium  (DO)  has  a  dark  color.  The  hydrate  has  a  violet 
color,  and  absorbs  carbonic  acid  from  the  air.  It  dissolves  readily  in  acids,  and 
expels  ammonia  from  its  salts,  but  is  a  weaker  base  than  oxide  of  lanthanium. 
Its  salts  have  a  pink  or  violet  color.  The  nitrate  crystallizes  with  difficulty,  and 
is  deliquescent ;  its  solution  has  a  deep  red  color.  The  sulphate  forms  red  crys- 
tals, which  are  more  soluble  in  cold  than  in  hot  water.  It  yields  a  double-salt 
with  sulphate  of  potassa. 

REACTIONS  OF  (OXIDES  OF)  CERIUM,  LANTHANIUM,  AND  DIDYMIUM. — 
Potassa,  soda,  ammonia,  and  sulphide  of  ammonium;  a  white  hydrate,  insolu- 
ble in  excess. — The  alkaline  carbonates;  precipitate,  very  sparingly  soluble  in 
excess. — Phosphate  of  soda;  a  white  precipitate. — Sulphate  of  potassa  ;  a  crys- 
talline precipitate.  With  a  borax-bead,  in  the  outer  blowpipe-flame,  a  reddish- 
yellow,  which  fades  on  cooling,  and  vanishes  in  the  inner  flame. 

The  reactions  of  lanthanium  closely  resemble  those  of  cerium,  but  the  former 
metal  is  not  precipitated  from  its  solutions  by  sulphate  of  potassa. 

The  solutions  of  didymium,  as  stated  above,  have  a  violet  color.  Sulphide  of 
ammonium  precipitates  them  with  difficulty  in  the  cold.  Sulphate  of  potassa 
gives  an  amethyst-colored  double-salt.  With  a  bead  of  phosphorus-salt,  in  the 
inner  flame,  a  red  glass  with  a  shade  of  violet 


326  CHROMIUM. 


ZIRCONIUM. 

Sym.  Zr.     Eq.  22.4. 

§  219.  This  rare  metal  exists  in  the  minerals  zircon  and  hyacinth,  which  are 
chiefly  composed  of  silicate  of  zirconia  (Zr203.Si03). 

The  metal,  which  is  prepared  by  the  action  of  potassium  upon  the  double 
fluoride  of  zirconium  and  potassium,  is  a  black  powder,  capable  of  assuming  a 
metallic  lustre.  When  heated  in  air,  it  is  converted  into  zirconia. 

Alkalies,  their  carbonates,  and  even  borax,  are  capable  of  oxidizing  this  metal, 
but  it  is  not  attacked  to  any  extent  by  acids,  except  hydrofluoric. 

The  only  oxide  of  this  metal,  zirconia  (Zr203),  is,  in  many  respects,  similar 
to  alumina. 

In  order  to  extract  this  base  from  hyacinth,  the  mineral  is  fused  with  hydrate 
of  potassa;  the  fused  mass  is  decomposed  with  hydrochloric  acid,  and  the  silica 
separated  in  the  usual  manner;  the  solution  freed  from  silica  is  treated  exactly 
as  in  the  extraction  of  cerium  from  cerite  (see  p.  324). 

Zirconia  is  a  white  powder,  slightly  soluble  in  carbonate  of  ammonia  and  in 
the  alkaline  bicarbonates.  After  ignition,  it  can  be  dissolved  only  by  sulphuric 
acid.  A  hydrate  of  zirconia  has  been  obtained.  The  neutral  salfs  of  zirconia 
redden  litmus.  The  nitrate  does  not  crystallize,  and  is  very  soluble.  The 
neutral  sulphate  is  crystalline  and  soluble;  other  sulphates  exist.  The  carbonate 
is  insoluble.  Anhydrous  sesquichloride  of  zirconium  is  not  volatile ;  the  hydratcd 
chloride  crystallizes. 

REACTIONS  OF  ZIRCONIA. — Potassa,  soda,  ammonia,  and  sulphide  of  ammo- 
nium; a  white  precipitate,  insoluble  in  excess.  Alkaline  carbonates;  precipi- 
tate, soluble  in  large  excess.  Phosphate  of  soda;  white  precipitate.  Sulphate 
of  potassa ;  a  double  sulphate,  sparingly  soluble  in  water  and  acids,  when  pre- 
cipitated from  hot  solutions. 


CHROMIUM. 

Sym.  Cr.     Eq.  26.7.     Sp.  Gr.  5.9. 

§  220.  Chromium  is  moderately  abundant  in  nature,  but  not  in  the  free  state. 

It  is  found  in  chrome-iron  (a  compound  of  the  oxides  of  chromium  and  iron), 
and  as  chromate  of  lead.  / 

The  ruby  also  contains  chromic  acid,  to  which  its  color  is  due;  this  gem  con- 
tains 82.5  per  cent,  alumina,  8.9  per  cent,  magnesia,  and  6.2  per  cent,  chromic 
acid. 

As  already  stated,  the  green  color  of  the  emerald  is  due  to  sesquioxide  of 
chromium. 

Preparation. — Chromium  may  be  prepared  by  exposing  to  a  very  high  tem- 
perature, in  a  crucible  lined  with  charcoal,  an  intimate  mixture  of  sesquioxide  of 
chromium  and  charcoal ;  the  spongy  mass  thus  obtained  is  powdered  in  an  iron 
mortar  and  mixed  with  a  little  more  sesquioxide  of  chromium  (to  oxidize  as 
much  of  the  carbon  as  possible) ;  the  mixture  is  again  exposed  to  a  very  high 
temperature,  in  a  porcelain  crucible,  when  a  coherent  mass  of  metal  is  obtained. 
The  chromium  thus  prepared  always  contains  more  or  less  carbon. 

It  may  be  obtained  in  a  purer  state  by  the  action  of  potassium  upon  sesqui- 
chloride of  chromium. 


OXIDES   OF   CHROMIUM.  327 

Properties. — The  metal  obtained  by  the  first  process  forms  a  grayish,  hard, 
brittle  mass,  which  assumes  the  metallic  lustre  when  burnished.  Chromium  is 
magnetic  only  at  very  low  temperatures;  and  is  very  infusible.  It  is  not  oxidized 
in  dry  air,  except  at  a  red  heat,  when  it  is  converted  into  sesquioxide.  This 
metal  does  not  decompose  water,  even  at  the  boiling-point.  It  is  attacked  with 
considerable  difficulty  by  acids,  but,  when  heated  with  hydrated  alkalies,  is  con- 
verted into  chromic  acid  with  evolution  of  hydrogen.  Chlorates  and  nitrates 
are  also  capable  of  converting  chromium  into  chromic  acid. 

When  the  metal  is  prepared  by  reducing  sesquichloride  of  chromium  with 
potassium,  it  forms  a  gray  powder,  which  is  oxidized  far  more  readily  than  the 
preceding,  and  dissolves  much  more  easily  in  acids  and  alkalies.1 

The  metal  itself  has  hitherto  received  no  practical  application. 


CHROMIUM    AND    OXYGEN.  3 

Oxide  (protoxide)  of  chromium     .....  CrO. 

Sesquioxide  of  chromium      .......  Cr203. 

Chromic  acid     ...........  Cr03. 

Perchromic  acid     ..........  Cr307. 

OXIDE  OP  CHROMIUM,  CrO. 

§  221.  This  oxide  possesses  little  practical  interest,  and  has  never  been  ob- 
tained in  a  pure  state.  It  is  precipitated  as  a  brown  hydrate,  when  (proto-) 
chloride  of  chromium  is  decomposed  by  potassa;  almost  as  soon  as  it  is  libe- 
rated, however,  it  decomposes  water,  seizing  its  oxygen  and  becoming  converted 
into  a  compound  of  oxide  and  sesquioxide  of  chromium.  It  is  a  feeble  base;  its 
salts  are  little  known.3 

SESQUIOXIDE  OF  CHROMIUM,  CHROME,  CHROMIC  OXIDE. 

Cr303-     Eq.llA. 

The  sesquioxide  is  found  in  nature  in  the  anhydrous  state,  and  in  combination 
with  water  }  the  chief  source  of  sesquioxide  of  chromium  is  the  chrome-iron  ore, 
which  may  be  represented  by  the  formula  FeO.Cr2O3.  It  is  sometimes  met  with 
in  octohedral  crystals,  being  isomorphous  with  spinelle  (MgO.Al203),  and  the 
magnetic-iron  ore  (FeO.Fe203).  Chrome-iron  is  found  chiefly  in  Sweden,  in 
Russia,  and  in  the  United  States.  (For  the  analysis  of  chrome-iron  ore,  see 
Quantitative  Analysis,  Special  Methods.) 

Preparation.  —  Sesquioxide  of  chromium  cannot  be  prepared  directly  from 
chrome-iron  ore,  but  is  always  first  converted  into  chromic  acid. 

Since  the  oxide  is  extensively  employed  for  coloring  porcelain  and  glass,  some 
attention  has  been  paid  to  its  preparation,  and  several  different  processes  have 
been  proposed,  which  furnish  products  varying  much  in  tint. 

I.  When  solutions  of  subnitrate  of  mercury  (Hg2O.N05)  and  of  chromate  of 
potassa  (KO.Cr03)  are  mixed,  a  red  precipitate  of  subchromate  of  mercury 


1  According  to  Berzelius,  this  difference  is  due  to  an  allotropic  state  of  the  metal. 

2  In  the  list  of  oxides,  we  have  refrained  from  mentioning  those  which  are  merely  com- 
pound, and  not  independent  oxides.     This  will  be  always  done,  unless  the  intemectiate 
oxides  are  of  considerable  importance. 

3  A  double  sulphate  of  oxide  of  chromium  and  potassa  (CrO.S03,KO.S03-|-6Aq),  iso- 
morphous with  the  double  sulphate  of  iron  and  potassa,  is  obtained  by  addition  of  alcohol 
to  a  mixture  of  solutions  of  sulphate  of  potassa  and  chloride  of  chromium.     Its  solution 
has  a  blue  color,  and  becomes  rapidly  green  when  exposed  to  the  air. 


328  CHROMIUM  AND  OXYGEN. 

(Hg2O.Cr03)  is  obtained;  if  this  precipitate  be  washed,  dried,  and  ignited,  mer- 
cury and  oxygen  are  expelled,  and  chromic  oxide  left : — 
2(Hg/).Cr03)=CrA+03-fHg4; 
the  oxide  thus  obtained  is  a  powder  of  a  fine  green  color. 

II.  If  bichromate  of  potassa  (K0.2Cr03)  be  mixed  with  an  equal  weight  of 
sulphur,  and  the  mixture  calcined,  a  residue  will  be  obtained,  which  consists  of 
sulphate  of  potassa  and  sesquioxide  of  chromium  : — 

K0.2CrOa  +  S=Cra03+KO.S08; 
the  sulphate  of  potassa  is  extracted  with  water. 

III.  By  calcining  a  mixture  of  the  bichromate  with  charcoal,  and  washing 
the  residue  with  water  : — 

2(K0.2Cr03)+C3=2(KO.C03)4-2Cra03+C03. 

IV.  A  very  fine  product  may  also  be  obtained  by  employing  starch  in  place 
of  charcoal. 

V.  The  precipitated  hydrate  of  sesquioxide  of  chromium  may  be  rendered 
anhydrous  by  a  moderate  heat. 

VI.  When  chromate  of  potassa  is  heated  to  redness  in  a  current  of  chlorine, 
green  crystalline  plates  of  the  sesquioxide  are  obtained  : — 

2(K0.003)  +Cla=2KCl-f  O303+ 05. 

VII.  Chromic  oxide  may  also  be  obtained  in  very  hard,  dense,  dark-green 
octohedra  (isomorphous  with  corundum)  by  passing  the  vapor  of  chlorochromic 
acid  (CrOaCl)  through  a  redhot  porcelain  tube :- — 

2CrOaCl=Cr203+0+Cla. 

VIII.  By  igniting  a  mixture  of  3  parts  of  chromate  of  potassa,  and  2  parts  of 
chloride  of  ammonium,  when  sesquioxide  of  chromium  and  chloride  of  potassium 
are  left ;  water  and  nitrogen  being  evolved. 

Properties. — Anhydrous  sesquioxide  of  chromium  is  a  bluish-green  powder, 
unaltered  by  exposure  to  air.  When  heated,  its  color  changes,  incandescence  is 
observed,  and  the  properties  of  the  sesquioxide  are  found  considerably  modified; 
it  becomes  almost  insoluble  in  acids  and -alkalies,  and  is  hence  said  to  be  con- 
verted into  the  insoluble  modification.  If  it  has  not  been  strongly  ignited,  how- 
ever, sesquioxide  of  chromium  is  soluble,  though  not  very  easily,  in  the  stronger 
acids,  and  in  solutions  of  potassa  and  soda;  from  the  latter  it  is  reprecipitated 
by  boiling. 

When  fused  with  oxidizing  agents  (hydrated  alkalies,  nitrates,  chlorates)  in 
the  presence  of  alkalies,  sesquioxide  of  chromium  is  converted  into  chromic  acid. 

The  sesquioxide  cannot  be  reduced  by  hydrogen,  and  is  acted  on  by  carbon 
only  at  a  very  high  temperature. 

HYDRATE  OF  SESQUIOXIDE  OP  CHROMIUM,  Cr^.lOHO.1 

Preparation. — A  pretty  strong  solution  of  bichromate  of  potassa  is  mixed  with 
a  moderate  quantity  of  hydrochloric  acid,  introduced  into  a  deep  vessel,  and  a 
stream  of  sulphurous  acid  (prepared  by  the  action  of  charcoal  on  oil  of  vitriol) 
passed,  until  the  red  color  has  changed  to  a  pure  green,  and  the  odor  of  sul- 
phurous acid  does  not  disappear  even  on  standing  : — 

KO.'2Cr03+HCl4-3SOa=KCl+HO+Cr2033S03; 

the  solution  containing  sulphate  of  sesquioxide  of  chromium  is  now  mixed  with 
a  slight  excess  of  ammonia,  and  heated,  when  the  whole  of  the  sesquioxide  of 
chromium  is  precipitated  as  a  bluish  hydrate,  which,  when  dried  at  the  ordinary 
temperature,  has  the  formula  given  above  : — 

Cr203.3S03+3NH3-fl3HO=Cr303,10HO-f3(NH04.SO,). 

1  Fremy  states  it  that  contains  9HO. 


POTASH-CHROME  ALUM.  329 

Properties,  —  This  hydrate  is  entirely  deprived  of  its  water  by  exposure  to  a 
temperature  of  392°  F.  (200°  C.)  ',  it  dissolves  with  facility  in  solutions  of 
potassa  and  soda,  forming  fine  green  solutions,  which  deposit  after  a  time  a 
hydrate  of  the  formula  O203.9HO,  which  is  insoluble  in  the  alkalies;  probably 
it  is  in  this  form  that  the  whole  of  the  sesquioxide  is  precipitated  (as  mentioned 
before)  on  boiling  the  alkaline  solutions. 

Hydrated  sesquioxide  of  chromium  dissolves  to  a  slight  extent  in  solution  of 
ammonia,  forming  a  pink  solution,  which  deposits  all  the  chromium  when  boiled.1 

The  soluble  salts  of  sesquioxide  of  chromium  have  an  acid  reaction. 

NITRATE  OF  SESQUIOXIDE  OF  CHROMIUM,  Cra03.3N05.  —  This  unimportant 
salt  may  be  prepared  by  dissolving  the  hydrated  sesquioxide  in  nitric  acid,  and 
evaporating;  it  has  a  green  color,  and  is  easily  decomposed  by  heat,  yielding  a 
brown  substance,  which  is  said  to  be  Cr303.Cr03.  This  nitrate  is  very  soluble 
in  water. 

SULPHATE  OF  SESQUIOXIDE  OF  CHROMIUM,  Cra03.3S03. 

This  salt  is  known  in  three  modifications,  exhibiting  a  difference  in  their  proper- 
ties which  justifies  us  in  describing  them  separately. 

Violet  Salt,  Cr203.3S034-15Aq.—  This  salt  is  obtained  when  8  parts  of  hydrat- 
ed sesquioxide  of  chromium,  which  has  been  dried  at  212°  F.,  are  digested  for 
some  weeks  with  8  or  10  parts  of  concentrated  sulphuric  acid;  in  this  way  a 
bluish-green  crystalline  mass  is  obtained,  which  is  purified  by  dissolving  in  water 
and  adding  alcohol,  which  throws  down  a  violet  crystalline  precipitate  ;  this  is 
redissolv.ed  in  weak  alcohol,  and  allowed  to  evaporate  spontaneously,  when  octo- 
hedral  crystals  are  deposited,  which  have  a  violet  color,  and  the  composition  given 
above.  This  salt  is  very  soluble  in  water;  the  solution  is  acid. 

Green  Salt,  Cr303.3S03-f  15  Aq.  —  The  green  sulphate  is  formed  when  hydrated 
sesquioxide  of  chromium  is  dissolved  in  concentrated  sulphuric  acid  with  the 
aid  of  a  gentle  heat.  It  may  also  be  obtained  by  rapidly  evaporating  a  solution 
of  the  violet  salt. 

This  green  salt  differs  from  the  violet  modification  by  its  solubility  in  alcohol. 
When  heated  it  undergoes  the  aqueous  fusion,  and  loses  10  eqs.  of  water  at 
212°  F.  (100°  C.)  It  has  been  stated  that  the  solution  of  this  salt  is  not 
entirely  decomposed  by  solution  of  baryta  in  the  cold,  and  therein  differs  from 
the  violet  sulphate. 

Red  Salt,  Cra03,3S03.  —  This  salt  is  prepared  by  heating  either  of  the  above 
modifications  with  an  excess  of  concentrated  sulphuric  acid  to  about  392°  F. 
(200°  C.),  and  evaporating  to  expel  excess  of  acid.  This  variety  of  sulphate 
of  sesquioxide  of  chromium  is  characterized  by  its  insolubility  in  water  and 
acids. 

Basic  sulphates  of  sesquioxide  of  chromium  are  known. 

Sesquioxide  of  chromium,  like  alumina,  forms  a  series  of  alums  perfectly 
analogous  to  those  of  the  latter  base. 

Potash-chrome  alum==KO.S03,Cr303.3S03-f24Aq. 
Soda          «         «    =NaO.S0,CraO.3S6a 


Ammonia  "    =NH4O.S03,Cr203.3S03-f  24Aq. 

POTASH-CHROME  ALUM. 

Preparation.  —  This  alum  is  very  conveniently  prepared  by  mixing  three  mea- 
sures of  a  saturated  solution  of  bichromate  of  potassa  with  one  measure  of 

1  Some  of  the  violet  salts  of  chromium  when  treated  with  alkalies,  yield  a  violet  preci- 
pitate which  dissolves  completely  in  ammonia.  Other  hydrates  of  sesquioxide  of  chromium, 
containing  3,  4,  and  8  eqs.  of  water,  are  said  to  have  been  obtained. 


330  CHROMIC   ACID. 

concentrated  sulphuric  acid,  and  saturating  with  sulphurous  acid  ;  after  a  time 
crystals  of  chrome  alum  are  deposited  :  — 


Another  method  consists  in  mixing  a  concentrated  solution  of  the  bichromate 
with  sulphuric  acid,  allowing  the  liquid  to  cool,  and  gradually  adding  alcohol 
(assisting  the  reaction,  if  necessary,  with  a  gentle  heat)  till  the  red  color  of  the 
solution  has  changed  to  violet  ;  on  standing  the  chrome-alum  is  deposited.  Sugar 
is  sometimes  employed  instead  of  alcohol  as  a  reducing  agent. 

Properties.  —  The  chrome-alum  thus  obtained  is  deposited  in  octohedral  crystals, 
of  a  purple-red  color,  which  appear  ruby-red  by  transmitted  light.  It  is  very 
soluble  in  water,  and  when  heated,  it  undergoes  the  aqueous  fusion,  and  at  392° 
F.  (200°  C.),  loses  22  eqs.  of  water,  and  is  converted  into  a  green  modification. 
At  about  662°  F.  (350°  C.),  it  becomes  anhydrous,  and  ultimately  yields  a  lilac 
powder,  which  is  soluble  only  in  oil  of  vitriol.  Chrome-alum  is  very  soluble  in 
water,  and  gives  an  acid  solution  of  a  dark  violet  color.  If  this  solution  be  al- 
lowed to  evaporate  spontaneously,  it  deposits  the  ordinary  crystals  of  chrome- 
alum,  but  if  evaporated  at  about  176°  F.  (80°  C.),  it  assumes  a  green  color,  and 
does  not  yield  any  crystals,  since  it  is  then  either  decomposed  or  converted  into 
the  alum  corresponding  to  the  green  sulphate  of  sesquioxide  of  chromium,  which 
does  not  crystallize,  but  is  left  as  a  green  mass  on  evaporation  ;  the  solution,  how- 
ever, resumes  its  normal  condition  after  long  standing.  Chrome-alum  is  insoluble 
in  alcohol.  It  is  employed  in  dyeing,  and  is  hence,  to  some  extent,  an  article 
of  commerce. 

The  action  of  ammonia  upon  a  solution  of  chrome-alum  tends  to  demonstrate 
the  existence  of  different  modifications  of  the  hydrates  of  sesquioxide  of  chro- 
mium, corresponding  to  the  different  varieties  of  the  sulphate.  When  solution 
of  chrome-alum  is  added,  drop  by  drop,  to  an  excess  of  ammonia,  the  precipi- 
tated hydrate  has  a  green  color,  and  yields  a  violet  solution  with  sulphuric  acid. 

If  the  chrome-alum  be  decomposed  by  a  quantity  of  ammonia  insufficient  to 
redissolve  any  portion  of  the  hydrate,  the  latter  will  have  a  violet  color,  and  will 
dissolve  in  sulphuric  acid  to  form  a  red  solution. 

A  basic  carbonate  of  sesquioxide  of  chromium  is  obtained,  as  a  green  precipi- 
tate, when  a  solution  of  sesquioxide  of  chromium  is  decomposed  by  an  alkaline 
carbonate.  Its  formula  is  4Cr303.C03-f  Aq  j  it  is  soluble  in  the  alkaline  car- 
bonates with  the  aid  of  heat. 

PROTOSESQUIOXIDE  OF  CHROMIUM,  Cr304=CrO.Cr203.  —  This  oxide  is  formed 
(as  we  have  seen  already)  when  a  solution  of  potassa  is  added  to  a  salt  of  (prot-) 
oxide  of  chromium,  water  being  decomposed  :  — 

3CrO+HO=Cr304-j-H. 

This  oxide  is  thus  obtained  as  a  brown  hydrate,  which  is  converted  into  sesqui- 
oxide when  heated  in  air. 

From  the  foregoing  description  of  the  properties  of  sesquioxide  of  chromium 
and  its  compounds,  it  will  be  seen  that  we  are  justified  in  placing  it  in  juxta- 
position with  alumina  and  the  other  earths. 

.^'  'v  CHROMIC  ACID,  Cr03. 

§  222.  It  has  already  been  stated  that  this  acid  occurs  in  nature  in  combi- 
nation with  oxide  of  lead. 

It  is  prepared  by  adding  to  one  measure  of  a  saturated  solution  of  bichromate 
of  potassa,  at  about  130°  F.  (54°  C.),  one  measure  and  a  half  of  concentrated 
sulphuric  acid,  by  small  portions  at  a  time,  and  allowing  the  solution  to  cool, 
when  chromic  acid  crystallizes  out,  and  bisulphate  of  potassa  remains  in  solution. 
The  crystals  of  chromic  acid  are  removed  with  a  platinum  knife,  drained  in  a 
funnel  stopped  with  a  loose  plug  of  asbestos,  and  dried  at  the  ordinary  tempera- 


CHROMATES.  331 

ture  upon  a  porous  tile;  they  must  not  be  heated,  or  brought  in  contact  with 
paper,  lest  they  suffer  decomposition.  In  order  to  free  them  from  adhering  sul- 
phuric acid,  they  may  be  dissolved  in  a  very  little  water,  the  solution  digested 
with  chromate  of  baryta,  which  precipitates  the  sulphuric  acid,  the  clear  liquid 
decanted,  and  evaporated  in  vacua  over  oil  of  vitriol. 

Properties. — Chromic  acid  crystallizes  in  fine  red  needles,  which  are  deliques- 
cent, and  very  soluble  in  water.  They  stain  the  skin  yellow.  When  heated, 
the  crystals  assume  a  very  dark  color,  and  are  afterwards  decomposed  into  ses- 
quioxide  of  chromium  and  oxygen,  often  with  incandescence. 

The  aqueous  solution  of  chromic  acid  has  an  orange-red  color ;  when  exposed 
to  sunlight,  it  evolves  oxygen,  and  deposits  the  chromate  of  sesquioxide  of 
chromium.  Chromic  acid  is  dissolved  by  weak  alcohol,  but  the  solution  soon 
decomposes,  from  the  action  of  the  chromic  acid  on  the  alcohol. 

When  absolute  alcohol  is  poured  upon  crystals  of  chromic  acid,  the  former  is 
rapidly  oxidized,  often  with  sufficient  energy  to  give  rise  to  combustion,  the 
chromic  acid  being  reduced  to  sesquioxide  of  chromium. 

Chromic  acid,  indeed,  is  one  of  the  most  powerful  oxidizing  agents  with  which 
we  are  acquainted.  The  deoxidizing  action  of  sulphurous  acid  upon  chromic 
acid  has  been  already  mentioned. 

When  chromic  acid  is  heated  with  hydrochloric  acid,  chlorine  is  evolved,  and 
sesquichloride  of  chromium  formed  : — 

2Cr03  +  6HCl=6HO+Cr3Cl3+Cl3. 

Sugar,  and  many  other  organic  substances,  are  also  capable  of  reducing  this 
acid. 

When  chromic  acid  (or  bichromate  of  potassa)  is  heated  with  concentrated 
sulphuric  acid,  oxygen  is  evolved  : — 

2Cr03+3(HO.S03)=Cr/)3.3S03+3HO+03; 

A  mixture  of  5  parts  of  bichromate  of  potassa  and  4  of  concentrated  sulphuric 
acid  has  been  recommended  for  the  preparation  of  oxygen  in  the  laboratory. 

If  crystals  of  chromic  acid  are  placed  in  a  bulb-tube,  and  gently  heated  in  a 
current  of  dry  ammonia,  vivid  incandescence  is  observed,  and  the  chromic  acid 
is  reduced ; — 

2Cr03+NH3=Cr203+N+3HO. 

Chromic  acid  is  extensively  used  as  an  oxidizing  agent  in  experiments  upon 
organic  substances. 

Compounds  of  chromic  acid  with  sulphuric  acid  have  been  obtained.1 

Chromic  acid  is  monobasic,  and  forms  an  extensive  series  of  salts,  which  have 
the  same  crystalline  form  as  the  corresponding  sulphates,  chromic  acid  being 
isomorphous  with  sulphuric  acid.  The  general  formula  of  the  neutral  chromates 
may  be  written  MO.Cr03.  The  neutral  chromates  of  the  alkalies  have  a  fine 
yellow  color ;  the  acid  chromates  are  orange-red. 

CHROMATE  OP  POTASSA,  KO.Cr03. 

This  salt  is  prepared  by  adding  carbonate  of  potassa  to  a  solution  of  the  bi- 
chromate, until  it  assumes  a  fine  yellow  color,  evaporating  and  crystallizing. 

Properties. — The  chromate  is  thus  obtained  in  bright  yellow  anhydrous  crys- 
tals, of  the  same  form  as  those  of  sulphate  of  potassa.  They  are  unaltered  in 
air. 

When  heated,  the  salt  changes  color  to  red,  fuses  at  a  red  heat,  but  does  not 
suffer  decomposition;  it  assumes  its  original  yellow  color  on  cooling. 

This  chromate  is  easily  soluble  in  cold  water,  and  much  more  so  in  hot;  the 

1  Schrotter  lias  recently  obtained  a  compound  of  anhydrous  sulphuric  and  chromic  acids . 


332  CHROMATES. 

solution  has  a  bright  yellow  color,  even  though  it  contain  very  little  chromate ; 
it  has  a  bitter  taste,  and  an  alkaline  reaction. 

When  solution  of  chromate  of  potassa  is  kept  in  bottles  of  ordinary  English 
glass,  these  are  attacked,  and  a  yellow  substance  (probably  chromate  of  lead) 
deposited  upon  the  interior  surface. 

Chromate  of  potassa  does  not  dissolve  in  alcohol ;  it  is  a  poisonous  salt. 

"When  the  yellow  solution  of  chromate  of  potassa  is  mixed  with  an  acid,  its 
color  changes  to  red,  from  production  of  the  bichromate. 

If  sulphuretted  hydrogen  be  added  to  an  aqueous  solution  of  the  chromate, 
sesquioxide  of  chromium  and  sulphur  are  precipitated,  while  sulphide  of  potas- 
sium is  found  in  solution : — 

2(KO.Cr03)+5HS=2KS  +  5HO  +  Cr303-fS8. 

BICHROMATE  OF  POTASSA,  K0.2O03. 

Preparation. — Chrome-iron  ore  is  reduced  to  powder,  and  fused  in  a  reverbe- 
ratory  furnace  with  half  its  weight  of  nitre,  with  continual  stirring;  in  this  way 
the  chromium  is  converted  into  chromate  of  potassa,  and  the  silica  and  alumina 
contained  in  the  ore  are  rendered  soluble  in  water;  the  mass  is  extracted  with 
boiling  water,  and  4he  solution  mixed  with  a  slight  excess  of  acid  (sulphuric, 
nitric,  or  acetic),  which  precipitates  the  alumina  and  silica,  and  converts  the 
chromate  into  bichromate,  which  may  be  crystallized  from  the  solution,  and 
purified  by  recrystallization. 

Bichromate  of  potassa  may  also  be  prepared  by  heating  a  mixture  of  chrome- 
iron  ore  and  chalk  in  an  oxidizing  flame.  The  mass,  containing  chromate  of  lime, 
is  suspended  in  water,  and  converted  into  bichromate  by  addition  of  sulphuric 
acid.  The  resulting  bichromate  of  lime  is  decomposed  with  carbonate  of  potassa.1 

Properties. — The  bichromate  forms  beautiful  red  tabular  crystals,  derived  from 
an  oblique  rhombic  prism ;  they  are  not  changed  by  exposure  to  air,  and  are  an- 
hydrous. 

When  heated,  this  salt  fuses  easily,  without  alteration,  but  at  a  high  tempera- 
ture is  decomposed  into  chromate  of  potassa,  crystalline  sesquioxide  of  chromium, 
and  oxygen  : — 

2(K0.2Cr03)=2(KO.Cr03)  +  Cra03+03. 

Bichromate  of  potassa  is  less  soluble  than  the  chromate,  one  part  of  the  former 
salt  requiring  ten  parts  of  cold  water.  It  is  more  soluble  in  hot  water ;  the  solu- 
tion has  a  fine  red  color  and  an  acid  reaction.  This  salt  is  insoluble  in  alcohol. 

The  bichromate  is  a  more  powerful  oxidizing  agent  than  the  chromate.  Most 
reducing  agents  decompose  it,  either  at  the  ordinary,  or  at  a  slightly  elevated 
temperature. 

Uses  of  Chromates  of  Potassa. — The  chromate  and  bichromate  of  potassa  are 
somewhat  extensively  used  in  dyeing,  and  in  the  manufacture  of  colors.  The 
bichromate  is  also  employed  in  bleaching  sperm-oil,  for  which  purpose  the  latter 
is  heated  with  a  mixture  of  bichromate  of  potassa  and  sulphuric  acid,  which  oxi- 
dizes the  coloring  matter;  the  sulphate  of  sesquioxide  of  chromium  thus  produced 
is  afterwards  reconverted  into  bichromate. 

Chromate  and  bichromate  of  potassa  are  employed  as  reagents.  A  mixture  of 
bichromate  of  potassa  and  sulphuric  acid  is  frequently  made  use  of  in  the  labora- 
tory as  an  oxidizing  agent.  These  salts  are  also  employed  for  the  preservation 
of  wood. 

1  Tilghman  has  proposed  to  expose  the  finely  powdered  chrome-ore,  mixed  with  sulphate 
of  potassa  and  lime,  to  a  red  heat,  in  the  oxidizing  fire  of  a  reverberatory  furnace  through 
•which  a  current  of  steam  is  passed.  He  also  recommends  the  ignition  of  the  ore  with 
powdered  feldspar  and  lime. 


CHLORIDES   OF   CHROMIUM.  333 

Bichromate  of  potassa  forms  a  double  salt  with  sulphate  of  potassa,  which  may 
be  obtained  in  bright  crystals  of  the  formula  K0.2Cr03,KO.S03.  It  is  very 
soluble,  arid  may  be  fused  without  decomposition. 

Tercliromate  of  Potassa,  K0.3O08,  is  obtained  in  anhydrous  red  crystals  by 
decomposing  bichromate  of  potassa  with  excess  of  nitric  acid. 

Bichromate  of  Chloride  of  Potassium)  Chlorochromate  of  Potassa,  KC1.2Cr03. 
— This  salt  is  deposited  in  fine  red  prisms,  from  a  mixture  of  bichromate  of  pot- 
assa and  hydrochloric  acid,  which  has  been  boiled  until  chlorine  begins  to  escape. 

Though  permanent  in  dilute  hydrochloric  acid,  it  is  decomposed  by  water  into 
hydrochloric  acid  and  bichromate  of  potassa  : — 

KCL2Cr03+HO=HCl+K0.2Cr03 ; 

this  decomposition  would  lead  us  to  regard  the  compound  as  bichromate  of 
potassa,  in  which  one  equivalent  of  chromic  acid  has  been  replaced  by  chloro- 
chromic  acid  (CrOaCl;  p.  334).^ 

When  treated  with  oil  of  vitriol,  it  evolves  chlorochromic  acid. 

The  Chromate  of  Soda  is  very  soluble  in  water  and  deliquescent;  its  crystals 
have  the  same  form  as  those  of  sulphate  of  soda  (NaO.S03-f-10Aq),  and  a  cor- 
responding formula,  NaO.Cr03  +  10Aq. 

The  Bichromate  of  Ammonia,  recently  examined  by  Richmond  and  John  Abel, 
has  the  formula,  NH40.2Cr03,  and  is  decomposed  by  heat  in  a  peculiar  manner, 
leaving  sesquioxide  of  chromium  : — 

NH40.2Cr03=N  +  4HO  +  Cr203. 

Several  chromates  of  sesquioxide  of  chromium  appear  to  exist. 

The  residue  left  on  gently  igniting  the  nitrate  of  sesquioxide  of  chromium  has 
the  formula  O203.Cr03,  and  is  viewed  by  some  as  a  binoxide  of  chromium. 

When  chromate  of  potassa  is  very  gradually  added  to  sulphate  of  sesquioxide 
of  chromium,  the  neutral  chromate  of  sesquioxide  of  chromium,  Cra03.3Cr03,  is 
precipitated.  The  chromic  acid  may  be  removed  from  this  compound  by  long 
washing. 

On  adding  chromate  of  potassa  to  a  solution  of  chrome-alum,  a  precipitate  is 
obtained  pf  the  formula  3Cr303.2Cr03+2Aq. 

Lastly,  a  red-brown,  soluble  acid  salt,  of  the  formula  Cr203.4Cr03,  is  obtained 
by  saturating  a  solution  of  chromic  acid  with  hydrated  sesquioxide  of  chromium. 

PERCHROMIC  ACID,  O207. 

When  solution  of  bichromate  of  potassa  is  mixed  with  hydrochloric  acid,  and 
a  little  binoxide  of  barium  added,  or  when  binoxide  of  hydrogen  is  added  to 
solution  of  chromic  acid,  a  fine  blue  solution  is  produced,  which  contains  per- 
chromic  acid.  This  acid  is  very  unstable,  and  has  never  been  obtained  in  the 
pure  state.  Its  solution  readily  loses  oxygen,  sesquioxide  of  chromium  (not 
chromic  acid)  being  produced. 

Its  salts  have  not  yet  been  prepared. 

§  223.  Nitride  of  Chromium  (Cr3N5)  is  obtained  as  a  brown  powder  when 
sesquichloride  of  chromium  is  heated  in  a  current  of  dry  ammonia.  When  heated 
in  air,  this  compound  burns,  and  is  converted  into  sesquioxide  of  chromium,  nitro- 
gen being  disengaged.  It  is  insoluble  in  water. 

CHLORIDE  OF  CHROMIUM,  PROTOCHLORIDE,  CrCl. 

This  chloride  is  prepared  by  passing  a  current  of  hydrogen  over  sesquichloride 
of  chromium  heated  to  redness. 

It  is  a  white  salt,  which  is  soluble  in  water;  the  solution  has  a  blue  color,  and 
is  very  prone  to  absorb  oxygen  from  the  air,  being  converted  into  an  oxycliloride. 


334  CHLOROCHROMIC   ACID. 

Cr2Cl30.     The  chloride  of  chromium  possesses  the  same  property  as  the  proto- 
salts  of  iron,  of  absorbing  the  binoxide  of  nitrogen. 

SESQUICHLORIDE  OF  CHROMIUM,  CrflCl3. 

The  anhydrous  sesquichloride  may  be  prepared  by  passing  a  current  of  dry 
chlorine  over  a  mixture  of  sesquioxide  of  chromium  and  charcoal  heated  to  red- 
ness ;  the  details  of  the  process  are  the  same  as  in  that  for  preparing  sesquichlo- 
ride of  aluminum;  a  very  high  temperature  is  required.  The  sesquichloride 
condenses  partly  on  the  upper  wall  of  the  tube,  and  partly  in  the  cool  extremity, 
in  fine  shining  leaflets,  of  a  peach-blossom  color.  These  are  unalterable  in  air, 
and  insoluble  in  cold  water.  When  boiled  with  water,  they  gradually  dissolve, 
yielding  a  green  solution.  It  is  a  very  peculiar  circumstance,  that,  if  a  small 
quantity  (a  mere  trace)  of  protochloride  of  chromium  be  dissolved  in  the  water, 
the  sesquichloride  dissolves  readily  in  the  liquid,  with  disengagement  of  heat, 
and  forms  a  green  solution.  A  solution  of  sesquichloride  of  chromium  may  be 
readily  prepared  by  dissolving  the  hydrated  sesquioxide  in  hydrochloric  acid,  or 
by  heating  bichromate  of  potassa  with  hydrochloric  acid  and  a  little  alcohol;  the 
solution  has  a  fine  green  color;  and  if  evaporated  in  vacuo,  leaves  a  deliquescent 
green  mass  of  the  formula  CraCl3  +  9Aq,  which  is  considered,  by  some  chemists, 
as  a  hydrochlorate  of  sesquioxide  of  chromium,  Cr^.SHCl-f-SAq.1  If  this 
green  mass  be  heated,  hydrochloric  acid  is  evolved,  and  the  residue  contains  both 
sesquioxide  and  sesquichloride  of  chromium  ;  when  heated  in  a  current  of  hydro- 
chloric acid  gas,  the  anhydrous  sesquichloride  is  left. 

A  violet  modification  of  the  hydrated  sesquichloride  of  chromium  is  obtained 
in  solution,  when  the  violet  sulphate  of  the  sesquioxide  is  decomposed  by  chloride 
of  barium. 

CHLOROCHROMIC  ACID,  BICHROMATE  OF  PERCHLORIDE  OF  CHROMIUM. 

CrCl3.2Cr03. 

This  substance  is  more  conveniently  regarded  as  a  new  acid  produced  by  the  sub- 
stitution of  1  eq.  Cl  for  1  eq.  O  in  chromic  acid ;  its  formula  will  then  be  Cr03Cl. 

Preparation. — 10  parts  of  common  salt  are  fused  with  17  parts  of  bichromate 
of  potassa  in  a  Hessian  crucible ;  the  fused  mass  is  poured  out  on  a  clean  slab, 
broken  up  into  small  fragments,  and  introduced  into  a  retort  with  30  parts  of 
concentrated  sulphuric  acid ;  the  retort  is  connected  with  a  good  condensing 
arrangement,  and  heat  applied  gradually  by  means  of  a  sand-bath,  when  the  sub- 
stance is  easily  distilled  over.  Its  production  is  represented  by  the  following 
equation : — 

Cr03+NaCl-fHO.S03=Cr02Cl+NaO.S03-fHO. 

Properties. — Chlorochromic  acid  is  a  deep  brown-red  oily  liquid,  somewhat 
similar  to  bromine;  its  sp.  gr.  is  1.71.  Even  at  ordinary  temperatures  this 
liquid  emits  dark-brown  vapors,  and  fumes  strongly  in  the  air ;  its  odor  is  very 
pungent,  and  recalls  that  of  chlorine.  Chlorochromic  acid  boils  at  about  250°  F. 
(121°  C.),  and  yields  a  vapor  of  sp.  gr.  5.55.  Water  decomposes  this  acid, 
yielding  chromic  and  hydrochloric  acids : — 

CrO,Cl+HO=Cr08+HCl; 

therefore,  when  brought  into  contact  with  solutions  of  the  alkalies,  it  yields 
chlorides  and  chromates. 

1  A  freshly  prepared  (green)  solution  of  this  compound  only  loses  two-thirds  of  its 
chlorine  when  treated  with  nitrate  of  silver ;  the  filtrate,  by  spontaneous  evaporation, 
deposits  green  crystals  of  the  formula  Cr202C1.2HCl-{-10Aq.  By  treating  a  solution  of 
this  compound  with  baryta,  precipitating  the  chloride  of  barium  with  alcohol,  and  evapo- 
rating the  solution  in  vacuo,  a  resinous  substance  is  left,  having  the  formula  O202Cl-f- 
3Aq. 


URANIUM   AND   OXYGEN,  335 

Cblorochromic  acid  is  a  very  powerful  oxidizing,  and  chlorinating  agent ;  few 
oxidizable  substances  can  withstand  its  action. 

It  is  occasionally  used  to  illustrate  the  nature  of  illuminating  flames  ;  for  if 
hydrogen  be  passed  through  a  Woulfe's  bottle,  at  the  bottom  of  which  a  few 
drops  of  this  liquid  are  placed,  the  gas  carries  up  a  quantity  of  the  vapor;  and  if 
it  be  then  kindled,  burns  with  a  brilliant  white  flame,  which  deposits  a  beautiful 
green  film  of  sesquioxide  of  chromium  upon  a  porcelain  dish  depressed  into  it. 

A  compound  of  chromium  with  fluorine  is  obtained,  as  a  red  gas,  condensable 
to  a  blood-red  liquid,  when  a  mixture  of  a  chromate  with  fluorspar  is  distilled 
with  concentrated  sulphuric  acid. 

The  Sulphides  of  Chromium  are  imperfectly  known. 

When  a  solution  of  a  sulphide  is  added  to  one  of  sesquioxide  of  chromium,  the 
latter  is  precipitated  as  hydrate,  with  disengagement  of  sulphuretted  hydrogen. 
If  vapor  of  bisulphide  of  carbon  be  passed  over  sesquioxide  of  chromium  at  a  red 
beat,  a  substance  resembling  graphite  is  obtained,  having  the  composition  Cr2S3. 

It  is  said  that  when  sulphate  of  sesquioxide  of  chromium  is  heated  in  a  current 
of  hydrogen,  a  brownish-black  pyrophoric  sulphide  of  chromium,  OS,  is  obtained. 

A  tersulphide,  CrS3,  is  also  said  to  exist. 


URANIUM. 

Sym.  U.    Eq.  60. 

§  224.  This  metal  occurs,  though  not  abundantly,  in  nature,  in  the  minerals 
pitchblende,  in  which  it  exists  as  black  oxide  (U40.),  associated  with  silica,  oxide 
of  lead,  and  oxide  of  iron,  uran-mica,  or  chalcolite,  which  contains  the  oxides  of 
uranium  and  copper  combined  with  phosphoric  acid  (Cu0.2U203.P05,8Aq),  and 
vranite,  which  is  a  double  phosphate  of  lime  and  sesquioxide  of  uranium  (CaO. 
2U,03-P05,8Aq). 

Uranium  may  be  isolated  in  the  same  way  as  magnesium,  by  heating  the 
(proto-)  chloride  with  potassium,  and  washing  the  product  with  water. 

The  metal  thus  obtained  is  a  dark  powder,  which,  when  aggregated,  forms  a 
lustrous  white  mass,  which  is  in  some  degree  malleable.  It  is  scarcely  altered 
by  exposure  to  air.  When  moderately  heated,  it  burns  vividly,  and  is  converted 
into  an  oxide  of  a  green  color.  Uranium  does  not  decompose  water  at  the  ordi- 
nary temperature,  but  in  the  presence  of  acids  it  dissolves  with  evolution  of 
hydrogen. 

URANIUM  AND  OXYGEN. 

Suboxide U403. 

Oxide  of  protoxide     .     .     .' UO. 

Sesquioxide  or  peroxide U3O3. 

The  suboxide  is  little  known,  and  has  been  obtained  by  decomposing  a  sub- 
chloride  of  uranium  (U4C13)  with  ammonia;  it  decomposes  water,  evolving  hy- 
drogen, and  forming  a  higher  oxide,  which  is  said  to  be  another  suboxide,  and  is 
still  further  oxidized  on  exposure  to  air. 

OXIDE  (PROTOXIDE)  OP  URANIUM,  UO. 

This  oxide  was  formerly  supposed  to  be  the  metal.  It  may  be  prepared  by 
heating  the  oxalate  of  sesquioxide  of  uranium  to  redness  in  a  current  of  hydrogen. 


336  SALTS   OP   URANIUM. 

It  is  thus  obtained  as  a  black  powder,  which  takes  fire  when  exposed  to  air, 
and  is  converted  into  the  oxide  U405. 

The  hydrate  of  (prot-)  oxide  of  uranium  is  precipitated  in  red-brown  flocks, 
where  ammonia  is  added  to  a  salt  of  this  base.  The  hydrate  is  soluble  in  acids. 

The  sulphate  of  (prot-)  oxide  of  uranium*  is  prepared  by  decomposing  the 
(proto-)  chloride  with  sulphuric  acid.  It  forms  yellow  crystals  of  the  formula 
UO.S03-f4Aq.  This  salt  is  easily  converted  by  oxidizing  agents  into  the  sul- 
phate of  sesquioxide;  if  treated  with  a  large  quantity  of  water,  a  subsulphate 
is  left. 

The  protosesquioxide  (black  oxide),  U405,  above  referred  to,  appears  to  be  a 
combination  of  (prot-)  oxide  and  sesquioxide  of  uranium  U405=2UO,U203. 
When  heated  to  redness  in  the  air  it  absorbs  oxygen,  and  is  converted  into  the 
green  oxide,  U304,  which  is  probably  another  protosesquioxide  of  uranium,  cor- 
responding to  the  magnetic  oxide  of  iron.  Heated  in  hydrogen  it  yields  (prot-) 
oxide  of  uranium.  •  ,;'J- 

SESQUIOXIDE  (PEROXIDE)  OF  URANIUM,  U803. 

This  is  the  most  important  of  the  oxides  of  uranium. 

It  may  be  prepared  by  exposing  the  nitrate  of  sesquioxide  of  uranium,  in  an 
oil-bath,  to  a  temperature  of  482°  F.  (250°  C.) 

The  hydrate,  U303.HO,  which  occurs  native  in  the  form  of  uranium-ochre,  is 
obtained  by  treating  the  nitrate  with  alcohol,  evaporating  the  solution,  and  ex- 
tracting the  residue  with  water,  which  leaves  the  yellow  hydrated  sesquioxide. 
This  hydrate  loses  its  water  at  572°  F.  (300°  C.),  and  at  a  higher  temperature, 
is  converted,  with  evolution  of  oxygen,  into  U304.  Another  hydrate,  containing 
2  eqs.  water,  is  obtained  when  the  result  of  the  preceding  operation  is  dried  by 
mere  exposure  to  air. 

Sesquioxide  of  uranium  dissolves  in  acids  forming  salts,  the  solutions  of  which 
have  a  fine  yellow  color  and  an  acid  reaction.  These  salts  present  a  very  anoma- 
lous composition,  since  their  general  formula  is  Ufl03.RO  (where  HO  represents 
acids  generally),  whereas  the  ordinary  formula  for  the  neutral  salts  of  sesquiox- 
ides  is  Ma03.3RO. 

Peligot  avoids  this  anomaly  by  assuming  the  existence  of  a  radical,  uranyle= 
U202,  of  which  U303  is  a  (prot-)  oxide.a 

Sesquioxide  of  uranium  occasionally  plays  the  part  of  an  acid,  forming  com- 
binations with  bases  which  appear  to  have  the  general  formula  M0.2U303,  and 
are,  for  the  most  part,  insoluble.  Sesquioxide  of  uranium  is  used  to  a  consider- 
able extent  for  imparting  a  yellow  color  to  glass  and  porcelain. 

NITRATE  or  SESQUIOXIDE  or  URANIUM,  U203.N05. 

This  salt  generally  serves  as  the  source  from  which  the  other  compounds  of 
uranium  are  obtained.  It  is  prepared  from  pitchblende,  which  has  been  already 
mentioned  as  containing  a  protosesquioxide  of  uranium,  together  with  silica, 
oxide  of  lead,  and  oxide  of  iron;  it  contains  moreover,  usually,  a  little  copper, 
arsenic,  and  sulphur.  4 

In  order  to  prepare  the  nitrate,  pitchblende  is  reduced  to  powder  and  extracted 
with  nitric  acid;  the  solution  is  evaporated  to  dryness;  on  extracting  the  residue 
with  water,  some  sulphate  of  lead  and  arseniate  of  sesquioxide  of  iron  are  left. 
The  solution  is  saturated  with  sulphuretted  hydrogen,  which  precipitates  the 

1  This  salt  occurs  in  nature  as  uranium-vitriol. 

2  This  view  is  supported  by  the  fact  that  when  (prot-)  oxide  of  uranium  (uranyle)  is 
placed  in  solution  of  nitrate  of  silver,  metallic  silver  is  deposited  and  replaced  by  the 
compound  U202,  producing  the  nitrate  of  sesquioxide  of  uranium  (or  oxide  of  uranyle) 
(U202)O.N06. 


SALTS   OF   URANIUM.  337 

remainder  of  the  lead,  arsenic,  and  copper,  and  the  filtered  liquid  evaporated  to 
dryness ;  the  residue  is  treated  with  water  (which  leaves  a  little  sesquioxide  of 
iron  undissolved),  and  the  solution  evaporated  to  crystallization.1  In  order  to 
purify  the  crystals  thus  obtained,  they  are  dissolved  in  ether,  crystallized  by 
spontaneous  evaporation,  and  recrystallized  from  water. 

This  salt  forms  fine  yellow  crystals,  of  the  formula  U303.N05+6Aq.  When 
heated,  it  undergoes  the  aqueous  fusion,  loses  water,  then  parts  with  its  acid, 
and  subsequently  with  more  or  less  oxygen.  It  is  very  soluble  in  water. 

Uranate  of  potassa  (K0.2U203)  is  obtained  as  a  yellow  powder  when  a  salt 
of  sesquioxide  of  uranium  is  precipitated  with  an  excess  of  potassa,  or  when 
sesquioxide  of  uranium  is  fused  with  carbonate  of  potassa.  A  corresponding 
compound  of  soda  is  obtained  in  a  similar  manner. 

Sulphate  of  Sesquioxide  of  Uranium  crystallizes  in  small  prisms,  having  the 
formula  Ua08.S08+3Aq.  When  heated  to  212°  R,  they  lose  2  eqs.  of  water, 
and  become  anhydrous  at  572°  F.  (300°  C.);  the  anhydrous  salt  absorbs  3Aq. 
when  exposed  to  air.  According  to  Ebelmen,  a  solution  of  this  salt  in  alcohol, 
when  exposed  to  the  sun's  rays,  deposits  the  whole  of  the  uranium  as  sulphate 
of  the  (prot-)  oxide.  It  combines  with  sulphate  of  potassa,  forming  a  double- 
salt  (not  an  alum)  of  the  formula  KO.S03,U303.S03-f2Aq. 

CHLORIDE  (OR  PROTOCHLORIDE)  OF  URANIUM,  UC1. — This  compound  is  pre- 
pared by  passing  chlorine,  at  a  red  heat,  over  an  intimate  mixture  of  (prot-) 
oxide  of  uranium  and  charcoal,  when  it  condenses  in  the  cool  part  of  the  tube  in 
dark  green  octohedra,  possessing  a  metallic  lustre.  It  is  deliquescent,  and  forms 
a  green  aqueous  solution. 

Ojcychloride  of  Uranium  or  Chloride  of  Uranyle  (U302C1)  is  formed  as  a 
yellow,  deliquescent,  crystalline  compound,  when  chlorine  is  passed  over  (prot-) 
oxide  of  uranium  at  a  red  heat;  its  vapor  has  an  orange-yellow  color.  Chloride 
of  uranyle  combines  with  the  chlorides  of  potassium  and  ammonium,  forming 
the  crystalline  compounds  U3OaCl.KCl+2Aq,  and  U202Cl.NH4Cl-f-2Aq. 

Subchloride  of  Uranium  (U4C13)  is  formed  when  the  (proto-)  chloride  is  heated 
in  a  current  of  hydrogen.  It  dissolves  in  water,  yielding  a  purple  solution,  which, 
after  a  time,  becomes  green,  hydrogen  being  disengaged,  and  (proto-)  chloride  of 
uranium  reproduced. 

When  sesquioxide  of  uranium  is  treated  with  hydrochloric  acid,  the  compound 
U203C1  is  produced,  which  speaks  strongly  in  favor  of  the  existence  of  uranyle : — 
U203+HC1=U203C1  +  HO. 

Little  is  known  of  the  sulphides  of  uranium  ;  the  sesquisulphide  appears  to  be 
a  sulphur-acid,  forming  sulphur-salts  with  the  sulphur- bases. 

HEACTIONS  OF  SESQUIOXIDE  OF  URANIUM. — Potassay  'soda,  and  ammonia  ; 
yellow  precipitates,  insoluble  in  excess. 

Alkaline  Carbonates  ;  yellow  precipitates,  soluble  in  excess,  and  reprecipitated 
,  on  boiling. 

1  Another  method  of  extracting  uranium  from  its  ores,  applicable  on  a  large  scale, 
consists  in  mixing  the  powdered  pitchblende  with  half  its  weight  of  quicklime,  and 
roasting  for  several  hours  in  a  reverberatory  furnace.  The  mass  is  treated  with  dilute 
sulphuric  acid,  the  copper  and  antimony  precipitated  by  metallic  iron,  and  the  solution 
mixed  with  a  large  quantity  of  water,  which  precipitates  the  basic  sulphate  of  sesqui- 
oxide of  uranium. 

Or,  the  powdered  ore  may  be  treated  with  a  mixture  of  sulphuric  and  nitric  acids,  the 
excess  of  acid  expelled  by  heat,  and  the  perfectly  dry  mass  treated  with  water,  which 
extracts  the  whole  of  the  sulphate  of  uranium,  leaving  the  silica  and  insoluble  sulphates. 
The  clear  liquid  is  poured  into  a  hot  solution  of  carbonate  of  soda,  with  constant  agita- 
tion, until  the  alkaline  reaction  is  nearly  destroyed.  The  solution  is  filtered  and  boiled. 
when  carbonate  of  lime,  magnesia,  and  copper  are  precipitated.  The  sesquioxide  of 
uranium  is  now  separated  from  the  solution,  by  slightly  acidifying  the  boiling  solution 
with  hydrochloric  or  sulphuric  acid. 
22 


338  IRON. 

Phosphate  of  Soda  ;  white  precipitate. 

Ferrocyanide  of  Potassium  y  red-brown  precipitate. 

Sulphide  of  Ammonium;  black  sulphide  of  uranium. 

With  borax,  in  the  outer  flame,  a  greenish-yellow  bead,  which  becomes  green 
in  the  inner  flame. 

Organic  matter  interferes  with  the  precipitation  of  sesquioxide  of  uranium  by 
alkalies. 


IKON. 

Sym.  Fe.     Eq.  28. 

§  225.  In  describing  this  most  important  of  metals,  we  shall  adopt  a  course 
which  it  is  our  intention  to  pursue  with  all  metals  in  common  use,  viz.,  that  of 
giving  first  a  purely  chemical  history  of  the  metal  and  its  compounds,  reserving 
for  subsequent  consideration  the  smelting  of  its  ores,  and  the  various  forms  in 
which  the  metal  is  found  in  commerce,  as  well  as  those  properties  which  belong 
rather  to  a  technical  than  to  a  chemical  work. 

Preparation. — In  order  to  obtain  iron  in  a  state  of  purity,  a  quantity  of  piano- 
wire  (which  is  contaminated  only  with  traces  of  carbon)  is  made  up  into  small 
bundles,  which  are  oxidized  at  the  surface  by  heating  to  redness  in  a  current  of 
steam;  these  bundles  are  introduced  into  a  porcelain  crucible,  and  covered  with 
a  quantity  of  powdered  green  glass  (free  from  lead) ;  the  porcelain  crucible  is  now 
inclosed  within  a  Hessian  crucible,  and  exposed  to  the  highest  temperature  of  a 
wind  furnace;  the  carbon  contained  in  the  iron  wire  is  oxidized  at  the  expense  of  the 
superficial  coating  of  oxide,  and  the  excess  of  the  latter  dissolves  in  the  fused 
glass,  leaving  the  pure  iron  in  the  form  of  a  button  at  the  bottom  of  the  crucible. 

For  the  ordinary  purposes  of  the  chemist,  however,  pure  iron  is  best  prepared 
by  reducing  the  sesquioxide  of  iron  by  means  of  hydrogen. 

This  oxide  is  obtained  by  precipitating  the  sesquichloride  by  excess  of  ammonia, 
heating,  and  washing  the  precipitate,  first  by  decantation,  and  subsequently  upon 
a  filter,  until  the  washings  are  free  from  chlorine ;  the  precipitated  hydrate  is  then 
dried  at  a  sand-heat,  reduced  to  powder,  and  introduced  into  a  tube  of  hard  glass 
drawn  out  to  a  point  at  one  extremity,  and  connected  at  the  other  with  an  appa- 
ratus for  the  disengagement  of  pure  hydrogen;  when  the  apparatus  is  filled  with 
the  latter  gas,  the  tube  is  heated  with  a  spirit-lamp  as  long  as  any  vapor  of  water 
is  disengaged ;  the  metal  is  thus  obtained  as  a  dark  gray  powder,  which  is  pyro- 
phoric,1  but  if  the  reduction  be  effected  at  a  very  high  temperature,  this  is  not 
the  case. 

The  button  of  pure  iron  is  white,  and  possesses  a  silvery  lustre. 

General  Properties  of  Iron. — Iron  generally  presents  a  dusky-gray  color  and 
a  rather  feeble  lustre,  which  is,  however,  greatly  increased  by  polishing,  for  iron 
is  possessed  of  considerable  hardness. 

Bar-iron  varies  in  specific  gravity  between  7.7  and  7.9. 

Iron  is  a  malleable  metal,  and  exceeds  all  others  in  tenacity ;  an  iron  wire  of 
J^  inch  in  diameter  is  capable  of  supporting  705  Ibs. 

Iron  is  eminently  magnetic  at  ordinary  temperatures,  but  loses  this  character 
entirely  at  a  very  high  temperature. 

This  metal  is  not  affected  by  dry  air  or  oxygen  at  the  ordinary  temperature ; 
when  heated  in  air,  it  is  covered  with  a  film  of  oxide,  which  presents  an  irides- 

1  Its  pyrophoric  properties  are  much  enhanced  by  the  presence  of  alumina  ;  a  mixture 
of  this  description  constitutes  the  pyrophoric  iron  of  Magnus. 


IRON   AND   OXYGEN.  339 

cent  appearance,  and  changes  in  color  as  it  increases  in  thickness ;  the  oxidation 
takes  place  rapidly  at  a  red  heat,  and  a  compound  of  (prot-)  oxide  and  sesquioxide 
of  iron  is  produced.  Iron  undergoes  a  rapid  combustion  when  heated  to  white- 
ness in  a  forge,  and  we  have  already  become  acquainted  with  its  combustion  in 
oxygen  gas  j  in  both  these  cases,  the  above-mentioned  proto- sesquioxide  is  pro- 
duced. The  combustion  of  iron  in  air  is  also  witnessed  when  a  piece  of  this 
metal  is  violently  struck  with  a  flint,  whereby  small  particles  of  metal  are  de- 
tached and  raised,  by  the  heat  evolved  in  the  stroke,  to  the  temperature  at  which 
they  burn  in  the  'air. 

Iron  is  rapidly  oxidized  when  exposed  to  moist  air  j  it  becomes  covered  with 
a  film  of  red-brown,  hydrated  sesquioxide  of  iron,  commonly  termed  rust.  Iron 
does  not  rust  under  water  containing  minute  quantities  of  the  alkalies '  or  their 
carbonates;  It  has  been  observed  that  the  rusting  of  iron  proceeds  mutih  more 
rapidly  after  the  first  spot  of  rust  is  formed',  since  this  forms  the  negative  pole  of 
a  voltaic  couple,  of  which  t,he  iron  is  the  positive  pole,  and  which  is  capable 'of 
decomposing  water,  eliminating  hydrogen,  which,'  in  its  nascent  state,  is^also  said 
to  combine  with  the  nitrogen  of  the  air,  forming  the  ammonia  which  is^ 'always 
contained  in  the  rust  of  iron,  and  may  be  elicited  by  heating  the  latter  with 
potassa.  Iron  is  more  rapidly  oxidized  in  air  containing  carbonic  acid  than  in 
pure  air. 

A  very  high  temperature  is  requisite  for  the  fusion  of  iron ;  its  fusing  point, 
in  fact,  ca>n  only  be  attained  in  a  good  wind-furnace,  but  it  becomes,  soft  long 
before  it  fuses,  and  is  then  capable  of  being  easily  welded.  If  iron  be  allowed 
to  cool  gradually  from  a  state  of  fusion,  it  deposits  cubical,  or  octohedral  crystals. 

Iron  combines  directly  with  most  of  the  non-metallic  elements.  We  have 
already  seen  that  this  metal  is  capable  of  decomposing  steam  at  a  red  heat. 

The  strongest  nitric  acid  acts  but  feebly  upon  iron,  but  when  it  is  aomewhat 
diluted,  the  metal  is  oxidized  and  dissolved  very  rapidly,  nitrate  of  sesquioxide 
of  iron  being  formed,  and  an  inferior  oxide  of  nitrogen  disengaged.  In-  nitric 
acid  of  a  certain  strength,  iron  dissolves  without  apparent  evolution  of  hydrogen, 
since  this  gas,  in  its  nascent  state,  is  capable  of  decomposing  the  nitric  acid, 
yielding  nitrate  of  ammonia. 

Iron  which  has  been  plunged  into  very  strong  nitric  acid,  is  found  to  be  un- 
affected by  the  dilute  acid,  and  the  same  is  observed  with  an  iron  wire,  one  end 
of  which  has  been  heated  to  redness.  In  both  these  cases,  the  iron  is  said  to 
have  assumed  the  passive  state;  and  if,  when  in  this  condition,  it  be  made  the 
positive  pole  of  a  galvanic  battery,  it  will  be  found  that  it  does  not  combine  with 
the  oxygen  which  is  liberated  at  its  surface.1  Hydrochloric  acid  acts  energetic- 
ally upon  iron,  chloride  of  this  metal  being  formed,  and  hydrogen  liberated. 
The  other  strong  hydrogen-acids  have  the  same  effect. 

When  iron  is  heated  with  concentrated  sulphuric  acid,  it  is  oxidized  at  the 
expense  of  the  latter,  sulphurous  acid  being  evolved,  and  sulphate  of  (prot-) 
oxide  of  iron  produced.2  Dilute  sulphuric  acid  dissolves  iron  with  disengage- 
ment of  hydrogen. 

IRON   AND   OXYGEN. 

(Prot-)  oxide  of  iron FeO 

Sesquioxide  of  iron Fea03 

Ferric  acid Fe03 

(Magnetic  oxide  of  iron •     .  Fe304) 

1  This  curious  phenomenon  has  been  attributed  in  a  plausible  manner  to  the  formation 
of  a  protecting  film  of  oxide  upon  the  surface  of  the  metal,  but  this  explanation  does  not 
account  for  all  the  properties  of  iron  in  its  passive  state. 

2  Or,  according  to  Levol,  sulphate  of  sesquioxide. 


340  SULPHATE    OF   IRON. 

The  last  of  these  is  inclosed  in  parentheses,  because  it  is  not  an  independent 
oxide. 

OXIDE,  OR  PROTOXIDE  OF  IRON. 
FeO.     Eq.  36. 

§  226.  This  oxide  has  .never  been  obtained  in  the  pure  state;  it  is  precipi- 
tated as  a  white  hydrate,  when  solution  of  potassa  is  added  to  solution  of  (proto-) 
sulphate  of  iron ;  the  precipitate,  however,  very  readily  absorbs  oxygen  from  the 
air,  being  converted,  first  into  the  green  hydrated  magnetic  oxide,  and  ultimately 
into  red-brown  hydrated  sesquioxide  of  iron.  If  the  two  solutions  be  mixed  in  a 
state  of  ebullition,  and  the  mixture  be  then  boiled,  a  black  precipitate  is  formed, 
which  appears  to  be  the  anhydrous  oxide  of  iron,  but  it  is  impossible  to  collect 
it  without  its  suffering  oxidation;  it  even  decomposes  water  at  the  boiling  point, 
eliminating  hydrogen. 

Hydrated  (prot-*)  oxide  of  iron  dissolves  in  ammonia,  but  the  solution  rapidly 
deposits  the  sesquioxide  when  exposed  to  air. 

This  oxide  is  a  very  powerful  base,  and  forms  well-defined  salts. 

NITRATE  OF  (PROT-)  OXIDE  OF  IRON,  PROTONITRATE  OF  IRON. 
FeO.N05. 

When  iron  is  dissolved  in  cold  dilute  nitric  acid,  and  the  solution  carefully 
concentrated,  crystals  of  a  double  nitrate  of  oxide  of  iron  and  oxide  of  ammonium 
are  deposited. 

The  nitrate  of  oxide  of  iron  is  best  prepared  by  decomposing  the  sulphate  with 
nitrate  of  baryta. 

It  is  of  a  green  color,  and  crystallizes  with  difficulty.  Its  aqueous  solution  is 
decomposed  by  ebullition,  depositing  a  basic  salt  of  the  sesquioxide;  the  solution 
must  therefore  be  concentrated  in  vacuo. 

SULPHATE  OF  (PROT-)OXIDE  OF  IRON,  PROTOSULPHATE  OF  IRON,  commonly 
called  SULPHATE  OF  IRON,  COPPERAS,  and  GREEN  VITRIOL. 

FeO.S03. 

§  227.  This  salt  is  found  when  iron,  or  sulphide  of  iron,  is  dissolved  in  dilute 
sulphuric  acid : — 

Fe-fHO.S03=FeO.S03+H. 

Preparation. — It  is  generally  prepared  from  the  mineral  known  as  iron- 
pyrites,  FeS3.  This  mineral  is  strongly  heated  in  a  retort,  in  order  to  separate 
part  of  the  sulphur  which  it  contains ;  the  residue  is  then  exposed  to  the  action 
of  air  and  moisture,  when  it  absorbs  oxygen,  and  is  converted  into  sulphate  of 
oxide  of  iron ;  the  mass  is  exhausted  with  water,  and  the  solution  evaporated  to 
crystallization.1 

It  will  be  remembered  that  a  considerable  quantity  of  this  salt  is  obtained  in 
the  manufacture  of  alum  (see  §  211). 

Properties. — Pure  sulphate  of  iron  has  a  slightly  bluish-green  color;  it  forms 
oblique  rhomboidal  prisms,  which  are  transparent,  and  have  the  composition 
FeO.S03.HO-f  6Aq.  When  exposed  to  air,  these  soon  become  covered  with 
an  ochreous  crust  of  a  basic  sulphate  of  sesquioxide  of  iron  (2Fea03.S03)  from 
absorption  of  oxygen :— 

10(FeO.S03H05=3(Fea03.3S03)+2Fe303.S03. 

The  crystals  lose  6  eqs.  water  of  crystallization  at  212°  F.  (100°  C.),  and  fall  to 

1  Any  copper  which  may  be  present  in  the  crude  lye  is  precipitated  by  means  of  me- 
tallic iron. 


SULPHATE   OF  IRON.  341 

a  grayish-white  powder  (Ferri  sulphas  exsiccatum),  which  dissolves  gradually 
when  treated  with  water;  at  a  higher  temperature,  the  last  equivalent  of  (con- 
stitutional) water  begins  to  go  off,  but  cannot  be  thoroughly  expelled  without 
partial  decomposition  of  the  salt.  After  strongly  heating,  the  sulphate  is  almost 
insoluble  in  water,  but  dissolves  in  nitric  acid. 

At  a  pretty  strong  red  heat,  sulphate  of  iron  is  completely  decomposed,  sesqui- 
oxide  of  iron  (colcothar}  being  left,  and  sulphurous  acid,  together  with  anhydrous 
sulphuric  acid,  passing  off: — 

2(FeO.S03)=Fea03+S02+S03; 

since  a  little  water  is  always  present,  the  sulphuric  acid  is  obtained  in  the  receiver 
as  a  hydrate  (see  Nordhausen  Sulphuric  Acid,  p.  159). 

The  crystals  of  sulphate  of  iron  dissolve  in  2  parts  of  cold  and  in  f-part  of 
boiling  water;  the  solution  has  a  pale  green  color;  it  is  perfectly  neutral,  and  of 
a  nauseous  metallic  taste.  When  exposed  to  the  air,  solution  of  sulphate  of  iron 
deposits  a  dirty-brown  basic  sulphate  of  sesquioxide  (2Fea03.S03),  the  neutral 
sulphate  of  sesquioxide  (Fe203  3S03)  remaining  in  solution  (see  the  above  equa- 
tion). If  a  solution  of  sulphate  of  iron  be  mixed  with  a  slight  excess  of  sulphuric 
acid,  and  crystallized  at  a  temperature  of  176°  F.  (80°  C.)>  the  formula  of  the 
crystals  is  Fe0.803.HO  +  3Aq.  If  a  large  excess  of  sulphuric  acid  be  present, 
the  crystals  are  FeO.S03.HO-r-2Aq.  On  adding  alcohol  to  solution  of  sulphate 
of  iron,  a  white  precipitate  is  obtained,  which  is  FeO.S03,HO ;  the  same  salt  is 
obtained  with  concentrated  sulphuric  acid.  The  sulphate  of  iron  is  easily  con- 
verted into  sulphate  of  sesquioxide  by  oxidizing  agents  (e.g.  chlorine,  nitric  acid). 
Sulphate  of  iron  in  solution  (like  all  other  protosalts  of  iron)  is  capable  of  absorb- 
ing the  binoxide  of  nitrogen,  forming  a  brown  solution,  which  contains  just  so 
much  of  the  binoxide  of  nitrogen  that  its  oxygen  would  suffice  to  convert  into 
sesquioxide  all  the  (prot-)  oxide  of  iron  present. 

Three  varieties  of  sulphate  of  iron  are  met  with  in  commerce;  viz.  1.  The 
pale  green  crystals  which  have  been  deposited  from  neutral  solutions.  2.  The 
bluish-green  crystals  obtained  when  the  solution  is  acid  ;  and  3.  The  bright  green 
crystals  formed  in  liquids  which  have  been  long  exposed  to  the  air;  the  differ- 
ence of  color  appears  to  be  due  to  the  sulphate  of  sesquioxide  of  iron  which  is 
present. 

The  sulphate  of  iron  prepared  on  the  large  scale  is  generally  contaminated 
with  sulphates  of  copper,  zinc,  manganese,  alumina,  magnesia,  and  lime;  the 
manufacturer  generally  separates  the  copper  by  digesting  the  iron-liquor  with 
scraps  of  metallic  iron. 

i^ses. — This  salt  is  very  largely  employed  by  dyers  and  calico-printers,  for  it 
is  the  basis  of  several  mordants  and  colors,  and  serves,  moreover,  for  the  prepa- 
ration of  others ;  thus,  it  is  employed  for  the  preparation  of  Prussian  blue,  and 
of  white  or  reduced  indigo,  where  the  deoxidizing  properties  of  the  salt  are  turned 
to  advantage. 

The  use  of  sulphate  of  iron  for  the  preparation  of  fuming  sulphuric  acid  and 
of  colcothar,  has  already  been  alluded  to.  A  considerable  quantity  is  consumed 
in  the  preparation  of  ink.  It  is  also  used  in  the  laboratory  as  a  reducing  agent. 

Sulphate  of  iron  is  also  an  important  medicinal  agent.  For  this  use  it  is  highly 
important  that  it  should  contain  no  sulphate  of  copper,  which  may  be  shown  by 
adding  a  few  drops  of  dilute  sulphuric  acid,  and  immersing  a  bright  steel  knife- 
blade  in  it,  which  would  become  covered  with  a  film  of  metallic  copper  after  the 
lapse  of  a  few  minutes. 

The  sulphate  of  (prot-)  oxide  of  iron  is  capable  of  forming  double-salts,  in  which 
the  water  of  constitution  in  the  sulphate  is  replaced  by  sulphate  of  potassa,  soda, 
ammonia,  or  oxide  of  manganese ;  these  salts  crystallize  with  4  equivalents  of 
water;  the  potassa-salt;  however,  contains  6  equivalents,  unless  deposited  from 


342  SALTS   OF  IRON. 

acid  solutions.  It  is  isomorplious  with  the  corresponding  compound  of  sulphate 
of  potassa  and  sulphate  of  magnesia. 

CARBONATE  or  (PROT-)  OXIDE  OF  IRON,  PROTOCARBONATE  OF  IRON. 

FeO.C02. 

This  carbonate  is  found  in  abundance  in  England,  where  it  forms  the  well- 
known  spathic  ore,  the  principal  ore  of  iron.  It  often  forms  rhombohedral  crys- 
tals, which  are  very  slowly  acted  upon  by  acids.  Crystals  resembling  these  may 
be  prepared  by  decomposition  of  sulphate  of  iron  with  carbonate  of  soda,  at  a 
high  temperature,  in  a  sealed  tube. 

Carbonate  of  protoxide  of  iron  is  obtained  as  a  white  hydrate,  when  a  solution 
of  sulphate  of  iron  is  mixed  with  an  alkaline  carbonate  j  it  becomes,  however, 
rapidly  green,  being  converted  into  hydrate  of  magnetic  oxide  of  iron  (Fe3O4) 
with  evolution  of  carbonic  acid  : — 

3(FeO.C03)-fO=Fe304-f3COa; 
it  is  in  this  state  that  the  iron  exists  in  the  mistura  ferri  composifa. 

When  (proto-)  carbonate  of  iron  is  heated  in  a  retort,  carbonic  oxide  and  car- 
bonic acid  are  disengaged,  and  magnetic  oxide  of  iron  (Fe304)  left: — 
* '     3(FeO.C03)==Fe304  +  CO+2C03. 

(Proto-)  carbonate  ,of  iron  is  dissolved  by  water  holding  carbonic  acid  in  solu- 
tion, which  accounts  for  the  presence  of  this  salt  in  mineral  waters.  When  such 
a  solution  is  exposed  to  the  air,  it  absorbs  oxygen,  and  deposits  sesquioxide  of 
iron. 

SESQUIOXIDE,  PEROXIDE,  OR  RED  OXIDE  OF  IRON. 
Fe3O3.     Eq.  80. 

§  228.  This  oxide  is  found  very  abundantly  in  nature,  generally  crystallized ; 
we  shall  have  to  refer  to  it  again,  when  describing  the  ores  of  iron. 

It  has  been  already  stated  that  sesquioxide  of  iron  may  be  obtained  by  calcin- 
ing the  (proto-)  sulphate ;  the  residue,  which  has  a  fine  red  color,  is  termed  col- 
cothar,  and  is  employed  in  painting,  and  for  polishing  plate  glass. 

The  residue  left  on  igniting  the  nitrate  of  sesquioxide  of  iron  consists  of  a 
nearly  black  variety  of  this  oxide  „• 

Hydrated  Sesquioxide  of  Iron  (Fea03.3HO)  is  obtained  as  a  red  brown  pre- 
cipitate, when  an  alkali  is  added  to  a  solution  of  a  salt  of  sesquioxide  of  iron ; 
it  is  usually  prepared  by  dissolving  sulphate  of  iron  in  water,  adding  a  quantity 
of  dilute  sulphuric  acid,  and  boiling  with  successive  additions  of  nitric  acid,  till 
no  more  red  fumes  are  evolved ;  in  this  way  the  sulphate  of  (prot-)  oxide  is  con- 
verted into  sulphate  of  sesquioxide  of  iron  : — 

6(FeO.S03)-t-8(HO.S03)  +  HO.N05=3(Fe203-3S03)+4HO-fN03, 
and  if  ammonia  in  excess  be  now  added  to  the  solution,  a  precipitate  of  hydrated 
sesquioxide  of  iron  is  obtained  : — 

Fea03.3S03  +  3NH3+6HO=Fea03.3HO-f3NH4O.S03; 

this  precipitate  should  be  collected  upon  a  calico  filter,  and  washed  with  hot  water 
till  the  washings  are  no  longer  precipitated  by  chloride  of  barium.  It  should  be 
dried  at  a  temperature  not  exceeding  180°  F.  (82°  C.) 

The  hydrated  sesquioxide  of  iron  is  easily  rendered  anhydrous.  Other  hydrates 
of  sesquioxide  of  iron,  of  the  formulae  Fea03.HO  (brown  iron  ore,  needle-iron 
ore),  2Fe3033HO  (fibrous  brown  iron  ore,  or  brown  haematite,  and  compact 
brown  iron  ore),  and  Fe303.2HO  (another  variety  of  brown  iron  ore). 

Sesquioxide  of  iron,  when  heated  nearly  to  whiteness,  evolves  oxygen,  and  is 
converted  into  the  magnetic  oxide,  Fe304,  and  hence  the  reason  that  this  latter, 


SESQUIOXIDE   OP  IRON.  343 

and  not  the  sesquioxide,  is  formed  when  iron  is  burnt  in  oxygen.  If  sesquioxide 
of  iron  be  heated  to  redness  in  a  stream  of  hydrogen  or  carbonic  oxide,  it  is  first 
reduced  to  the  magnetic  oxide,  and  afterwards  to  the  metallic  state. 

Sesquioxide  of  iron,  when  calcined,  exhibits  a  sudden  incandescence,  and  is 
converted  into  a  modification  which  is  almost  insoluble  in  nitric  and  sulphuric 
acids,  and  dissolves  but  slowly  in  hydrochloric  acid. 

The  sesquioxide  is  not  so  powerful  a  base  as  the  protoxide  of  iron,  and  appears 
occasionally  to  be  capable  of  playing  the  part  of  an  acid,  since  it  retains  potassa 
and  soda  with  great  obstinacy,  when  precipitated  from  its  solutions  by  these 
alkalies,  and  it  is  said  that  true  compounds  of  these  latter  with  the  sesquioxide 
may  be  obtained.  ^ 

Salts  of  sesquioxide  of  iron,  like  those  of  alumina,  have  generally,  an  acid 
reaction. 

Uses. — Sesquioxide  of  iron  is  sometimes  employed  for  coloring  glass. 

It  is  used  medicinally  in  various  forms. 

The  ferri  sesquioxidum  of  the  London  Pharmacopoeia  (formerly  called  ferri 
sesguicarbonas)  is  a  variable  mixture  of  sesquioxide  with  protocarbonate  and 
protoxide  of  iron,  formed  by  the  oxidizing  action  of  air  upon  the  carbonate  of 
iron  precipitated  by  mixing  carbonate  of  soda  and  sulphate  of  iron  in  solution. 

Ferri  oxidum  rubrum  of  Edinburgh  is  a  similar  compound,  whilst  that  of 
Dublin  is  merely  colcothar. 

Rubigo  ferri  is  simply  rust. 

The  hydrated  sesquioxide  of  iron  is  employed  as  an  antidote  in  cases  of  poison- 
ing by  arsenic. 

NITRATE  OP  SESQUIOXIDE  OF  IRON,  Fea03.3N05. 

This  salt  may  be  obtained  by  dissolving  iron  in  nitric  acid,  with  the  aid  of  heat, 
or  by  dissolving  the  hydrated  sesquioxide  in  that  acid. 

It  crystallizes  in  yellowish  four-sided  rectangular  prisms,  which  are  easily  de- 
composed by  heat,  and  are  very  soluble  in  water. 

The  basic  nitrates  of  sesquioxide  of  iron  have  been  little  studied. 

SULPHATE  OF  SESQUIOXIDE  OF  IRON,*  Fefl03.3S03. 

The  sulphate  of  sesquioxide  of  iron  is  produced,  according  to  Levol,  when 
concentrated  sulphuric  acid  acts  upon  iron,  with  the  aid  of  heat : — 
Fe3-f6(HO.S03)=FeaO3.3S03+3S03-f6HO. 

It  may  be  prepared  by  heating  either  metallic  iron  or  sulphate  of  iron  with  con- 
centrated sulphuric  acid,  and  expelling  the  excess  of  acid  by  heat.  The  dirty- 
white  residue  thus  obtained  can  only  be  dissolved  by  protracted  digestion  with 
water. 

It  is  also  prepared  (ag  already  indicated)  by  oxidizing  the  sulphate  of  iron  with 
nitric  acid  (see  hydrated  sesquioxide  of  iron) ;  the  solution  is  mixed  with  a  little 
sulphuric  acid,  and  evaporated  to  dryness. 

The  formula  of  the  sulphate  of  sesquioxide  of  iron  thus  obtained,  if  not  too 
strongly  heated  is  Fefl03.3S03-f  9Aq.  The  salt  is  naturally  very  soluble  in  water, 
but  after  drying,  it  dissolves  with  difficulty.  Its  solution,  if  pretty  dilute,  deposits 
basic  sulphate  when  boiled. 

Several  basic  sulpliates  are  known. 

The  most  important,  which  has  been  above  mentioned  as  resulting  from  the 
action  of  the  air  on  the  (proto-)  sulphate,  has  the  composition  2Fe303.S03,  and 
is  employed  in  painting  on  glass  and  porcelain. 

Ifc  occurs  in  nature,  with  6  equivalents  of  water,  as  vitriol-ochre. 

1  This  salt  has  been  found  native,  as  coquimbite. 


344  MAGNETIC   OXIDE   OF  IRON. 

The  sulphate  of  sesquioxide  of  iron,  like  those  of  alumina  and  sesquioxide  of 
chromium,  combines  with  sulphates  of  the  alkalies  to  form  alums. 

Potassa  Iron- Alum  may  be  prepared  directly  from  its  constituent  salts;  it  may 
be  crystallized,  though  with  some  difficulty,  in  nearly  colorless  octohedra,  of  the 
formula  KO.S03,Fe203.3S03-f-24Aq. 

PHOSPHATE  OF  SESQUIOXIDE  OF  IRON  is  formed  as  a  white  precipitate,  when 
solution  of  common  phosphate  of  soda  is  added  to  sesquichloride  of  iron ;  its 
formula  is  said  to  be  Fe303,P05+4Aq. 

This  salt  occurs  in  certain  iron  ores,  and  much  injures  the  quality  of  the  metal 
obtained  from  them,  which  is  found  to  contain  phosphorus,  rendering  it  brittle. 

The  phosphate  of  sesquioxide  of  iron  has  been  employed  medicinally. 

No  pure  carbonate,  of  sesquioxide  of  iron  has  yet  been  obtained;  when  a  salt 
of  the  sesquioxide  is  decomposed  by  an  alkaline  carbonate,  carbonic  acid  is  dis- 
engaged, and  hydrated  sesquioxide  of  iron  precipitated.  The  hydrated  sesqui- 
oxide dissolves  in  the  alkaline  bicarbonates,  yielding  red  solutions,  which  appear 
to  contain  double  carbonates  of  the  alkalies  and  of  sesquioxide  of  iron  ;  these 
solutions  are  not  decomposed  by  boiling. 

Several  silicates  of  sesquioxide  of  iron  are  found  in  the  mineral  kingdom. 
Anthosiderite  has  the  formula  Fe263.3Si03-fAq;  hisinyerite,  FeO.Si03,  FeaOr 
Si03+6Aq. 

MAGNETIC  OXIDE,  OR  BLACK  OXIDE  OF  IRON. 

(Proto-sesquioxide  of  Iron,  Ferroso-ferric  Oxide.') 

Fe304=FeO.Fe9O3. 

§  229.  This  oxide  occurs  in  nature  in  the  form  of  the  loadstone,  and  consti- 
tutes a  very  important  ore  of  iron.  It  is  often  met  with  in  fine  octohedral  crys- 
tals. It  may  be  obtained  in  a  pure  state  by  exposing  fine  iron  wire  to  the  action 
of  steam  at  a  red  heat;  it  then  forms  minute  octohedra,  which  are  highly 
magnetic. 

The  hydrated  magnetic  oxide  may  be  prepared  by  dividing  an  aqueous  solu- 
tion of  sulphate  of  iron  into  three  equal  parts,  peroxidizing  two  of  these  with 
nitric  acid,  adding  the  other,  and  pouring  the  mixture,  with  frequent  stirring, 
into  an  excess  of  solution  of  ammonia;  if  the  operation  were  reversed,  and  the 
ammonia  added  to  the  mixture,  the  sesquioxide  would  be  first  precipitated,  then 
the  (prot-)oxide,  so  that  a  mixture,  and  not  a  combination  of  the  two,  would  be 
obtained. 

The  hydrated  magnetic  oxide  has  a  dark-green  color,  and  is  attracted  by  the 
magnet. 

It  appears  that  the  magnetic  oxide  of  iron  is  a  compound  of  the  (prot-)  oxide 
with  the  sesquioxide,  for  if  it  be  dissolved  in  an  acid,  the  solution  gives  the 
reactions  of  both  these  oxides,  and  when  an  alkali  is  gradually  added,  the 
sesquioxide  is  first  precipitated. 

The  black  oxide  of  iron,  known  as  smithy  scales,  from  their  being  detached  in 
the  forging  of  iron,  varies  in  composition  according  to  the  circumstances  under 
which  it  is  formed,  but  always  contains  both  sesquioxide  and  (prot-)  oxide  of 
iron. 

FERRIC  ACID,  FeO3. 

This  acid  has  not  been  obtained  in  the  separate  state ;  several  of  its  salts  have, 
however,  been  examined. 

FERRATE  OF  POTASSA  may  be  obtained  by  oxidizing  iron-filings  with  nitre  at 
a  very  high  temperature. 

A  better  method  of  preparing  it  consists  in  passing  a  current  of  chlorine 


CHLORIDES   OP   IRON.  345 

through  a  very  concentrated  solution  of  potassa,  in  which  hydrated  sesquioxide 
of  iron  is  suspended : — 

5KO-fCl3-fFe203=3KCl+2(KO.Fe03). 

The  operation  is  terminated  when  the  black  precipitate  which  is  formed  dis- 
solves perfectly  in  water.  This  black  precipitate  is  the  ferrate  of  potassa,  which 
may  be  freed  from  alkali  by  draining  on  a  porous  tile. 

The  salt  is  insoluble  in  strong  alkaline  solutions,  but  very  soluble  in  water, 
giving  a  fine  red  liquid ;  it  is  a  very  unstable  salt,  for  even  when  its  solution 
is  evaporated  in  vacua,  it  is  decomposed  into  potassa,  sesquioxide  of  iron,  and 
oxygen,  so  that  it  has  never  been  crystallized.  The  above  decomposition  is  very 
easily  effected  by  heat,  by  organic  matters,  and  by  (even  the  weakest)  acids. 
Even  ammonia  reduces  the  ferrate  of  potassa : — 

2(KO.FeO3)  +  NH3=N+Fe203-f  2KO  +  3HO. 

Ferrate  of  Soda  resembles  the  potassa-salt.  The  ferrates  of  baryta,  strontia, 
lime,  &c.,  may  be  obtained  by  double  decomposition;  they  have  a  fine  red  color, 
and  are  insoluble. 

§  230.  NITRIDE  or  IRON. — The  compound  of  iron  with  nitrogen  is  little 
known  ;  it  is  said  to  be  formed  when  iron  is  heated  to  redness  for  some  time  in 
a  current  of  ammonia,  the  metal  becoming  white  and  brittle.  A  similar  (per- 
haps identical)  product  is  obtained  by  passing  ammonia  over  (proto-)  chloride  of 
iron,  when  a  silvery-white,  lustrous,  spongy  mass  remains. 

(PROTO-)  CHLORIDE  OP  IRON,  Fed. 

The  anhydrous  (proto-)  chloride  is  prepared  by  passing  hydrochloric  acid  gas 
over  iron  at  a  red  heat,  when  it  is  obtained  as  a  brown,  fused  mass,  which  crys- 
tallizes on  cooling,  and  sublimes,  at  a  higher  temperature,  in  yellowish  crystals. 

This  compound  is  sometimes  employed  as  a  source  of  pure  iron ;  for  when 
heated  in  a  current  of  hydrogen,  it  yields  this  metal  in  crystals. 

By  dissolving  iron  in  a  slight  excess  of  hydrochloric  acid,  and  evaporating  the 
solution,  pale  green,  oblique,  rhomboidal  prisms  are  obtained,  the  formula  of 
which  is,  FeCl+4Aq. 

(Proto-)  chloride  of  iron  is  very  soluble  in  water  and  alcohol;  it  is  capable  of 
forming  double-salts  with  the  chlorides  of  potassium  and  ammonium. 

SESQUICHLORIDE,  OR  PERCHLORIDE  OF  IRON,  Fe2Cl3. 

To  obtain  this  salt  in  the  anhydrous  state,  coils  of  iron  wire  may  be  introduced 
into  a  tube  of  hard  glass,  and  moderately  heated  in  a  pretty  abundant  supply  of 
chlorine.  It  then  sublimes  in  brown,  crystalline  scales,  which  are  deliquescent, 
and  very  soluble  in  water,  alcohol,  and  ether,  yielding  red-brown  solutions. 

Hydrated  sesquichloride  of  iron  is  prepared  by  dissolving  iron  in  a  mixture  of 
hydrochloric  and  nitric  acids,  or  by  treating  the  sesquioxide  with  hydrochloric 
acid.  On  evaporating  the  solution,  yellow  scaly  crystals  may  be  obtained,  of  the 
formula  Fe2Cl3  + 5Aq.  When  these  are  heated,  they  evolve  hydrochloric  acid, 
and  a  compound  of  sesquichloride  with  sesquioxide  of  iron  remains.  A  similar 
compound  is  deposited  as  a  brown  precipitate,  when  a  solution  of  sesquichloride 
of  iron  suffers  spontaneous  decomposition,  or  when  it  is  boiled  for  some  time. 

The  alcoholic  and  ethereal  solutions  of  this  salt  are  decolorized  by  exposure 
to  light,  (proto-)  chloride  being  formed,  together  with  products  of  oxidation  of 
alcohol  or  ether. 

Sesquichloride  of  iron  is  decomposed  by  vapor  of  water  at  a  red-heat,  hydro- 
chloric acid  and  crystallized  sesquioxide  of  iron  being  produced  : — 
FeaCl34-3HO=HCl+Fea03. 


346  IRON   AND   SULPHUR. 

This  salt  is  used  medicinally,  in  the  form  of  tincture  (alcoholic  solution).  It 
is  also  a  useful  reagent. 

If  a  solution  of  sesquichloride  of  iron  be  mixed  with  chloride  of  potassium, 
or  chloride  of  ammonium,  and  evaporated,  fine  red  crystals  are  obtained,  of  the 
formulae,  respectively  : — 

2KCl,Fe3 
2NH4Cl,Fe3 

The  latter  salt  is  employed  in  medicine,  under  the  name  of  ammonio-cliloride 
of  iron. 

The  Bromides  of  Iron  correspond  in  composition  to  the  chlorides,  and  may  be 
prepared  in  a  similar  manner. 

IODIDE,  OR  PROTIODIDE  OF  IRON,  Fel. 

Preparation.  In  order  to  prepare  this  salt,  a  quantity  of  iodine  is  mixed 
•with  water,  one-third  of  its  weight  of  iron  filings  added,  and  the  whole  digested 
for  some  time,  in  a  flask,  at  a  gentle  heat ;  the  clear  liquid  is  poured  off,  the 
residue  in  the  flask  washed  with  hot  water,  the  washings  being  added  to  the 
solution,  and  the  whole  evaporated  in  contact  with  iron,  at  a  heat,  not  exceeding 
212°  F. 

Properties. — Iodide  of  iron  is  very  soluble  in  water,  yielding  a  pale  green 
solution,  from  which,  by  careful  evaporation,  greenish  crystals  may  be  obtained, 
of  the  formula  FeI-f-4Aq.  When  the  aqueous  solution  is  exposed  to  air,  it 
absorbs  oxygen,  part  of  the  iron  being  converted  into  sesquioxide,  and  yielding 
its  iodine  to  another  portion  of  the  iodide,  producing  a  sesqui-iodide,  which  is 
precipitated  in  combination  with  the  sesquioxide  as  a  brown  powder : — 

6FeI-f03=2Fe3T3+Fe303. 

In  order  to  avoid  this,  a  long  turning  of  iron,  or  a  coil  of  clean  iron  wire  should 
be  kept  in  the  solution. 

When  gently  heated,  iodide  of  iron  fuses,  and  on  cooling,  solidifies  to  a  gray 
crystalline  mass,  which  has  a  metallic  lustre  and  is  deliquescent.  If  it  be  strongly 
heated  with  free  access  of  air,  the  iodine  is  expelled,  and  the  iron  converted  into 
sesquioxide. 

The  iodide  of  iron  is  largely  used  in  medicine,  and  is  sometimes  employed 
for  the  preparation  of  iodide  of  potassium. 

The  Sezqui-iodide  of  Iron  (FeJ3)  may  be  prepared  by  dissolving  the  hydrated 
sesquioxide  in  hydriodic  acid,  or  by  treating  iron  with  excess  of  iodine  ;  it  has  a 
red  color,  is  volatile,  deliquescent,  and  soluble  in  water  and  alcohol. 


IRON  AND  SULPHUR. 

(Proto-)  sulphide FeS 

Sesquisulphide Fe3S3 

Bisulphide FeS3 

Tersulphide FeS3 

§  23 1.  Two  sulsulphides  of  iron  also  exist;  Fe8S,  prepared  by  reducing  the  basic 
persulphate  of  iron  by  hydrogen,  and  Fe3S,  which  is  formed  when  hydrogen 
acts  upon  the  anhydrous  (proto-)  sulphate.  Both  these  dissolve  in  acids,  evolving 
hydrogen  and  sulphuretted  hydrogen,  and  producing  proto-salts  of  iron. 


SULPHIDES  OF  IRON.  347 

SULPHIDE  OF  IRON.     PROTOSULPHIDE  OF  IRON.     SULPHURET  OF  IRON. 

FeS. 

This  compound  is  occasionally  met  with  in  nature. 

Preparation. — It  may  be  prepared  by  the  direct  combination  of  iron  and 
sulphur  j  this  combination  may  even  take  place  at  the  ordinary  temperature ;  a 
mixture  of  sulphur  and  iron  filings,  if  kept  for  some  time  in  a  moist  state, 
become  converted  into  sulphide  of  iron ;  such  a  mixture  is  sometimes  called 
Lemery's  volcano;  the  combination  takes  place  with  considerable  evolution  of 
heat,  and  if  the  mixture  be  buried  in  sand  it  forms  a  sort  of  mimic  volcano. 

The  best  method  of  preparing  sulphide  of  iron,  however,  consists  in  project- 
ing, by  small  portions  at  a  time,  into  a  redhot  crucible,  an  intimate  mixture  of 
30  parts  of  iron-filings  with  21  parts  of  flowers  of  sulphur,  always  waiting  till 
one  portion  has  combined  before  adding  another. 

A  hydrated  (proto-)  sulphide  of  iron  is  obtained  when  a  solution  of  a  pro- 
tosalt  of  iron  is  mixed  with  an  alkaline  sulphide. 

Properties. — (Proto-)  Sulphide  of  iron  is  a  dark  gray  substance,  having  a 
metallic  appearance  '}  it  is  easily  oxidized  when  exposed  to  moist  air,  being  con- 
verted into  sulphate  of  the  (prot-)  oxide ;  when  large  masses  of  sulphide  are 
oxidized  in  this  way,  sufficient  heat  is  often  evolved  to  set  fire  to  the  rest  of  the 
mass,  and  hence  the  dangerous  fires  in  coal-mines  where  large  quantities  of  this 
mineral  exist. 

When  heated  with  free  access  of  air,  sulphurous  acid  is  evolved,  and  the  iron 
converted  into  magnetic  oxide. 

Sulphide  of  iron  is  perfectly  insoluble  in  water,  but  dissolves  in  most  acids, 
with  evolution  of  sulphuretted  hydrogen,  and  production  of  a  proto-saltof  iron : — 

FeS-f-HO.S03=FeO.S03-fHS. 

The  hydrated  sulphide  of  iron  forms  a  black  precipitate,  which,  when  exposed 
to  the  air,  is  very  rapidly  converted  into  sulphate.  It  is  somewhat  soluble  in 
alkaline  sulphides,  but  is  precipitated  from  the  solutions  by  boiling  ;  the  hydrate 
dissolves  very  easily  in  most  acids. 

Uses. — Sulphide  of  iron  is  very  largely  used  in  the  laboratory,  for  the  evo- 
lution of  sulphuretted  hydrogen.  The  hydrated  sulphide  has  been  recommended 
as  an  antidote  to  corrosive  sublimate  and  the  salts  of  lead  and  copper ;  it  is 
prepared  for  this  purpose  by  precipitating  solution  of  sulphate  of  iron  with  sul- 
phide of  ammonium,  collecting  on  a  cloth  filter,  and  washing  rapidly  with  hot 
water  till  the  washings  are  no  longer  precipitated  black  by  acetate  of  lead ;  the 
moist  sulphide  is  then  preserved  in  well-stoppered  bottles. 

SESQUISULPHIDE  OF  IRON,  FeaS3. 

This  sulphide  is  found  in  nature  associated  with  the  sulphide  of  copper,  in 
copper-pyrites.  It  may  be  prepared  by  decomposing  sesquioxide  of  iron  by  sul- 
phuretted hydrogen  at  212°  F.  (100°  C.)  It  forms  a  grayish  mass,  which  is 
decomposed  when  heated  in  close  vessels,  sulphur  being  evolved,  and  magnetic 
pyrites  (Fe7S8)  left. 

The  sesquisulphide  of  iron  is  obtained  as  a  black  precipitate,  when  a  solution 
of  sesquioxide  of  iron  is  added  to  an  alkaline  sulphide ;  if  the  experiment  be  re- 
versed, a  mixture  of  (proto-)  sulphide  of  iron  and  sulphur  is  precipitated. 

BISULPHIDE  OF  IRON.     IRON  PYRITES.     MARTIAL  PYRITES. 

FeS3. 

The  bisulphide  of  iron  is  found  abundantly  in  nature  in  a  crystallized  state, 
often  in  well-defined  cubes  and  dodecahedra.  Its  specific  gravity  is  4.98.  It 


348  SULPHIDES   OP   IRON. 

has  a  fine  brass-yellow  color,  and  metallic  lustre.  It  is  generally  unalterable  in 
air  at  the  ordinary  temperature,  but  when  roasted  in  air  it  disengages  sulphurous 
acid,  and  is  converted  into  sesquioxide  of  iron  : — 

2FeS3-f011=Fe303+4S03. 

When  heated  in  close  vessels,  it  gives  up  a  part  of  its  sulphur,  and  leaves 
magnetic  pyrites. 

Some  varieties  of  iron  pyrites  are  oxidized  by  exposure  to  moist  air,  being  con- 
verted into  sulphate  of  iron  and  sulphuric  acid;  this  property  is  generally  attri- 
buted to  the  presence  of  an  inferior  sulphide. 

Bisulphide  of  iron  is  not  affected  by  water  or  by  hydrochloric  acid.  Nitric 
acid  converts  it  into  sulphate  of  sesquioxide  of  iron,  with  separation  of  sulphur, 
unless  the  acid  be  very  concentrated.  Boiling  concentrated  sulphuric  acid  also 
dissolves  it,  sulphurous  acid  being  disengaged. 

The  bisulphide  may  be  obtained  artificially  by  heating  the  (proto-)  sulphide 
with  half  its  weight  of  sulphur,  when  it  is  left  as  a  yellow  powder. 

Yellow  octohedral  crystals,  resembling  iron  pyrites,  may  be  obtained  by  heating 
a  mixture  of  sesquioxide  of  iron,  sulphur,  and  sal-ammoniac,  in  a  sand-bath,  to 
the  temperature  at  which  the  latter  is  volatilized.  It  is  also  formed  when  the 
sesquioxide  is  acted  on  by  sulphuretted  hydrogen  at  a  temperature  exceeding 
212°  F. 

Iron  pyrites  is  employed  as  a  source  of  sulphur ;  it  is  also,  as  before  mentioned, 
turned  to  account  in  the  preparation  of  alum  and  of  various  compounds  of  iron 
(green  vitriol,  &c.) 

MAGNETIC  PYRITES,  Fe7S8=FeS3+6FeS=Fe3S3,5FeS. 

This  variety  of  pyrites,  named  from  its  magnetic  properties,  is  found  in  nature 
in  six-sided  prisms  of  a  bronze  color.  It  is  much  more  easily  oxidized  than  the 
bisulphide,  and  evolves  sulphuretted  hydrogen  when  treated  with  sulphuric  acid. 
It  is  always  formed  when  either  of  the  oxides  of  iron  is  strongly  heated  with 
an  excess  of  sulphur,  or  when  iron  at  a  white  heat  is  brought  in  contact  with 
sulphur. 

Another  variety  of  magnetic  pyrites,  corresponding  in  composition  to  the  mag- 
netic oxide,  is  said  to  exist,  its  formula  being  Fe3S4. 

The  Tersulphide  of  Iron^  FeS3,  is  not  known  in  the  separate  state,  but  is 
said  to  be  obtained  in  combination  with  sulphide  of  potassium  when  sulphuretted 
hydrogen  is  passed  into  a  solution  of  ferrate  of  potassa  in  potassa ;  the  tersul- 
phide  is  decomposed,  with  separation  of  sulphur,  when  an  attempt  is  made  to 
isolate  it. 

SUBPHOSPHIDE  OF  IRON,  FeJ?. 

This  compound  may  be  obtained  by  reducing  the  phosphate  of  (prot-)  oxide 
of  iron  with  charcoal  at  a  high  temperature ;  it  is  a  gray,  very  hard,  fusible 
substance.  The  presence  of  a  very  small  quantity  of  this  substance  in  a  speci- 
men of  iron  is  capable  of  rendering  it  brittle,  and  hence  unfit  for  the  purposes 
of  bar- iron. 

IRON  WITH  CARBON. 

§  232.  Only  one  carbide  of  iron  of  definite  composition  is  known  ;  this  is  ob- 
tained when  ferrocyanide  of  potassium  is  calcined  in  close  vessels,  and  the  cyanide 
of  potassium  washed  out  of  the  residue  with  water ;  the  black  compound  thus 
obtained  has  the  composition,  FeC3 ;  when  heated  in  contact  with  air,  it  is  con- 
verted into  sesquioxide  of  iron  and  carbonic  acid. 

When  iron  is  heated  in  contact  with  carbon,  it  never  takes  up  more  than  six 
per  cent.,  which  would  cause  the  compound  to  approach  to  the  formula  Fe4C. 


METALLURGY   OF   IRON.  349 

However,  much  smaller  quantities  of  carbon  are  capable  of  giving  rise  to  a 
notable  alteration  in  the  properties  of  the  metal,  a  circumstance  which  will  be 
further  considered  when  we  treat  of  the  metallurgy  of  iron. 

When  iron  containing  carbon  is  dissolved  in  hydrochloric  acid,  a  peculiar  com- 
pound of  carbon  and  hydrogen  is  evolved,  which  communicates  a  nauseous  odor 
to  the  hydrogen  thus  produced. 

A  boride  of  iron  has  been  obtained  by  reducing  the  borate  of  iron  by  hydrogen. 

IRON  WITH  SILICON. — A  compound  of  these  elements  may  be  obtained  by 
strongly  heating  a  mixture  of  iron  filings,  silicic  acid,  and  carbon;  the  mass  thus 
obtained  has  a  metallic  appearance,  is  malleable,  and  contains  9  or  10  per  cent, 
of  silicon.  Most  varieties  of  the  iron  of  commerce  contain  1  or  2  per  cent,  of 
silicon.  When  treated  with  acids,  the  silicide  of  iron  is  decomposed,  leaving  a 
residue  of  silica. 


METALLURGY   OF   IRON. 

§  233.  The  following  are  the  chief  forms  in  which  this  metal  is  found  in 
nature. 

Meteoric  Iron,  as  its  name  implies,  occurs  in  the  metallic  masses  which  occa- 
sionally fall  upon  the  earth,  and  are  known  as  aeroliths,  or  meteoric  stones  ;  in 
these,  it  is  associated,  in  the  metallic  state,  generally  with  cobalt,  nickel,  manga- 
nese, and  some  other  metals,  and  with  certain  nonmetallic  substances,  as  sulphur, 
carbon,  phosphorus,  and  silicon. 

Sesquioxide  of  iron,  in  the  anhydrous  state,  is  found  in  several  minerals. 

Oliyist  or  specular  iron  (iron-glance),  Fe303,  occurs  in  rhombohedral  crystals, 
which  possess  a  certain  metallic  lustre,  and  spec.  grav.  5.22.  It  usually  con- 
tains a  small  quantity  of  the  magnetic  oxide.  This  mineral  occurs  chiefly  in 
Elba. 

Micaceous  iron  consists  also  of  sesquioxide;  it  is  found  in  thin,  hexagonal 
tables,  with  metallic  lustre. 

Red  haematite  (sometimes  called  blood-stone)  is  another  form  of  the  sesquioxide, 
occurring  generally  in  reniform  masses  of  a  radiated  fibrous  structure;  its  spec. 
grav.  is  about  5,  and  its  hardness  very  considerable;  this  latter  property  renders 
it  useful  for  burnishing.  Hematite  has  a  brownish-red  color,  which  changes, 
under  some  aspects,  to  steel-gray;  its  powder  is  red. 

Brown  hsematite  is  a  hydrated  sesquioxide  of  iron :  its  form  is  similar  to  that 
of  the  red  haematite. 

jEtite,  kidney-form  clay -ironstone,  or  eagle-stone  forms  globular  masses,  con- 
sisting of  hydrated  sesquioxide  of  iron  associated  with  clay. 

Oolitic  iron-ore  has  a  similar  composition,  and  is  found  in  small  round  grains, 
aggregated  together,  like  the  milt  of  a  fish,  whence  its  name. 

The  ores  known  as  morass-ore,  swamp-ore,  and  meadow-ore,  consist  of  hydrated 
sesquioxide  of  iron. 

Magnetic  iron-stone  (Fe3O4)  is  found  chiefly  in  Sweden ;  its  color  is  dark  gray, 
and  spec.  grav.  about  5.1 

Iron-sand,  which  has  a  black  color  and  metallic  lustre,  is  composed  chiefly  of 
the  magnetic  oxide;  it  generally  contains  titanium. 

The  mineral  termed  umber,  which  is  used  as  a  pigment,  consists  of  the  hy- 
drated oxides  of  iron  and  manganese. 

1  Andrews  has  recently  examined  a  specimen  of  this  ore,  in  which  part  of  the  protoxide 
of  iron  was  replaced  by  magnesia. 


350  METALLURGY  OF  IRON. 

The  two  varieties  of  pyrites,  viz.  magnetic  pyrites  (Fe.Ss),  and  common,  or 
cubical  pyrites  (sometimes  called  radiated  pyritei)  have  been  already  mentioned. 
(Proto-)  Carbonate  of  iron  occurs  in  two  varieties ;  fpathic  (or  fparry)  iron-ore 
is  sometimes  found  in  amorphous  masses,  and  sometimes  crystallized  in  rhombs, 
octohedra,  and  dodecahedra.  Its  color  varies  between  brown  and  yellow,  and 
its  spec.  grav.  from  3.6  to  3.8.  It  becomes  dark  when  exposed  to  air,  or  when 
heated.  Spathic  iron-ore  often  contains  a  little  manganese.  The  other  variety, 
common  clay-iron-stone  (black-band)  is  yellow,  or  red-brown,  and  varies  in  spec. 
grav.  from  2.9  to  3.5;  it  is  generally,  as  its  name  imports,  associated  with  clay. 
The  above  minerals,  though  containing  iron  in  abundance,  are  not  all  made 
use  of  for  the  extraction  of  iron,  and  therefore  should  not,  strictly  speaking,  be 
designated  ores  of  that  metal. 

In  this  sense,  the  only  true  ores  of  iron  are,  the  magnetic  oxide,  the  anhydrous 
sesquioxide,  the  hydrated  sesquioxide,  and  the  (proto-')  carbonate.  The  minerals 
containing  sulphur  and  phosphorus  are  not  employed,  since  they  would  yield  an 
inferior  product. 

The  manufacture  of  iron  may  conveniently  be  divided  into  1.  The  prepara- 
tion of  the  ores,  2.  the  extraction  of  the  metal,  and  3.  its  purification. 

The  preparation  of  the  iron  ores  is  very  simple;  the  earthy  ores  are  merely 
subjected  to  a  species  of  rough  levigation,  by  which  the  greater  part  of  the  clay 
is  separated.  Those  ores  which  occur  in  rocks  or  large  masses,  clay  iron-stone, 
for  example,  are  roasted,  by  which  the  water  and  carbonic  acid  are  expelled,  and 
the  ore  is  rendered  more  friable. 

The  extraction  and  purification  of  the  iron,  when  the  ore  is  very  pure  and 
rich,  are  sometimes  effected  in  one  process. 

A  large  rectangular  crucible- is  employed,  the  sides  of  which  are  formed  of 
thick  plates  of  cast-iron,  and  the  bottom  of  very  refractory  stone;  this  crucible 
is  furnished  with  a  tuyere,  or  air-pipe,  of  copper,  by  which  a  rapid  stream  of  air 
may  be  directed  into  the  crucible.  In  order  to  charge  the  latter,  a  quantity  of 
redhot  charcoal  is  thrown  into  the  bottom,  and  an  iron-shovel  is  then  held  so  as 
to  divide  the  space  above  the  charcoal  into  two  compartments,  one  of  which  is 
charged  with  the  previously  roasted  mineral,  and  the  other  with  charcoal;  the 
shovel  is  then  withdrawn,  and  a  gradually  increasing  current  of  air  supplied  by 
the  tuykre,  whilst  the  workman  stirs  the  mass;  in  this  manner,  a  spongy  mass 
of  metal  is  obtained,  which  is  freed  from  the  fused  slag  by  hammering,  and  is 
then  forged  into  bars.  The  explanation  of  this  process  is  simple  enough;  the 
carbon  is  converted  into  carbonic  acid  at  the  expense  of  the  air  introduced  into 
the  crucible;  this  carbonic  acid  then  coming  in  contact  with  a  mass  of  redhot 
charcoal,  is  reduced  to  the  state  of  carbonic' oxide,  which,  in  its  turn,  abstracts 
the  oxygen  from  the  iron-ore,  thus  reducing  it  to  the  state  of  metal,  which  is 
at  first  disseminated  through  the  mass,  and  afterwards  accumulated  by  the  work- 
man into  a  spongy  state ;  the  whole  of  the  iron,  however,  is  not  reduced,  for 
part  of  it,  in  the  state  of  (prot-)  oxide,  combines  with  the  silicic  acid  con- 
tained in  the  ore  to  form  a  fusible  scoria  or  slag,  which  flows  to  the  bottom  of 
the  crucible,  whence  it  is  drawn  off  from  time  to  time. 

The  process  lasts  about  six  hours,  and  yields  from  2|  cwts.  to  3  cwts.  of  mar- 
ketable iron  for  every  9i  cwts.  of  ore,  with  a  consumption  of  about  10  cwts.  of 
charcoal. 

The  process  above  described  is  very  seldom  employed,  since  it  involves  a  con- 
siderable loss  of  metal,  and  can  only  be  carried  into  operation  with  particular 
ores. 

We  shall  now  proceed  to  consider  the  process  generally  used  for  smelting  iron- 
ores,  which  consists  in  converting  the  iron  into  a  fusible  carbide,  by  exposing 
the  oxide  to  a  very  high  temperature  in  contact  with  carbon,  and  in  a  subse- 
quent purification  of  the  resulting  product. 


METALLURGY   OP   IRON.  351 

The  extraction  of  the  metal  from  the  ore  is  effected  in  a  llast-furnace,  which 
has  the  form  of  two  truncated  cones  joined  together  at  their  bases,  and  is  lined 
with  very  refractory  brick  or  stone. 

Air  is  forced  into  this  furnace,  by  means  of  a  steam-engine,  through  two  or 
three  tuyere-pipes. 

In  order  to  obtain  the  compound  of  iron  with  carbon  in  a  fused  state,  it  is  of 
course  necessary  that  a  fusible  slag  should  be  formed  which  contains  all  the 
impurities  of  the  ore.  These  impurities  (technically  termed  ganyue)  consist 
generally  of  silica  and  alumina  (combined  in  the  form  of  clay),  and  since  these 
are  very  infusible,  it  is  necessary  to  add  some  substance  which  shall  form  a 
liquid  combination  with  them  at  the  temperature  of  the  furnace.  For  this  pur- 
pose, carbonate  of  lime  is  employed,  which  produces  with  the  clay  a  double  sili- 
cate of  alumina  and  lime,  fusing  with  comparative  readiness.1  Should  the  gangue 
consist  of  quartz  only,  the  ore  is  mixed  with  an  argillaceous  iron-ore,  and  a 
quantity  of  limestone  added.  When  the  gangue  consists  of  carbonate  of  lime,  a 
proper  quantity  of  clay,  or  of  argillaceous  ore  is  added.  The  substances  thus 
added  to  promote  the  fusion  of  the  slag  are  termed  fluxes. 

The  carbonate  of  lime  not  only  acts  as  a  flux,  but  likewise  prevents  any  loss 
of  iron  which  would  otherwise  result  from  the  production  of  a  double  silicate  of 
alumina  and  oxide  of  iron,  the  latter  base  being  replaced  in  the  combination 
by  an  equivalent  proportion  of  lime. 

The  operation  is  commenced  by  charging  the  furnace  to  a  certain  height  with 
fuel,  and,  after  this  has  fairly  kindled,  introducing  a  quantity  of  ore,  mixed  with 
flux,  from  the  top  of  the  furnace ;  the  blast  is  increased  gradually,  and  alternate 
layers  of  fuel  and  ore  introduced  from  time  to  time.  The  fused  combination  of 
iron  with  carbon  collects  at  the  bottom  of  the  furnace,  and  above  it,  a  layer  of 
slag;  these  are  drawn  off  from  time  to  time,  through  different  apertures,  the 
former  being  allowed  to  run  into  moulds  of  sand,  in  which  it  is  cast  into  rough 
masses,  sent  into  the  market  as  pig-iron,  or  cast-iron.  The  process  is  not  inter- 
rupted till  the  furnace  is  in  want  of  repair. 

The  fuel  employed  in  the  blast-furnaces  is  either  charcoal,  wood,  or  coke;  the 
latter  is  preferred  where  (as  in  England)  coal  can  be  obtained  in  abundance. 

When  charcoal  is  employed,  the  amount  of  lime  present,  in  proportion  to  the 
clay,  is  so  regulated  that  the  most  fusible  slag  shall  be  formed,  and  a  lower  tem- 
perature is  required  than  when  coke  is  employed ;  for,  since  this  latter  always 
contains  more  or  less  sulphur  (as  iron-pyrites),  it  is  necessary  to  employ  more 
limestone,  in  order  to  convert  the  sulphur  into  sulphide  of  calcium,  and  thus  to 
prevent  its  passing  into  the  pig-iron,  the  quality  of  which  it  would  injure.  The 
excess  of  limestone,  however,  renders  the  slag  less  fusible,  and  it  becomes 
necessary  to  build  the  furnace  higher,  in  order  to  raise  the  temperature  to  the 
required  extent. 

A  considerable  saving  of  fuel  has  been  effected  by  feeding  the  furnace  through 
the  tuyeres  with  air  heated  to  400°  or  500°  F.,  instead  of  with  cold  air,  the  air 
being  raised  to  that  temperature  by  the  waste  heat  of  the  furnace.  This  is 
generally  known  as  the  hot-blast  process. 

The  reactions  which  take  place  in  the  interior  of  the  blast-furnace  are  easily 
followed,  if  we  bear  in  mind  the  existence  of  an  ascending  column  of  atmospheric 
air  and  other  gases,  and  of  a  descending  column  consisting  of  a  mixture  of  ore, 
fuel,  and  slag.  The  air  entering  through  the  tuyeres,  at  the  lower  part  of  the 
furnace,  is  at  once  deoxidized  by  the  fuel,  its  oxygen  being  entirely  converted 
into  carbolic  acid ;  the  latter,  coming  in  contact  with  another  portion  of  heated 
fuel,  is  reduced  to  carbonic  oxide,  by  which  the  reduction  of  the  ore  is  chiefly 

1  The  most  fusible  slag  is  that  in  which  the  oxygen  in  the  acid  is  double  that  in  the 
two  bases.  The  presence  of  manganese  augments  the  fusibility  of  the  slag. 


352  METALLURGY   OP  IRON. 

effected.  The  ore,  slag,  and  fuel  lose  their  moisture  and  carbonic  acid  in  the 
higher  part  of  the  furnace ;  the  oxide  of  iron  is  then  reduced,  at  a  lower  stage, 
where  the  temperature  is  more  elevated,  by  the  carbonic  oxide,  and  the  earthy 
matters  separate  in  the  form  of  a  fusible  slag.  At  a  still  lower  level  in  the  fur- 
nace, the  reduction  of  the  iron  is  completed  by  the  carbon,  a  portion  of  which 
also  combines  with  the  difficultly  fusible  iron,  forming  a  compound  which  fuses 
at  the  temperature  existing  in  that  part  of  the  furnace,  and  runs  down  into  the 
crucible,  where  it  forms  a  layer  beneath  the  more  fusible  and  lighter  slag;  this 
is  allowed  to  run  off  over  the  side  of  the  crucible,  so  that  the  latter  becomes  filled, 
after  a  time,  with  metallic  iron. 

Although  hydrogen  exists  in  every  part  of  the  blast-furnace,  it  has  no  share 
in  the  reduction  of  the  ore,  since,  in  its  affinity  for  oxygen,  it  has  been  proved 
to  be  inferior  to  carbonic  oxide. 

The  gas  which  issues  from  the  chimney  (or  tunnel,  as  it  is  commonly  called) 
of  the  blast-furnace,  consists  chiefly  of  carbonic  acid,  carbonic  oxide,  hydrogen, 
and  nitrogen;  this  gas  is  inflammable,  and  has  been  used,  in  some  works,  for 
heating  the  steam-boilers,  and  for  other  purposes.  The  hydrogen,  of  course, 
arises  from  the  decomposition  of  the  water  contained  in  the  ore,  and  in  the  fuel, 
and  the  nitrogen,  from  the  atmospheric  air  supplied  to  the  furnace. 

The  cast-iron  obtained  by  the  above  process,  contains  three  or  four  per  cent,  of 
carbon  and  silicon,  with  traces  of  sulphur,  phosphorus,  and  manganese ;  these 
impurities  render  it  brittle,  and  hence  unfit  for  many  purposes ;  it  must,  there- 
fore, be  refined,  or  purified,  and  this  is  usually  called  the  conversion  of  piy-iron 
into  bar-iron. 

This  process  may  be  divided  into  two  operations,  the  refining  and  puddling. 
The  refining  furnace  is  constructed  of  iron,  lined  with  refractory  clay,  and  is 
furnished  with  tuyere-pipes.  In  this  furnace,  the  pig-iron  is  kept  in  fusion  for 
about  two  hours,  under  a  strong  blast  of  air:  its  surface  is  oxidized  by  the  lat- 
ter, and  the  mass  being  stirred  by  the  workman,  so  as  to  bring  all  parts  of  it  in 
contact  with  the  oxide,  this  latter  converts  the  carbon  into  carbonic  oxide,  and 
the  silicon  into  silicic  acid,  which  forms,  with  a  portion  of  oxide  of  iron,  a  fusible 
silicate  which  constitutes  the  slag. 

When  the  operation  is  completed,  the  fused  iron  is  run  out  into  a  cistern  of 
cold  water,  in  order  that  it  may  be  suddenly  cooled,  and  thus  rendered  brittle. 
In  this  way  the  pig-iron  is  deprived  of  the  greater  part  of  its  impurities,  and  is 
converted  into  fine  metal,  or,  as  it  is  also  called,  cold-short  iron. 

The  fine  metal  is  now  broken  up  and  puddled,  in  order  to  complete  the  purifi- 
cation. The  process  of  puddling  consists  in  fusing  the  fine  metal,  in  a  reverbe- 
ratory-furnace,  with  a  certain  amount  of  oxide,  obtained  as  scoria,  in  a  former 
.operation.  The  supply  of  air  to  the  furnace  is  limited,  in  order  to  prevent  ex- 
cessive oxidation  of  the  metal.  The  mass  is  well-stirred  during  the  process,  so 
that  each  portion  may  be  subjected  to  purification. 

As  the  operation  proceeds,  the  metal,  which  is  at  first  pretty  liquid,  becomes 
pasty,  at  the  same  time  evolving  bubbles  of  carbonic  oxide;  when  the  workman 
judges  that  the  process  is  completed,  he  collects  all  the  particles  of  metal  with 
his  stirrer,  and  forms  them  into  masses,  which  are  called  puddler'x  balls,  or 
blooms;  these  are  hammered  (or  shingled),  and  subsequently  rolled,  in  order  to 
free  them  from  slag.  The  bars  thus  obtained  are  laid  in  bundles,  raised  to  a 
welding  heat  in  another  furnace,  and  welded  together,  which  at  once  improves 
their  strength  and  texture.  They  are  then  considered  marketable  bar-iron. 


METALLURGY  OF  IRON.  353 

CAST-IRON. 

Cast-iron  contains,  besides  iron,  carbon,  silicon,  phosphorus,  and  traces  of 
manganese;1  its  properties  differ  according  to  the  quantity  of  each  of  these  sub- 
stances. 

There  are  three  varieties  of  cast-iron,  known  as  Mack,  gray,  and  white  cast- 
iron. 

Mottled  cast-iron  is  a  mixture  of  gray  and  white  iron.  The  black  variety  is 
the  most  unequal  in  texture,  the  most  fusible,  and  least  cohesive  of  these.  Its 
color  is  due  to  the  presence  of  graphite,  formed  during  the  manufacture.  When 
dissolved  in  acids,  it  evolves  hydrogen  of  a  fetid  odor,  and  leaves  a  residue  of 
graphite.  It  is  always  formed  when  a  considerable  excess  of  carbon  is  employed 
in  the  reduction  of  the  ore,  and  is  much  prized  for  casting. 

According  to  Berthier's  analysis,  black  iron  contains  generally  from  3  to  3.5 
per  cent,  of  carbon,  from  0.07  to  0.5  per  cent,  of  silicon,  and  some  manganese. 

Gray  cast-iron  is  granular  in  structure,  and  of  sp.  gr.  between  6.79  and  7.05; 
when  this  variety  is  treated  with  acids,  it  leaves  a  residue  of  graphite,  which  is 
smaller  in  quantity  than  that  obtained  from  black  iron.  Gray  iron  is  more 
easily  oxidized  by  exposure  to  air  than  the  white  iron,  from  its  superior  porosity. 
This  variety  contains  more  phosphorus  than  the  others,  which  renders  it  brittle, 
but,  at  the  same  time,  more  fusible  and  fit  for  casting. 

It  appears  to  contain  from  2  to  3  per  cent,  of  carbon,  rather  less  silicon,  from 
0.5  to  1'per  cent,  of  phosphorus,  and  traces  of  manganese. 

Gray  cast-iron  is  the  ordinary  product  of  a  good  operation  by  the  English 
method.  It  is  used  for  artillery. 

White  cast-iron  is  generally  produced  when  a  deficient  supply  of  carbon  is 
employed  in  the  reduction  of  the  ore,  or  when  the  ores  contain  a  considerable 
quantity  of  manganesfi. 

White  cast-iron  has  a  fine  metallic  lustre  and  a  silvery-white  color;  its  density 
varies  between  7.4  and  7.8;  it  is  exceedingly  hard  and  brittle.  White  iron 
fuses  more  readily  than  gray  iron,  but  the  fused  mass  is  pasty,  not  liquid. 

It  would  appear  that  the  carbon  is  contained  in  a  different  form  of  combination 
m  white  iron,  for  it  leaves  no  carbonaceous  residue  when  dissolved  in  acids. 

White  cast-iron  contains  from  2  to  2.5  per  cent,  of  carbon,  about  0.5  per 
cent,  of  silicon,  0.2  to  0.3  per  cent,  of  phosphorus,  and  about  2  per  cent,  of 
manganese. 

Gray  cast-iron  may  be  converted  into  white  iron  by  sudden  cooling,  or,  in- 
versely, the  white  variety  into  gray  iron,  by  a  high  temperature  and  gradual 
cooling.2 

Bar-iron  (wrouyht-irori)  has  a  bluish-gray  color,  is  very  malleable  and  ductile, 
and  possesses,  in  most  respects,  the  properties  of  pure  iron.  The  carbon  in  bar- 
iron  may  amount  to  0.25  per  cent,  without  injury  to  the  properties  of  the  metal. 
Iron  containing  2  per  cent,  of  carbon  is  no  longer  fit  for  forging. 

It  will  be  inferred,  from  what  has  been  already  stated,  that  the  quality  of  bar- 
iron  is  much  injured  by  the  presence,  even  in  small  quantities,  of  phosphorus 
and  sulphur;  the  latter,  especially,  exerts  an  injurious  influence  upon  the  metal. 
The  presence  of  arsenic  is  also  attended  with  great  inconvenience;  0.0005  of 
phosphorus  will  render  bar-iron  unfit  for  working,  an  effect  which  is  produced  by 
even  0.0001  of  sulphur. 

The  structure  of  bar-iron  is  granular,  and  the  finer  the  grain,  the  better,  in 
general,  the  quality  of  the  iron;  when  hammered,  it  becomes  fibrous,  but  re- 

1  Only  the  principal  impurities  are  here  enumerated ;  traces  of  other  metals  are  also 
contained  in  cast-iron ;  e.  -g.  cobalt,  chromium,  calcium,  potassium,  and  sodium. 

2  This  variety  (white  iron)  is  only  employed  for  coarse  castings,  neve-r  for  machinery. 

23 


354  .STEEL. 

sumes  its  granular  structure  if  heated  and  cooled  suddenly.  When  a  bar  of 
fibrous  iron  is  exposed  to  frequent  vibrations,  it  often  assumes  a  crystalline 
structure;  this  is  observed  in  iron  railroads,  and  similar  works,  and  sometimes 
induces  a  dangerous  brittleness  in  the  metal.  A  bar  of  iron  also  becomes  crys- 
talline if  it  be  repeatedly  heated  and  allowed  to  cool. 

The  specific  gravity  of  hammered  bar-iron  is  7.9. 

In  welding  bars  of  iron  together,  it  is  of  course  necessary  that  their  surfaces 
should  be  free  from  oxide;  this  is  generally  insured  by  sprinkling  them  with 
sand,  which  combines  with  the  oxide  to  form  a  fusible  silicate. 

The  purest  kind  of  commercial  iron  is  found  in  piano-wire,  since  the  metal 
could  not  be  drawn  out  into  fine  wire  unless  it  were  nearly  pure. 

STEEL. 

Steel  contains  more  carbon  than  bar-iron,  but  less  than  cast-iron;  the  amount 
of  this  element  never  exceeding  1  per  cent.  Steel  also  contains  small  quantities 
of  phosphorus  and  silicon.  A  specimen  of  the  best  English  steel  was  found  by 
Gay-Lussac  to  contain — 

Carbon 0.62 

Silicon    , 0.03 

Phosphorus 0.03 

Iron 99.32 

100.00 

Small  quantities  of  manganese  are  also  found  in  most  varieties  of  steel. 

Steel  (natural  steel}  is  sometimes  obtained  by  partially  refining  the  pig-iron 
until  it  contains  only  the  proper  amount  of  carbon;  the  steel  thus  obtained, 
however,  is  chiefly  used  for  agricultural  instruments.  Pig-iron  containing  man- 
ganese is  found  to  answer  best  for  this  purpose.  Steel,  however,  is  most  com- 
monly made  by  a  process  termed  cementation,  in  which  bar-iron  is  arranged  in 
alternate  layers  with  charcoal-powder,  in  a  closed  chest  of  refractory  clay,  which 
is  exposed  to  a  high  temperature  for  seVeral  hours.  In  this  process,  it  is  proba- 
ble that  the  carbon  first  combines  with  the  oxygen  of  the  air,  inclosed  in  the 
chest,  to  form  carbonic  oxide,  which  then  yields  up  part  of  its  carbon  to  the  iron, 
and  is  converted  into  carbonic  acid,  from  which  carbonic  oxide  is  again  formed 
by  the  action  of  the  heated  charcoal.  The  result  of  this  operation  is  termed 
Mistered  steel,  from  the  appearance  of  its  surface. 

In  order  to  convert  blistered  steel  into  shear-steel,  several  bars  are  welded  to- 
gether, and  the  bar  thus  obtained  again  divided  and  welded,  until  steel  of  the 
requisite  quality  is  obtained.  The  cutting  and  welding  are  designed  to  improve 
the  texture  of  the  metal,  and  to  render  it'  homogeneous. 

Oast-steel,  which  is  the  best  variety,  is  obtained  by  fusing  blistered  steel, 
casting  it  into  ingots,  and  bringing  these  under  the  hammer. 

Properties  of  Steel. — Steel  differs  much  from  iron  ;  it  is  much  harder,  of  finer 
grain,  and  more  sonorous.  The  specific  gravity  of  steel  is  generally  7.74. 

The  most  important  and  useful  property  of  steel,  is  that  of  acquiring  very 
great  hardness  when  heated  and  afterwards  suddenly  cooled  by  immersion  in 
water.  The  degree  of  hardness  thus  acquired  depends  upon  the  temperature  to 
which  the  steel  has  been  raised.  For  most  purposes  the  steel  is  too  much  hard- 
ened by  this  process,  and  it  then  becomes  necessary  to  temper  the  articles  by 
exposing  them  to  a  moderate  heat  in  an  annealing-furnace.  The  necessary  tem- 
pering heat  varies  for  different  articles,  and  is  recognized  by  the  workman  from 
the  color  which  the  steel  assumes,  in  consequence  of  the  formation  of  a  thin 
film  of  oxide  upon  its  surface. 


MANGANESE.  355 

Thus,  at  430°  F.  (221°  C.),  the  surface  assumes  a  yellow  color,  and  at  this 
temperature  pen-knives  and  razors  are  sufficiently  tempered;  at  490°  F.  (254° 
C.),  a  brown  color  appears,  showing  that  scissors,  &c.,  are  annealed  ;  again,  the 
temperature  for  watch-springs  and  swords  is  about  550°  F.  (288°  C.),  indicated 
by  a  bright  blue  color.1 

It  appears  that  hardened  steel  contains  carbon  in  a  state  of  combination  dif- 
ferent from  that  in  which  it  exists  before  hardening,  for  it  then  leaves  a  consider- 
able residue  of  carbon  when  treated  with  acids;  whereas,  in  the  case  of  hardened 
steel,  all  the  carbon  is  evolved  in  combination  with  hydrogen,  suggesting  that  it 
had  been  in  more  intimate  combination  with  the  iron. 

Steel  which  has  taken  up  too  much  carbon  in  the  process  of  cementation,  is 
sometimes  reduced  in  hardness  by  imbedding  it  in  finely  powdered  sesquioxide 
of  iron  or  manganese,  and  exposing  it  to  a  high  temperature,  when  a  portion  of 
the  carbon  is  oxidized  at  the  expense  of  the  metallic  oxides.2 

Instruments  of  comparatively  soft  metal  are  sometimes  hardened  externally 
by  exposing  them  to  partial  cementation ;  the  metal  is  then  called  case-hardened. 

Steel  may  readily  be  distinguished  from  malleable  iron,  by  moistening  with 
dilute  nitric  acid,  and  observing  the  color  of  the  resulting  stain ;  that  produced 
upon  steel  is  dark-gray,  while  that  obtained  upon  malleable  iron  is  green. 

A  method  of  analyzing  iron-ores,  which  should  comprehend  every  constituent 
which  they  might  contain,  would  be -exceedingly  complicated,  difficult  of  execu- 
tion, and  of  little  practical  value.  For  nearly  all  technical  purposes  it  is  suffi- 
cient to  ascertain  the  quantities  of  iron,  of  clay,  sand,  water,  carbonic  acid,  lime 
and  magnesia  contained  in  the  ore. 

The  determination  of  the  iron  may  be  effected  either  by  the  dry  or  the  wet 
process. 

The  dry  assay  of  iron-ores  consists  in  fusing  200  or  300  grs.  of  the  ore,  in  a 
crucible  lined  with  charcoal,  with  a  flux  consisting  of  chalk  or  clay  (free  from 
iron)  according  to  the  nature  of  the  gangue.  The  crucible  is  exposed  to  a  very 
high  temperature  for  about  an  hour  and  a  half,  allowed  to  cool,  and  the  button 
or  buttons  of  iron  freed  from  adhering  slag,  and  their  weight  determined.  The 
button  may  afterwards  be  broken  by  a  sharp  blow,  and  the  fracture  examined ; 
if  the  metal  present  a  grayish  or  mottled  appearance,  and  be  slightly  flattened 
under  the  hammer,  it  may  be  considered  as  of  good  quality ;  but  should  it  be 
very  brittle,  and  its  fracture  white  and  crystalline,  the  ore  cannot  be  regarded  as 
yielding  an  iron  of  the  best  description. 

For  the  method  of  analyzing  iron-ores  in  the  wet  way,  see  Quantitative  Analysis, 
Special  Methods. 


MANGANESE. 

Sym.  Mn.     Eq.  27.6.     Sp.  Gr.  7.05. 

§  234.  This  metal  is  found  in  considerable  abundance  in  nature,  in  combina- 
tion with  oxygen.  It  generally  accompanies  iron. 

Preparation. — Manganese  is  prepared  by  reducing  its  oxide  with  carbon  at  a 
high  temperature.  The  carbonate  of  (protoxide  of)  manganese  is  calcined  in  a 
closed  crucible,  when  its  carbonic  acid  is  expelled ;  the  residual  oxide  is  then 

1  Faraday  and  Stodart  have  observed  that  the  hardness  of  steel  may  be  much  increased 
by  alloying  it  with  a  very  small  quantity  of  either  silver,  platinum,  iridium,  or  rhodium. 

2  Cast-iron  is  sometimes  submitted  to  an  analogous  process,  when  it  is  desirable  to 
transform  castings  into  malleable  metal. 


356  MANGANESE   AND    OXYGEN. 

mixed  with  oil  and  fine  charcoal  to  a  paste,  which  is  moulded  into  pellets  and 
introduced  into  a  crucible  lined  with  charcoal ;  this  latter  is  heated  for  two  or 
three  hours  in  a  wind-furnace,  after  which  a  button  of  metal  will  be  found  at  the 
bottom  of  the  crucible.  This  button,  however,  bears  the  same  relation  to  pure 
manganese  as  cast-iron  does  to  the  pure  metal ;  in  order  to  separate  the  carbon 
from  it,  it  must  be  again  fused,  with  a  little  carbonate  of  manganese  and  vitrified 
borax. 

Properties. — Manganese  is  an  iron-gray,  feebly  lustrous,  hard,  brittle  metal. 
It  is  as  difficult  of  fusion  as  iron.  When  exposed  to  air  (especially  if  moist)  it 
is  soon  oxidized,  and  should  therefore  be  kept  in  sealed  tubes,  or  under  coal- 
naphtha. 

It  has  but  little  action  upon  water  at  the  ordinary  temperature,  but  decom- 
poses it  rapidly  at  the  boiling-point,  or  in  presence  of  an  acid. 

MANGANESE   AND   OXYGEN. 

(Prot-)  oxide  of  manganese MnO. 

Sesquioxide  "          Mn203. 

Binoxide  or  Peroxide      "  Mn03. 

Manganic  acid Mn03. 

Permanganic  acid Mn30r 

Some  intermediate  oxides  of  manganese  also  exist. 

OXIDE,  OR  PROTOXIDE,  OF  MANGANESE. 
MnO.     %  35.6. 

§  235.  The  anhydrous  oxide  is  prepared  by  heating  the  carbonate  in  a  bulb- 
tube,  through  which  a  stream  of  dry  hydrogen  is  passing ;  the  latter  only  serves 
to  exclude  the  air,  and  exerts  no  reducing  action. 

It  'has  a  green  color,  and  is  not  decomposed  by  heat.  When  exposed  to  air, 
it  soon  absorbs  oxygen,  and  becomes  brown ;  it  is  less  liable  to  oxidize  after 
powerful  ignition ;  when  heated  in  air  or  oxygen,  it  is  converted  into  an  oxide 
having  the  composition  Mn304  (red  oxide). 

Hydrated  Oxide  of  Manganese  is  precipitated  when  a  protosalt  of  this  metal 
is  decomposed  by  an  alkali ;  it  is  a  white  precipitate,  which  rapidly  absorbs  oxy- 
gen from  the  air,  becoming  brown. 

The  oxide  of  manganese  is  a  pretty  powerful  base ;  it  dissolves  in  acids,  and 
forms  some  important  salts. 

Solutions  of  the  neutral  salts  of  this  oxide  do  not  change  the  color  of  test- 
papers. 

SULPHATE  OF  OXIDE  OF  MANGANESE,  SULPHATE  OF  MANGANESE. 

MnO.S03. 

Preparation. — To  prepare  this  salt,  powdered  binoxide  of  manganese  is  heated 
with  concentrated  sulphuric  acid  : — 

MnOa+HO.S03=MnO.S03-fHO  +  0. 

The  pasty  mass  is  heated  with  water,  the  solution  filtered,  and  digested  with  an 
excess  of  carbonate  of  manganese,  which  precipitates  the  sesquioxide  of  iron ; 
the  clear  liquid,  when  evaporated,  yields  crystals  of  the  sulphate. 

Sulphate  of  manganese  is  also  prepared  by  heating  to  dull  redness  a  mixture 
of  equal  weights  of  sulphate  of  iron  and  binoxide  of  manganese ;  the  salt  is 
extracted  from  the  mass  by  water,  and  sesquioxide  of  iron  is  left,  together  with 
the  excess  of  binoxide  of  manganese. 


CARBONATE  OP  MANGANESE.  357 

Properties. — Sulphate  of  manganese  forms  large  transparent  crystals,  which 
have  a  pink  color,  of  varying  intensity.  The  shape  and  composition  of  these 
crystals  differ  with  the  temperature  at  which  they  are  deposited. 

When  a  hot  concentrated  solution  of  sulphate  of  manganese  is  allowed  to  cool, 
the  crystals  which  are  deposited  between  68°  and  86°  F.  (20°  and  30°  C.),  have 
the  formula  MnO.S03.HO  +  3Aq,  and  are  isornorphous  with  the  correspond- 
ing iron-salt.  Those  which  are  deposited  between  43°  and  68°  F.  (6°  and  20° 
C),  are  composed  of  MnO.S03.HO-f  4Aq  ;  they  have  the  same  form  as  the 
crystals  of  sulphate  of  copper.  Below  43°  F.  (6°  C.)  the  formula  of  the  crys- 
tals is  MnO.S03.HO-f-6Aq,  and  their  form  is  the  same  as  that  of  the  sulphate 
of  iron  with  7  equivalents  of  water. 

The  ordinary  crystals  of  this  salt  are  those  containing  4  equivalents  of  water. 
They  are  readily  soluble  in  water,  but  insoluble  in  alcohol,  which  abstracts  part 
of  their  water  of  crystallization.  If  these  crystals  are  dried  at  a  temperature 
of  about  400°  F.  (204°  C.),  they  lose  their  water  of  crystallization,  leaving  the 
salt  MnO.S03.HO,  which  is  also  deposited  when  an  aqueous  solution  is  boiled 
for  some  time.1 

The  perfectly  anhydrous  salt  may  be  obtained  by  moderately  igniting  the 
crystals.  It  readily  absorbs  3  equivalents  of  water  from  the  air. 

When  heated  to  redness,  sulphate  of  manganese  is  decomposed,  sulphuric  and 
sulphurous  acids  are  evolved,  and  the  red  oxide  of  manganese  left : — 

8(MnO.SOa)=SOa+2SO,+Mna04. 

Sulphate  of  manganese  is  used  in  dyeing  and  calico-printing ;  occasionally,  also, 
in  medicine. 

The  equivalent  of  constitutional  water  in  sulphate  of  manganese  may  be 
replaced  by  the  sulphates  of  potassa  and  ammonia,  double  salts  being  formed 
which  are  represented  by 

KO.S03,MnO.S03+6Aq,  and 
NH4O.S03,  MnO.S03  +  6Aq. 
A  doulle  sulphate  of  manganese  and  alumina,  of  the  formula 

AlaOa.3S08,MnO.SOa+24Aq, 

is  found  in  colorless  fibrous  crystals,  in  Algoa  Bay  (Africa) ;  it  is  soluble  iu 
water.     This  salt  is  evidently  manganese-alumina-alum. 

Phosphate  of  Manganese,  2MnO.HO.P03,  occurs  in  the  mineral  kingdom. 

CARBONATE  OF  MANGANESE,  MnO.C03. 

This  salt  is  also  found  in  nature,  sometimes  in  rose-colored  rhombohedra 
(manganese  spar).  It  is  generally  associated  with  the  carbonates  of  iron  and 
lime,  with  which  it  is  isomorphous. 

Carbonate  of  manganese  may  be  prepared  by  precipitating  solution  of  the 
sulphate  with  carbonate  of  soda,  and  washing  the  precipitate  till  free  from  sul- 
phuric acid. 

It  has  a  pinkish-white  color,  and  when  heated  in  air,  is  easily  converted  into 
the  red  oxide  (Mn304) ; 

3(MnO.C02)  +  0=Mn304+3C02. 

This  carbonate  is  insoluble  in  water,  but  dissolves  in  carbonic  acid  water. 

It  is  employed  for  the  preparation  of  other  compounds  of  manganese. 

Silicates  of  Manganese  are  found  in  nature.  The  silicate  of  the  formula  3 
MnO.Si03-f  3Aq,  is  black,  and  may  be  decomposed  by  acids,  while  another,  the 
composition  of  which  is  3Mn0.2Si03,  resists  the  action  of  acids. 

1  Other  hydrated  salts  have  been  obtained,  of  the  formulae  MnO.S08.HO+Aq,  and 
MnO.S03.HO-f-2Aq. 


358  OXIDES  OF  MANGANESE. 

SESQUIOXIDE  OF  MANGANESE. 

Mn.0,- 

§  236.  This  oxide  constitutes  the  minerals  Iraunite  and  manganite ;  the  former 
is  the  anhydrous  sesquioxide,  whilst  the  latter  contains  Mn203.HO.  The  sesqui- 
oxide  is  often  associated  with  the  binoxide. 

It  is  a  brownish-black  substance,  which  possesses  feeble  basic  properties;  at 
a  low  temperature  it  forms  sesquichloride,  when  dissolved  in  hydrochloric  acid, 
but  this  solution  evolves  chlorine  when  heated,  the  (proto-)  chloride  of  manganese 
being  formed — 

Mna03+3HCl=3HO-f-2MnCl+Cl. 

The  Jiydrated  sesquioxide  of  manganese  is  formed  when  the  hydrated  (prot-) 
oxide  is  exposed  to  air. 

The  salts  of  sesquioxide  of  manganese  are  not  very  well  known ;  they  are 
unstable,  easily  evolving  oxygen,  and  being  converted  into  salts  of  the  (prot-) 
oxide. 

The  Sulphate  of  Sesquioxide  of  Manganese,  Mna03.3S03,  is  obtained  by  dis- 
solving the  sesquioxide  in  sulphuric  acid,  at  a  very  gentle  heat;  it  crystallizes 
with  difficulty ;  the  solution  has  a  red  color,  and  is  instantly  decomposed  by  heat, 
or  by  deoxidizing  agents.  By  adding  sulphate  of  potassa,  or  of  ammonia,  to  the 
solution,  fine  crystals  of  manganese-alums  may  be  obtained,  the  formulae  of  which 
are: — 

KO.S03,Mn203,3S03+ 24Aq,  and 
NH4O.S03,Mn203.3S03+24Aq. 

RED  OXIDE  OF  MANGANESE,  OR  PROTOSESQUIOXIDE  OF  MANGANESE, 
Mn304=MnO,Mn203. 

This  oxide  occurs  in  nature,  and  is  known  by  the  name  of  Hausmanite. 

It  is  the  most  stable  (with  respect  to  heat)  of  all  the  oxides  of  manganese,  and 
is  always  formed  when  they  are  heated  in  air.  This  oxide  constitutes  the  residue 
left  in  the  retort  after  the  preparation  of  oxygen  from  binoxide  of  manganese, 
and  may  be  employed  for  the  preparation  of  chlorine  from  hydrochloric  acid. 

With  acids,  it  behaves  like  a  combination  of  MnO  with  Mn203. 

Manganese  is  always  determined  in  the  form  of  the  red  oxide. 

BINOXIDE,  OR  PEROXIDE,  OF  MANGANESE. 
Mn02.     Eq.  43.6. 

This  most  important  of  the  oxides  of  manganese  is  found  naturally  in  abund- 
ance, sometimes  in  prismatic  crystals,  sometimes  in  radiated  crystalline  masses. 
When  pure,  it  is  called  by  mineralogists  pyrolusite;  it  is,  however,  generally 
associated  with  manganite,  fluorspar,  sesquioxide  of  iron,  carbonates  of  lime  and 
baryta,  &c.  It  is  sometimes  found  in  combination  with  baryta,  as  psilomelane. 

The  natural  binoxide  may  be  purified  by  washing  with,  dilute  nitric  acid,  to 
remove  earthy  carbonates. 

Hydrate  of  Binoxide  of  Manganese  may  be  obtained  as  a  black  precipitate 
by  adding  a  solution  of  hypochlorite  (chloride)  of  lime  to  one  of  sulphate  of 
manganese. 

Properties. — The  natural  binoxide  of  manganese  has  a  steel-gray  color,  and 
metallic  lustre;  its  powder  is  black.  When  heated,  it  is  decomposed  as  before 
mentioned,  into  oxygen  and  red  oxide  of  manganese. 

Binoxide  of  manganese  is  an  indifferent  oxide,  its  characters  are  neither  basic 
nor  acid.  It  is  a  powerful  oxidizing  agent;  it  is  capable  of  converting  sulphur- 
ous acid  into  hyposulphuric  or  sulphuric  acid,  according  to  the  temperature. 


MANGANATES.  359 


When  in  contact  with  oxalic  acid,  it  yields  oxalate  of  manganese  and  carbonic 
acid : — 

2(HO.C203)+MQ03=MnO.C203+2C02+2HO. 

A  mixture  of  dilute  sulphuric  acid  with  this  oxide  is  frequently  used  as  an 
oxidizing  agent,  especially  in  organic  chemistry ;  it  will  be  remembered  that  such 
a  mixture  evolves  oxygen  when  heated : — 

MnOa+HO.SO.=MnO.SOa+HO+0. 

"When  precipitated  hydrate  of  binoxide  of  manganese  is  treated  with  hydro- 
chloric acid  in  the  cold,  it  entirely  dissolves,  forming  a  dark  brown  liquid,  which 
appears  to  contain  bichloride  of  manganese,  MnCl2,  and  becomes  colorless  when 
heated,  evolving  chlorine,  the  bichloride  being  converted  into  (proto-)  chloride : — 

Mn02+2HCl==MnCl3-f-2HO,  {n  the  cold; 
Mn02+ 2HCl=MnCl  +  Cl-f  2HO,  when  heated. 

The  natural  binoxide  of  manganese  is  decomposed,  though  less  readily,  in  the 
same  way,  and  this  principle  is  applied  in  the  preparation  of  chlorine. 

Hydrobromic,  hydriodic,  and  probably  also  hydrofluoric  acid,  evolve  their  salt- 
radicals  when  heated  with  binoxide  of  manganese. 

When  heated  in  a  closed  vessel  with  caustic  potassa,  the  binoxide  is  decom- 
posed into  sesquioxide  and  manganic  acid : — 

3Mn02+KO.HO=KO.Mn03+Mna03+HO. 

If  air  be  allowed  access,  all  the  manganese  is  converted  into  manganate  of  po- 
tassa : — 

Mn02+KO.HO+0=KO.Mn03+HO. 

Binoxide  of  manganese  dissolves  in  fused  glass,  to  which  it  imparts  a  fine 
purple-violet  color,  which  is  often  observed  in  window-glass. 

Uses. — Binoxide  of  manganese  is  largely  employed  for  preparing  chlorine,  and 
is  thus  of  great  importance  to  the  manufacturer  of  bleaching-powder.  Moreover, 
glass-makers  employ  considerable  quantities  to  decolorize  their  glass,  either  by 
peroxidizing  any  (prot-)  oxide  of  iron  which  may  be  present,  or  by  oxidizing  any 
carbonaceous  matters.  It  is  also  used  in  coloring  glass. 

The  calico-printer  makes  use  of  it  for  obtaining  a  black  or  brown  color,  for 
which  purpose  the  hydrated  binoxide  is  precipitated  in  the  fabric  by  the  action 
of  chloride  of  lime  upon  the  sulphate  of  manganese.  We  have  encountered  many 
examples  of  the  use  of  this  oxide  in  the  laboratory. 

MANGANIC  ACID,  Mn03. 

§  237.  This  acid  has  not  yet  been  isolated,  in  consequence  of  its  instability; 
but  it  is  well  known  in  its  combinations  with  bases. 

MANGANATE  OF  POTASSA,  CHAMELEON  MINERAL,  KO.Mn03. 

This  salt  is  always  formed  when  a  compound  of  manganese  is  fused  with 
potassa  or  its  carbonate  in  presence  of  an  oxidizing  agent. 

Preparation. — The  best  method  of  preparing  it  consists  in  fusing  an  intimate 
mixture  of  binoxide  of  manganese  and  hydrate  of  potassa  in  a  current  of  oxygen. 
One  part  of  binoxide  in  impalpable  powder  is  mixed  with  one  part  of  hydrate  of 
potassa  dissolved  in  a  little  water ;  the  paste  is  dried,  introduced  into  a  tube  of 
hard  glass,  and  heated  to  dull  redness  for  some  time  in  a  current  of  oxygen. 
When  the  mass  is  afterwards  digested  with  a  little  cold  water,  it  gives  a  dark 
emerald-green  solution,  which  must  be  filtered  through  asbestos,  and  carefully 
evaporated  in  vacuo  over  oil  of  vitriol ;  fine  green  crystals  are  thus  obtained, 
which  are  freed  from  mother-liquor  by  draining  on  a  porous  tile.1 

1  Another  process  for  obtaining  this  salt  in  larger  quantity,  though  in  an  impure  state, 
will  be  described  in  the  method  for  preparing  permanganate  of  potassa. 


360  PERMANGANATES. 

Properties. — These  crystals  dissolve  without  alteration  in  solution  of  potassa, 
but  they  are  decomposed  by  water,  yielding  a  red  solution  of  ^permanganate  of 
potassa,  and  a  brown  precipitate  of  the  hydrated  binoxide  of  manganese : — 

3(KO.Mn03)+2HO=KO.Mn207+Mn024-2(KO.HO). 

A  similar  decomposition  may  be  effected  by  adding  a  large  quantity  of  water  to 
the  alkaline  solution,  especially  if  the  temperature  be  raised.  The  changes  of 
color  thus  produced  have  caused  the  name  chameleon  mineral  to  be  bestowed 
upon  the  mass  obtained  by  fusing  the  binoxide  of  manganese  with  alkalies  and 
oxidizing  agents. 

Solution  of  manganate  of  potassa  is  easily  decomposed  by  reducing  agents ; 
contact  with  organic  matters  speedily  changes  it,  so  that  it  must  not  be  filtered 
through  paper;  in  these  cases,  the  manganic  acid  is  converted  generally  into 
sesquioxide  of  manganese. 

The  solution  of  manganate  of  potassa  is  easily  converted  inrto  the  permanga- 
nate by  acids : — 
5(KO.Mn03)+4(HO.N05)=MnO.N05+3(KO.N05)+2(KO.Mn307)-f-4HO. 

Manganate  of  potassa  possesses  a  very  high  coloring  power;  a  very  small 
quantity  of  this  salt  will  color  a  large  amount  of  liquid ;  hence  its  production  is 
frequently  employed  as  an  indication  of  the  presence  of  manganese. 

The  Manganate  of  Soda  much  resembles  the  potassa-salt,  the  other  manga- 
nates  are  insoluble. 

Manganic  acid  is  isomorphous  with  sulphuric,  selenic,  and  chromic  acids,  their 
salts  having  the  same  crystalline  form. 

PERMANGANIC  ACID,  HYPERMANGANIC  ACID,  MnaO7. 

This  acid  is  prepared  by  decomposing  permanganate  of  baryta  with  sulphuric 
acid  (dilute),  decanting  the  clear  liquid,  and  evaporating  in  vacua  over  oil  of 
vitriol,  at  as  low  a  temperature  as  possible. 

It  forms  a  brown  crystalline  mass,  which  is  very  readily  soluble  in  water. 

Permanganic  acid  is  also  very  unstable.  It  is  decomposed  at  80°  or  90°  F.  into 
oxygen  and  binoxide  of  manganese ;  organic  matters,  ammonia,  and  reducing 
agents  generally,  decompose  it  with  facility. 

PERMANGANATE  OF  POTASSA,  KO.Mn207. 

Preparation. — In  order  to  prepare  this  salt  in  a  pure  state,  4  parts  of  finely- 
powered  binoxide  of  manganese  are  intimately  mixed  with  3  J  parts  of  chlorate  of 
potassa ;  to  this  mixture  are  added  5  parts  of  hydrate  of  potassa,  dissolved  in  a  very 
small  quantity  of  water;  the  pasty  mass  is  dried,  and  fused  for  an  hour  or  so  in 
an  earthen  crucible.  When  cold,  it  is  extracted  with  a  considerable  quantity  of 
water,  the  solution  filtered  through  asbestbs,  and  evaporated  at  as  low  a  tempe- 
rature as  possible,  when  fine  crystals  of  the  permanganate  are  deposited. 

Properties. — These  crystals  have  a  dark-red  color;  they  are  soluble  in  about 
16  parts  of  cold  water.  Permanganate  of  potassa  is  a  powerful  oxidizing  agent; 
it  is  deoxidized  under  the  same  circumstances  as  the  manganate,  and  with  simi- 
lar results ;  even  the  organic  matters  floating  in  the  air  are  capable  of  decom- 
posing this  salt. 

If  a  solution  of  permanganate  of  potassa  be  mixed  with  an  excess  of  caustic 
potassa,  its  color  changes  to  green,  manganate  of  potassa  being  formed,  and 
oxygen  liberated : — 

KO.Mn207-fKO=2(KO.Mn03)+0. 

Uses. — Permanganate  of  potassa  is  employed  for  the  detection  of  sulphurous 
acid  in  officinal  hydrochloric  acid,  and  of  the  inferior  oxides  of  nitrogen  in  nitric 
acid,  since  its  very  intense  red  color  is  destroyed  with  the  greatest  ease  by 


SULPHIDE   OF   MANGANESE.  361 

reducing  agents.  It  also  receives  application  in  the  determination  of  iron,  in 
quantitative  analysis. 

Permanganate  of  Baryta,  which  serves  for  the  preparation  of  the  acid,  may 
be  obtained  by  igniting  binoxide  of  manganese  with  nitrate  of  baryta,  or  by  decom- 
posing a  hot  solution  of  permanganate  of  silver  with  chloride  of  barium,  when 
chloride  of  silver  is  precipitated,  and  permanganate  of  baryta  remains  in  solution. 

The  permanganate  of  silver  may  be  prepared  by  adding  nitrate  of  silver  to  a 
hot  concentrated  solution  of  permanganate  of  potassa;  the  silver-salt  crystallizes 
out  on  cooling. 

CHLORIDE,  OR  PROTOCHLORIDE,  OF  MANGANESE,  MnCl. 

§  238.  This  salt  is  prepared  from  the  residues  left  after  the  preparation  of 
chlorine  from  hydrochloric  acid,  and  binoxide  of  manganese.  The  solution  is 
evaporated  to  dryness,  the  residue  dissolved  in  a  little  water,  and  the  chloride  of 
manganese  allowed  to  crystallize  out  ;  the  crystals  are  redissolved  in  water,  the 
solution  boiled  with  a  little  carbonate  of  manganese  to  precipitate  the  sesquioxide 
of  iron,  filtered,  and  again  evaporated  to  crystallization. 

The  chloride  crystallizes  in  pink,  four-sided  tables,  of  the  formula  MnCl+GAq. 
They  deliquesce  in  moist  air.  When  heated,  these  become  anhydrous,  and 
undergo  the  igneous  fusion;  if  the  fused  salt  be  ignited  in  air,  chlorine  is  expelled, 
and  the  manganese  oxidized.  Anhydrous  chloride  of  manganese  dissolves  in  2 
parts  of  water  at  144°  F.  (62°  C.),  which  is  its  point  of  greatest  solubility. 
It  also  dissolves  in  alcohol.  This  chloride  is  used  in  dyeing.  It  is  also  employed, 
occasionally,  for  the  purification  of  gas,  since  it  readily  decomposes  the  sulphide 
of  ammonium  and  carbonate  of  ammonia  found  among  the  products  of  the  dis- 
tillation of  coal. 

Chloride  of  manganese  forms  a  crystallizable  double-salt  with  chloride  of 
ammonium. 

The  tSesquichloride  of  Manganese  (Mn3Cl3)  is  only  known  in  solution,  which 
has  a  deep-brownish  color,  and  is  decomposed  by  heat,  evolving  chlorine  ;  it  is  ob- 
tained when  hydrated  sesquioxide  of  manganese  is  dissolved  in  hydrochloric  acid. 

The  same  remarks  apply  to  the  bichloride. 

SULPHIDE  OF  MANGANESE,  MnS. 

This  compound  is  found  native  in  compact  brilliant  masses  of  a  black  color, 
becoming  green  when  powdered;  it  is  called  manganese-blende.  The  anhydrous 
sulphide  may  be  prepared  by  heating  to  redness  a  mixture  of  binoxide  of  manga- 
nese and  sulphur  :  — 


it  is  thus  obtained  as  a  dark  green  powder. 

When  heated  in  air,  sulphide  of  manganese  is  converted  into  sulphurous  acid, 
and  protosesquioxide  of  manganese.  It  is  decomposed  by  acids,  especially  nitric. 

Hydrated  sulphide  of  manganese  is  obtained  as  a  flesh-colored  precipitate,  when 
a  solution  of  a  salt  of  manganese  is  decomposed  by  an  alkaline  sulphide  ;  when 
exposed  to  air,  it  soon  becomes  brown,  being  partially  converted  into  one  of  the 
higher  oxides  of  manganese.  If  heated  out  of  contact  with  air,  it  loses  water, 
and  is  converted  into  the  dark  green  anhydrous  sulphide.  The  hydrate  is 
dissolved  by  sulphuric,  hydrochloric,  and  nitric  acids. 

An  oxysulphide  of  manganese  is  formed  when  hydrogen  is  passed  over  sulphate 
of  manganese  at  a  red  heat  ;  it  has  a  green  color,  and  burns  when  heated  in  air, 
being  converted  into  sulphurous  acid  and  proto-sesquioxide  of  manganese.  It 
dissolves  in  acids,  with  evolution  of  hydro-sulphuric  acid. 

Compounds  of  sulphide  of  manganese  with  the  sulphides  of  potassium  and 
having  the  composition  KS.3MnS;  and  NaS.3MnS,  are  obtained  by 


362  ZINC. 

heating  a  mixture  of  dry  sulphate  of  manganese  "with  -l  part  of  charcoal,  3  parts 
of  carbonate  of  potassa  or  soda,  and  an  excess  of  sulphur.  "When  the  fused 
mass  is  treated  with  water,  the  double  sulphide  is  left  as  a  dark-red,  crystalline 
powder,  which  is  easily  oxidized  when  exposed  to  air,  and  is  readily  acted  upon 
by  acids. 


ZINC. 

Sym.  Tin.     Eq.  32.6. 

§  239.  This  metal  is  pretty  abundant  in  nature,  and  is  important  from  its 
numerous  applications.  We  shall  therefore  devote  a  section  to  the  technical 
history  of  zinc,  after  we  have  become  acquainted  with  its  chemical  properties. 

Preparation. — The  zinc  of  commerce  contains  about  1  per  cent,  of  impurities, 
consisting  of  lead,  iron,  tin,  carbon,  copper,  cadmium,  and  arsenic.  In  order  to 
purify  it,  it  is  subjected  to  distillation  in  an  earthen  crucible,  furnished  with  an 
earthen  tube  which  passes  through  the  bottom  of  the  crucible  and  extends  nearly 
to  the  top;  this  tube  projects  downwards  through  the  bars  of  the  furnace,  and 
nearly  touches  the  surface  of  water  in  a  reservoir  situated  in  the  ash-pit.  The 
crucible  is  half  filled  with  zinc,  and  strongly  heated,  when  the  metal  condenses 
in  the  water.  The  distilled  metal  still  contains  a  little  lead,  cadmium,  and  arse- 
nic ;  it  is  freed  from  the  latter  by  fusing  with  about  J  its  weight  of  nitre,  which 
converts  it  into  arseniate  of  potassa ;  the  mass  is  treated  with  water,  and  the 
metal  dissolved  in  dilute  sulphuric  acid,  which  leaves  the  lead  as  insoluble  sul- 
phate; a  current  of  sulphuretted  hydrogen  is  now  passed  through  the  highly  diluted 
solution,  to  removed  the  cadmium  as  sulphide ;  the  filtered  liquid  contains  only 
sulphate  of  zinc,  which  may  be  precipitated  by  carbonate  of  soda,  and  reduced 
by  charcoal. 

Properties. — Zinc  is  a  bluish-white,  lustrous  metal,  with  a  lamellar,  crystalline 
structure;  it  is  somewhat  brittle  at  the  ordinary  temperature,  but  becomes  malle- 
able at  a  little  above  212°  F.  (100°  C.),  and  may  be  rolled  into  plates,  or  drawn 
out  into  fine  wires.  At  about  400°  F.  (204°  C.),  it  again  becomes  brittle,  and 
may  be  reduced  to  powder. 

This  metal  fuses  below  a  red  heat,  and  boils  at  a  white  heat,  when  it  may  be 
distilled  unchanged.  If  fused  zinc  be  allowed  to  cool  gradually,  it  crystallizes 
in  prisms  with  hexagonal  bases.  If  it  be  poured  into  water,  it  is  divided  into 
small  irregular  masses,  or  granulated.  The  sp.  gr.  of  cast-zinc  is  6.8;  that  of 
rolled  zinc,  7.2.  It  possesses  very  little  tenacity;  a  wire  of  y1^  inch  in  diameter 
will  only  support  26  Ibs. 

Zinc  is  unaltered  by  exposure  to  dry  air,  but  in  moist  air  it  soon  becomes 
covered  with  a  thin  film  of  oxide  of  zinc,  which  absorbs  a  little  carbonic  acid  from 
the  air.  When  heated  in  air  a  little  above  its  fusing-point,  it  takes  fire,  and 
burns  with  a  greenish-white,  highly  luminous  flame,  producing  a  thick,  white 
smoke  of  oxide  of  zinc  (philosopher's  loooT). 

Water  free  from  air  and  carbonic  acid  has  no  action  upon  zinc,  but  common 
water  converts  a  portion  of  the  metal  into  carbonate  of  zinc,  since  it  is  oxidized 
either  by  the  air  in  the  water,  or  even  at  the  expense  of  the  latter,  hydrogen  being 
disengaged.  When  vapor  of  water  is  passed  over  zinc  at  an  elevated  temperature, 
oxide  of  zinc  is  formed,  and  hydrogen  evolved ;  the  decomposition  of  the  water 
commences  even  at  212°  F.  (100°  C.) 

Zinc  decomposes  water  very  readily  at  the  ordinary  temperature,  in  presence 
of  acids;  thus,  with  sulphuric  acid: — 

Zn+HO.SO=ZnO.S03+H. 


«  l|  OXIDES    OF   ZINC.  363 

If  pure  zinc  be  immersed  in  dilute  sulphuric  acid,  it  becomes  covered  with  a 
number  of  hydrogen  bubbles,  which  protect  it  from  further  action,  but  if  a  nega- 
tive plate  be  provided,  from  which  the  bubbles  may  be  disengaged,  the  action  is 
continuous;  in  ordinary  zinc,  the  impurities  supply  a  series  of  such  negative 
plates. 

The  readiness  with  which  weak  acids  act  upon  zinc  warns  us  against  employ- 
ing this  metal  largely  for  culinary  purposes,  since  its  salts  are  poisonous. 

The  hydrogen  acids  readily  dissolve  zinc,  concentrated  sulphuric  acid  in  the 
cold  scarcely  affects  it.  Solutions  of  potassa,  soda,  and  even  of  ammonia,  are 
capable  of  dissolving  zinc,  with  evolution  of  hydrogen  and  formation  of  com-* 
pounds  of  oxide  of  zinc  with  the  alkalies. 

Zinc  is  capable  of  precipitating  a  great  many  metals  from  their  solutions ; 
copper,  tin,  antimony,  and  silver  may  serve  as  examples. 


ZINC    AND    OXYGEN. 

Suboxide  of  zinc Zn20. 

(Prot-)  oxide  "       ........     ZnO. 

Peroxide         "...     .,    £'>     .     .     ZnOa. 

SUBOXIDE  OF  ZINC,  Zn20. 

§  240.  The  existence  of  this  oxide  is  not  very  certain,  since  it  has  never  been 
obtained  in  a  pure  state ;  it  is  said  to  be  formed  when  zinc  tarnishes  in  moist 
air.  When  oxalate  of  zinc  is  carefully  heated  in  a  close  vessel,  it  leaves  a  dark 
gray  substance,  which  is  supposed  to  be  the  suboxide;  it  is  decomposed  by  acids 
into  oxide  of  zinc  and  metal. 

OXIDE,  OR  PROTOXIDE  OF  ZINC. 
ZnO.-'   Eq.  40.6. 

This  oxide  occurs  in  nature  as  red  zinc-ore. 

Anhydrous  oxide  of  zinc  is  formed  when  zinc  is  burnt  in  air,  or  heated  in  an 
atmosphere  of  steam;  in  the  latter  case  it  is  crystalline.1 

Preparation. — It  is  best  prepared  by  calcining  the  precipitate  produced  by 
mixing  solutions  of  sesquicarbonate  of  ammonia  and  sulphate  of  zinc. 

On  the  large  scale  it  is  made  by  vaporizing  zinc  in  earthen  cylinders  through 
which  a  current  of  air  is  passed. 

Properties. — It  forms  a  light  white  powder  which  becomes  yellow  when 
heated,  and  white  again  on  cooling.  Oxide  of  zinc  is  perfectly  fixed  and  cannot 
be  decomposed  by  heat.  When  exposed  to  air,  it  becomes  partly  converted  into 
carbonate.  It  is  insoluble  in  water,  but  dissolves  easily  in  acids ;  its  salts  have 
the  same  crystalline  form  as  those  of  magnesia  and  oxide  of  iron,  with  which  it 
is  isomorphous.  Even  those  salts  which  are  neutral  in  constitution,  are  found 
to  have  an  acid  reaction. 

Oxide  of  zinc  is  not  easily  soluble  in  solutions  of  potassa  and  soda,  but  if  it 
be  fused  with  these  in  a  silver  crucible,  it  forms  compounds  soluble  in  water,  in 
which  the  oxide  of  zinc  appears  to  play  the  part  of  an  acid. 

This  oxide  has  been  used,  of  late  years,  as  a  substitute  for  white-lead  (car- 
bonate of  lead)  as  a  pigment  (zinc-wliite)\  it  possesses  the  advantages  of  not 
affecting  the  health  of  the  painters,  and  of  being  unaltered  by  sulphuretted 
hydrogen,  which  blackens  lead-paint. 

Oxide  of  zinc  is  also  used  in  medicine. 

1  Kectangular  four-sided  prisms  of  this  oxide  have  been  formed  accidentally  in  the  dis- 
tillation of  zinc. 


364  SALTS   OF   ZINC. 

Uydrated  Oxide  of  Zinc  (ZnO.HO)  may  be  prepared  by  adding  solution  of 
potassa  to  solution  of  sulphate  of  zinc,  avoiding  an  excess ;  it  forms  a  white  pre- 
cipitate which  should  be  dried  by  simple  exposure.  When  freshly  precipitated 
it  is  easily  soluble  in  potassa,  soda,  or  ammonia,  but  after  drying,  not  so  readily. 

Prismatic  crystals  of  this  hydrate  may  be  obtained  by  introducing  a  voltaic 
couple  of  zinc  and  iron  into  a  solution  of  potassa  or  ammonia. 

§  241.  NITRATE  OF  ZINC  (ZnO.N05)  prepared  by  dissolving  zinc  in  dilute 
nitric  acid,  crystallizes  in  four-sided  prisms,  containing  6  eqs.  water.  It  is 
deliquescent,  and  very  soluble  in  water  and  alcohol. 

SULPHATE  or  OXIDE  or  ZINC.    SULPHATE  OF  ZINC.    WHITE  VITRIOL. 

ZnO.S03. 

Preparation. — This  salt  is  obtained  on  the  large  scale  by  roasting  native  sul- 
phide of  zinc  (blende),  extracting  with  water,  and  evaporating  the  solution  to 
the  crystallizing  point ;  for  convenience  of  transport,  the  salt  is  generally  fused 
in  its  water  of  crystallization,  and  sent  into  commerce  in  white  masses.  These 
are  generally  contaminated  with  the  sulphates  of  magnesia,  iron,  and  copper. 

To  prepare  pure  sulphate  of  zinc,  commercial  zinc  is  dissolved  in  dilute  sul- 
phuric acid,  and  a  Jittle  chlorine  added  to  peroxidize  any  iron  which  may  be 
present ;  the  solution  is  then  heated  with  carbonate  of  zinc,  which  precipitates 
the  sesquioxide  of  iron,  filtered,  and  evaporated  to  crystallization. 

Pure  sulphate  of  zinc,  when  dissolved  in  water  and  boiled  with  a  little  nitric 
acid,  should  give  no  brown  precipitate,  with  excess  of  ammonia  (indicating  iron), 
and  no  blue  color  (due  to  copper). 

Properties. — The  formula  of  the  ordinary  crystals  of  this  salt  is  ZuO.S03, 
HO-f  6Aq,  but  salts  containing  less  water  of  crystallization  have  been  obtained. 

A  sulphate  of  the  formula  ZnO.S03.HO+4Aq  may  be  obtained  by  boiling 
the  ordinary  crystals  for  some  time  with  alcohol;  another  salt,  containing  only 
2  eqs.  of  water  of  crystallization,  is  precipitated  when  concentrated  sulphuric 
acid  is  added  to  a  strong  solution  of  the  sulphate.  The  ordinary  salt  forms 
prismatic  crystals,  which  lose  their  6  eqs.  of  water  of  crystallization  at  212°  F. 
(100°  C.),  undergoing  the  aqueous  fusion;  at  a  higher  temperature,  the  water 
of  constitution  is  expelled,  and  if  the  heat  be  still  continued,  sulphurous  acid 
and  oxygen  pass  off,  and  a  basic  sulphate  is  left,  which  is  decomposed  at  a  red 
heat  into  sulphurous  acid,  oxygen,  and  oxide  of  zinc. 

The  crystals  are  soluble  in  about  2J  parts  of  water  at  the  ordinary  tempera- 
ture, and  insoluble  in  alcohol. 
L   The  solution  of  sulphate  of  zinc  has  an  acid  reaction  to  test-papers. 

Uses. — Sulphate  of  zinc  is  employed  to  induce  vomiting;  it  is  poisonous  in 
moderately  large  quantities.  Sulphate  of  zinc  is  used  by  dyers. 

Several  basic  sulphates  of  zinc  are  said  to  exist. 

Sulphate  of  zinc  is  capable  of  combining  directly  with  ammonia,  forming 
definite  compounds,  which  are  easily  decomposed  by  heat. 

This  salt  forms  double  sulphates  with  those  of  potassa,  ammonia,  magnesia, 
and  (prot-)  oxide  of  iron.  The  potassa  and  ammonia  salts  have  the  formula; 
ZnO.S03,KO.S08+ 7Aq,  and  ZnO.S03,NH4O.S03+7Aq. 

CARBONATE  OF  ZINC,  ZnO.COa. 

This  salt  occurs  in  nature  as  calamine}  which  is  sometimes  found  in  amorph- 
ous masses,  sometimes  in  crystals  of  the  same  form  as  those  of  carbonate  of  lime. 
Crystals  of  this  compound  have  been  prepared  by  exposing  to  the  air  solutions 
of  oxide  of  zinc  in  potassa  and  soda. 

It  may  be  prepared  by  a  process  similar  to  that  described  for  the  preparation 
of  anhydrous  carbonate  of  magnesia  (see  p.  307). 


SULPHIDE   OF    ZINC.  365 

When  heated,  carbonate  of  zinc  is  easily  converted  into  oxide.  It  is  insolu- 
ble in  water,  but  dissolves  to  a  slight  extent  in  solution  of  carbonic  acid.  Car- 
bonate of  zinc  also  dissolves  in  solution  of  carbonate  of  ammonia;  after  a  time, 
the  solution  deposits  crystals  of  the  formula  2(ZnO.C02),NH3. 

Carbonates  of  potassa  and  soda  form  double  carbonates  with  that  of  oxide  of 
zinc. 

The  precipitate  produced  by  alkaline  carbonates  in  solutions  of  zinc-salts  is  a 
variable  compound  of  hydrate  and  carbonate,  of  which  the  most  common  formula 
is  2(ZnO.C02),  8(ZnO.HO)  :— 


+3C02. 

Calamine  is  the  chief  ore  of  zinc;  when  previously  prepared  by  levigation  it 
is  sometimes  used  in  surgery. 

The  silicate  of  zinc  is  found  in  nature,  and  is  sometimes  termed  electric  cala- 
mine  (zinc-glance}. 

BINOXIDE  OF  ZINC,  Zn03. 

This  oxide  has  been  obtained  by  the  action  of  binoxide  of  hydrogen  upon 
hydrated  oxide  of  zinc.  It  is  insoluble  in  water,  and  is  easily  decomposed,  even 
at  ordinary  temperatures,  the  second  equivalent  of  oxygen  being  disengaged. 

CHLORIDE  OF  ZINC,  ZnCl. 

§  242.  The  chloride  is  formed,  with  combustion,  when  finely  divided  zinc  is 
introduced  into  chlorine. 

Preparation.  —  It  may  be  prepared  by  dissolving  granulated  zinc  in  hydro- 
chloric acid,  and  evaporating,  when  it  may  be  obtained  in  the  form  of  a  semisolid 
hydrated  mass,  known  as  butter  <of  zinc',  if  this  be  further  heated,  it  fuses  and 
becomes  anhydrous,  when  it  may  be  poured  upon  a  slab  and  allowed  to  solidify. 

Properties.  —  Chloride  of  zinc  forms  white  masses,  which  readily  deliquesce 
when  exposed  to  air  ;  it  fuses  easily,  and  may  be  distilled.  This  salt  is  remark- 
ably soluble  in  water;  alcohol  also  dissolves  it,  and  combines  with  it  to  form  a 
crystallizable  compound. 

When  heated  strongly  in  air,  chloride  of  zinc  is  partly  converted  into  oxide, 
chlorine  being  evolved.  The  hydrated  chloride,  when  strongly  heated,  evolves 
hydrochloric  acid,  and  leaves  a  residue  of  oxychloride  of  zinc,  so  that  it  is  better 
to  dry  it  in  a  current  of  hydrochloric  acid. 

Uses.  —  The  great  affinity  of  chloride  of  zinc  for  water  often  renders  it  useful 
in  experiments  upon  organic  substances. 

Chloride  of  zinc  is  also  sometimes  employed  to  purify  the  air  from  sulphu- 
retted hydrogen,  which  it  converts  into  sulphide  of  zinc.  Sir  W.  Burnett's  dis- 
infecting fluid  is  a  solution  of  this  salt. 

A  solution  of  chloride  of  zinc  is  also  sometimes  employed  as  an  antiseptic  for 
the  preservation  of  subjects  for  dissection;  it  does  not  aflect  the  knives,  like 
corrosive  sublimate,  which  is  sometimes  used  for  that  purpose. 

A  bath  of  fused  chloride  of  zinc  is  occasionally  substituted  for  an  oil-bath  in 
chemical  operations. 

Three  oxychlorides  of  zinc  are  said  to  exist,  containing  respectively  3,  6,  and 
9  equivalents  of  oxide,  combined  with  1  equivalent  of  chloride.  They  all  con- 
tain water. 

SULPHIDE  OF  ZINC.     ZnS. 

This  compound  is  found  in  nature,  and  is  termed  by  mineralogists  blende.  It 
is  met  with  both  crystalline  and  amorphous;  the  crystals  are  derived  from  a 
cube.  Blende  is  yellow,  or  brownish-black,  and  translucent;  it  is  not  easily 


366  METALLURGY   OF   ZINC. 

attacked  by  acids.  It  is  usually  contaminated  with  iron,  cadmium,  lead,  copper, 
arsenic,  alumina,  silica,  magnesia,  and  fluoride  of  calcium.  When  blende  is 
roasted  in  air,  sulphurous  acid  is  evolved,  and  a  mixture  of  oxide  and  sulphate 
of  zinc  is  first  produced,  which  is  decomposed  by  a  higher  temperature,  leaving 
oxide  of  zinc  only. 

Sulphide  of  zinc  may  be  prepared  by  the  direct  combination  of  its  elements, 
or  by  heating  a  mixture  of  oxide  of  zinc  with  flowers  of  sulphur;  it  is  also 
formed  when  the  sulphate  is  heated  with  charcoal;  thus  obtained,  it  is  a^ellow 
powder. 

Hydrated  sulphide  of  zinc  is  obtained  as  a  white  precipitate  by  adding  an 
alkaline  sulphide  to  a  solution  of  a  zinc-salt;  it  dissolves  readily  in  hydrochloric 
or  nitric  acid. 

Sulphide  of  zinc  is  capable  of  combining  with  the  sulphides  of  the  alkali- 
metals  at  a  high  temperature. 

When  hydrogen  is  passed  over  anhydrous  sulphate  of  zinc  at  a  red  heat,  an 
oxy  sulphide  is  obtained,  which  has  the  formula  ZnO.ZnS. 

Another  oxysulphide,  of  the  formula  Zn0.4ZnS  occurs  in  nature  in  a  crystal- 
line state,  and  has  been  also  obtained  in  metallurgic  processes. 

METALLURGY  OF  ZINC. 

§  243.  The  only  ores  from  which  this  metal  is  extracted  are  the  carbonate,  or 
calamine,  and  the  sulphide,  known  as  blende  or  Hack-jack  ;  the  former  is  the 
most  abundant  ore  of  zinc. 

Calamine  is  calcined  to  expel  water  and  carbonic  acid,  before  being  reduced. 

Blende  is  first  roasted  with  access  of  air,  by  which  it  is  converted  into  oxide 
of  zinc. 

The  reduction  of  the  metal  is  very  simple.  The  ore,  prepared  as  above,  is 
mixed  with  coal  or  charcoal,  and  strongly  heated  in  clay  retorts,  which  vary  in 
construction,  but,  in  England,  consists  of  crucibles  furnished  with  an  iron  tube, 
which  penetrates  to  some  distance  within  the  crucible,  and  passes  through  the 
bottom ;  the  zinc  is  converted  into  vapor  which  condenses  in  the  tube.  The 
metal  thus  obtained  is  fused,  and  cast  into  ingots. 

The  progress  of  the  distillation  of  the  zinc  is  judged  of  by  the  workmen  from 
the  flame  with  which  the  vapors  burn  at  the  mouth  of  the  tube ;  at  the  beginning 
of  the  operation,  the  flame  has  a  brownish  hue,  and  the  zinc  which  distils  con- 
tains much  cadmium  and  arsenic ;  this  stage  of  the  operation  is  termed  the 
brown  blaze.  When  a  bluish-white  flame  appears  (the  blue  blaze),  due  to  the 
combustion  of  carbonic  oxide  and  vapor  of  zinc,  the  metal  is  obtained  in  a  pretty 
pure  state. 

In  the  continental  smelting  works,  the  ores  are  reduced  upon  the  same  prin- 
ciple, but  various  forms  of  retorts  are  employed  instead  of  crucibles. 

Zinc  is  sometimes  termed  spelter  in  commerce. 

The  uses  of  zinc  are  numerous  and  important.  It  serves  for  gutters  and  water- 
pipes,  for  covering  the  roofs  of  houses,  for  coating  iron  to  preserve  it  from  rust 
(galvanized  iron),  for  preparing  zinc-white,  and  other  pigments,  and  as  an  in- 
gredient of  many  useful  alloys,  as  brass,  German  silver,  &c.,  which  will  be 
further  noticed  in  their  proper  places. 

Ores  of  zinc  may  be  roughly  assayed  in  the  dry  way,  by  mixing  them  (after 
previous  roasting)  with  charcoal,  and  if  the  ore  be  a  silicate,  with  black  flux, 
and  heating  rapidly  to  whiteness,  when  the  zinc  is  volatilized,  and  may  be  de- 
termined by  loss  after  burning  off  the  excess  of  charcoal. 

The  wet  assay  is,  however,  far  more  satisfactory,  but  since  other  metals  must 
be  separated  before  we  can  determine  the  zinc,  it  would  be  out  of  place  to  de- 
scribe the  process  here. 


OXIDE   OF   NICKEL.  367 


NICKEL. 

Sym.  Ni.     Eq.  29.6.     Sp.  Gr.  8.5. 

§  244.  Nickel,  in  the  combined  state,  is  tolerably  abundant  in  nature  ;  it  is 
generally  found,  together  with  iron,  in  the  meteoric  stones  to  which  we  have 
before  alluded. 

Pure  nickel  may  be  obtained  by  strongly  igniting  the  oxalate  in  a  closed  cru- 
cible. 

NiO.C303==Ni+2C03. 

It  is  also  obtained  in  a  pyrophoric  state,  by  heating  oxide  of  nickel  in  a 
current  of  hydrogen. 

Of  the  method  of  extracting  nickel  from  its  ores  we  shall  speak  hereafter. 

Properties. — Nickel  is  a  grayish- white  metal,  with  considerable  lustre ;  it  is 
malleable  and  ductile.  This  metal,  like  iron,  is  attracted  by  the  magnet  at 
ordinary  temperatures ;  it  fuses  rather  more  easily  than  iron,  and  becomes  more 
fusible  when  combined  with  carbon.  Nickel  is  not  altered  at  the  ordinary  tem- 
perature by  exposure  to  moist  air,  but  is  oxidized  when  heated  to  redness ;  it 
burns  in  oxygen,  like  iron,  and  is  capable  of  decomposing  water  at  a  red  heat. 

Nickel  dissolves  readily  in  nitric  acid,  being  oxidized  and  converted  into  the 
nitrate;  hydrochloric  and  dilute  sulphuric  acids  act  upon  it,  though  less  rapidly, 
hydrogen  being  evolved. . 


NICKEL  AND  OXYGEN. 

Oxide  of  nickel    .     .     ."'..    ^.\  'J.~  V   ..^" ' ..     .     NiO 
Sesquioxide Ni203 

The  existence  of  a  higher  oxide  than  this  last  has  been  alleged ',  but  is  not  certain. 

OXIDE,  OR  PROTOXIDE  OF  NICKEL. 
NiO.     .%37.6. 

§  245.  When  nickel  is  heated  to  redness  in  aqueous  vapor,  it  becomes  covered 
with  a  light  olive-green  crystalline  powder,  which  consists  of  anhydrous  oxide  of 
nickel.  This  oxide  may  also  be  prepared  by  heating  the  hydrate  or  the  basic 
carbonate  of  nickel.  The  oxide  thus  obtained  is  said  to  contain  a  little  sesqui- 
oxide  of  nickel,  from  which  it  may  be  purified  by  gently  heating  in  a  current  of 
hydrogen.1  It  has  an  ash-gray  color,  and  is  not  fused  or  decomposed  by  heat. 

Oxide  of  nickel  is  reduced  to  the  metallic  state  by  hydrogen  or  carbon  at  an 
elevated  temperature. 

This  oxide  is  a  pretty  powerful  base,  and  forms  well-defined  salts,  which  redden 
litmus-paper. 

The  Hydrated  Oxide  of  Nickel,  NiO.  HO,  is  thrown  down  as  an  apple-green 
precipitate,  on  adding  a  fixed  alkali  to  a  solution  of  a  nickel-salt.  It  is  de- 
posited in  a  crystalline  state  from  a  solution  of  carbonate  of  nickel  in  ammonia. 

The  hydrate  is  insoluble  in  the  fixed  alkalies,  but  dissolves  with  a  fine  blue 
color  in  ammonia.  Its  water  is  easily  expelled  by  heat. 

NITRATE  OF  OXIDE  OF  NICKEL,  NITRATE  OF  NICKEL,  NiO.N05. — This  salt 

1  The  crystalline  anhydrous  oxide  has  been  found  in  the  mineral  kingdom,  in  the  form 
of  minute  octohedra,  which  were  not  attacked  by  any  solvent  except  boiling  sulphuric 
acid. 


368  SALTS   OF   NICKEL. 

forms  green  crystals,  which  are  deliquescent,  and  very  soluble  in  water.  The 
crystals  contain  6  eqs.  of  water.  It  is  decomposed  by  heat,  leaving  sesquioxide 
or  (prot-)  oxide  of  nickel,  according  to  the  temperature  employed. 

This  salt  combines  with  ammonia  to  form  a  soluble  compound  of  the  formula 
NiO.N05,2NH3+Aq. 

SULPHATE  OF  OXIDE  OF  NICKEL,  SULPHATE  OF  NICKEL. 
NiO.S03. 

The  sulphate  of  nickel  may  be  prepared  by  dissolving  the  metal,  its  oxide,  or 
carbonate,  in  dilute  sulphuric  acid,  and  evaporating  the  liquid  to  crystallization. 

When  the  crystals  are  formed  at  the  ordinary  temperature,  they  are  rectangu- 
lar four-sided  prisms,  of  the  formula  NiO.S03.HO-f6Aq;  but  those  deposited 
above  60°  F.  (15°. 5  C.),  are  octohedra,  with  the  formula  NiO.S03.HO-f  5Aq. 
The  water  of  crystallization  is  expelled  at  a  little  above  the  boiling  point,  but 
the  water  of  constitution  is  not  expelled  below  5*27°  F.  (275°  C.) 

The  crystals  have  a  fine  emerald-green  color;  when  exposed  to  air  they 
lose  their  water  of  crystallization,  becoming  yellow  and  opaque. 

Sulphate  of  nickel  is  very  soluble  in  water,  but  insoluble  in  alcohol  and 
ether.  Its  aqueous  solution  is  acid  to  test-papers. 

Anhydrous  sulphate  of  nickel  combines  with  ammoniacal  gas,  producing  a 
compound  of  the  formula  NiO.S03,3NH3. 

When  solution  of  sulphate  of  nickel  is  mixed  with  solution  of  ammonia,  a 
compound  is  produced  which  crystallizes  in  rectangular  prisms  of  a  fine  blue 
color,  having  the  composition  NiO.S03,2NH3-f-2Aq. 

The  equivalent  of  water  of  constitution  in  crystallized  sulphate  of  nickel 
may  be  replaced  by  an  alkaline  sulphate,  and,  in  this  way,  well-defined  crys- 
tallizable  double-salts  are  produced.  The  formula  of  the  potassa-salt  is  KO.S03, 
NiO.S03-r-6Aq. 

An  insoluble  basic  sulphate  of  nickel  is  obtained  when  the  sulphate  is  mo- 
derately heated,  or  decomposed  by  an  insufficient  quantity  of  potassa. 

No  neutral  carbonate  of  nickel  has  been  obtained ;  the  precipitate  produced 
by  carbonate  of  soda  in  solutions  of  nickel-salts,  has  the  composition  2NiO.C02, 
3NiO.HO-f2Aq.1 

SESQUIOXIDE  OR  PEROXIDE  OF  NICKEL,  Ni303. 

This  oxide  may  be  prepared  by  decomposing  the  nitrate  at  a  moderate  heat. 
It  is  also  formed  when  hydrated  oxide  of  nickel  comes  in  contact  with  chlorine 
or  with  a  hypochlorite : — 

3NiO+Cl=Nia08+NiCl; 
4NiO+CaO.C10=2(NU33)-f-CaCl. 

If  the  solution  be  decanted  from  the  precipitated  sesquioxide  of  nickel,  and 
boiled,  a  precipitate  of  hydrated  sesquioxide,  of  the  formula  Ni303.3HO,  is 
obtained. 

Sesquioxide  of  nickel  forms  a  black  powder,  which  evolves  oxygen  when 
heated,  and  is  converted  into  the  (prot-)  oxide. 

It  is  an  indifferent  oxide;  when  heated  with  sulphuric  acid,  sulphate  of 
nickel  is  formed,  and  oxygen  disengaged  : — 

Ni303+2(HO.S03)=2(NiO.S03)-f2HO  +  0. 

Hydrochloric  acid  converts  it  into  chloride  of  nickel,  with  disengagement  of 
chlorine : — 

Ni303-f3HCl==2NiCl-j-Cl-f3HO. 

1  If  a  solution  of  a  nickel-salt  be  precipitated  by  bicarbonate  of  potassa,  a  double-salt 
of  the  composition  K0.2C02,NiO.C02-flOAq  is  formed. 


METALLURGY   OP   NICKEL.  869 

Ammonia  also  decomposes  the  sesquioxide  of  nickel : — 
3Ni303+NH3=6NiO-f3HO-fN. 

The  hiyher  oxide  of  nickel  mentioned  above,  the  composition  of  which  was  said 
to  be  doubtful,  was  obtained  by  treating  the  bydrated  oxide  of  nickel  with  solu- 
tion of  biuoxide  of  hydrogen ;  it  has  a  dirty-green  color,  and  is  very  unstable. 

CHLORIDE  OF  NICKEL,  NiCl. 

§  246.  The  anhydrous  chloride  may  be  obtained  by  passing  chlorine  over 
nickel  at  a  red  heat,  or  by  gently  heating  the  hydrated  chloride;  in  either  case 
it  sublimes  in  fine  golden  yellow  scales,  since  it  is  volatile  at  a  moderately  high 
temperature.  It  dissolves  when  long  boiled  with  water,  yielding  a  green  solution. 
Chloride  of  nickel,  when  heated  to  redness  in  hydrogen,  yields  brilliant  metal. 

Ilydrated  chloride  of  nickel  is  prepared  by  dissolving  the  metal,  or  its  oxide, 
in  hydrochloric  acid;  it  forms  yellowish-green  crystals,  containing  nine  eqs.  of 
water;  they  become  emerald-green  on  exposure  to  air,  absorbing  moisture.  An- 
hydrous chloride  of  nickel  absorbs  ammonia,  forming  a  compound  of  the  com- 
position NiC1.3NH3,  which,  when  heated,  leaves  metallic  nickel. 

NICKEL  AND  SULPHUR. 

Subsulphide Ni3S 

(Proto-)  sulphide NiS 

Bisulphide NiSa 

The  subsulphide  is  obtained  when  sulphate  of  nickel  is  decomposed  by  hydro- 
gen at  a  red  heat. 

SULPHIDE,  OR  PROTOSULPHIDE,  OF  NICKEL,  NiS. 

The  anhydrous  sulphide  occurs  in  nature  as  capillary  pyrites.  It  may  be 
formed  by  the  direct  combination  of  its  elements,  which  takes  place  energetically 
at  a  high  temperature.  If  a  mixture  of  oxide  of  nickel,  carbonate  of  soda,  and 
sulphur  be  strongly  heated,  a  lustrous  button  of  sulphide  of  nickel  maybe  obtained. 

Anhydrous  sulphide  of  nickel  has  a  bronze  color;  it  is  insoluble  in  hydrochlo- 
ric acid,  but  dissolves  in  nitric,  or  in  nitrohydrochloric  acid. 

The  hydrated  sulphide  is  obtained  as  a  black  precipitate,  when  a  nickel-salt  is 
decomposed  by  an  alkaline  sulphide.  It  is  slowly  oxidized  and  converted  into 
sulphate  when  exposed  to  air. 

Hydrated  sulphide  of  nickel  dissolves  with  difficulty  in  hydrochloric  acid,  but 
easily  in  nitric,  or  in  nitro- hydrochloric  acid. 

The  bisulphide  of  nickel  is  prepared  by  calcining  an  intimate  mixture  of  car- 
bonate of  nickel,  carbonate  of  potassa,  and  sulphur;  on  treating  the  mass  with 
water,  the  bisulphide  is  left  as  a  steel-gray  powder. 

METALLURGY  OF  NICKEL. 

§  247.  The  chief  mineral  containing  nickel  is  that  termed  copper-nickel 
(^Kupfer  nickel)  j  so  called  by  the  German  miners,  because  they  frequently  mis- 
took it  for  an  ore  of  copper;  it  is  an  arsenide  (arseniuret)  of  nickel,  of  the 
formula  NiAs. 

Copper-nickel  is  amorphous,  and  has  a  reddish  metallic  appearance;  when 
roasted  in  air,  it  is  converted  into  a  basic  arseniate  of  nickel.  This  mineral  is 
unaffected  by  hydrochloric  acid,  but  dissolves  in  nitric  acid,  or  in  aqua  reyia. 
It  is  often  associated  with  binarsenide  of  nickel,  NiAs3. 

The  arsenio-sulphide  of  nickel,  or  gray  nickel-ore  (iiickel- glance) ,  has  the 
formula  NiS3-r-NiAsa. 

Nickel-antimony  is  a  similar  compound,  containing  antimony  in  place  of 
24 


370  COBALT. 

arsenic.  Nickel  also  occurs  in  nature  as  oxide,  as  sulphide,  as  arsenite  and 
arseniate,  and  as  silicate  (in  the  mineralp/raefo'fc). 

This  metal  is  always  extracted  from  copper-nickel,  or  from  speiss;  the  latter  is 
a  compound  of  nickel,  arsenic,  and  sulphur,  containing  small  quantities  of 
cobalt,  copper,  and  antimony;  it  is  found  at  the  bottom  of  the  crucibles  in  which 
smalt  is  manufactured  (see  p.  373). 

The  separation  of  the  nickel  and  arsenic  is  attended  with  very  considerable 
difficulty;  numerous  methods  have  been  proposed  for  this  purpose,  but  we  must 
content  ourselves  with  describing  only  one  of  them,  in  order  to  convey  an  idea 
of  the  principles  upon  which  the  separation  is  based. 

The  ore  is  first  roasted  with  access  of  air,  which  expels  the  sulphur,  as  sul- 
phurous acid,  and  a  great  part  of  the  arsenic,  as  arsenious  acid.  It  is  then 
fused  in  an  earthen  crucible  with  carbonate  of  potassa  and  sulphur;  the  nickel 
and  arsenic  are  thus  converted  into  sulphides,  a  quantity  of  sulphide  of  potas- 
sium being  formed  at  the  same  time;  when  the  mass  is  treated  with  water,  the 
sulphide  of  potassium  enters  into  solution,  and  dissolves  the  sulphide  of  arsenic, 
whilst  the  sulphide  of  nickel  is  left,  and  may  either  be  converted'  at  once  into  a 
nickel  salt,  or  may  be  roasted  and  transformed  into  oxide,  in  which  state  it  may 
be  employed  for  the  preparation  of  the  alloys  of  nickel,  which  are  used  in  the 
arts  (e.  g.  German -silver). 


COBALT. 

Sym.  Co.     Eg.  29.5.     Sp.  Gr.  8.5. 

§  248.  In  abundance,  cobalt  may  rank  by  the  side  of  nickel,  to  which  metal 
it  presents  a  very  striking  resemblance  in  most  of  its  properties;  for  this  reason, 
the  separation  of  cobalt  from  nickel,  so  as  to  obtain  either  metal  in  a  state  of 
purity,  is  a  matter  of  great  difficulty,  and  yet  of  frequent  necessity,  since  these 
metals  are  generally  associated  in  the  same  ore. 

Metallic  cobalt  may  be  obtained  either  by  calcining  the  oxalate,  or  by  reducing 
the  oxide  by  hydrogen;1  or,  at  a  very  high  temperature,  by  charcoal. 

The  metal  resembles  steel  in  its  aspect.  Cobalt  is  fused  with  great  difficulty, 
but  wore  readily  when  combined  with  a  little  carbon;  it  is  unalterable  in  moist 
air,  but  oxidizes  readily  at  a  high  temperature.  This  metal  dissolves  slowly  in 
hydrochloric  and  sulphuric  acids,  but  readily  in  nitric  acid. 

COBALT  AND  OXYGEN. 

(Prot-)  oxide CoO 

Sesquioxide Co303 

Two  intermediate  oxides  also  exist. 

OXIDE,  OR  PROTOXIDE  OF  COBALT,  CoO. 

§  249.  The  anhydrous  oxide  is  obtained  by  calcining  the  hydrate  or  carbonate, 
with  exclusion  of  air.  It  is  a  nearly  black  powder,  which,  when  heated  in  air, 
absorbs  oxygen,  and  is  converted  into  an  oxide  of  the  formula  Co304.  Oxide  of 
cobalt  colors  fluxes  dark  blue,  and  this  color  resists  the  action  of  a  high  tem- 
perature, so  that  it  is  of  great  service  in  the  decorative  arts. 

Oxide  of  cobalt  is  soluble  in  ammonia,  giving  a  fine  red  liquid. 

1  When  reduced  at  a  low  temperature,  the  cobalt  is  pyrophoric. 


SALTS  OP   COBALT.  371 

When  this  oxide  is  fused  with  potassa,  in  a  silver  crucible,  it  forms  a  fine 
blue  compound,  which  is  decomposed  by  water. 

Oxide  of  cobalt  combines,  at  a  high  temperature,  with  magnesia,  alumina,  and 
oxide  of  zinc,  producing,  with  the  first,  a  pink  compound,  and  with  the  last  two, 
blue  and  green  compounds  respectively,  which  are  used  as  colors. 

Hydrated  Oxide  of  Cobalt  (CoO.HO)  is  obtained  as  a  pink  precipitate,  when 
a  solution  of  a  cobalt-salt  is  treated  with  excess  of  potassa;  this  precipitate  is 
very  liable  to  retain  small  quantities  of  potassa.  When  exposed  to  air  it 
assumes  a  dirty  green  color,  from  absorption  of  oxygen. 

Oxide  of  cobalt  forms  salts  with  the  acids,  which  are  red  when  hydrated,  and 
become  blue  on  expulsion  of  their  water.  The  solutions  of  cobalt-salts  are 
always  acid  to  test-papers.  They  exhibit  a  remarkable  tendency  to  form  double- 
compounds  with  ammonia  and  ammoniacal  salts.1 

NITRATE  OP  OXIDE  OF  COBALT,  OR  NITRATE  OF  COBALT,  CoO.N05. 

To  prepare  the  nitrate,  the  metal  or  its  oxide  may  be  dissolved  in  nitric  acid; 
it  forms  small  red  deliquescent  crystals,  which  are  easily  decomposed  by  heat, 
leaving,  unless  at  a  very  high  temperature,  the  oxide  Co304.  The  crystals  con- 
tain 6  eqs.  water. 

A  solution  of  this  salt  is  employed  as  a  reagent. 

SULPHATE  OF  OXIDE  OF  COBALT,  OR  SULPHATE  OF  COBALT,  CoO.S03. 

This  salt  occurs  in  nature ;  it  is  obtained  by  dissolving  the  oxide  in  sulphuric 
acid. 

Sulphate  of  cobalt  may  be  prepared,  as  a  source  of  other  compounds  of  cobalt, 
from  a  Norwegian  mineral  containing  cobalt,  iron,  arsenic,  and  sulphur.  The 
finely  powdered  mineral  is  roasted  in  a  muffle,  with  successive  additions  of  pow- 
dered charcoal,  as  long  as  any  arsenical  odor  is  perceptible.  The  residue  is  treated 
with  a  mixture  of  sulphuric  and  (a  little)  hydrochloric  acids,  and  the  sesquioxide 
of  iron  precipitated  from  the  solution  by  boiling  with  chalk ;  the  solution  is  then 
treated  with  sulphuretted  hydrogen,  to  separate  the  remainder  of  the  arsenic, 
&c.,  filtered,  and  evaporated  to  crystallization,  when  pure  sulphate  of  cobalt  is 
deposited. 

At  the  ordinary  temperature  it  crystallizes  in  oblique  rhombic  prisms  of  the 
formula  CoO  S03,HO-f-6Aq,  but  which,  at  a  somewhat  higher  temperature,  have 
a  different  form,  and  contain  less  water  by  one  equivalent. 

The  water  of  constitution  may  be  replaced  by  alkaline  sulphates,  forming  double 
salts  with  6  eqs.  water  of  crystallization. 

The  neutral  carbonate  of  cobalt  is  not  known;  basic  carbonates  are  precipitated 
when  solutions  of  cobalt-salts  are  decomposed  by  alkaline  carbonates ;  the  most 
common  of  these  precipitates  has  a  rose  color,  and  the  formula  2(CoO.C03), 
3(CoO.HO)+Aq ;  it  is  obtained  when  a  hot  solution  of  a  salt  of  cobalt  is  pre- 
cipitated by  an  alkaline  carbonate.  If  the  precipitation  be  effected  in  the  cold, 
the  formula  of  the  precipitate  is  2(CoO.C02),(2CoO.HO)  +  5Aq.2 

SESQUIOXIDE  OR  PEROXIDE  OP  COBALT,  Coa03. 

The  anhydrous  sesquioxide  may  be  obtained  by  gently  heating  the  nitrate,  or 
in  a  crystalline  state,  by  fusing  the  (prat-)  oxide  with  potassa  for  a  considerable 
period. 

1  By  exposing  to  the  air  ammoniacal  solutions  of  cobalt-salts,  Fremy  has  obtained 
several  crystalline  salts  containing  ammonia  combined  with  cobalt  in  different  degrees  of 
oxidation.     A  nitrate  of  this  description,  deposited  when  ammoniacal  nitrate  of  cobalt  is 
exposed  to  the  air,  is  decomposed  by  cold  water,  with  evolution  of  oxygen. 

2  If  a  solution  of  cobalt  is  mixed  with  an  excess  of  bicarbonate  of  potassa  in  the  cold, 
a  compound  of  the  formula  KO.C02,CoO.C02-f  lOAq  is  obtained. 


372  CHLORIDES   OP   COBALT. 

The  hydrate,  Coa03.HO,  is  obtained  by  passing  a  current  of  chlorine  through 
water  in  which  hydrated  protoxide  or  carbonate  of  cobalt  is  suspended  (.see  Ses- 
quioxide  of  Nickel). 

Sesquioxide  of  cobalt,  whether  anhydrous  or  hydrated,  is  black  ;  when  heated, 
it  is  converted  into  the  proto-sesquioxide  of  cobalt,  Co304.  Sesquioxide  of  cobalt 
possesses  feeble  basic  properties  j  it  dissolves  in  dilute  acids,  yielding  brown 
liquids  which  evolve  oxygen  when  heated,  leaving  salts  of  the  (prot-)  oxide  of 
cobalt.  When  this  oxide  is  heated  with  hydrochloric  acid,  chlorine  is  disengaged.1 

Sesquioxide  of  cobalt  is  capable  of  combining  with  the  (prot-)  oxide,  and  of 
forming  certain  proto-sesquioxides. 

It  has  already  been  noticed  that  a  black  oxide  of  the  formula  Co304(=CoO.Co303) 
is  obtained  when  the  Sesquioxide  is  decomposed  by  heat. 

When  the  (prot-)  oxide  of  cobalt,  or  its  carbonate  is  heated  in  air,  it  is  con- 
verted into  Co304,  or  Co607(=4CoO.Co203)  according  to  the  temperature. 

CHLORIDE  or  COBALT,  CoCl. 

§  250.  This  salt  may  be  prepared  by  dissolving  the  oxides  of  cobalt,  or  the 
carbonate,  in  hydrochloric  acid ;  the  pink  solution  yields,  on  evaporation,  rose- 
colored  crystals  of  the  hydrated  chloride.  If  the  pink  solution  be  mixed  with  an 
excess  of  acid,  it  becomes  of  a  blue  color,  or  green  if  iron  or  nickel  be  present. 
The  solution  resumes  its  original  red  color  when  largely  diluted  with  water. 

When  the  crystals  of  hydrated  chloride  are  heated,  they  lose  their  water,  and 
evolve  hydrochloric  acid,  oxide  of  cobalt  being  left,  while  a  portion  of  anhydrous 
chloride  sublimes.  If  only  moderately  heated,  the  crystals  merely  lose  their 
water,  becoming  blue;  this  property  renders  it  useful  as  a  sympathetic  ink,  for 
letters  written  with  the  pink  solution  are  invisible  until  they  are  held  before  the 
fire,  when  the  chloride  loses  its  water  and  becomes  blue,  but  resumes  its  pink 
color  when  exposed  to  air. 

Anhydrous  chloride  of  cobalt  combines  with  ammonia,  forming  the  compound 
CoC1.2NH3.3 

The  sesquichloride  of  cobalt  formed  when  the  Sesquioxide  is  dissolved  in  hydro- 
chloric acid,  is  exceedingly  unstable. 

COBALT  AND  SULPHUR. 

(Proto-)  sulphide  ; -'\ •': ''''S'\.[   .    ''.\   .  CoS. 

Sesquisulphide Co^Sg. 

Bisulphide    .     .     . CoS3. 

1  Some  remarkable  conjugate  compounds  of  Sesquioxide  of  cobalt  have  been  examined 
by  Genth.     By  mixing  chloride  or  sulphate  of  cobalt  with  a  large  quantity  of  chloride  of 
ammonium,  adding  ammonia  in  excess,  and  acidifying  the  mixture  with  hydrochloric  acid, 
after  four  or  five  weeks'  exposure  to  air,  a  Solution  is  obtained  which,  when  boiled,x  de- 
posits a  carmine  salt  of  the  formula  Co203.3NH4Cl,  which  its  discoverer  regards  as  the 
chloride  of  a  new  radical,  Co203.3NH4,  other  compounds  of  which  have  been  obtained  by 
double  decomposition. 

2  By  the  action  of  ammonia  upon  a  solution  of  chloride  of  cobalt,  mixed  with  chlo- 
ride of  ammonium,  Claudet  has  obtained  a  red  crystalline  compound,  composed  of  2CoCl, 
NH4C1,4NH3. 

At  a  later  period,  in  investigating  the  same  subject,  Rogojski  obtained  a  chloride  of  the 
formula  C02C13,3N2H6,  which  is  possessed  of  basic  properties. 

Fremy  has  examined  the  action  of  hydrochloric  acid  upon  the  ammoniacal  salts  of 
cobalt ;  he  has  obtained  a  new  series  of  salts,  in  which  part  of  the  oxygen  is  replaced  by 
chlorine  ;  they  have  a  fine  violet  color,  and  are  nearly  insoluble  in  water ;  the  chlorine 
in  these  compounds  cannot  be  precipitated  by  nitrate  of  silver  until  the  solution  is  boiled, 
when  the  chlorine  is  replaced  by  oxygen,  the  original  ammonio-cobaltic  salts  being  re- 
produced. 

More  recently,  the  same  chemist  has  published  a  full  investigation  of  this  subject,  in 
which  he  describes  a  numerous  and  interesting  series  of  ammonio-cobaltic  salts.  (Ann. 
dt  Chim.  et  de  Phys.  3d  ser.  vol.  xxxv.  p.  257.) 


ORES   OF   COBALT.  373 

SULPHIDE  OP  COBALT,  CoS. 

This  compound  may  be  obtained  by  the  direct  combination  of  its  elements  at 
a  high  temperature,  or  by  heating  one  of  the  oxides  of  cobalt  with  excess  of  sul- 
phur. It  is  a  gray  crystalline  substance,  possessing  a  metallic  lustre. 

Hyd rated  sulphide  of  cobalt  is  thrown  down  as  a  black  precipitate  when  an 
alkaline  sulphide  is  added  to  a  solution  of  cobalt-salt.  The  hydrate  is  not  dis- 
solved to  any  great  extent  by  dilute  hydrochloric  acid,  but  is  easily  soluble  in 
nitric  acid. 

When  sulphate  of  cobalt  is  reduced  by  hydrogen,  an  oxysulphide,  CoS,CoO,  is 
formed,  which  is  decomposed  into  its  proximate  constituents  by  treatment  with 
acids. 

The  sesquisulphide,  Co2S3,  is  met  with  in  nature  in  gray  octohedra  (cobalt- 
pyrites)-,  it  is  obtained  by  passing  sulphuretted  hydrogen  over  sesquioxide  of 
cobalt  heated  to  about  500°  F.  (260°  C.) 

Bisulphide  of  cobalt,  CoS3,  is  formed  when  a  mixture  of  carbonate  of  cobalt 
and  sulphur  is  heated  to  a  certain  point ;  it  is  a  black,  amorphous  powder,  which 
is  decomposed  by  heat  into  sulphur  and  sulphide  of  cobalt.  The  bisulphide  is 
not  readily  attacked  by  acids  or  alkalies.  , 

§251.  Technical  History  of  Cobalt. — The  chief  minerals  containing  cobalt  are 
the  following : — 

White  cobalt  ore,  which  is  the  most  common,  and  contains  cobalt  associated 
with  arsenic,  iron,  and  sulphur. 

Gray  cobalt  ore,  containing  arsenic,  iron,  cobalt,  and  silica. 

Glance  cobalt,  or  Tuna-berg  cobalt,  which,  when  pure,  has  the  formula  CoAs3, 
CoS3.  This  is  the  richest  of  the  cobalt  ores.  It  can  be  dissolved  only  by  nitric 
acid.  These  ores  generally  contain  more  or  less  nickel. 

Since  cobalt  is  never  used  in  the  metallic  state,  the  reduction  of  the  ores  of 
this  metal  has  for  its  object  the  production  of  a  pretty  pure  oxide. 

It  is  generally  thought  sufficient  to  roast  the  ore  in  order  to  expel  the  greater 
part  of  its  arsenic  and  sulphur,  and  thus  to  convert  it  into  an  impure  oxide, 
which  is  sent  into  commerce  under  the  name  of  zaffre.  Cobalt  is  also  extracted 
by  a  process  similar  to  that  described  for  nickel. 

Cobalt  is  extensively  employed  in  the  preparation  of  colors ;  two  of  the  most 
important  of  these  are  smalt  and  Thenard's  blue. 

Smalt  is  a  kind  of  glass  colored  with  oxide  of  cobalt,  and  reduced  to  a  fine 
powder. 

In  order  to  prepare  this  pigment,  a  quantity  of  zaffre  is  fused  with  sand  and 
carbonate  of  potassa  in  a  large  earthen  crucible ;  the  silicic  acid  (sand)  combines 
with  the  potassa,  forming  a  vitreous  silicate,  which  dissolves  the  oxide  of  cobalt, 
while  the  arsenic,  iron,  and  nickel  contained  in  the  ore,  are  deposited  as  a  metal- 
lic-looking mass  of  speiss,  at  the  bottom  of  the  crucible.  The  fused  mass  is 
reduced  to  a  fine  powder,  and  subsequently  levigated. 

Thenard's  blue  consists  of  phosphate  of  cobalt  and  phosphate  of  alumina,  and 
is  prepared  by  calcining  an  intimate  mixture  of  the  precipitates  obtained  by 
adding  phosphate  of  soda  to  solutions  of  the  bases  in  question. 


374  VANADIUM. 


VANADIUM. 

Sym.  V.     Eq.  68.6. 

§  252.  This  rare  metal  is  found  in  certain  Swedish  iron-ores,  remarkable  for 
their  malleability ;  it  is  also  met  with  in  the  form  of  vanadiate  of  lead. 

It  may  be  obtained  by  heating  vanadic  acid  with  potassium  in  a  platinum 
crucible,  and  extracting  the  potassa  with  water. 

Vanadium  is  a  white  metal  which  dissolves  in  nitric  acid,  yielding  a  blue 
solution.  It  is  not  readily  attacked  by  sulphuric  or  hydrochloric  acid. 

Three  independent  oxides  of  vanadium  are  known. 

The  (prot-)  oxide,  VO,  is  formed  when  vanadic  acid  is  reduced  by  carbon  or 
hydrogen  at  a  red  heat.  It  is  an  indifferent  oxide. 

Binoxide  of  Vanadium,  V02,  may  be  precipitated  as  a  hydrate  by  adding 
potassa  to  a  solution  of  the  bichloride,  prepared  by  heating  vanadic  acid  with 
hydrochloric  acid.  It  is  white  when  freshly  precipitated,  and  becomes  brown 
upon  drying.  When  binoxide  of  vanadium  is  exposed  to  air,  it  absorbs  oxygen, 
and  assumes  a  greenish  color,  due  to  the  formation  of  an  intermediate  oxide ;  it 
sometimes  plays  the  part  of  an  acid,  but  generally  that  of  a  base,  for  it  dissolves 
in  acids,  forming  crystallizable  salts,  which  have  a  blue  color. 

VANADIC  ACID,  V03. 

To  prepare  this  acid,  the  natural  vanadiate  of  lead  is  heated  with  nitric  acid, 
evaporated,  and  the  residue  extracted  with  water,  which  leaves  vanadic  acid  un- 
dissolved;  this  latter  is  dissolved  in  ammonia,  when  crystals  of  the  ammonia-salt 
are  obtained  on  evaporation ;  this  salt,  ignited  in  air,  leaves  the  vanadic  acid. 

This  acid  has  a  yellow  color ;  it  fuses  at  a  red  heat,  and  when  cooled,  solidifies 
again,  with  evolution  of  light;  it  is  not  decomposed  at  a  high  temperature.  It 
is  very  slightly  soluble  in  water,  giving  a  yellow  solution,  which  reddens  litmus- 
paper.  Organic  matters,  and  reducing  agents  in  general,  convert  vanadic  acid 
into  the  oxide. 

When  vanadic  acid  is  dissolved  in  hydrochloric  acid,  and  the  solution  heated, 
chlorine  is  disengaged,  and  bichloride  of  vanadium  formed  : — 

V03-f3HCl=3HO  +  VCls+Cl. 

Vanadic  acid    combines  with   bases,  forming  crystallizable  vanadiates.      The 
vanadiates  of  the  alkalies  are  soluble  in  water. 

Vanadic  acid  also  behaves  like  a  basic  teroxide,  in  combining  with  acids  to 
form  definite  salts,  which  may  be  crystallized;  thus,  the  compound  with  sul- 
phuric acid  has  the  composition,  VO3.3S03.  Similar  compounds  have  been 
obtained  with  nitric,  arsenic,  and  phosphoric  acids.  They  have  a  yellow  or  red 
color,  and  are  soluble;  their  solutions  lose  their  color  when  heated,  and  are 
rendered  blue  by  sulphuretted  hydrogen  and  organic  matters,  in  consequence  of 
the  reduction  of  the  acid  to  the  state  of  binoxide  of  vanadium. 

Binoxide  of  vanadium  also  combines  with  vanadic  acid,  forming  compounds 
which  dissolve  in  water  with  a  fine  green  color;  these  compounds  contain,  re- 
spectively, V03.2V03  and  V03.4V03,  and  are  obtained  either  by  heating  vanadic 
acid  with  the  binoxide,  or  by  adding  a  solution  of  an  alkaline  vanadiate  to  a  salt 
of  binoxide  of  vanadium. 

Terchloride  of  Vanadium,  VC13,  is  a  volatile,  yellow,  fuming  liquid,  obtained 
by  passing  chlorine  over  a  mixture  of  vanadic  acid  and  charcoal  at  a  red  heat. 

Bisulphide  of  Vanadium,  VS2,  constitutes  the  black  precipitate  which  is 
produced  by  an  alkaline  sulphide  in  a  salt  of  the  binoxide;  it  dissolves  in 
an  excess  of  the  precipitant,  forming  a  purple  solution. 


VANADIUM.  375 

REACTIONS  OF  VANADIUM. — Potassa,  soda,  and  their  carbonates  ;  a  grayish 
precipitate  of  hydrate,  soluble  in  excess,  yielding  a  blue  or  brown  solution. 

Ammonia  ;  a  brown  precipitate,  insoluble  in  excess. 

Sulphide  of  ammonium ;  a  dark-brown  precipitate,  soluble  in  excess,  yielding 
a  dark  purple  solution. 

Ferrocyanide  of  potassium  ;  a  yellowish-green  precipitate. 

Hydrosulphuric  acid,  in  acid  solutions  of  vanadic  acid,  a  blue  color,  due  to 
reduction. 

With  a  borax-bead,  in  the  outer  flame,  a  yellow  glass,  becoming  green  in  the 
inner  flame,  and  brown  while  hot,  if  much  vanadium  be  present.  If  the  bead 
contain  but  little  vanadium,  it  may  be  perfectly  decolorized  in  the  outer  flame. 


376  CADMIUM. 


METALS  OF  THE  FOURTH  GROUP. 


CADMIUM. 

Sym.  Cd.    Eq.  56.    Sp.  Gr.  8.6. 

§  253.  THIS  metal  is  associated  in  nature  with  the  ores  of  zinc,  and  does 
not  occur  very  frequently  or  in  large  quantities. 

Preparation. — In  the  description  already  given  of  the  extraction  of  zinc  from 
its  ores,  it  was  mentioned  that  the  first  portions  of  the  vapor  which  passed  over 
when  the  roasted  ore  was  distilled  with  charcoal,  burnt  with  a  brown  flame 
(brown  blaze),  due  to  the  presence  of  cadmium.  In  order  to  obtain  this  metal 
in  a  pure  state,  these  vapors  are  condensed,  and  the  mixture  of  zinc,  cadmium, 
and  a  little  copper,  thus  obtained,  is  dissolved  in  hydrochloric  or  sulphuric  acid, 
and  the  solution  treated  with  sulphuretted  hydrogen,  which  precipitates  the 
sulphides  of  copper  and  cadmium ;  these  are  washed,  redissolved  in  concentrated 
hydrochloric  acid;  after  evaporating  the  solution  to  expel  excess  of  acid,  carbo- 
nate of  ammonia  in  excess  is  added,  which  precipitates  the  carbonate  of  cadmium, 
and  redissolves  that  of  copper;  the  carbonate  is  calcined  to  expel  carbonic  acid, 
and  distilled  with  carbon,  when  metallic  cadmium  distils  over. 

Cadmium  may  also  be  obtained  by  collecting  the  oxides  of  zinc  and  cadmium 
resulting  from  the  brown  blaze,  and  distilling  these,  at  a  moderate  heat  with 
charcoal,  when  most  of  the  zinc  is  left  in  the  residue;  by  repeating  the  opera- 
tion, the  cadmium  may  be  still  further  purified. 

Properties. — Cadmium  has  a  grayish-white  color,  and  much  resembles  tin  in 
its  physical  properties.  It  is  very  soft,  malleable,  and  ductile ;  when  bent,  it 
emits  a  crackling  sound,  like  tin ;  its  internal  structure  is  crystalline. 

This  metal  fuses  very  easily,  and  is  converted  by  a  higher  temperature  into  an 
inodorous  vapor ;  the  fused  metal,  if  slowly  cooled,  crystallizes  in  octohedra. 

Cadmium  is  not  sensibly  affected  by  dry  air  at  the  ordinary  temperature; 
when  heated  in  air,  it  oxidizes  more  readily  than  zinc,  burning  with  a  luminous 
flame,  and  producing  a  red-brown  oxide.  It  dissolves  readily  in  dilute  acids, 
with  disengagement  of  hydrogen.  Hydrated  alkalies  also  dissolve  cadmium 
at  a  high  temperature. 

Only  one  oxide  of  cadmium,  CdO,  is  known. 

OXIDE  or  CADMIUM,  CdO. 

The  oxide  is  formed  when  cadmium  is  heated  in  air;  if  the  metal  be  heated 
in  a  close  crucible,  the  oxide  condenses,  as  a  red-brown  film,  upon  the  cover.  It 
has  a  yellow,  brown,  or  black  color,  according  to  the  temperature  to  which  it 
has  been  exposed;  it  is  sometimes  crystallized  in  needles. 

This  oxide  is  infusible,  and  does  not  volatilize;  it  combines  with  acids,  forming 
well-defined  salts.  It  is  capable  of  absorbing  carbonic  acid  from  the  air. 

The  hydrattd  oxide  is  obtained  as  a  gelatinous  precipitate,  when  an  alkali  is 
added  to  a  solution  of  a  salt  of  cadmium;  the  hydrate  (CdO.HO)  is  white,  but 
becomes  brown  when  heated,  from  loss  of  water.  It  is  easily  reduced  by  char- 
coal at  a  low  red  heat. 


COPPER.  377 

Nitrate  of  Cadmium  (CdO.NOg)  is  obtained  by  dissolving  the  metal  in  nitric 
acid  ;  it  forms  hydrated  prisms,  which  are  deliquescent  and  very  soluble  in  water. 

SULPHATE  OF  CADMIUM  (CdO.S03)  may  be  prepared  by  dissolving  cadmium, 
its  oxide  or  carbonate,  in  sulphuric  acid.  It  crystallizes  in  colorless,  rectangular 
prisms,  of  the  formula  CdO.S03-f4Aq;  they  are  very  soluble  in  water,  and  are 
decomposed  by  a  high  temperature. 

Anhydrous  sulphate  of  cadmium  absorbs  three  equivalents  of  ammonia. 

A  basic  sulphate  of  cadmium,  of  the  formula  CdO.S03,CdO.HO,  is  obtained 
when  neutral  sulphate  is  heated,  or  partially  decomposed  by  alkalies. 

Basic  carbonates  of  cadmium  are  obtained  by  the  action  of  alkaline  carbonates 
on  solutions  of  cadmium-salts,  varying  in  composition  with  the  quantity  of  car- 
bonate employed  in  the  precipitation. 

CHLORIDE  OF  CADMIUM,  CdCl. — To  prepare  this  salt,  cadmium  may  be 
heated  in  a  current  of  chlorine,  or  may  be  dissolved  in  hydrochloric  acid.  It 
forms  rectangular  four-sided  prisms,  which  are  hydrated ;  these  crystals  effloresce 
in  dry  air,  and  lose  their  water  when  heated,  subsequently  undergoing  the  igne- 
ous fusion,  and  finally  subliming  in  crystalline  scales.  Chloride  of  cadmium 
dissolves  very  readily  in  water,  and  is  capable  of  forming  double-salts  with  the 
chloride  of  the  alkali-metals. 

The  anhydrous  chloride  absorbs  three  equivalents  of  ammonia;  its  solution 
in  ammonia  deposits  crystals  of  the  formula  CdCl,NH3. 

SULPHIDE  OF  CADMIUM,  CdS. — This  compound  is  found  in  nature,  crystal- 
lized in  hexagonal  prisms  of  a  yellow  color. 

It  may  be  obtained  by  heating  a  mixture  of  sulphur  and  oxide  of  cadmium, 
or  by  precipitating  a  salt  of  cadmium  by  sulphuretted  hydrogen,  or  a  soluble 
sulphide.  Thus  prepared,  it  has  a  bright-yellow  color,  and  is  employed  in  paint- 
ing. Its  color  becomes  red  on  the  application  of  heat,  and  yellow  again  on 
cooling.  It  fuses  at  a  red  heat,  and  becomes  crystalline  on  cooling.  The  preci- 
pitated sulphides  dissolve  readily  in  acids. 

Neither  cadmium  nor  its  compounds  have  received  any  very  important  appli- 
cation in  the  arts. 


COPPER. 

Sym.  Cu.   Eq.  31.7.    Sp.  Gr.  8.8. 

§  254.  In  describing  this  metal,  we  shall  pursue  the  same  course  as  with  iron. 

Copper  is  found  abundantly  in  nature,  both  in  the  pure  state,  and  in  combina- 
tion ;  the  ores  of  copper  will  be  described  hereafter. 

Commercial  specimens  of  copper  are  often  sufficiently  pure  for  most  chemical 
purposes.  Copper-turnings  are  frequently  employed  in  the  laboratory;  in  order 
to  free  them  from  the  grease  with  which  they  are  usually  contaminated,  they  are 
heated  to  redness  in  air,  until  covered  with  a  superficial  coating  of  black  oxide ; 
they  are  then  introduced  into  a  piece  of  combustion-tube,  through  which  a  stream 
of  pure  and  dry  hydrogen  is  passed;  when  the  apparatus  is  filled  with  hydrogen, 
the  tube  is  heated,  either  by  a  charcoal-furnace  or  a  gas  flame,  and  the  hydrogen 
passed  over  the  heated  turnings,  until  no  more  steam  is  evolved,  and  the  copper 
appears  to  be  free  from  oxide ;  the  metal  should  be  allowed  to  cool  in  an  atmo- 
sphere of  hydrogen. 

Pure  copper  may  also  be  obtained,  in  a  finely-divided  state,  by  reducing  the 
oxide,  at  a  high  temperature,  by  means  of  hydrogen. 

A  very  good  method  of  obtaining  small,  compact  masses  of  copper,  consists  in 
reducing  the  metal  from  the  pure  sulphate  by  the  electrotype  process. 


378  COPPER  AND   OXYGEN. 

Properties. — Copper  has  a  red-brown  color,  and  is  capable  of  a  high  lustre  j1 
it  is  a  very  malleable  and  ductile  metal.  Only  two  metals,  gold  and  silver,  are 
more  malleable  than  copper;  in  ductility  it  ranks  after  gold,  silver,  platinum,  and 
iron  ,  only  the  latter  metal  surpasses  it  in  tenacity;  a  copper  wire  of  one-tenth  of 
an  inch  in  diameter,  is  capable  of  supporting  a  weight  of  385  pounds.  It  is  the 
most  sonorous  of  metals.  Copper  is  not  so  hard  as  iron  ;  it  has  a  metallic  taste, 
and  a  disagreeable  smell  when  rubbed.  The  specific  gravity  of  copper  varies 
from  8.78  to  8.96,  according  as  it  has  been  cast  or  drawn  into  wire. 

This  metal  fuses  at  a  bright-red  heat,  and  at  a  white  heat  is  slightly  volatile ; 
its  vapor  burns  with  a  fine  green  flame,  which  is  perceived  when  a  copper-wire  is 
heated  in  the  flame  of  a  gauze-burner.  When  fused  copper  is  allowed  to  cool 
gradually,  it  crystallizes  in  rhombohedra.  It  is  precipitated  from  its  solutions, 
by  other  metals,  in  small  cubical  crystals.  This  metal  is  unaltered  by  exposure 
to  dry  air  or  oxygen ;  in  moist  air  it  becomes  covered  with  a  coating  of  oxide, 
which  absorbs  carbonic  acid,  and  is  converted  into  a  green  basic  carbonate. 

When  copper  is  heated  in  air,  it  becomes  covered,  at  first,  with  a  red  film  of 
suboxide,  which  passes  ultimately  into  the  black  oxide.  It  does  not  decompose 
water  at  the  ordinary  temperature,  even  in  presence  of  acids ;  at  a  white  heat,  it 
is  capable  of  decomposing  it  to  a  slight  extent  only. 

Nitric  acid  easily  ..dissolves  copper,  with  evolution  of  binoxide  of  nitrogen  : — 
4(HO.N05)-l-Cu3=3(CuO.N05)+4HO+N02. 

When  copper  is  exposed  to  air,  in  contact  with  solution  of  ammonia,  it  is 
converted  into  oxide  of  copper,  which  dissolves  in  ammonia,  forming  a  blue 
solution. 

Hydrochloric  acid  dissolves  copper  to  a  slight  extent,  probably,  however,  only 
\vith  the  co-operation  of  atmospheric  oxygen. 

A  dilute  solution  of  chloride  of  sodium  is  capable  of  dissolving  copper,  though 
a  concentrated  solution  scarcely  affects  it.3 

Strong  sulphuric  acid  dissolves  copper  with  the  aid  of  heat,  sulphurous  acid 
being  evolved : — 

2(HO.S03)+Cu=CuO.S03+S03+2HO. 

According  to  some  authorities,  the  sulphate  of  suboxide  of  copper  is  also 
formed  in  this  case. 

Copper  is  easily  oxidized  when  exposed  to  air  in  presence  of  acids  or  of  fatty 
matters ;  hence  this  metal  can  only  be  used  for  a  few  culinary  purposes  with 
perfect  safety,  since  its  compounds  are  very  poisonous^ 

Copper  combines  directly  with  most  of  the  elements,  and,  in  some  cases,  very 
energetically. 

COPPER    AND    OXYGEN. 

Suboxide  Cu2O 

(Prot-)  oxide CuO 

Binoxide  Cu03 

and  a  higher  oxide,  the  composition  of  which  is  not  known;  it  has  been  termed 

cupric  acid. 

SUBOXIDE,  OR  RED  OXIDE,  OF  COPPER,  CuaO. 
§  255.  The  red  oxide  of  copper  is  found  in  nature  as  red  copper-ore. 

1  Copper  in  a  state  of  extreme  tenuity  has  a  green  color  by  transmitted  light. 

2  The  effect  of  a  solution  of  salt  upon  metallic  copper  is  probably  to  be  ascribed  to  the 
formation  of  galvanic  circles  between  the  copper  and  the  small  particles  of  foreign  metals 
and  other  impurities  existing  in  it. 


OXIDES  or  COPPER.  379 

Preparation. — I.  Suboxide  of  copper  is  obtained  when  a  mixture  of  the  sub- 
chloride  with  carbonate  of  soda  is  calcined ;  the  residue  is  washed  with  water,  to 
remove  the  chloride  of  sodium  and  the  excess  of  carbonate  of  soda. 

II.  A  mixture  of  5  parts  of  (prot-)  oxide  of  copper  and  4  parts  of  copper- 
filings  may  be  strongly  heated  in  a  closed  crucible. 

III.  A  solution  of  sulphate  of  copper  is  mixed  with  a  quantity  of  sugar-solu- 
tion (which  has  been  previously  boiled  with  a  few  drops  of  dilute  sulphuric  acid, 
to  convert  the  cane-sugar  into  grape-sugar),  and  potassa  added  until  the  preci- 
pitate at  first  produced  is  redissolved  to  a  violet-blue  fluid ;  on  boiling  this  for 
some  time,  the  suboxide  of  copper  is  precipitated. 

Properties. — By  the  first  and  third  processes,  the  suboxide  is  obtained  in  a 
crystalline  state ;  it  has  a  fine  red  color,  and  is  not  altered  by  exposure  to  air. 
When  heated,  it  fuses  easily,  and  if  air  be  allowed  access,  is  converted  into  the 
(prot-)  oxide. 

Nitric  acid  oxidizes  the  suboxide  of  copper,  and  dissolves  it  in  the  form  of 
nitrate  of  (prot-)  oxide. 

Suboxide  of  copper  is  a  feeble  base. 

Treated  with  concentrated  hydrochloric  acid,  it  yields  water  and  subchloride 
of  copper,  which  dissolves  in  the  acid : — 

Cu30+HCl==Cu3Cl+HO. 

Dilute  acids  generally  decompose  it  into  metallic  copper,  and  the  (prot-)  oxide 
which  dissolves  in  the  acid. 

The  suboxide  dissolves  in  ammonia,  forming  a  colorless  liquid,  which,  when 
exposed  to  air,  rapidly  absorbs  oxygen,  and  becomes  blue ;  if  the  blue  solution 
be  kept  in  a  closely  stoppered  bottle,  in  contact  with  copper,  it  again  becomes 
colorless. 

Suboxide  of  copper  imparts  a  fine  red  color  to  fluxes,  and  is  hence  used  for 
coloring  glass ;  with  access  of  air,  the  color  passes  into  green,  from  the  conver- 
sion of  the  suboxide  into  oxide. 

Hydrated  Suboxide  of  Copper,  4Cu2O.HO,  is  prepared  by  decomposing  the 
subchloride  of  copper  with  potassa.  It  dissolves  in  acids,  forming  the  salts  of 
suboxide  of  copper.  The  hydrate  has  a  yellow  color,  and  is  rapidly  oxidized  in 
air,  it  should  therefore  be  dried  in  vacua. 

The  salts  of  suboxide  of  copper  possess  little  practical  interest. 

A  solution  of  sulphate  of  suboxide  of  copper  may  be  prepared  by  reducing  a 
solution  of  the  sulphate  of  the  (prot-)  oxide  with  sulphurous  acid  or  sulphate  of 
iron : — 

2(CuO.S03)  +  S03=Cu3O.S03+ 2S03. 
2(CuO.S03)-|-2(FeO.S03)=CuaO.S034-Fe303.3S03. 

OXIDE  OR  PROTOXIDE  OP  COPPER,  BLACK  OXIDE. 
CuO.     Eg.  39.7. 

This  oxide  is  also  occasionally  found  in  nature.  It  is  formed  when  copper  is 
heated  in  air. 

Preparation. — Metallic  copper  is  oxidized  by  nitric  acid,  the  mass  dried,  and 
heated  in  a  Hessian  crucible  until  no  more  fumes  of  peroxide  of  nitrogen  are 
evolved;  the  mass  should  be  stirred  occasionally. 

It  is  also  prepared  by  mixing  the  nitrate  of  copper  with  half  its  weight  of 
copper-filings,  exposing  the  mixture  to  the  air,  and  igniting  the  basic  nitrate  thus 
obtained. 

Properties. — Oxide  of  copper  is  a  black  powder,  which  is  very  hygroscopic. 
When  strongly  heated,  it  fuses,  and  at  a  very  high  temperature  loses  part  of  its 
oxygen,  being  converted  into  a  compound  of  suboxide  and  oxide  of  copper. 


380  NITRATE   OP   COPPER. 

Oxide  of  copper  is  quite  insoluble  in  water,  but  dissolves  in  acids,  yielding 
important  salts. 

This  oxide  is  easily  reduced,  at  a  moderately  high  temperature,  by  carbon  or 
hydrogen,  or  by  organic  substances  containing  these  elements,  and  this  property 
renders  it  useful  in  the  ultimate  analysis  of  organic  substances. 

When  oxide  of  copper  is  fused  with  hydrate  of  potassa  or  soda,  it  combines 
with  the  alkali  to  form  a  blue  or  green  mass,  which  is  decomposed  by  water;  by 
allowing  the  fused  mass  to  cool  slowly,  tetrahedral  crystals  of  oxide  of  copper 
have  been  obtained. 

Hyd  rated  Oxide  of  Copper  Cu0.2HO  (dried  in  vacvo\  is  obtained  as  a  blue 
precipitate  by  decomposing  a  solution  of  a  copper-salt  with  an  excess  of  potassa; 
if  too  little  alkali  be  added,  a  basic  copper-salt  is  precipitated.  The  hydrate  is 
very  unstable;  if  it  be  boiled  with  the  liquid  in  which  it  is  suspended,  it  is  at 
once  converted  into  the  dense,  black,  anhydrous  oxide ;  the  same  change  takes 
place,  though  more  slowly,  when  the  precipitated  hydrate  is  exposed  to  the  air. 
The  pigment  known  as  blue  verditer  consists  of  hydrated  oxide  of  copper.  The 
hydrate  dissolves  very  readily  in  acids;  it  is  also  soluble  in  ammonia,  forming  a 
fine  blue  liquid.  Two  definite  compounds  of  oxide  of  copper,  ammonia,  and 
water,  have  been  obtained;  viz.  CuO,2NH3,4HO,  and  3CuO,2NH3,6HO. 

The  hydrate  dissolves  to  a  slight  extent  in  cold  concentrated  solutions  of  potassa 
and  soda,  forming  blue  liquids,  which  deposit  the  anhydrous  oxide  when  heated. 
Oxide  of  copper  is  occasionally  employed  to  impart  a  blue  or  green  color  to  glass. 
The  salts  of  oxide  of  copper  have  generally  a  blue  or  green  color,  and  are  very 
poisonous ;  their  solutions  have  an  acid  reaction. 

NITRATE  OF  OXIDE  OF  COPPER,  NITRATE  OF  COPPER. 
CuO.N03. 

§  256.  This  salt  is  prepared  by  dissolving  copper  in  moderately  strong  nitric 
acid,  and  evaporating  to  crystallization. 

It  forms  dark  blue  prismatic  crystals,  which  contain  4  or  6  equivalents  of  water, 
according  to  the  temperature  at  which  they  have  been  deposited;  those  with  4  eqs. 
are  the  more  common.  These  crystals  deliquesce  in  air,  and  are  very  soluble  in 
water;  they  dissolve  also  in  alcohol.  The  crystals  with  6  eqs.  of  water  are  lighter 
in  color.  Anhydrous  nitrate  of  copper  is  not  known;  when  the  crystals  are  heated, 
they  are  converted,  first,  into  a  sparingly  soluble  basic  nitrate,  of  the  formula 
4CuO.N05,  and  subsequently  into  oxide. 

Nitrate  of  copper  is  capable  of  oxidizing  some  metals  with  considerable  energy; 
thus,  if  a  crystal  of  this  salt  be  wrapped  in  a  piece  of  tinfoil,  and  struck  with  a 
hammer,  the  tin  is  converted  into  binoxide  with  a  sort  of  explosion;  again,  ignition 
is  observed  when  a  little  of  the  nitrate  is  placed  on  tinfoil,  a  very  small  quantity 
of  water  added,  and  the  foil  tightly  wrapped  up. 

When  a  solution  of  nitrate  of  copper  is  treated  with  a  small  quantity  of  am- 
monia, the  above-mentioned  basic  salt  is  obtained  as  a  blue  precipitate,  which 
readily  dissolves  in  excess  of  ammonia.  The  solution  deposits  a  blue  crystalline 
substance,  termed  ammonio-nitrate  of  copper. 

By  passing  aminoniacal  gas  into  a  concentrated  solution  of  nitrate  of  copper, 
and  carefully  evaporating,  crystals  have  been  obtained,  of  the  formula  CuNH3, 
NH4O.N05,  indicating  a  compound  of  ainidide  of  copper  with  nitrate  of  ammonia. 

SULPHATE  OF  (PaoT-)  OXIDE  OF  COPPER.  SULPHATE  OF  COPPER.  BLUE 

VITRIOL.  BLUE  STONE.  BLUE  COPPERAS. 

CuO.S03. 

Preparation. — This  salt  is  sometimes  obtained  by  roasting  copper-pyrites 
(Fe2S3,Cu2S)  with  free  access  of  air,  when  the  sulphides  are,  in  part,  converted 


SULPHATE  OP   COPPER.  881 

into  sulphates,  which  may  be  extracted  with  water  and  purified  by  crystallization; 
the  blue  vitriol  thus  obtained  always  contains  much  sulphate  of  iron. 

If  too  low  a  temperature  be  applied  in  roasting  the  copper-pyrites,  sulphate  of 
iron  only  is  formed,  which  would,  however,  be  decomposed  if  the  proper  degree 
of  heat  had  been  applied,  and  would  become,  in  great  measure,  insoluble. 

Another  process  consists  in  heating  old  pieces  of  copper  in  contact  with  sul- 
phur, air  being  excluded,  and  thus  converting  them  superficially  into  subsulphide 
of  copper,  CuaS,  which  is  then  roasted  in  air,  and  converted  into  a  basic  sulphate, 
and  the  latter,  heated,  with  diluted  sulphuric  acid,  is  converted  into  sulphate. 

It  is  also  prepared  by  moistening  copper-turnings  with  dilute  sulphuric  acid, 
exposing  them  to  the  air  for  some  hours,  and  repeating  the  treatment  with  the 
acid  until  the  copper  is  entirely  converted  into  sulphate. 

Considerable  quantities  of  sulphate  of  copper  are  obtained  as  a  by-product  in 
that  step  of  the  process  of  silver-refining  which  consists  in  reducing  that  metal 
from  the  sulphate  by  means  of  copper. 

In  order  to  obtain  perfectly  pure  sulphate,  pure  oxide  of  copper  should  be  dis- 
solved in  sulphuric  acid. 

Properties. — Sulphate  of  copper  forms  fine,  transparent,  blue,  oblique  rhombic 
prisms,  of  the  formula  CuO.S03,HO-f-4Aq;  these  are  occasionally  opaque  in 
parts,  from  the  presence  of  some  sulphate  of  copper  destitute  of  water  of  crystal- 
lization; this  is  especially  the  case  when  the  crystals  are  deposited  from  a  strongly 
acid  solution. 

Exposed  to  dry  air  the  crystals  lose  2  eqs.  water,  and  become  opaque;  at  212° 
F.  (100°  C.)  they  lose  all  their  water  of  crystallization,  and  crumble  to  a  bluish- 
white  powder,  of  the  formula  CuO.S03.HO;  the  water  of  constitution  is  expelled 
at  about  390°  F.  (199°  C.)>  leaving  the  anhydrous  salt  as  a  grayish  powder,  which 
becomes  blue  immediately  when  in  contact  with  water,  with  which  it  combines 
very  energetically.  At  a  very  high  temperature  the  salt  is  completely  decomposed. 

Crystallized  sulphate  of  copper  dissolves  in  4  parts  of  cold,  and  2  of  boiling 
water,  yielding  a  blue  solution,  which  has  an  acid  reaction,  and  a  nauseous  me- 
tallic taste.  This  salt  is  insoluble  in  alcohol.  It  is  very  poisonous. 

The  water  of  constitution  in  sulphate  of  copper  may  be  replaced  by  an  alkaline 
sulphate,  a  crystallizable  double-salt  being  thus  produced. 

Sulphate  of  copper  is  capable  of  combining  in  variable  proportions,  with  the 
sulphates  of  iron,  zinc,  and  nickel,  with  which  it  is  isomorphous.  The  salts  thus 
formed  contain  5  equivalents  of  water  when  the  sulphate  of  copper  predominates, 
and  7  equivalents  when  this  forms  the  smaller  portion  of  the  compound. 

Anhydrous  sulphate  of  copper  absorbs  dry  ammonia,  forming  a  compound 
represented  by  2(CuO.S03),5NH3.  It  also  forms  a  hydrated  compound  with 
ammonia,  which  will  be  presently  described. 

According  to  Kane,  crystallized  sulphate  of  copper,  when  dissolved  in  hydro- 
chloric acid,  causes  considerable  depression  of  temperature,  and  yields  a  green 
liquid,  from  which  chloride  of  copper  alone  is  deposited  upon  evaporation,  pro- 
vided not  less  than  1  equivalent  of  the  acid  has  been  used  for  each  equivalent  of 
salt;  on  allowing  the  crystals  to  remain  for  some  time  in  contact  with  the  mother- 
liquor,  which  contains  all  the  sulphuric  acid,  crystals  of  blue  vitriol  are  repro- 
duced. Powdered  crystals  of  sulphate  of  copper  eagerly  absorb  hydrochloric  acid, 
evolving  much  heat,  and  losing  water ;  a  green  mass  is  obtained,  which  is  very 
deliquescent,  and  fumes  in  air. 

Uses. — This  salt  is  sometimes  used  in  medicine  as  an  emetic  and  escharotic. 
It  is  also  employed  to  prevent  smut  in  grain.  Sulphate  of  copper  is,  moreover, 
used  in  dyeing,  and  in  the  electrotype  process.  The  anhydrous  salt  has  been 
applied  to  the  abstraction  of  water  from  alcohol. 

The  blue  vitriol  of  commerce  is  often  contaminated  with  the  sulphates  of  iron 
and  zinc ;  in  order  to  ascertain  the  purity  of  a  specimen,  its  solution  should  be 


382  SALTS   OP  COPPER. 

acidified  with  hydrochloric  acid,  the  whole  of  the  copper  precipitated  by  a  rapid 
current  of  sulphuretted  hydrogen,  and  the  filtered  liquid  (shown  to  be  free  from 
copper  by  adding  more  sulphuretted  hydrogen)  concentrated  by  evaporation  with 
a  few  drops  of  nitric  acid,  tested  for  iron  by  adding  an  excess  of  ammonia,  and 
subsequently  for  zinc,  with  sulphide  of  ammonium,  after  filtering  off  the  iron 
precipitate. 

Three  basic  sulphates  of  copper  have  been  examined,  and  are  composed  re- 
spectively of 

3CuOS03.2HO 

4CuO.S03.4H01 
and  5CuO.S03.5HO. 

They  are  obtained  either  by  digesting  solution  of  the  neutral  sulphate  with  the 
hydrated  oxide,  or  by  decomposing  that  salt  with  an  insufficient  quantity  of  potassa. 
Ammonio-sulphate  of  Copper,  CuO.S03,2NH3HO. — When  sulphate  of  copper 
is  dissolved  in  solution  of  ammonia,  fine  crystals  of  the  above  formula  may  be 
obtained  by  spontaneous  evaporation ;  these  crystals  are  celebrated  for  their  re- 
markably fine  blue  colour ;  the  ammoniated  copper  of  the  pharmacopoeia,  pre- 
pared by  triturating  2  parts  of  crystallized  sulphate  of  copper  with  3  parts  of 
sesquicarbonate  of  ammonia,  is  probably  a  compound  of  sulphate  of  copper  with 
sulphate  of  ammonia,  containing  also  the  above  combination  of  sulphate  of  copper 
with  ammonia,  and  probably  a  basic  sulphate  of  copper;  its  formation  is  attended 
with  evolution  of  much  carbonic  acid,  showing  that  part  of  the  ammonia  is  con- 
verted into  sulphate. 

CARBONATES  OP  COPPER. 

The  Neutral  Carbonate  of  Copper  (CuO.C02)  is  found  in  nature  as  the  rather 
rare  mineral  mysorine  ;  it  occurs  in  earthy  masses,  of  a  dark-brown  color. 

BIBASIO  CARBONATE  OF  COPPER,  2CuO.COa,HO. — This  compound  forms  the 
mineral  malachite,  which  sometimes  serves  as  an  ore  of  copper. 

Malachite  is  a  very  hard  mineral,  of  the  spec.  grav.  3.5 ;  it  is  sometimes  found 
crystallized,  but  generally  in  compact  concentric  masses,  of  a  fine  green  color ;  it 
dissolves  easily  in  acids.  This  mineral  is  occasionally  used  for  ornamental  pur- 
poses. 

When  a  solution  of  a  copper-salt  is  decomposed  by  an  alkaline  carbonate,  car- 
bonic acid  is  evolved,  and  the  above  basic  carbonate  precipitated  : — 
2(CuO.S03)+2(NaO.COa)  +  2HO=2CuO.C02,2HO  + 

2(NaO.S03)+C03. 

This  precipitate  has  a  blue  color,  and  is  very  bulky,  but  if  it  be  gently  heated 
with  the  supernatant  liquid,  it  becomes  granular  and  green,  having  now  the 
formula  2CuO.C02,HO.  This  latter  compound  is  used  as  a  pigment,  under  the 
name  of  mineral  green. 

When  long  boiled  with  the  supernatant  liquid,  the  precipitate  is  converted 
into  black  oxide  of  copper. 

Sesquibastc  Carbonate  of  Copper,  3Cu0.2COa,HO. — This  carbonate  is  found 
in  nature  as  blue  malachite,  mountain-blue,  or  copper-azure,  and  is  employed  as 
a  color. 

A  Tribasic  Carbonate,  of  the  formula  3CuO.COa,  is  said  to  exist. 

An  ammoniacal  carbonate  of  copper,  CuO.COa,NH3,  has  been  obtained  by  dis- 
solving the  bibasic  carbonate  in  carbonate  of  ammonia,  and  adding  alcohol ;  it 
crystallizes  in  fine  blue  needles. 

Compounds  of  carbonate  of  copper  with  carbonate  of  potassa  or  of  soda  may 
be  crystallized  from  a  solution  of  the  bibasic  carbonate  of  copper  in  the  bicar- 
bonate of  one  of  these  bases. 

1  This  salt  is  found  in  nature  as  the  mineral  Brochantite. 


CHLORIDES   OP   COPPER.  383 

The  silicate  of  copper  forms  the  rare  mineral  diopfase,  or  emerald  copper-ore^ 
so  termed  from  the  transparent  green  color  of  its  hexahedral  crystals. 
Chrysocolla  is  also  a  silicate  of  copper. 

BINOXIDE  OR  PEROXIDE  or  COPPER,  Cu02. 

§  257.  This  oxide  has  been  obtained  by  the  action  of  binoxide  of  hydrogen  on 
hydrated  oxide  of  copper.  It  has  a  yellowish-brown  color,  and  is  very  easily 
decomposed  into  oxygen  and  oxide  of  copper  by  heat  or  acids. 

CUPRIC  ACID. 

This  acid  is  not  known  in  the  separate  state ;  it  is  formed  as  a  potassa-salfc 
when  finely-divided  copper  is  fused  with  hydrate  of  potassa  and  nitre,  or  when 
hydrated  oxide  of  copper  is  dissolved  in  a  solution  of  hypochlorite  of  potassa. 

The  potassa-salt  is  exceedingly  unstable ;  its  aqueous  solution  is  blue,  and  is 
very  easily  decomposed  into  potassa,  oxygen,  and  oxide  of  copper,  which  is  pre- 
cipitated. 

A  compound  of  copper  with  hydrogen,  of  the  formula  Cu2H,  has  been  obtained 
by  Wurtz,  by  the  action  of  hypophosphorous  acid  upon  solution  of  sulphate  of 
copper. 

It  is  a  brown  powder,  easily  decomposed  into  its  elements  by  heat,  oxidizing  in 
air,  and  dissolving  in  hydrochloric  acid,  with  disengagement  of  hydrogen. 

Schrotter  has  obtained  a  compound  of  copper  with  nitrogen,  to  which  he  has 
assigned  the  formula  Cu6N,  by  passing  ammonia  over  oxide  of  copper,  heated  to 
509°  F.  (265°  C.)>  and  removing  the  excess  of  oxide  from  the  resulting  com- 
pound by  treatment  with  solution  of  ammonia. 

This  compound  forms  a  dark-green  amorphous  powder,  which  is  decomposed 
with  some  violence  below  a  red  heat,  and  dissolves  in  hydrochloric  acid,  forming 
chloride  of  copper  and  sal-ammoniac. 

SUBCHLORIDE  OF  COPPER,  CuaCl. 

§  258.  Preparation. — I.  A  solution  of  chloride  of  copper  is  mixed  with  hydro- 
chloric acid,  and  boiled  with  metallic  copper,  until  the  green  colour  of  the  solu- 
tion has  changed  to  brown;  the  clear  liquid  is  then  rapidly  decanted,  and  mixed 
with  a  large  quantity  of  water,  which  precipitates  the  subchloride;  the  precipitate 
must  be  washed  by  decantation,  as  rapidly  as  possible,  with  water  which  has  been 
freed  from  air  by  boiling,  and  preserved  under  a  layer  of  water  in  a  well-stoppered 
bottle. 

II.  Solution  of  chloride  of  copper  is  mixed  with  a  concentrated  solution  of 
(proto-)  chloride  of  tin,  containing  a  little  free  acid,  when  the  subchloride  is  pre- 
cipitated : — 

2  CuCl-fSnCl=Cu3Cl+SnCl3. 

III.  Copper  is  heated  to  redness  in  a  current  of  chlorine. 

IV.  Chloride  of  mercury  is  distilled  with  copper  filings. 

Properties. — Subchloride  of  copper  is  white ;  it  fuses  below  a  red  heat,  and 
volatilizes  at  a  higher  temperature.  When  exposed  to  the  air,  it  is  converted 
into  a  green  compound  of  oxide  and  subchloride.  It  is  nearly  insoluble  in  water, 
but  dissolves  in  hydrochloric  acid,  and  forms  a  brown  liquid,  from  which  water 
precipitates  the  subchloride.  The  salt  may  be  crystallized  from  the  hydrochloric 
solution,  in  tetrahedral  crystals. 

Ammonia  readily  dissolves  the  subchloride,  giving  a  colorless  solution  which 
rapidly  becomes  blue,  from  oxidation,  when  exposed  to  air.  This  solution  is 
sometimes  employed  to  absorb  oxygen  from  gaseous  mixtures. 

Subchloride  of  copper  is  decomposed  by  the  fixed  alkalies,  the  hydrated  sub- 
oxide  being  formed. 


884  COPPER   AND    SULPHUR. 

CHLORIDE  OR  PROTOCIILORIDE  OF  COPPER,  CuCl. 

Anhydrous  chloride  of  copper  may  be  obtained  by  heating  the  metal  in  an 
excess  of  chlorine,  when,  if  finely  divided,  it  undergoes  combustion. 

The  anhydrous  chloride  has  a  yellowish-brown  color.  When  heated  to  dull 
redness,  it  loses  chlorine,  and  CuaCl  is  left. 

Hydrated  chloride  of  copper  is  prepared  by  dissolving  the  oxide  in  hydrochloric 
acid,  and  evaporating.  It  forms  beautiful  green  needles,  of  the  formula  CuCl-f 
2Aq;  they  are  deliquescent,  and  very  soluble  in  water;  the  solution  is  blue  when 
diluted,  and  has  a  green  color  when  concentrated,  or  when  mixed  with  a  large 
quantity  of  hydrochloric  acid. 

Chloride  of  copper  is  easily  soluble  in  alcohol,  to  the  flame  of  which  it  imparts 
a  green  colour. 

The  anhydrous  chloride  is  capable  of  absorbing  3  eqs.  of  ammonia,  forming  a 
blue  compound. 

When  ammonia  is  passed  into  a  hot  solution  of  chloride  of  copper,  a  compound 
is  formed  which  crystallizes,  on  cooling,  in  dark  blue  prisms,  of  the  formula  CuCl, 
2NH3,HO.  At  300°  F.  (149°  C.)  these  are  decomposed,  leaving  CuCl,NH3. 

OXYCHLORIDES  OF  COPPER. — Three  compounds  of  chloride  and  oxide  of  cop- 
per are  known,  containing  one  equivalent  of  the  former  compound,  and  two,  three, 
or  four  equivalents  of  the  latter. 

The  oxychloride  having  the  formula  CuCl,3CuO,4HO,  is  precipitated  when  a 
solution  of  chloride  of  copper  is  decomposed  with  an  insufficient  quantity  of 
potassa. 

This  compound  is  used  in  painting,  under  the  name  of  Brunswick  green,  and 
is  prepared  on  a  large  scale  by  moistening  copper  with  hydrochloric  acid,  or  solu- 
tion of  sal-ammoniac,  and  exposing  it  to  the  air,  whefl  it  becomes  covered  with  a 
green  coating  of  the  above  oxychloride. 

This  oxychloride  is  found  crystallized  in  the  mineral  kingdom,  as  atacamite. 

COPPER  AND  SULPHUR. 

Subsulphide  of  copper CuaS. 

Sulphide  "          CuS. 

SUBSULPHIDE  OF  COPPER.  Cu3S. 

§  259.  The  subsulphide  exists  in  nature,  and  forms  one  of  the  richest  ores  of 
copper  (copper-glance).  Its  crystalline  form  is  the  six-sided  prism;  it  is  soft, 
and  has  a  feeble  metallic  lustre.  This  ore  usually  contains  a  little  iron  and  silver. 

It  may  be  artificially  obtained  by  heating  3  parts  of  sulphur  with  8  parts  of 
copper-turnings,  when  combination  takes  place  with  disengagement  of  heat  and 
light. 

This  sulphide  fuses  more  easily  than  the  metal,  and  is  not  decomposed  by 
heat;  when  roasted  in  air,  it  is  partly  converted  into  sulphate;  it  is  not  attacked 
by  hydrochloric  acid,  but  is  dissolved  by  nitric  and  nitro-hydrochloric  acids. 

Subsulphide  of  copper  is  not  decomposed  by  hydrogen,  and  is  reduced  with 
difficulty  by  carbon. 

When  fused  with  caustic  alkalies,  metallic  copper  is  separated. 

If  a  mixture  of  subsulphide  of  copper  and  sulphate  of  copper  be  strongly  heated, 
the  copper  is  reduced : — 

CuaS+  CuO.S03=2S03-f  Cus. 

This  sub-sulphide  is  sometimes  found  crystallized,  in  octohedra,  in  the  copper- 
smelting  furnaces. 


METALLURGY   OF   COPPER.  385 

SULPHIDE  OF  COPPER,  CuS. 

This  sulphide  occurs  in  nature  as  indigo-copper,  or  Hue-copper  ;  it  is  precipi- 
tated by  decomposing  a  solution  of  a  copper-salt  with  hydrosulphuric  acid  or  a 
soluble  sulphide. 

It  is  a  black  powder,  which,  when  exposed  to  the  air,  especially  in  a  moist 
state,  soon  becomes  green,  from  production  of  sulphate  of  copper. 

When  heated  in  close  vessels,  or  in  an  atmosphere  of  hydrogen,  it  is  converted 
into  Cu2S. 

Sulphide  of  copper  is  not  attacked  by  boiling  in  moderately  dilute  sulphuric 
acid ;  hydrochloric  acid  scarcely  affects  it,  but  nitric  acid  dissolves  it  readily, 
sulphur  being  separated. 

This  sulphide  is  insoluble  in  sulphide  of  potassium,  but  dissolves  in  small 
quantity,  in  yellow  sulphide  of  ammonium. 

Higher  sulphides  of  copper  are  said  to  be  precipitated  from  solutions  of  copper- 
salts  by  the  poly  sulphides  of  the  alkali-metals. 

An  Oxysulphide  of  Copper,  of  the  formula  5CuS.CuO.HO  is  precipitated, 
according  to  Pelouze,  when  a  soluble  sulphide  is  added  to  a  boiling  solution  of 
nitrate  of  copper  mixed  with  excess  of  ammonia. 

COPPER-PYRITES,  Fe3S3.Cu3S. 

This  is  one  of  the  commonest  ores  of  copper. 

It  has  a  fine  brass-yellow  color,  and  a  metallic  lustre,  and  is  found  crystallized 
in  forms  derived  from  the  octohedron. 

The  spec.  grav.  of  copper-pyrites  is  4.17  ;  it  fuses  at  a  moderate  heat;  when 
heated  in  air,  it  yields  the  sulphates,  and  ultimately  the  oxides  of  iron  and  cop- 
per, sulphurous  acid  being  disengaged. 

It  is  not  acted  on  by  hydrochloric  acid,  but  nitric  and  nitro-hydrochloric  acids 
readily  dissolve  it. 

Variegated  Copper-ore  (peacock  ore)  is  also  composed  of  sulphur,  iron,  and 
copper,  but  in  variable  proportions.  It  is  distinguished  by  its  beautifully  iride- 
scent appearance,  due  probably  to  a  superficial  oxidation.  Variegated  copper-ore 
is  generally  amorphous,  but  sometimes  crystallized  in  forms  derived  from  the 
cube ;  its  specific  gravity  is  4.98,  and  it  is  fused,  but  not  decomposed,  when 
heated  in  close  vessels.  It  is  dissolved  by  nitric  acid. 

PHOSPHIDES  OF  COPPER. — Copper  may  be  made  to  unite,  at  a  red  heat,  with 
about  twenty  per  cent,  of  phosphorus,  to  form  a  gray,  hard,  brittle  mass,  of 
metallic  appearance,  and  more  fusible  than  copper. 

When  hydrogen  is  passed  over  phosphate  of  copper  at  a  moderately  high 
temperature,  a  phosphide  of  the  formula  Cu2P  is  obtained.  Another  phosphide 
of  copper  (Cu3P)  is  thrown  down  as  a  black  precipitate  when  phosphuretted 
hydrogen  is  passed  into  a  solution  of  a  copper-salt.  Other  phosphides  appear  to 
exist. 

METALLURGY   OF   COPPER. 

§  260.  The  chief  ores  of  copper  are  the  following  : — 

Native  copper  (the  metal  itself),  which  is  found  crystallized  in  cubes  and 
six-sided  prisms. 

Red  copper-ore,  composed  of  the  suboxide,  generally  associated  with  sesqui- 
oxide  of  iron. 

Black  oxide  of  copper. 

Blue  carbonate  of  copper,  3Cu0.2C03.HO=2(CuO.C03)-f-CuO.HO. 

Malachite,  CuO.C03+CuO.HO. 
25 


386  METALLURGY   OF    COPPER. 

Subsulphide  of  copper,  CuaS  (copper-glance). 

Copper-pyrites,  Fe2S3,Cu3S=2(FeCuS2.) 

Variegated  copper-ore. 

Gray  copper-ore,  containing  sulphides  of  copper,  antimony,  arsenic,  lead,  and 
silver. 

All  these  ores  are  more  or  less  used  for  the  extraction  of  copper,  but  this  is 
the  case  chiefly  with  copper-pyrites  and  gray  copper-ore,  and  since  these  are 
the  most  difficult  to  reduce,  a  description  of  the  process  employed  to  effect  that 
purpose  will  best  exhibit  the  general  principles  of  the  smelting  of  copper-ores. 

The  ore  freed  from  gangue,  is  first  roasted  on  the  hearth  of  a  reverberatory 
furnace  by  the  flame  of  a  coal-fire;  during  this  process,  part  of  the  sulphur  is 
volatilized,  another  portion  is  converted  into  sulphurous  acid,  and  the  remainder 
into  sulphuric  acid,  which  is  left  in  combination  with  the  oxides  of  iron  and  cop- 
per; moreover,  part  of  the  arsenic  is  expelled  as  arsenious  acid  or  as  a  sulphide 
of  arsenic,  and  the  rest  is  left  in  the  form  of  an  arseniate.  The  roasted  ore, 
therefore,  consists  chiefly  of  oxides  of  copper  and  of  iron,  of  unaltered  sulphides  of 
these  metals,  and  of  arsenic  acid.  It  is  now  fused  in  another  reverberatory  furnace, 
with  some  oxidized  silicious  slags  from  a  former  operation,  and  some  oxidized 
ores  of  copper;  a  quantity  of  fluor-spar  being  also  added,  to  promote  the  fusion  of 
the  slag.  In  this  operation,  the  oxides  and  sulphides  undergo  a  mutual  decom- 
position, the  copper  combining  chiefly  with  the  sulphur,  whilst  the  iron  takes 
the  oxygen,'  and  passes  into  the  slag,  which  consists  chiefly  of  silicate  of  oxide  of 
iron.  A  product  is  thus  obtained  which  contains  about  33  per  cent,  of  copper, 
combined  chiefly  with  sulphur;  it  is  run  out  into  a  cistern  of  water,  and  thus 
granulated. 

This  is  again  oxidized  by  roasting,  and  afterwards  fused  with  certain  ores  and 
slags  rich  in  oxide  of  copper,  which,  by  a  double  decomposition,  converts  almost 
all  the  sulphide  of  iron  into  a  sulphide  of  copper  and  oxide  of  iron,  the  latter 
combining  with  the  silica  to  form  a  fusible  slag.  The  result  of  this  operation  is 
a  subsulphide  of  copper  containing  very  little  iron,  arsenic,  and  other  impurities 
of  the  original  ore;  it  is  roasted  in  a  peculiar  manner,  with  access  of  air,  which 
oxidizes  the  greater  part  of  the  impurities,  and  the  crude  copper  is  afterwards 
refined  by  fusion  in  contact  with  air,  and  with  a  little  silica,  by  which  the  whole 
of  the  sulphur  is  removed,  and  the  foreign  metals  are  oxidized  and  dissolved  in 
the  slag.  But  the  copper  thus  obtained  contains  still  a  little  suboxide,  which 
affects  its  malleability;  it  is  purified  by  fusion  in  contact  with  charcoal,  and  stir- 
ring with  a  pole  of  green  wood,  which  disengages  highly  reducing  gases. 

The  copper  is  then  in  a  marketable  state. 

Copper  ores  are  sometimes  worked  for  silver  and  copper  at  the  same  time,  when, 
of  course,  other  processes  are  had  recourse  to  for  the  economical  separation  of 
these  metals.  / 

According  to  Brankart's  process,  a  certain  amount  of  copper  is  obtained  by 
reducing,  with  metallic  iron,  the  solution  of  sulphate  of  copper  obtained  by 
washing  the  roasted  sulphureous  ores  with  water. 

The  process  of  Rivot  and  Phillips  consists  in  reducing  the  ores,  previously 
oxidized  by  roasting,  by  means  of  metallic  iron  at  a  high  temperature. 

Napier's  process  depends  upon  the  same  principle,  the  abstraction  of  the  sul- 
phur being  assisted  by  the  employment  of  soda-ash  or  salt-cake.  The  sulphide 
of  sodium  then  formed  is  afterwards  removed  by  treating  the  crude  metal  with 
water,  which  also  dissolves  the  sulphur-salts  of  antimony  and  tin,  thus  entirely 
removing  these  metals,  which  would  much  injure  the  quality  of  the  copper. 

The  best  specimens  of  commercial  copper  are  nearly  pure;  they  contain  only 
traces  of  iron.  A  very  small  quantity  of  arsenic  or  of  phosphorus  injures  the 
color  of  the  metal,  rendering  it  whitish,  at  the  same  time  causing  it  to  be  some- 
what brittle. 


ALLOYS  OF  COPPER.  387 

USES  OP  COPPER. 

§  261.  This  metal  is  chiefly  employed  for  sheathing  the  bottoms  of  ships,  to 
protect  them  from  the  action  of  sea-water,  and  to  diminish  the  friction  of  the 
latter  upon  the  bottom  and  sides  of  the  vessel.  It  is,  moreover,  largely  used  for 
boilers,  stills,  and  culinary  vessels. 

Copper-plates  are  used  for  engraving;  they  are  covered  with  a  particular  varnish, 
through  which  the  subject  is  engraved  with  a  tool;  the  plate  is  then  acted  on  by 
nitric  acid,  which  eats  into  the  lines  of  the  engraving,  leaving  the  varnished  por- 
tion untouched;  the  varnish  is  then  cleaned  off,  and  the  work  finished  by  graving- 
tools.  But  the  largest  quantity  of  copper  is  employed  for  making  various  highly 
important  alloys.  We  must  not  omit  to  mention  the  use  of  copper  for  coinage. 

Alloys  of  Copper  and  Zinc. — Copper  may  be  readily  alloyed  with  zinc,  which 
materially  alters  its  physical  properties;  a  small  quantity  of  this  last  metal  changes 
the  red  color  of  copper  to  a  shade  of  yellow,  which  passes  through  various  gra- 
dations as  the  quantity  of  zinc  is  increased,  until  it  arrives  at  a  bluish-gray. 

The  specific  gravity  of  an  alloy  of  copper  and  zinc  is  generally  higher  than 
would  be  expected  from  the  mere  mixture  of  the  two  metals,  rendering  it  probable 
that  a  combination  has  taken  place. 

The  alloys  of  copper  and  zinc  are  more  fusible  than  copper  itself,  and  lose  part 
of  their  zinc  at  high  temperatures;  this  metal  may  be  expelled  almost  entirely  by 
a  strong  heat.  When  they  are  fused  in  contact  with  air,  a  film  of  oxide  of  zinc 
is  formed  upon  the  surface,  and  if  this  be  removed,  from  time  to  time,  the  whole 
of  the  zinc  may  be  extracted  from  the  alloy. 

A  little  lead  added  to  these  alloys  prevents  them  from  "greasing  the  file,"  i.  e. 
filling  up  the  cavities  of  that  tool.  Tin  hardens  the  alloys. 

The  most  important  alloys  of  copper  and  zinc  are  brass,  Dutch  gold,  pinclibecJc, 
and  tombac. 

Brass  differs  in  composition  according  to  the  purposes  to  which  it  is  to  be  applied, 
but  it  always  consists  of  about  f  copper  and  £  zinc,  with  small  quantities  of  lead 
(varying  from  2  to  0.5  per  cent.)  and  of  tin  (from  025  to  0.£  per  cent.). 

At  the  present  day,  brass  is  generally  prepared  by  the  direct  combination  of  the 
metals,  but  formerly  it  was  customary  to  fuse  metallic  copper  with  calamine  and 
charcoal. 

Tombac,  which  is  employed  for  articles  intended  for  gilding,  generally  contains 
from  10  to  14  per  cent,  of  zinc. 

Alloys  of  Copper  and  Tin. — Although  we  have  not  yet  described  the  properties 
of  tin,  yet  since  copper  forms  several  alloys  with  it  which  contain  this  metal  (copper) 
as  their  principal  ingredient,  we  will  remark  upon  them  in  this  place. 

Tin  does  not  easily  combine  with  copper,  and  the  compound,  when  formed,  is 
very  easily  decomposed ;  a  portion  of  the  tin  is  separated  in  the  liquid  form  when 
the  alloy  is  gradually  heated,  or  allowed  to  cool  slowly  from  the  fused  state. 

An  alloy  of  tin  and  copper  is  much  harder  than  either  of  these  metals,  and  was 
used  by  the  ancients  for  making  swords  and  knives,  before  iron  was  employed  for 
these  purposes.  When  such  alloys  are  allowed  to  cool  slowly,  they  become  hard, 
and  sometimes  brittle,  but  they  may  be  rendered  malleable  by  being  heated  to 
redness  and  plunged  into  water;  just  the  opposite  effect  to  that  which  this  treat- 
ment has  upon  steel. 

The  two  metals  may  be  entirely  separated  by  fusing  the  alloy  for  a  sufficient 
length  of  time  in  contact  with  air,  when  the  tin  is  oxidized. 

The  specific  gravity  of  alloys  of  copper  and  tin  is  higher  than  that  of  a  mixture 
of  these  metals  should  be. 

The  chief  alloys  of  copper  and  tin  are  bronze,  gun-metal,  bell-metal,  speculum- 
metal,  and  the  metal  of  which  certain  musical  instruments  (cymbals,  &c.)  are  made. 


888  METALLURGY   OF   COPPER. 

Bronze  varies  much  in  the  proportions  of  copper  and  tin  which  it  contains;  small 
quantities  of  iron,  zinc,  and  lead  are  often  added  to  it. 

GUN-METAL  (employed  for  pieces  of  ordnance)  should  possess  great  tenacity, 
considerable  hardness,  and  a  moderate  fusibility,  in  order  that  it  may  be  easily 
cast  into  moulds.  The  only  metals,  possessing  considerable  tenacity,  which  can 
be  used  for  this  purpose,  are  copper  and  iron;  the  latter,  when  pure,  is,  however, 
too  infusible;  and  the  comparatively  small  tenacity  of  cast-iron  renders  it  neces- 
sary to  give  to  guns  of  this  material  a  thickness  which  would  render  them  useless 
in  service  requiring  rapid  transport  of  artillery;  this  metal  is  therefore  almost 
exclusively  employed  for  guns  of  heavy  caliber.  Copper  is  too  soft  to  be  em- 
ployed in  the  pure  state,  its  hardness  is  therefore  increased  by  adding  a  quantity 
of  tin  insufficient  to  diminish  to  any  great  extent  the  tenacity  of  the  copper. 

In  consequence  of  the.  tendency  exhibited  by  the  alloys  of  copper  and  tin  to 
separate  into  their  constituents,  the  guns  never  have  a  uniform  composition 
throughout,  however  perfectly  the  mixture  of  metals  was  effected  during  the 
fusion,  the  proportion  of  tin  being  found  to  increase  gradually  from  the  breech 
to  the  muzzle  of  the  gun. 

The  alloy  of  which  the  smaller  cannon  are  made,  consists,  with  slight  varia- 
tions on  either  side,  of 

Copper 90.5 

Tin 9.5 

100.0 

The  proportion  of  tin  is  sometimes  slightly  increased  in  guns  of  larger  caliber. 

Since  a  certain  quantity  of  tin  is  always  separated  by  oxidation  during  the 
fusion,  it  is  necessary  to  employ  originally  a  quantity  of  that  metal  in  addition 
to  the  above  proportion.  The  alloy  is  prepared  by  fusing  together  copper,  tin, 
old  gun-metal,  and  bronze.  The  copper  employed  is  almost  chemically  pure; 
the  tin  is  also  very  pure;  Banca  tin  (Cornwall)  is  preferred. 

The  reverberatory  furnace  in  which  the  fusion  is  effected  is  so  constructed  that 
no  air  shall  enter  which  has  not  been  deoxidized  by  passing  through  a  layer 
of  ignited  fuel,  and  the  draught-holes  are  so  arranged  that  the  flame  is  forced  to 
spread  itself  over  the  hearth. 

The  alloy  was  formerly  prepared  by  first  fusing  together  the  old  gun-metal,  the 
bronze,  and  the  copper,  and  afterwards  adding  the  tin;  but  the  latter  metal  was 
always  found  to  be  very  unequally  distributed,  portions  occurring  in  the  alloy 
which  contained  a  very  large  percentage  of  tin ;  it  has  therefore  been  found  far 
better  first  to  alloy  the  tin  with  copper,  in  the  proportions  contained  in  speculum- 
metal  (2Cu  to  ISn),  and  afterwards  to  add  this  alloy  to  the  fused  mixture  of 
gun-metal  and  copper.  In  this  way  a  far  more  complete  admixture  of  metals  is 
effected,  and  the  loss  of  tin  by  oxidation  is  less,  since  the  metal  need  not  be 
maintained  in  fusion  for  so  long  a  period  as  in  the  former  case.  Long  wooden 
stirrers  are  used  to  mix  the  metals  thoroughly,  and  at  the  same  time  to  deoxidize 
them.  When  the  fusion  is  completed,  and  mixture  is  perfect,  the  oxide  is  re- 
moved from  the  surface,  and  the  metal  run  into  moulds  formed  of  loam  and 
sand  (which  give  to  it  merely  its  external  form),  the  gun  being  cast  perpendicu- 
larly, the  muzzle  upwards.  In  the  original  casting,  the  latter  is  lengthened  into 
a  cylindrical  mass  of  metal,  about  3  feet  high,  which  is  afterwards  cut  off,  before 
the  gun  is  turned  and  bored.  *  The  object  of  adding  this  superfluous  portion  to 
the  casting,  above  the  gun,  is,  by  the  pressure  of  this  column  of  fused  metal,  to 
render  the  solidification  more  rapid,  thus  allowing  the  metals  less  time  to  sepa- 
rate, and  to  increase  the  density  of  the  alloy  at  the  breech  of  the  gun,  where 
the  greatest  tenacity  is  required.  Particles  of  oxide,  or  dross,  will  also  rise  into 


ASSAY   OF   COPPER-ORES.  389 

this  portion  of  the  casting  when   the  metal  is  fluid;  any  defects  which  they 
might  occasion  in  the  gun  are  thus  obviated. 

Bell-mclal  contains  usually  about  1  part  of  tin,  and  3  of  copper ;  small  quan- 
tities of  zinc  and  lead  are  sometimes  added;  these  diminish  the  sonorosity  of  the 
compound. 

Speculum-metal,  employed  in  making  telescopes,  consists  of  1  part  of  tin,  and 
2  of  copper,  and  generally  contains  a  little  zinc,  arsenic,  and  silver;  it  is  a  hard, 
brittle  alloy,  capable  of  a  high  polish. 

The  metal  of  which  musical  instruments  are  made,  contains  4  parts  of  copper, 
and  1  of  tin. 

The  alloy  known  as  paclc-fong,  argentan,  or,  more  commonly,  German  silver, 
consists  of  2  parts  of  copper,  1  of  nickel,  and  1  of  zinc.  The  copper  and  nickel 
are  first  fused  together,  and  the  zinc  afterwards  added. 

German  silver  has  a  yellowish-white  color,  is  malleable  and  ductile.  It  should 
not  be  employed  in  making  culinary  vessels,  since  it  is  easily  oxidized  and  dis- 
solved by  contact  with  air  and  acids. 

For  some  purposes,  copper  is  covered  with  a  thin  layer  of  tin,  by  spreading 
the  fused  metal  over  the  heated  surface  of  copper  to  which  it  adheres. 

Pins  made  of  brass  wire  are  tinned  by  boiling  with  bitartrate  of  potassa, 
granulated  tin,  and  water;  the  tin  is  oxidized  at  the  expense  of  the  latter,  and 
dissolved  by  the  bitartrate  of  potassa;  from  this  solution,  it  is  deposited  in  the 
metallic  state  upon  the  pins,  which  reduce  it  by  galvanic  action. 

§  262.  ASSAY  OF  COPPER-ORES. — The  ores  of  copper  are  assayed  by  different 
methods,  according  to  the  nature  of  their  constituents. 

They  may  be  conveniently  divided  into  three  classes. 

1st  class.  Ores  containing  no  other  metals  besides  copper  and  iron,  and  which 
are  perfectly  free  from  sulphur  and  arsenic. 

2d  class.  Ores  similar  to  the  above,  but  containing  sulphur. 

3d  class.  Ores  containing  other  metals  besides  copper  and  iron. 

Assay  of  Ores  belonging  to  the  \st  Class. — About  400  grs.  of  ore  are  mixed 
with  3  times  their  weight  of  black  flux,  and  gradually  heated  in  an  earthen  cru- 
cible placed  in  a  coke  fire,  the  heat  being  at  last  raised  to  bright  redness,  and 
this  temperature  maintained  for  about  fifteen  minutes.  The  copper  is  thus 
reduced  to  the  metallic  state,  and  fused  into  a  button  at  the  bottom  of  the  cruci- 
ble. When  cool,  the  latter  is  broken,  the  button  carefully  extracted,  and 
weighed. 

If  the  ore  be  very  poor,  it  is  usual  to  fuse  it  with  a  quantity  of  sulphur,  in 
the  same  manner  as  if  it  were  an  ore  of  the  2d  class. 

Assay  of  Ores  belonging  to  the  2d  Class. — The  powdered  ore  is  mixed  with  an 
equal  weight  of  dried  borax,  and  fused  in  an  earthen  crucible,  at  a  dull  red  heat. 
In  this  way  the  earthy  matters  (gangue)  are  separated  from  the  sulphide  of 
copper,  which  forms  a  button  (niatt)  at  the  bottom  of  the  crucible.  The  con- 
tents of  the  latter  are  then  poured  into  an  elliptical  iron  mould  (scorifier*),  and 
the  slag  separated  from  the  button  by  means  of  a  hammer. 

The  button,  or  matt,  is  then  finely  powdered  in  an  iron  mortar,  and  intro-  . 
duced  into  an  earthen  crucible,  which  is  placed  obliquely  in  a  furnace,  the 
draught  of  which  is  almost  entirely  cut  off,  so  that  only  a  gentle  heat  is  obtain- 
ed. In  this  way,  the  ore  is  roasted  for  some  time,  and  constantly  stirred  with  a 
steel  rod.  The  heat  is  gradually  raised,  and  when  no  more  sulphurous  acid  is 
evolved,  the  crucible  is  exposed  for  a  few  minutes  to  a  white  heat  (in  order  to 
decompose  the  sulphates),  and  removed  from  the  fire. 

The  roasted  ore  is  now  mixed  with  3  or  4  parts  of  black  flux,  returned  to  the 
same  crucible,  covered  with  a  layer  of  fused  borax,  and  heated  for  twenty  minutes 
in  a  wind-furnace.  The  crucible  is  then  allowed  to  cool,  the  button  extracted  by 


390  BISMUTH. 

breaking  the  crucible,  and  weighed,  after  removing  all  adhering  impurities  by 
gently  striking  it  with  a  hammer. 

Assay  of  Ores  of  the  3d  Class. — The  powdered  ore  is  first  fused  as  in  the  pre- 
ceding case,  to  obtain  a  matt,  which  is  then  roasted,  very  gradually,  so  as  not  to 
fuse  the  ore,  in  order  to  expel  the  arsenic,  sulphur,  &c. 

When  the  ore  contains  .arsenic,  it  is  well  to  mix  it,  after  roasting  as  long  as 
any  arsenical  fumes  are  perceptible,  with  some  powdered  charcoal,  and  to  heat  a 
second  time  to  bright  redness,  so  as  to  expel  the  remainder  of  the  arsenic,  as  far 
as  possible. 

The  matt  is  then  to  be  reduced  as  in  the  last  case,  with  black  flux  and  borax. 
The  button  of  impure  copper  thus  obtained  is  fused  in  a  bone-ash  cupel,  placed 
in  a  muffle,  and  a  little  pure  lead  added  to  it.  This  latter,  together  with  the 
other  more  oxidizable  metal,  is  then  converted  into  oxide,  which,  in  a  fused  state, 
dissolves  the  other  oxides,  and  is  absorbed,  together  with  these,  by  the  cupel. 
When  the  cupellation  is  terminated,  which  is  known  by  the  sudden  brightening 
of  the  fused  globule,  and  by  the  cessation  of  the  rotatory  motion  which  it  exhibits 
during  the  process,  a  little  vitrified  borax  is  thrown  over  it;  the  cupel  is  then 
withdrawn,  allowed  to  cool,  and  the  button  (which  should  be  perfectly  malleable) 
removed,  lightly  struck  with  a  hammer,  to  detach  adhering  slag,  and  weighed. 

The  above  is  only  a  general  outline  of  the  methods  pursued  in  the  assaying  of 
copper-ores.  It  would  be  far  beyond  the  scope  and  intention  of  this  work  to 
enter  into  the  various  details  of  these  processes,  for  which  we  refer  to  the  tech- 
nical works  on  assaying. 


BISMUTH. 

Sym.  Bi.     Eq.  213.     Sp.  Gr.  9.8. 

§  263.  This  metal  is  tolerably  abundant  in  the  mineral  kingdom,  where  it  is 
generally  found  in  the  metallic  state. 

Preparation. — The  bismuth  of  commerce,  the  extraction  of  which  will  be 
presently  described,  contains  small  quantities  of  sulphur,  arsenic,  lead,  silver,  and 
other  impurities.  It  may  be  rendered  sufficiently  pure  for  most  purposes  by 
fusing  it  with  y1^  its  weight  of  nitre,  in  an  earthen  crucible,  at  such  a  tempera- 
ture that  the  salt  shall  begin  to  evolve  a  little  oxygen,  which  will  act  upon  the 
more  oxidizable  metals,  and  upon  the  sulphur,  thus  causing  these  impurities  to 
pass  into  the  slag. 

If  it  is  desired  to  obtain  perfectly  pure  bismuth,  the  product  of  the  above  opera- 
tion is  dissolved  in  nitric  acid,  the  silver  precipitated  by  hydrochloric  acid,  the 
lead  by  sulphuric  acid,  and  lastly,  the  teroxide  of  bismuth  by  potassa;  the  pre- 
cipitate is  well  washed,  and  reduced  by  charcoal. 

Properties. — Bismuth  has  a  grayish-white  colour,  with  a  tinge  of  red,  and  me- 
tallic lustre.  It  is  brittle,  and  very  crystalline;  it  fuses  at  the  low  temperature 
of  476°. 5  F.  (247°  C.),  and  volatilizes  at  a  considerably  higher  temperature. 
Fused  bismuth  suffers  considerable  expansion  in  the  act  of  solidifying.  When 
allowed  to  cool  very  slowly,  it  crystallizes  in  large  rhombohedra,  similar  to  those 
of  common  salt,  and  aggregated,  like  these  latter,  into  the  form  of  steps;  this  may 
be  easily  seen  on  breaking  the  crust  as  soon  as  it  has  formed  upon  the  surface  of 
the  fused  metal,  and  pouring  out  the  liquid  portion,  when  a  crystallized  mass 
remains  in  the  vessel.  The  bismuth  employed  for  this  experiment  should  be 
very  pure. 

Bismuth  is  not  affected  by  dry  air,  but  tarnishes  if  moisture  be  present;  when 
heated  in  air,  it  burns  with  a  bluish  flame,  giving  off  yellow  fumes  of  oxide. 


BISMUTH   AND   OXYGEN.  391 

This  metal  decomposes  water  only  at  a  very  high  temperature ;  and  does  not 
decompose  it  at  the  ordinary  temperature  in  presence  of  acids. 

Nitric  acid  readily  dissolves  bismuth,  producing  nitrate  of  the  teroxide. 

Hydrochloric  and  dilute  sulphuric  acids  have  scarcely  any  action  upon  bis- 
muth; concentrated  sulphuric  acid  oxidizes  and  dissolves  it  with  the  aid  of  heat; 
sulphate  of  teroxide  of  bismuth  being  formed,  and  sulphurous  acid  evolved. 


BISMUTH   AND  OXYGEN. 

Teroxide  of  bismuth    ....     . <*..>;  .     .     Bi03 
Bismuthic  acid Bi05 

§  264.  A  suboxide  of  bismuth  is  also  said  to  be  formed  when  the  metal  is  heated 
in  air  to  a  temperature  a  little  above  its  fusing-point;  it  is  black,  and  burns  when 
heated  in  air,  forming  teroxide  of  bismuth.  Dilute  nitric  acid  decomposes  it  into 
metal  and  teroxide,  the  latter  dissolving  in  the  acid. 

Some  chemists  estimate  the  equivalent  of  bismuth  at  106.5,  when  the  first  of 
the  above  oxides  is  written  Bia03,  and  the  second,  Bia05. 

TEROXIDE  or  BISMUTH  (sometimes  called  PROTOXIDE,  and  sometimes 
SESQUIOXIDE  OF  BISMUTH). 

Bi03.     Eq.  237. 

The  anhydrous  teroxide  is  formed  when  bismuth  is  heated  with  free  access  of 
air;  it  may  also  be  obtained  by  heating  the  basic  nitrate  of  bismuth. 

It  has  a  yellow  color,  is  tasteless  and  inodorous.  When  heated,  it  fuses  easily, 
and  assumes  a  brownish  color.  Fused  teroxide  of  bismuth  soon  penetrates  an 
earthen  crucible,  giving  rise  to  a  fusible  silicate.  It  is  not  volatile,  and  may  be 
easily  reduced  by  carbon  or  hydrogen  at  a  high  temperature. 

Teroxide  of  bismuth  combines  with  acids,  forming  salts,  which  have  always  an 
acid  reaction. 

Hydrated  teroxide  of  bismuth,  Bi03.HO,  is  precipitated  when  a  solution  of  a 
bismuth-salt  is  mixed  with  a  slight  excess  of  potassa  or  ammonia. 

It  forms  a  white  precipitate,  which,  when  boiled  in  the  supernatant  liquid,  is 
converted  into  a  collection  of  small  yellowish  needles  of  the  anhydrous  teroxide. 

NITRATE  OF  TEROXIDE  OF  BISMUTH,  OR  NITRATE  OF  BISMUTH.  Bi03.3N05. 

To  prepare  this  salt,  bismuth  is  dissolved  in  dilute  nitric  acid,  with  the  aid  of 
heat,  and  the  solution  concentrated  by  evaporation,  when  it  deposits,  on  cooling, 
deliquescent  four-sided  prisms,  of  the  formula  Bi03.3N05+10Aq,  which  are  de- 
composed by  exposure  for  some  hours  to  a  temperature  of  302°  F.  (150°  C.), 
leaving  BiO3.N05+HO;  at  500°  F.  (260°  C.),  the  acid  and  water  are  com- 
pletely expelled. 

These  crystals  dissolve  very  easily  in  dilute  nitric  acid,  but  are  decomposed 
by  water  into  an  acid  salt,  which  passes  into  solution,  and  a  basic  salt,  which 
remains  undissolved. 

This  basic  salt,  which  is  known  as  Bismuthum  album,  trisnitrate  of  bismuth, 
or  flake- white,  varies  in  composition  according  to  the  temperature,  the  quantity 
of  water  added,  and  the  length  of  time  for  whicfc  it  is  washed,  but  its  general 
formula  might  be  written  Bi03.N05+HO.  The  nitric  acid  may  be  gradually 
removed  by  washing  with  boiling  water. 

The  basic  nitrate  of  bismuth  is  occasionally  employed  in  medicine;  it  is  used, 
moreover,  as  a  cosmetic  for  whitening  the  skin,  but  becomes  black  under  the 
influence  of  sulphuretted  hydrogen. 


392  SULPHIDES   OP  BISMUTH. 

SULPHATE  OP  TEROXIDE  OF  BISMUTH  (Bi03.3S03)  is  left  as  a  white  fusible 
powder  when  finely-divided  bismuth  is 'heated  with  concentrated  sulphuric  acid. 

When  treated  with  water,  this  salt  is  decomposed,  an  acid  salt  being  dissolved, 
while  the  residue  is  found  to  consist  of  a  basic  salt,  the  composition  of  which  is 
Bi03.S03-fAq. 

An  intermediate  salt,  of  the  formula  Bi08.2S03-f  3Aq,  has  also  been  obtained. 

Sulphate  of  bismuth  forms  a  double-salt  with  sulphate  of  potassa,  of  the  for- 
mula Bi03,3S03,3(KO.S08). 

A  basic  carbonate  of  bismuth,  of  the  formula  Bi03  C0a  +  Aq,  is  precipitated 
when  carbonate  of  soda  is  added  to  an  acid  solution  of  nitrate  of  bismuth  : — 1 

BiO;.3N05+3(NaO.C03)=Bi03.C03+3(NaO.N05)+2C02. 

From  the  tendency  of  teroxide  of  bismuth  to  form  basic  salts,  it  will  be  seen 
that  it  is  a  feeble  base. 

BISMUTHIC  ACID,  Bi05. 

This  acid  is  but  little  known. 

It  is  formed  by  heating  a  mixture  of  teroxide  of  bismuth  with  potassa  and 
chlorate  of  potassa. 

In  order  to  prepare  it,  a  current  of  chlorine  may  be  passed  through  a  very 
concentrated  solution  of  potassa  in  which  teroxide  of  bismuth  is  suspended ;  the 
insoluble  bismuthate  of  potassa  is  thus  obtained  as  a  red  powder,  which  is  treated 
with  nitric  acid  to  remove  the  potassa  and  any  excess  of  teroxide  of  bismuth, 
when  bismuthic  acid  is  left  as  a  bright  red  substance  which  is  easily  decomposed 
by  heat,  leaving  an  intermediate  oxide,  which  may  be  represented  as  Bi03,Bi05 : 
it  is  also  decomposed  when  heated  with  sulphuric  acid,  sulphate  of  teroxide  of 
bismuth  being  produced,  and  oxygen  evolved. 

The  above-mentioned  intermediate  oxide  may  be  obtained  by  heating  a  mix- 
ture of  potassa  and  teroxide  of  bismuth  in  contact  with  air;  it  is  a  brown  sub- 
stance which  evolves  oxygen  when  heated  with  acids,  yielding  salts  of  teroxide 
of  bismuth. 

TERCHLORIDE  OP  BISMUTH,  BiCl3. 

§  265.  Preparation. — In  order  to  prepare  the  terchloride,  powdered  bismuth 
may  be  gently  heated  in  a  retort  through  which  a  current  of  dry  chlorine  is 
passed,  when  combination  takes  place,  with  great  disengagement  of  heat,  and  if 
the  temperature  be  afterwards  raised,  the  terchloride  distils  over. 

It  may  also  be  obtained  by  distilling  1  part  of  powdered  bismuth  with  2  parts 
of  chloride  of  mercury  (corrosive  sublimate). 

When  bismuth  is  dissolved  in  nitro-hydrochloric  acid,  or  when  its  oxide  is 
dissolved  in  hydrochloric  acid,  and  the  solution  evaporated,  hydrated  terchloride 
of  bismuth  is  obtained. 

Properties. — The  anhydrous  terchloride  deliquesces  in  air;  it  is  fusible  and 
volatile ;  it  dissolves  in  water  acidulated  with  hydrochloric  acid,  but  is  decom- 
posed by  pure  water,  a  white  oxychloride  of  bismuth  being  precipitated.  A 
similar  crystalline  precipitate  is  formed  when  a  concentrated  solution  of  the 
terchloride  is  poured  into  water,  and  this  reaction  is  turned  to  advantage  in  the 
detection  of  bismuth  in  analysis. 

The  composition  of  this  oxychloride  is  BiCl3,2Bi03,GHO;  and  its  formation 
may  be  represented  by  the  equation  : — 

3BiCl,+  6HO=BiCl,,2BiO,+6IICl. 

1  If  the  solution  be  nearly  neutral,  the  precipitate  is  anhydrous. 


METALLURGY   OF   BISMUTH.  393 

When  heated,  a  part  of  the  terchloride  is  volatilized,  and  the  residue  has  the 
composition  BiCl3,6Bi03. 

Terchloride  of  bismuth  forms  crystallizable  double-salts  with  the  alkaline 
chlorides. 

The  above-mentioned  hyd rated  oxychloride  of  bismuth  is  sometimes  used  as  a 
cosmetic,  under  the  name  of  pearl-white.  It  is  prepared  for  this  purpose  by 
pouring  an  acid  solution  of  nitrate  of  bismuth  into  solution  of  chloride  of  sodium. 

There  appear  to  be  two  sulphides  of  bismuth. 

Bisulphide  of  bismuth  (BiSa),  is  sometimes  found  native;  it  may  be  prepared 
by  the  direct  combination  of  its  elements,  or  by  fusing  the  tersulphide  with  an 
equal  weight  of  bismuth,  when  it  crystallizes  on  cooling,  and  the  excess  of  metal 
may  be  decanted. 

Tersulphide  of  bismuth  (BiSa),  occurs  in  the  mineral  kingdom  as  bismuth- 
glance;  it  has  a  gray  color  and  metallic  lustre;  its  crystals  are  prismatic,  and  it 
is  therefore  isomorphous  with  the  tersulphide  of  antimony. 

The  tersulphide  of  bismuth  fuses  when  heated,  and,  with  access  of  air,  is  con- 
verted into  teroxide,  sulphurous  acid  being  evolved. 

When  sulphuretted  hydrogen  is  passed  through  a  solution  of  a  salt  of  bismuth, 
a  black  precipitate  of  tersulphide  of  bismuth  is  obtained.  This  precipitate  is 
insoluble  in  the  alkaline  sulphides,  and  in  dilute  sulphuric  acid;  it  dissolves  very 
sparingly  in  hydrochloric  acid,  but  readily  in  nitric. 

METALLURGY  OF  BISMUTH. 

§  266.  The  chief  forms  in  which  bismuth  occurs  in  nature  are  the  following : — 

Native  bismuth. 

Teroxide  of  bismuth,  which  forms  a  very  rare  mineral  known  as  bismuth-ochre. 

Carbonate  of  bismuth. 

Bisulphide  of  bismuth. 

Tersulphide  of  bismuth,  which  is  often  associated  with  the  sulphides  of  lead, 
copper,  and  silver. 

Arsenide  of  bismuth. 

Silicate  of  bismuth,  or  bismuth-blende. 

Bismuth  is  always  extracted  from  the  ores  which  contain  it  in  the  state  of  metal. 
These  are  introduced  into  cast-iron  cylinders  placed  in  an  inclined  position  across 
a  furnace;  the  upper  end  of  the  cylinder  is  closed,  and  the  lower  only  partially 
so,  by  a  plate  pierced  with  a  hole  which  allows  the  bismuth  to  flow  into  a  recep- 
tacle placed  beneath;  the  cylinders  are  moderately  heated,  when  the  metal  fuses, 
and  is  thus  separated  from  the  earthy  matters  with  which  it  was  surrounded. 

The  uses  of  bismuth  are  very  limited. 

It  forms  certain  alloys  which  are  remarkable  for  their  great  fusibility. 

An  alloy  of  8  bismuth,  5  lead,  and  3  tin  is  known  as  Newton's  fusible  alloy, 
and  is  employed  for  taking  moulds,  &c.  This  alloy  fuses  at  about  203°  F.  (95  C.), 
although  the  most  fusible  of  its  constituents  requires  a  much  higher  temperature. 

The  fusibility  of  these  alloys  may  be  varied  to  almost  any  extent  by  altering 
the  proportions  of  their  ingredients;  they  are  sometimes  employed  in  the  con- 
struction of  the  safety-valves  of  steam  engines,  which  fuse,  and  allow  the  egress 
of  steam  when  the  pressure  (and,  therefore,  the  temperature)  has  attained  a  cer- 
tain point;  but  since  the  alloy,  when  heated  for  some  time,  is  capable  of  separating 
into  a  less  fusible  compound  and  one  that  is  more  fusible,  these  valves  have  been 
found  unsafe.  Bismuth  enters  into  the  composition  of  some  kinds  of  pewter;  it 
is  also  employed  in  type-metal,  where  its  property  of  expanding  during  solidification 
causes  it  to  enter  the  very  finest  parts  of  the  mould. 

For  the  analysis  of  Newton's  fusible  alloy,  see  Quantitative  Analysis,  Special 
Methods. 


394  GOLD. 

Assay  of  Ores  of  Bismuth. — Ores  of  this  metal  are  assayed  by  fusion,  at  a 
moderate  heat,  with  considerable  quantities  of  borax  and  black  flux.  The  button 
is  extracted  in  the  usual  manner,  and  weighed. 


GOLD. 

Sym.  Au.     Eq.  197.1     Sp.  Gr.  19.3. 

§  267.  Preparation  of  Pure  Gold. — Standard  gold  is  alloyed  with  copper  and 
silver;  in  order  to  purify  it,  we  may  dissolve  it  in  a  mixture  of  1  part  of  nitric 
and  4  parts  of  hydrochloric  acid,  which  leaves  the  silver  as  insoluble  chloride. 
The  solution  is  diluted  and  filtered,  the  filtered  liquid  carefully  evaporated  almost 
to  dryness,  to  expel  excess  of  acid;  water  is  then  added,  and  the  solution  boiled 
with  solution  of  sulphate  of  iron;  the  precipitated  gold  (in  the  form  of  a  dark 
purple  powder)  is  heated  with  hydrochloric  acid,  and  subsequently  well  washed 
with  water;  if  great  care  be  taken  to  expel  excess  of  acid,  oxalic  acid  may  be 
advantageously  substituted  for  the  iron-salt,  since  the  gold  is  then  precipitated  in 
large  flakes,  which  cohere  readily,  and  may  easily  be  washed. 

Properties. — Gold,  in  its  ordinary  form,  has  a  reddish-yellow  color  and  metallic 
lustre,  which  may  be  greatly  improved  by  burnishing;  it  is  capable  of  crystallizing 
in  forms  derived  from  the  cube,  and  is  often  found  in  nature  in  well-defined  crystals. 

When  very  much  extended,  gold  transmits  a  green  light;  in  very  fine  powder, 
it  is  bluish-purple  by  transmitted,  and  brown-red  by  reflected  light. 

The  spec.  grav.  of  fused  gold  is  19.26,  that  of  hammered  gold,  19.37. 

Gold  is  almost  as  soft  as  lead;  it  is  the  most  malleable  and  ductile  of  metals, 
insomuch  that  it  may  be  beaten  into  leaves  of  -j^  Jo^o"  °f  an  mc^  lu  thickness, 
one  grain  of  the  metal  being  made  to  cover  56£  square  inches. 

The  tenacity  of  gold  is  inferior  to  that  of  iron,  copper,  platinum,  and  silver,  for 
a  wire  y^  inch  in  diameter  will  only  support  191  Ibs. 

The  fusion  of  gold  requires  a  very  strong  white  heat,  and  its  conversion  into 
vapor  cannot  be  exhibited  in  any  furnace,  but  is  very  perceptible  when  the  metal 
is  held  in  the  focus  of  a  powerful  burning  glass,  or  in  the  oxyhydrogen  blowpipe- 
flame,  or  placed  between  the  charcoal  points  of  a  galvanic  battery. 

Gold  suffers  greater  contraction  in  solidifying  than  any  other  metal.  It  under- 
goes no  change  by  exposure  to  air,  even  in  the  fused  state.  Like  iron,  gold  is 
capable  of  being  welded  at  a  high  temperature;  indeed,  even  at  ordinary  tem- 
peratures, precipitated  gold  can  be  made,  by  pressure,  to  cohere  into  a  malleable 
mass. 

Gold  does  not  combine  directly  with  any  of  the  non-metallic  elements  except 
chlorine,  bromine,  fluorine,  and  phosphorus.  It  does  not  decompose  water  under 
any  circumstances. 

Neither  sulphuric,  hydrochloric,  nor  nitric  acid  will  act  upon  gold,  but  a  mix- 
ture of  hydrochloric  acid  with  any  substance  (such  as  nitric  acid,  chromic  acid, 
binoxide  of  manganese)  capable  of  oxidizing  its  hydrogen,  will  readily  dissolve 
it  in  the  form  of  chloride;  selenic  acid  oxidizes  gold,  being  converted  into  selenious 
acid. 

The  hydrated  alkalies  do  not  act  upon  gold,  even  when  fused  with  it,  unless 
air  have  access,  when  the  gold  is  converted  into  auric  acid,  which  combines  with 
the  alkali. 

The  higher  alkaline  sulphides  dissolve  this  metal  in  the  form  of  tersulphide. 

1  The  equivalent  of  gold  is  often  represented  by  -^-=98.5,  in  which  case  the  two  oxides 
become  Au80  and  Au203,  and  so  on  for  the  corresponding  chlorides,  &c. 


GOLD    AND   OXYGEN. 


GOLD   AND   OXYGEN. 

(Prot-)  oxide  of  gold AuO. 

Teroxide Au03. 

Neither  of  these  is  capable  of  combining  with  the  oxygen-acids. 

OXIDE  OR  PROTOXIDE  OF  GOLD,  AuO. 

§  268.  This  oxide  is  precipitated  as  a  violet- colored  powder,  when  the  (proto-) 
chloride  of  gold  is  decomposed  by  a  dilute  solution  of  potassa. 

It  is  easily  decomposed  by  heat,  and  is  not  affected  by  oxygen-acids ;  hydro- 
chloric acid  decomposes  it,  forming  terchloride  of  gold,  a  portion  of  the  metal 
being  separated : — 

3AuO+3HCl=AuCls-f3HO-f  Au2. 

This  oxide  is  soluble  in  alkalies  only  at  the  moment  of  precipitation.1 

Although  oxide  of  gold  does  not  combine  directly  with  oxygen-acids,  a  salt 
has  been  obtained  which  is  regarded  as  a  compound  of  the  hyposulphite  of  soda 
with  hyposulphite  of  oxide  of  gold,  AuO.SaOa,3(NaO.S302),4Aq. 

This  salt  has  been  obtained  in  white  needles,  by  mixing  dilute  solutions  of 
terchloride  of  gold  and  hyposulphite  of  soda,  and  adding  alcohol ;  it  is  insoluble 
in  the  latter,  but  readily  soluble  in  water ;  the  solution  has  a  sweet  taste.  The 
salt  is  decomposed  by  heat  into  sulphate  of  soda  and  metallic  gold.  Nitric  acid 
also  causes  a  separation  of  metal.  It  is  worthy  of  remark  that  the  properties  of 
the  oxide  of  gold  and  of  the  hyposulphurous  acid  have  suffered  considerable 
alteration  in  this  combination ;  thus,  sulphate  of  iron,  chloride  of  tin,  and  oxalic 
acid  do  not  reduce  the  gold ;  again,  no  deposition  of  sulphur,  or  evolution  of  sul- 
phurous acid  is  observed  on  mixing  the  solution  with  dilute  sulphuric  acid.  When 
the  solution  is  treated  with  chloride  of  barium,  a  gelatinous  precipitate,  containing 
barium  in  place  of  sodium,  is  formed. 

A  solution  of  the  soda-salt  is  employed  for  fixing  the  pictures  obtained  by  the 
Daguerreotype  process. 

PURPLE  or  CASSIUS,  AuO.Sn02,SnO.Sn03-f  4HO. 

Preparation. — Several  methods  have  been  proposed  for  the  preparation  of  this 
substance. 

I.  The  best  process  for  obtaining  it  in  the  pure  state  is  said  to  be  the  follow- 
ing: 310  grs.  of  gold  are  dissolved  in  1550  grs.  of  aqua  regia,  consisting  of  1 
part  of  commercial  nitric,  and  4  parts  of  commercial  hydrochloric  acid ;  the  solu- 
tion is  evaporated  to  dryness  on  a  water-bath,  the  residue  dissolved  in  water,  the 
solution  filtered,  diluted  with  20  or  30  ounces  of  water,  and  placed  in  contact 
with  granulated  tin;  the  purple  precipitate  is  washed,  and  dried  at  a  gentle  heat. 

II.  1  part  of  granulated  tin  is  dissolved  in  hydrochloric  acid ;  2  other  parts  of 
tin  are  dissolved  in  a  mixture  of  3  parts  of  nitric  and  1  part  of  hydrochloric  acid; 
7  parts  of  gold  are  dissolved  in  aqua  regia,  composed  of  1  part  of  nitric  and  6 
parts  of  hydrochloric  acid ;  this  last  solution  is  diluted  with  a  considerable  quan- 
tity of  water,  and  mixed  with  the  solution  of  tin  in  aqua  rcgia  (bichloride  of 
tin) ;  to  the  mixed  solution,  that  of  (proto-)  chloride  of  tin  is  added,  drop  by 
drop,  till  the  precipitate  has  a  fine  purple  color ;  an  excess  of  this  reagent  renders 
it  brown. 

1  According  to  the  recent  experiments  of  Fremy,  this  oxide  is  decomposed  by  alkalies 
into  metallic  gold  and  auric  acid,  which  combines  with  the  alkali. 


396  AURATES. 

III.  An  alloy  is  made  by  fusing  together  1  part  of  gold,  \  part  of  tin,  and  4 
or  5  parts  of  silver;  this  alloy  is  treated  with  nitric  acid,  which  dissolves  the 
silver,  leaving  the  gold  and  tin  in  an  oxidized  state  as  a  purple  residue. 

Properties. — The  nature  of  purple  of  Cassius  has  been  the  subject  of  much 
discussion,  but  the  formula  given  above  explains  most  of  the  reactions  exhibited 
by  this  compound. 

Purple  of  Cassius,  when  heated,  evolves  water  only,  leaving  a  residue  which 
consists  of  1  eq.  gold,  and  2  eqs.  binoxide  of  tin.  When  freshly  precipitated, 
purple  of  Cassius  dissolves  in  ammonia,  but  the  solution  is  decomposed  by  expo- 
sure to  light,  becoming  blue,  and  finally  colorless,  metallic  gold  being  precipi- 
tated, whilst  binoxide  of  tin  remains  in  solution.  It  is  decomposed  by  hydrochloric 
acid,  bichloride  of  tin  being  formed,  and  metallic  gold  left. 

The  purple  of  Cassius  is  employed  for  imparting  a  purple-red  color  to  glass  and 
pycelain. 

TEROXIDE  OP  GOLD,  AURIC  ACID,  Au03. 

In  order  to  prepare  this  oxide,  a  solution  of  terchloride  of  gold  is  heated  with 
pure  magnesia,  and  the  mixture  of  magnesia  and  aurate  of  magnesia  thus  ob- 
tained, boiled  with  nitric  acid,  which  dissolves  the  magnesia,  leaving  hydrated 
auric  acid.1 

This  substance  has  a  yellow  or  brown  color ;  it  is  reduced  when  exposed  to 
light ;  the  water  is  easily  expelled  by  a  gentle  heat,  anhydrous  auric  acid  being 
left  j  at  a  higher  temperature,  this  last  is  decomposed  into  its  elements.  Auric 
acid  is  insoluble  in  water,  but  dissolves  in  hydrochloric  acid : — 

Au03-f3HCl=AuCl3  +  3HO. 

It  also  dissolves,  to  some  extent,  in  sulphuric,  nitric,  and  acetic  acids,  but  is  pre- 
cipitated from  these  solutions  by  water ;  it  is  soluble  in  solutions  of  potassa  and 
soda.  This  oxide  is  very  easily  reduced  to  the  metallic  state  by  hydrogen  or 
carbon,  with  the  aid  of  a  gentle  heat ;  alcohol  and  most  other  organic  substances 
also  separate  metallic  gold. 

The  hydrate  of  auric  acid  is  obtained  by  carefully  neutralizing  solution  of  ter- 
chloride of  gold  with  potassa. 

Aurate  of  potassa  is  prepared  by  dissolving  auric  acid  in  solution  of  potassa, 
and  evaporating  in  vacua.  The  salt  crystallizes  in  yellow  tufts,  the  formula  of 
which  is  KO.AuOg-f  6Aq.  It  is  easily  decomposed  by  heat,  leaving  a  residue 
of  peroxide  of  potassium  and  metallic  gold.  Aurate  of  potassa  is  very  soluble 
in  water ;  the  solution  is  yellow,  has  an  alkaline  reaction,  and  is  very  easily 
reduced.  This  salt  may  be  used  for  electro-gilding. 

Aurate  of  soda  resembles  the  potassa-salt. 

Aurate  of  ammonia  is  not  known ;  when  auric  acid  is  digested  with  solution 
of  ammonia,  a  gray  compound  is  obtained,  the  formula  of  which  is  said  to  be 
Au03.2NH3.HO;  this  compound  is  known  as  fulminating  gold,  since  it  explodes 
with  great  violence  when  rubbed,  or  gently  heated,  and  often  spontaneously.3 

The  alkaline  aurates  yield,  with  the  salts  of  various  metals,  precipitates  of 
aurates,  which  are  mostly  soluble  in  excess  of  the  precipitants. 

A  compound,  in  which  the  teroxide  of  gold  appears  to  play  the  part  of  a  base 
is  precipitated  when  sulphite  of  potassa  is  added  to  a  solution  of  the  aurate  j  it 
forms  long  silky  needles,  of  the  composition  Au03.3S03,5(KO.SOa)-f  5Aq. 

This  compound  is  sometimes  called  aurosulphite  of  potassa.3      Its  solution 

1  A  better  process  consists  in  boiling  terchloride  of  gold  with  potassa  until  the  color  has 
almost  disappeared,  precipitating  by  sulphuric  acid,  and  purifying  the  teroxide  thus  ob- 
tained by  dissolving  in  nitric  acid,  and  precipitating  by  water. 

2  Another  fulminating  compound  of  gold  exists,  and  is  described  at  page  398. 

3  Since  the  reactions  of  teroxide  of  gold  are  to  some  extent  masked  in  this  combination, 


TERCIILORIDE    OF   GOLD.  397 

yields  a  fine  coherent  deposit  of  gold  when  heated,  and  decomposes  after  a  time 
when  kept. 

An  intermediate  oxide  of  gold,  having  the  composition  AuOa,  is  said  by  some 
to  be  produced,  when  chloride  of  tin,  and  certain  organic  substances,  act  upon 
terchloride  of  gold. 

An  oxide  of  the  formula  Au05,  has  been  pointed  out  by  Figuier. 

CHLORIDE,  OR  PROTOCHLORIDE,  OF  GOLD,  AuCl. 

§  269.  This  chloride  is  prepared  by  heating  the  terchloride  to  about  392°  F. 
(200°  C.)  ;  it  is  then  obtained  as  a  pale  yellow  insoluble  substance,  easily  de- 
composed, by  the  action  of  light  or  heat,  into  metallic  gold,  and  the  terchloride. 

TERCHLORIDE  OF  GOLD,  AuCls. 

When  gold  is  dissolved  in  aqua  reyia  (one  part  nitric,  and  four  parts  hydro- 
chloric acid),  and  the  solution  carefully  evaporated  on  a  water-bath,  a  red-brown, 
deliquescent,  crystalline  mass  of  the  terchloride  is  obtained.  This  compound  is 
decomposed  by  heat,  evolving  chlorine,  and  leaving  (proto-)  chloride  of  gold,  or 
metallic  gold,  according  to  the  temperature. 

The  terchloride  is  very  readily  soluble  in  water  and  alcohol;  its  solution  is 
yellow,  has  an  acid  reaction,  and  stains  the  skin  of  a  purple  color,  due  to  reduc- 
tion. Ether,  however,  dissolves  it  most  readily;  for,  if  an  aqueous  solution  be 
shaken  with  ether,  the  latter  abstracts  the  whole  of  the  salt,  and  forms  a  yellow 
layer  upon  the  surface  of  the  colorless  aqueous  liquid;  the  ethereal  solution  is 
called  aurum  potabile,  and  has  been  used  medicinally;  it  deposits  metallic  gold 
when  kept  for  some  time. 

Terchloride  of  gold  is  easily  reduced,  even  by  feeble  deoxidizing  agents;  thus 
hydrogen,  carbon,  carbonic  oxide,  binoxide  of  nitrogen,  phosphorus,  sulphurous 
and  phosphorous  acids  and  their  salts,  terchloride  of  antimony,  the  proto-salts  of 
iron,  nearly  all  the  metals,  most  organic  substances,  and  especially  oxalic  acid, 
precipitate  metallic  gold  from  a  solution  of  the  terchloride. 

The  alkalies  and  their  carbonates  decompose  terchloride  of  gold,  giving  rise  to 
alkaline  aurates,  and  to  chlorides  of  the  alkali-metals ;  the  alkaline  aurates  re- 
main in  solution,  and  yield  a  precipitate  of  auric  acid  upon  addition  of  a  stronger 
acid.  The  action  of  potassa  upon  terchloride  of  gold  may  be  expressed  by  the 
equation . — 

AuGl3  +  4KO=KO.Au03+3KCl. 

Terchloride  of  gold  combines  with  hydrochloric  acid  to  form  a  hydrochlorate, 
which  is  deposited  in  golden-yellow  prisms,  when  the  mixed  solutions  are  allowed 
to  evaporate  spontaneously. 

Terchloride  of  gold  is  capable  of  forming  very  definite  crystallizable  salts  with 
the  hydrochlorates  of  organic  bases,  and  since  these  compounds  always  leave 
metallic  gold  upon  ignition,  their  analysis  may  be  effected  with  great  precision, 
and  the  high  atomic  weight  of  gold  enables  us  to  ascertain  very  correctly,  from 
the  amount  of  this  metal,  the  equivalent  of  the  alkaloid  contained  in  the  double- 
salt. 

The  terchloride  is  capable  of  combining  with  many  other  chlorides  to  produce 
double-salts,  which  are  generally  well  crystallized,  and  much  more  stable  than 
the  terchloride  itself. 

The  aurochloride  of  potassium,  as  it  is  commonly  called,  crystallizes  in  yellow 
prisms  or  tables,  of  the  composition  KCl.AuCl3-f  5Aq;  it  is  decomposed  by 

Fremy  suggests  that  it  may  be  regarded  as  KO.  Au03,4(K0.2S02)-f5Aq.  This  salt  must 
be  preserved  in  alkaline  liquids,  since  it  is  decomposed  by  pure  water,  sulphurous  acid 
being  evolved,  and  metallic  gold  deposited. 


398  METALLURGY    OP   GOLD. 

heat,  evolving  chlorine,  and  leaving  a  compound  of  chloride  of  potassium  and 
(proto-)  chloride  of  gold. 

The  corresponding  sodium  and  ammonium  salts  have  the  formulae  respect- 
ively : — 

NaCl.AuCl3+ 4Aq,  and 
NH4Cl.AuCl,+2Aq. 

Terchloride  of  gold  and  some  of  its  double  salts  are  occasionally  employed  in 
medicine. 

When  terchloride  of  gold  is  digested  with  an  excess  of  ammonia,  a  powerful 
fulminating  compound  is  obtained,  the  constitution  of  which  is  uncertain;  it 
contains  gold,  chlorine,  nitrogen,  hydrogen,  and  oxygen. 

SULPHIDES  OF  GOLD. 

The  sulphides  of  gold  are  but  little  known,  but  they  appear  to  correspond  to 
the  oxides. 

(Proto-}  sulphide  of  gold  is  obtained  as  a  dark  brown  precipitate,  when  sul- 
phuretted hydrogen  is  passed  into  a  boiling  solution  of  the  terchloride : — * 
2AuCl3+3HS+3HO=2AuS-f6HCl  +  S03. 

When  a  cold  dilute  solution  of  terchloride  is  employed,  a  black  precipitate  of 
tersulphide  of  gold  (AuS3)  is  obtained;  this  tersulphide  is  a  sulphur  acid;  it 
dissolves  (though  not  very  readily)  in  solutions  of  alkaline  sulphides,  and  is  even 
capable  of  expelling  the  bydrosulphuric  acid  from  the  hydrosulphates  of  alkaline 
sulphides. 

According  to  Levol,  the  precipitate  obtained  by  passing  sulphuretted  hydrogen 
into  a  boiling  solution  of  terchloride  of  gold,  is  not  the  sulphide,  but  the  metal : — 
4AuCl3  +  3HS  +  9HO==Au4+12HCl+3S03. 

When  a  cold  solution  is  employed,  the  precipitate  has  the  formula  AuS  +  AuS3. 


METALLURGY  OF  GOLD. 

§  270.  Gold  is  always  found  in  the  metallic  state,  generally  alloyed  with  other 
metals,  especially  with  silver  and  tellurium.3 

It  occurs  sometimes  in  veins,  most  commonly  associated  with  quartz ;  these 
veins  often  contain  iron-pyrites,  and  ores  of  copper,  lead,  silver,  &c. 

When  the  rocks  which  are  traversed  by  such  veins  are  disintegrated  and  swept 
away  by  torrents  and  rivers,  the  heavy  particles  of  gold  are  deposited,  together 
with  part  of  the  quartz,  forming  an  auriferous  sand,  more  or  less  rich  in  the 
precious  metal  (alluvial  gold). 

Native  gold  is  generally  found  either '  in  scales,  or  crystallized  in  cubes  and 
octohedra,  or  forms  derived  from  these.  Nodules  of  gold  of  large  size  are  also 
sometimes  found. 

This  metal  is  found  in  considerable  quantity  in  veins  of  sulphide  of  silver,  in 
Mexico,  Peru,  and  the  Uralian  mountains  in  Siberia.  Sand  very  rich  in  gold  is 
found  in  the  beds  of  streams  in  Brazil  and  Africa;  alluvial  gold  is  also  met  with 
in  very  minute  quantity  in  some  European  rivers,  especially  in  France.  The 
recent  discoveries  of  this  metal,  both  in  the  massive  and  disseminated  states,3  in 
California  and  Australia,  are  well  known  to  all. 

1  Double  compounds  of  sulphide  of  gold  with  the  sulphides  of  potassium  and  sodium 
have  been  obtained. 

2  A  native  amalgam  of  gold  has  also  been  met  with. 

3  From  7  to  9  per  cent,  of  silver  has  been  found  in  the  gold-dust  from  California. 


METALLURGY   OP  GOLD.  399 

Gold  cannot  justly  be  termed  a  rare  metal,  for  it  is  very  extensively  diffused 
over  the  surface  of  the  earth,  though  in  small  quantities. 

EXTRACTION  OF  GOLD. — The  alluvial  gold  is  readily  separated  from  the  sand 
by  a  process  of  washing;  the  arrangements  for  this  purpose  differ  in  different 
countries,  but  all  proceed  upon  the  principle  of  washing  away  the  earthy  impuri- 
ties, and  leaving  the  heavier  particles  of  gold;  when  the  grains  of  gold  are  mixed 
with  those  of  platinum  (as  is  sometimes  the  case),  they  are  shaken  with  mercury, 
which  dissolves  only  the  gold,  to  be  afterwards  separated  by  distillation. 

The  gold  obtained  by  washing  is  known  in  commerce  as  gold-dust. 

The  extraction  of  gold  from  rocky  ores  is  effected  either  by  fusion,  by  washing, 
or  by  amalgamation. 

The  process  of  fusion  consists  in  extracting  the  metal  with  which  the  gold 
happens  to  be  associated  (lead,  copper,  &c.),  and  separating  the  gold  from  the 
alloy  thus  obtained  (which  contains  the  whole  of  that  metal)  by  cupellation,  which 
will  be  described  in  the  section  upon  lead,  or  by  amalgamation,  a  process  to  be 
presently  noticed. 

The  washing  of  gold-ores  depends  upon  the  same  principle  as  the  extraction 
of  alluvial  gold. 

The  extraction  of  gold  by  amalgamation  is  carried  out  especially  with  auri- 
ferous pyrites.  The  mineral  is  well  agitated  in  a  sort  of  mill,  with  mercury,  a 
stream  of  water  being  at  the  same  time  employed  to  wash  away  the  earthy  im- 
purities; the  gold  and  silver,  if  any  be  present,  dissolve  in  the  mercury,  forming 
a  solid  amalgam,  which  is  collected  on  a  chamois  leather,  in  order  to  separate  it 
from  the  excess  of  mercury,  and  distilled,  when  an  alloy  of  gold  and  silver  remains, 
which  is  subjected  to  the  refining  process. 

REFINING  OF  GOLD. — It  is  frequently  necessary  in  practice  to  separate  this 
metal  from  silver  and  copper;  this  is  the  case  in  working  the  American  ores  of 
silver,  and  in  the  separation  of  gold  from  old  coins.  The  process  applied  to  se- 
parating gold  and  silver  is  termed  the  parting  of  gold. 

The  alloy  is  granulated  by  being  poured,  in  a  fused  state,  into  water;  it  is  then 
boiled  in  a  vessel  of  platinum  or  of  cast  iron,  with  concentrated  sulphuric  acid; 
the  copper  and  silver  are  thus  oxidized,  and  dissolved  as  sulphates,  sulphurous 
acid  being  evolved,  which  is  often  conducted  into  leaden  chambers,  and  reconverted 
into  oil  of  vitriol.1 

The  residual  gold  still  contains  silver,  and  must  be  again  treated  with  sul- 
phuric acid,  well  washed,  and  fused. 

In  order  to  separate  the  silver  and  copper,  the  solution  containing  the  two 
sulphates  is  heated  with  metallic  copper,  which  precipitates  the  whole  of  the 
silver  in  a  spongy  state,  to  be  afterwards  washed,  dried,  and  fused. 

The  solution  of  sulphate  of  copper  is  evaporated  to  crystallization,  and  the 
acid  mother-liquors  are  made  use  of  to  economize  the  sulphuric  acid  in  a  fresh 
refining  process. 

For  the  complete  success  of  this  process  it  is  necessary  that  the  alloy  should 
not  contain  more  than  20  per  cent,  of  gold,  nor  more  than  10  per  cent,  of  copper. 
If  it  be  too  rich  in  gold,  it  is  fused  with  a  quantity  of  auriferous  silver. 

Alloys  poor  in  gold  and  silver  are  submitted  to  a  preliminary  roasting,  and 
afterwards  treated  with  dilute  sulphuric  acid,  which  dissolves  the  oxide  of  cop- 
per, leaving  an  alloy  sufficiently  rich  to  be  refined  in  the  ordinary  way. 

1  The  extraction  of  the  silver  proceeds  rapidly  at  first,  but  afterwards  very  slowly,  and 
is  never,  according  to  Pettenkoft'er,  absolutely  perfect.  This  chemist  recommends  fusion 
with  bisulphate  of  soda  for  the  complete  purification  of  the  gold. 

Moreover,  the  residual  metal  contains  traces  of  sulphate  of  lead,  and  basic  sulphate  of 
iron,  from  which  it  may  be  freed  by  treatment,  first  with  carbonate  of  soda,  and  afterwards 
with  nitric  acid. 


400  METALLURGY   OP   GOLD. 

By  this  process,  gold  may  be  economically  extracted  from  alloys  containing 
only  0  05  per  cent,  of  this  metal. 

The  refined  gold  has  a  degree  of  purity  represented  by  the  fraction  y9/^,  which 
indicates  that  1000  parts  of  metal  contain  995  of  gold. 

The  purification  may  be  carried  still  farther,  by  fusing  the  metal  with  three 
times  its  weight  of  silver,  and  boiling  the  alloy  with  nitric  acid,  which  leaves  the 
gold  undissolved  (quartatiort). 

Perfectly  pure  gold  is  far  too  soft  to  be  employed  for  the  fabrication  of  coins, 
vessels,  ornaments,  &c. 

Gold  for  coin  is  alloyed  with  1  part  of  copper  to  11  parts  of  pure  gold. 

Jewellers1  gold,  for  ornamental  purposes,  is  an  alloy  containing  3  parts  of  gold 
to  1  of  copper. 

These  alloys  also  contain  a  small  quantity  of  silver. 

Goldleaf,  is  made  by  rolling  out  a  bar  of  pure  gold  to  a  long  ribbon,  which  is 
then  cut  up  into  squares,  and  extended  by  beating,  between  layers  of  fine  vellum, 
with  a  heavy  hammer ;  the  thin  squares  are  then  subjected  to  a  second  beating, 
between  layers  of  goldbeater' s-skin  (prepared  from  the  intestines  of  the  ox),  till 
they  have  acquired  the  requisite  degree  of  extension ;  in  this  way,  an  ounce  of 
gold  may  be  spread  over  a  surface  of  100  square  feet.  But  the  division  of  gold 
is  carried  still  further  in  the  manufacture  of  the  gold-thread  used  in  embroidery; 
a  cylinder  of  silver  is  covered  with  a  quantity  of  goldleaf,  amounting  to  about 
g1^  of  its  weight ;  it  is  then  drawn  through  holes  in  iron  plates  till  it  is  reduced 
to  a  wire  as  thin  as  a  hair ;  6  ounces  of  gold  may  thus  extend  over  a  wire  above 
200  miles  in  length,  and  yet,  if  this  wire  be  dipped  in  nitric  acid,  the  silver  is 
dissolved  out,  and  a  hollow  cylinder  of  gold  remains. 

Gold  combines  directly  with  almost  all  other  metals. 

Copper  imparts  a  deeper  color  to  gold,  renders  it  harder  and  more  fusible,  but 
diminishes  its  malleability  and  ductility. 

The  alloys  of  gold  and  copper  have  a  lower  specific  gravity  than  would  be  ex- 
pected in  a  mere  mixture  of  the  two  metals.  A  minute  quantity  of  lead  is  capable 
of  injuring  the  malleability  of  these  alloys.  Alloys  of  copper  and  gold,  being 
more  fusible  than  the  latter  metal,  are  employed  for  soldering  pieces  of  gold  to- 
gether. 

GILDING. — In  order  to  gild  glass  or  porcelain,  goldleaf  is  powdered  and  mixed 
with  oil  of  turpentine  and  borax;  the  mixture  is  painted  on  the  ware,  which  is 
then  strongly  heated  in  a  muffle. 

Wood,  plaster,  &c.,  are  covered  with  goldleaf,  by  the  intervention  of  some 
adhesive  substance  (size,  varnish,  &c.). 

Metals  are  covered  with  gold  either  by  the  use  of  an  amalgam,  or  by  mere 
immersion  in  a  solution  of  gold,  or  by  the  electrotype  process. 

The  amalgam  of  gold  is  prepared  by  dissolving  gold-leaf  in  mercury,  with  the 
aid  of  heat,  and  separating  the  excess  of  mercury  from  the  semi-solid  amalgam 
by  pressure. 

The  articles  to  be  coated  with  gold,  having  been  perfectly  cleaned,  are  amal- 
gamated by  rubbing  them  with  a  brush  which  has  been  dipped  into  a  solution  of 
nitrate  of  mercury,  and  covered  with  the  amalgam;  they  are  then  heated,  to  expel 
the  mercury,  and  burnished. 

The  gilding  of  copper  ornaments  is  sometimes  effected  by  immersing  them  in 
a  boiling  solution  of  an  alkaline  aurate,  prepared  by  mixing  terchloride  of  gold 
with  an  excess  of  an  alkaline  carbonate. 

The  process  of  electro-gilding  consists  in  decomposing  a  solution  of  gold  by  a 
galvanic  current,  in  such  a  manner  that  the  metal  shall  be  deposited  upon  the 
objects  to  be  gilt.  A  solution  of  tercyanide  of  gold  in  cyanide  of  potassium  is 
generally  employed ;  this  is  placed  in  a  wooden  vessel,  varnished  interiorly,  and 
the  articles  to  be  operated  upon  are  suspended  in  it ;  these  are  connected  with  the 


METALLURGY   OP   GOLD.  401 

negative  (copper)  pole  of  the  battery,  whilst  the  positive  (amalgamated  zinc)  pole 
communicates  with  a  plate  of  gold  suspended  in  the  solution,  and  intended  to 
dissolve,  and  thus  to  replace,  the  gold  deposited. 

Copper  and  its  alloys,  as  well  as  iron,  steel,  and  tin,  may  be  gilt  in  this  way, 
provided  that  the  last  three  are  first  covered  with  a  film  of  copper,  for  which 
purpose  they  are  immersed  in  a  solution  of  cyanide  of  copper  in  cyanide  of  po- 
tassium. 

§  271.  ASSAY  OP  ALLOYS  OP  GOLD. — For  practical  purposes,  the  value  of 
alloys  of  gold  is  often  estimated  by  means  of  the  touchstone.  This  is  a  hard 
black  stone,  originally  brought  from  Lydia,  but  now  obtained  from  Silesia;  the 
Silesian  touchstone  is  a  species  of  basalt. 

The  alloy  to  be  examined  is  rubbed  upon  this  stone,  when  it  leaves  a  streak 
varying  in  appearance  according  to  the  composition  of  the  alloy;  the  first  few 
streaks  are  unnoticed,  since  most  alloys  are  improved  in  color  by  refining  the 
gold  at  the  surface ;  by  comparing  the  streaks  left  upon  the  stone  with  those  pro- 
duced by  auriferous  alloys  of  known  composition,  the  operator  is  enabled,  after 
a  little  experience,  to  judge,  approximatively,  of  the  proportion  of  gold ;  this  is 
rendered  still  easier  by  moistening  the  streaks  with  a  mixture  of  98  parts  of  nitric 
acid  of  sp.  gr.  1.34  and  2  parts  of  hydrochloric  of  1.17,  which  readily  dissolves 
the  copper,  but  not  gold  ;  the  effect  of  the  acid  upon  the  streaks  is  compared  with 
that  upon  streaks  made  by  the  standard  alloys. 

In  experienced  hands  this  mode  of  testing  gives  results  which  are  correct  within 
1  per  cent. 

Assay  of  Alloys  of  Gold  by  Cupellation. — The  only  alloys  of  gold,  the  assay  of 
which  is  of  practical  importance,  are  those  containing  silver  or  copper,  or  both. 
The  amount  of  gold  existing  in  the  alloy  is  first  roughly  ascertained  by  means  of 
the  touchstone ;  7  or  8  grs.  of  the  alloy  are  then  fused,  upon  a  cupel  made  of 
bone-ash,  and  placed  in  a  muffle,  with  so  much  silver  (accurately  weighed)  as, 
together  with  the  silver  previously  existing  in  the  alloy,  will  give  a  proportion 
of  3  or  4  parts  for  1  part  of  gold;  in  addition,  a  quantity  of  pure  lead  is  employed 
equal  to  about  3  or  4  times  that  of  the  gold  and  silver;  the  lead  is  first  introduced 
into  the  heated  cupel,  and  when  it  is  in  complete  fusion,  the  gold  and  silver  are 
thrown  in,  wrapped  up  together  in  a  piece  of  paper. 

When  the  cupellation  is  finished,  which  the  operator  recognizes  by  the  clear 
appearance  and  tranquil  state  of  the  metallic  button,  the  latter  is  allowed  to  cool, 
and  its  weight  carefully  determined  ;  by  subtracting  this  weight  from  that  of  the 
alloy  and  silver  originally  employed,  the  amount  of  copper  is  ascertained. 

The  alloy  of  gold  and  silver  is  now  annealed  and  beaten  into  a  thin  plate,  which 
is  rolled  up  and  heated  in  a  flask  with  moderately  dilute  nitric  acid;  when  this 
ceases  to  act  it  is  decanted,  and  the  cornet  (as  it  is  termed)  is  boiled  with  a  more 
concentrated  acid;  it  is  afterwards  washed  with  water  till  the  washings  are  no 
longer  rendered  turbid  by  hydrochloric  acid;  the  flask  is  then  filled  with  water, 
closed  with  the  thumb,  and  carefully  inverted  into  a  crucible  filled  with  water, 
so  that  the  cornet  may  fall  into  the  crucible,  where  it  is  dried,  ignited,  and  after- 
wards weighed;  its  weight,  subtracted  from  that  of  the  original  cornet,  gives  that 
of  the  silver. 

The  first  of  these  operations,  where  the  gold  is  alloyed  with  three  parts  of 
silver,  is  known  as  quartation,  while  the  separation  of  the  two  metals  by  nitric 
acid  is  termed  parting. 

The  theory  of  the  cupellation  is  very  simple;  the  copper  and  lead  are  oxidized 
by  the  current  of  air  passing  through  the  muffle,  and  the  suboxide  of  copper  is 
dissolved  by  the  fused  oxide  .of  lead  (litharge),  and  absorbed  by  the  bone-ash 
cupel;  whilst  the  gold  and  silver  remain  untouched. 

If  there  were  less  silver  than  amounted  to  three  times  the  weight  of  the  gold, 
the  parting  by  nitric  acid  would  not  be  complete,  whereas,  if  considerably  more 
26 


402  METALLURGY   OF   GOLD. 

silver  were  employed,  the  gold  would  be  left  in  a  very  finely  divided  state,  and 
could  not  readily  be  weighed. 

This  process,  though  not  absolutely  correct,  is  sufficiently  so  for  all  commercial 
purposes. 

For  the  analysis  of  alloys  of  gold,  silver,  and  copper,  see  Quantitative  Analy- 
sis, Special  Methods. 

The  quantity  of  gold  contained  in  auriferous  sand  may  be  determined  roughly 
by  washing  a  large  quantity,  and  weighing  the  residual  gold,  but  more  accurately 
by  extracting  the  metal  with  nitro-hydrochloric  acid,  and  reducing  the  gold  with 
oxalic  acid,  with  the  precautions  mentioned  above. 

Assay  of  Auriferous  Ores. — If  the  ore  to  be  examined  contains  oxide  of 
lead,  it  is  only  necessary  to  fuse  it  in  an  earthen  crucible  with  a  sufficient  quan- 
tity of  black  flux. 

If  the  ore  contain  no  oxide  of  lead,  it  should  be  fused  with  a  mixture  of 
litharge  and  black  flux. 

When  considerable  quantities  of  deoxidizing  agents  are  present,  such  as  pyrites, 
&c.,  litharge  only  may  be  used. 

Sometimes,  when  the  quantity  of  reducing  minerals  present  is  very  large,  so 
that  too  much  lead  would  be  reduced  if  enough  litharge  were  added  to  oxidize 
and  remove  the  whole  of  the  sulphur,  a  little  nitre  is  added,  together  with  the 
litharge. 

If  400  grains  of  ore  are  employed,  they  should  be  mixed  with  about  an  equal 
weight  of  litharge,  and  about  300  grains  of  black  flux. 

The  button  of  lead  obtained  should  never  weigh  more  than  200  grains. 

The  fusion  is  conducted  in  a  wind  furnace.  The  button,  which  consists  of 
lead,  silver,  gold,  copper,  &c.,  is  then  cupelled  and  parted  as  in  the  analysis  of 
alloys  of  gold  (p.  401). 

When  the  amount  of  gold  is  required  in  a  mixture  of  gold  and  quartz  free 
from  other  minerals,  it  may  be  very  readily  calculated  from  the  specific  gravities 
of  the  constituents  as  compared  with  that  of  the  mixture.  If  possible,  a  piece 
of  pure  quartz  may  be  separated  from  the  mass,  and  its  actual  specific  gravity 
determined;  but  if  this  cannot  be  done,  the  number  2.6  may  be  taken  as  suffi- 
ciently accurate  for  practical  purposes. 

The  calculation  is  effected  as  follows : — 

Let  m  =  specific  gravity  of  the  gold. 
"    n  =  "  "       quartz. 

"   p  =  «  «       mixture. 

«    x  =  weight  of  gold  per  cent. 
Then  100  —    x  =  weight  of  quartz  per  cent. 

—  =  volume  of  gold  in  100  parts  by  weight. 

100  ~x =  volume  of  quartz         "  « 

n 

=  volume  of  100  parts,  by  weight,  of  the  mixture. 

x_      100 -x^  100 
m  n  p 

npx  +  100  mp  —  mpx  =  100  mn 

(np  —  rap)  x  =  100  (mn  —  mp) 
_100(mn  — mp) 
np  —  mp 

A  result  expressed  by  saying  that  the  quantity  of  gold  per  cent,  in  a  mixture 
of  gold  and  quartz,  is  the  quotient  obtained  by  dividing,  by  the  difference  of  the 


PLATINUM.  403 

products  of  the  specific  gravities  of  gold  and  quartz  multiplied  with  that  of  the 
mixture,  100  times  the  difference  between  the  products  of  the  specific  gravity  of 
(/old  into  that  of  quartz,  and  of  the  specific  gravity  of  gold  into  that  of  the 
mixture. 


PLATINUM. 

Sum.  Pt.    Eq.  98.7.     Sp.  Gr.  21.5. 

§  272.  This  somewhat  rare  metal  was  not  applied  to  any  useful  purpose  before 
the  commencement  of  the  present  century.  Its  name  is  derived  from  the  Spanish 
word  platina,  signifying  little  silver. 

Preparation. — The  extraction  of  this  metal  from  its  ores  will  be  described 
hereafter;  the  platinum  of  commerce  is  nearly  pure,  containing  merely  a  little 
iridium,  which  renders  it  harder,  but  somewhat  less  malleable  than  pure  plati- 
num; in  order  to  purify  the  ordinary  metal,  it  is  dissolved  in  nitre-hydrochloric 
acid,  the  solution  evaporated  to  expel  excess  of  acid,  the  residue  redissolved  in 
water,  and  mixed  with  solution  of  chloride  of  potassium,  which  produces  a  yellow 
crystalline  precipitate  containing  the  double  chlorides  of  platinum  and  potassium, 
and  of  iridium  and  potassium.  This  is  dried,  mixed  with  carbonate  of  potassa, 
and  heated  to  redness  in  an  earthen  crucible;  the  bichloride  of  platinum  is 
decomposed  according  to  the  equation  : — 

PtCl2+2(KO.C03)=Pt+2KCl-f03+2COa; 

the  iridium  is  converted  into  oxide,  which  is  left  behind,  together  with  the  plati- 
num, when  the  fused  mass  is  washed  with  water;  this  residue  is  heated  with 
dilute  nitro-hydrochloric  acid,  which  dissolves  only  the  platinum  ;  the  solution 
is  mixed  with  chloride  of  ammonium,  and  the  platinum  thus  precipitated  as  a 
double  chloride  of  platinum  and  ammonium,  which  may  be  washed  and  heated 
to  redness,  when  the  chloride  of  ammonium  and  chlorine  are  expelled,  and  the 
metal  left  as  a  spongy  mass,  the  conversion  of  which  into  malleable  platinum  will 
be  presently  described. 

Properties — Platinum  is  a  nearly  white  metal,  capable  of  a  high  lustre;  it  is 
the  heaviest  substance  known,  its  specific  gravity  being  21.5.  It  is  very  malle- 
able and  ductile,  standing  next  to  gold  and  silver  with  respect  to  the  latter 
quality.  Platinum  is  remarkable  for  its  tenacity,  in  which  it  is  only  surpassed 
by  iron  and  copper.  A  wire  of  this  metal,  of  T10-  inch  in  diameter,  will  sustain 
a  weight  of  361  Ibs. 

Platinum  is  rather  a  soft  metal ;  it  is  harder  than  copper,  but  not  so  hard  as 
silver.  It  is  less  expansive  by  heat  than  any  other  metal,  and  conducts  it  very 
slowly.  Platinum  is  employed  in  three  different  forms,  viz.,  malleable  platinum, 
spongy  platinum,  and  platinum-Uack,  which  is  in  an  extremely  divided  state.  We 
have  already  mentioned  that  spongy  platinum  is  obtained  by  igniting  the  double 
chloride  of  platinum  and  ammonium.  The  preparation  of  platinum- black  will 
be  presently  described. 

In  either  of  these  forms,  platinum  possesses  the  remarkable  property  of  con- 
densing gases  in  its  pores,  and  thus  seeming  to  absorb  a  certain  quantity  of  them ; 
even  malleable  platinum  exhibits  this  property  in  a  high  degree ;  hence,  a  per- 
fectly clean  plate  of  this  metal  is  capable  of  inducing  the  combination  of  hydrogen 
and  oxygen  at  a  comparatively  low  temperature.  This  property  may  also  be  ex- 
hibited by  suspending  a  helix  of  platinum-wire  in  the  flame  of  a  spirit-lamp, 
which  is  allowed  to  heat  the  wire  to  redness,  and  then  suddenly  blown  out;  the 


404  PLATINUM-BLACK. 

wire  will  then  continue  for  any  length  of  time  at  a  red  heat,  in  consequence  of 
the  energetic  combination  of  the  vapor  of  alcohol  with  the  atmospheric  oxygen 
induced  by  the  peculiar  surface-action  of  the  metal.  In  this  case  the  alcohol  is 
not  completely  burnt ;  acrid  odors,  due  to  the  imperfect  oxidation  of  this  body, 
are  evolved.  The  experiment  is  even  more  satisfactory  when  a  platinum  crucible 
is  heated  to  bright  redness  in  the  flame  of  a  gauze  gas-burner,  and  the  gas  extin- 
guished, and  rapidly  turned  on  again,  when  the  cold  stream  of  gas  will  maintain 
the  temperature  of  the  crucible. 

This  interesting  property  of  platinum  will  be  reverted  to  in  the  description  of 
platinum-black. 

Platinum  is  not  in  the  least  affected  by  exposure  to  air,  even  at  high  tempera- 
tures; it  is  very  infusible,  and  does  not  undergo  a  change  of  state  in  the  hottest 
furnaces ;  it  may,  however,  be  easily  fused  in  the  oxyhydrogen  blowpipe-flame, 
or  between  the  charcoal  points  of  a  powerful  galvanic  battery.  A  platinum  wire, 
held  in  the  flame  of  the  oxyhydrogen  blowpipe,  emits  brilliant  white  sparks  (due 
to  the  combustion  of  the  metal  ?).  A  very  high  temperature  appears  to  volatilize 
it  slightly. 

Platinum  is  very  easily  welded,  especially  at  a  high  temperature. 
This  metal,  like  gold,  is  unalterable  by  many  chemical  agents,  and  hence  is 
largely  employed  iff  the  forms  of  crucibles,  spatulas,  dishes,  wire,  and  foil,  in 
chemical  operations ;  since,  however,  it  is  very  costly,  it  is  necessary  that  the 
chemist  be  fully  acquainted  with  the  circumstances  under  which  platinum  vessels 
are  acted  upon,  in  order  that  he  may  avoid  accidents. 

Platinum  does  not  decompose  water  under  any  circumstances;  it  is  not  attacked 
by  nitric,  hydrochloric,  or  sulphuric  acid ;  but  a  mixture  of  nitric  and  hydrochloric 
acids  dissolves  it  in  the  form  of  bichloride.  Potassa  and  soda,  in  the  fused  state, 
act  upon  platinum,  probably  in  the  same  way  as  upon  gold,  by  inducing  the  ac- 
tion of  the  oxygen  of  the  air  upon  the  metal. 

Lithia  acts  upon  platinum  much  more  rapidly  than  the  above  alkalies. 
A  mixture  of  potassa  and  nitrate  of  potassa  (which  is  produced  by  the  action 
of  heat  upon  the  latter),  attacks  this  metal  very  readily. 

Several  other  oxides,  which  are  not  reduced  by  heat,  also  affect  platinum. 
Chlorine  slowly  attacks  platinum;  iodine  and  bromine  have  no  effect  upon  it. 
In  the  nascent  state,  however,  these  elements  are  capable  of  acting  upon  the 
metal. 

Fluorine  appears  to  combine  readily  with  platinum. 

Malleable  platinum  is  scarcely  affected  by  sulphur,  even  at  a  high  tempera- 
ture ;  spongy  platinum,  however,  combines  with  it. 

Phosphorus  and  arsenic  act  upon  platinum  at  a  high  temperature,  forming  a 
very  fusible  phosphide,  or  arsenide ;  hence,  substances  containing  phosphorus  in 
an  unoxidized  state  (brain,  blood,  &c.),  should  never  be  burnt  in  a  crucible  of 
this  metal,  neither  should  phosphates  be  heated  in  contact  with  reducing  agents 
in  a  platinum  crucible. 

Silicon  in  the  nascent  state  converts  platinum  into  a  brittle  silicide ;  hence, 
silicic  acid  and  carbon  should  never  be  allowed  to  come  simultaneously  in  contact 
with  platinum  at  a  high  temperature;  for  this  reason,  platinum  vessels  are  never 
directly  heated  by  a  coal,  coke,  or  charcoal  fire,  but  are  imbedded  in  a  layer  of 
magnesia,  and  inclosed  in  a  Hessian  crucible. 

Most  metals  are  capable  of  combining  directly  with  platinum,  if  the  tempera- 
ture be  sufficiently  high,  so  that  we  should  avoid  the  contact  of  this  metal  with 
easily  reducible  metallic  oxides  in  the  presence  of  reducing  agents  (filter-paper, 
for  instance). 

When  platinum  is  alloyed  with  silver,  it  becomes  soluble  in  nitric  acid;  this 
is  often  cited  as  an  example  of  catalytic  action. 

Platinum-black. — This  form  of  platinum,  which  derives  importance  from  the 


OXIDE   OF   PLATINUM.  405 

interesting  processes  of  oxidation  which  it  is  capable  of  inducing,  may  be  pre- 
pared by  several  methods  : — 

I.  (Proto-)  chloride  of  platinum  is  dissolved  in  a  concentrated  solution  of  po- 
tassa, with  the  aid  of  heat,  and  alcohol  is  added,  by  degrees,  with  constant  stirring, 
to  the  hot  liquid;  the  platinum  is  precipitated  as  a  black  powder,  which  is  boiled, 
successively,  with  alcohol,  hydrochloric  acid,  potassa,  and  water. 

II.  A  solution  of  bichloride  of  platinum  is  boiled,  with  constant  agitation,  with 
carbonate  of  soda  and  sugar,  when  the  sodium  takes  the  chlorine  of  the  bichloride 
of  platinum,  and  the  metaj  is  precipitated,  the  oxygen  of  the  soda  serving  to 
convert  the  carbon  and  hydrogen  of  the  sugar  into  carbonic  acid  and  water. 

III.  By  boiling  a  solution  of  (proto-)  sulphate  of  platinum  with  alcohol. 

By  whichever  method  the  platinum-black  is  prepared,  it  must  be  very  carefully 
washed,  and  dried  between  blotting-paper. 

It  will  be  remembered  that  when  platinum-black  (or  spongy  platinum)  is 
thrown  into  a  mixture  of  hydrogen  and  oxygen,  it  causes  combination,  attended 
by  explosion,  and  that  a  jet  of  hydrogen  may  be  inflamed  by  directing  it  upon 
platinum  in  one  of  these  states,  air  being  present  (see  p.  119). 

If  a  mixture  of  sulphurous  acid  and  oxygen  be  passed  over  platinum-black,  or 
sponge,  anhydrous  sulphuric  acid  is  produced. 

A  mixture  of  binoxide  of  nitrogen,  or  ammonia,  with  an  excess  of  oxygen, 
passed  over  heated  spongy  platinum,  or  platinum-black,  gives  rise  to  nitric  acid : — 
NH3  +  08=HO.N05-f-2HO. 

On  the  other  hand,  the  oxides  of  nitrogen,  when  mixed  with  an  excess  of  hydro- 
gen, and  exposed  to  the  action  of  the  heated  platinum,  yield  ammonia  and  water: — 
N03-fH5=NH3-f2H0.1 

Both  spongy  platinum  and  platinum-black  lose  these  peculiar  properties  after 
some  time,  but  they  may  be  revived  by  heating  with  nitric  acid,  washing  with 
water,  drying  at  a  gentle  heat,  and,  in  the  case  of  spongy  platinum,  heating  to 
redness. 


PLATINUM    AND   OXYGEN. 

(Prot-)  oxide PtO 

Binoxide PtOa 

OXTDE  OR  PROTOXIDE  OF  PLATINUM. 
PtO. 

§  273.  This  oxide  is  known  only  in  the  form  of  hydrate,  which  is  obtained,  as 
a  black  powder,  by  decomposing  the  (proto-)  chloride  of  platinum  with  potassa. 

1  It  is  in  the  department  of  organic  chemistry  that  we  find  the  most  interesting  examples 
of  the  action  of  platinum-black. 

If  a  drop  of  alcohol  be  projected  upon  a  little  platinum-black,  the  latter  becomes  vividly 
incandescent,  and  the  excess  of  alcohol  takes  fire ;  again,  when  platinum-black  is  placed 
in  a  capsule  and  covered  with  a  bell-jar,  the  sides  of  which  are  wetted  with  alcohol,  the 
latter  is  gradually  oxidized,  and  converted  into  acetic  acid: — 

C4H602+04=C4H303.HO-|-2HO. 

Alcohol.  Acetic  acid. 

Formic  acid,  moreover,  is  immediately  converted  into  carbonic  acid  and  water,  by  contact 
with  platinum-black: — 

C2H03.H04-02=2C02-f2HO. 

Formic  acid. 


406  PLATINUM   AND    OXYGEN. 

The  hydrated  oxide,  when  freshly  precipitated,  dissolves  in  excess  of  potassa. 

If  the  hydrate  be  heated,  it  parts  with  water  and  oxygen,  leaving  metallic 
platinum  ;  in  fact,  this  oxide  is  very  unstable;  most  reducing  agents  decompose 
it  with  facility.  Oxide  of  platinum  possesses  feeble  basic  characters;  it  dissolves 
slowly  in  sulphuric,  nitric,  and  acetic  acids,  yielding  brown  solutions. 

When  this  oxide  is  heated  with  hydrochloric  acid,  the  metal  is  separated,  and 
bichloride  of  platinum  formed  : — 

2PtO+2HCl=PtCla+Pt-f2HO. 

The  salts  of  (prot-)  oxide  of  platinum  are  little  known,  and,  for  the  most  part, 
do  not  crystallize ;  the  oxalate  has  been  obtained  in  copper-red  needles  by  heating 
hydrated  binoxide  of  platinum  with  oxalic  acid.1 

Solutions  of  (prot-)  oxide  of  platinum  are  not  precipitated  by  chloride  of  am- 
monium, and  may  thus  be  distinguished  from  those  of  the  binoxide. 

BINOXIDE  OF  PLATINUM,  PLATINIC  ACID. 
Pt02. 

Anhydrous  binoxide  of  platinum  may  be  obtained  by  gently  heating  the 
hydrate ;  it  is  a  black  powder,  which  does  not  dissolve  in  acids  or  alkalies. 

The  hydrate  (Pt02  2HO),  is  prepared  by  mixing  a  solution  of  bichloride  of 
platinum  with  an  excess  of  potassa,  when  a  double  chloride  of  platinum  and 
potassium  is  first  precipitated,  but  redissolves  on  gently  heating,  being  converted 
into  platinate  of  potassa;  if  the  solution  be  now  mixed  with  excess  of  acetic 
acid,  the  hydrated  binoxide  of  platinum  is  precipitated. 

This  hydrate  forms  a  red-brown  precipitate,  somewhat  resembling  the  sesqui- 
oxide  of  iron ;  when  heated,  it  loses  first  its  water,  and  then  the  oxygen.  It  is 
easily  decomposed  by  reducing  agents. 

The  hydrate  dissolves  in  acids  and  alkalies,  yielding  brown  solutions ;  hence, 
binoxide  of  platinum  is  another  example  of  an  oxide  which  plays,  indifferently, 
the  part  of  a  weak  base  and  that  of  a  weak  acid. 

Fulminating  Platinum. — This  substance,  which  is  probably  a  compound  of 
binoxide  of  platinum  with  ammonia,  is  obtained  by  adding  the  latter  reagent  to 
a  solution  of  sulphate  of  binoxide  of  platinum,  and  digesting  the  basic  double- 
salt  then  precipitated,  with  a  dilute  solution  of  soda. 

It  is  a  brown  powder,  insoluble  in  water,  nitric  and  hydrochloric  acids,  but 
soluble  in  sulphuric  acid.  It  is  not  exploded  by  friction  or  percussion,  but  deto- 
nates violently  when  heated  to  about  400°  F.  (204°  C.)  Care  should  therefore 
be  taken,  lest  it  should  be  formed,  unexpectedly,  in  examining  the  compounds  of 
platinum. 

The  platinates  of  potassa  and  soda  may  be  crystallized ;  they  are  decomposed 
by  acids,  platinic  acid  (hydrated  binoxide  of  platinum)  being  separated. 

Nitrate  of  binoxide  of  platinum  is  formed  when  an  alloy  of  platinum  and 
silver  is  dissolved  in  nitric  acid;  it  may  be  prepared  by  dissolving  the  hydrated 
binoxide  in  nitric  acid,  or  by  decomposing  bichloride  of  platinum  with  nitrate  of 
silver. 

This  nitrate  does  not  crystallize;  it  has  a  dark-brown  color,  and  leaves  metallic 
platinum  when  exposed  to  heat. 

Nitrate  of  binoxide  of  platinum  forms  double-salts  with  the  alkaline  nitrates. 

In  order  to  prepare  the  Sulphate  of  Binoxide  of  Platinum,  the  bisulphide  is 
oxidized  with  fuming  nitric  acid,  and  the  liquid  evaporated  to  dryness  with  a 
little  sulphuric  acid.  The  sulphate  has  a  dark- brown  color,  and  is  very  soluble 

1  A  double-salt  of  the  formula  2(PtO  2S02,3(KO.S02))-|-5Aq,  is  deposited  as  a  white 
precipitate,  when  the  double  chloride  of  platinum  and  potassium  (KCl.PtCl2)  is  heated 
with  sulphide  of  potassa,  and  the  colorless  solution  concentrated  by  evaporation. 


PLATINUM   AND    CHLORINE.  407 

in  water;  it  does  not  crystallize.  Sulphate  of  binoxide  of  platinum  combines 
with  the  alkaline  sulphates  to  form  double-salts. 

An  intermediate  oxide  of  platinum  is  said  to  have  been  obtained  by  the  action 
of  nitric  acid  on  fulminating  platinum. 

Some  chemists  assert  that  a  crystalline  compound  of  platinum  with  hydrogen 
is  obtained,  when  an  alloy  of  platinum  and  potassium  is  decomposed  by  water. 

CHLORIDE  OR  PROTOCHLORIDE  OF  PLATINUM,  PtCl. 

§  274.  Preparation. — In  order  to  prepare  the  (proto-)  chloride,  platinum  is 
dissolved  in  aqua  reyia,  the  solution  evaporated  to  dry  ness,  and  the  residue 
heated  on  an  oil-bath  to  about  400°  F.  (204°  C.)  as  long  as  any  chlorine  is 
disengaged. 

This  chloride  is  also  precipitated  when  sulphurous  acid  is  passed  through 
solution  of  bichloride  of  platinum  not  containing  an  excess  of  acid  : — 
PtCl2+2HO  +  S03=HO.S03+HCl+PtCl. 

Properties. — (Proto-)  chloride  of  platinum  has  a  grayish-green  color;  it 
blackens  slightly  when  exposed  to  light;  all  the  chlorine  may  be  expelled  by  a 
high  temperature;  it  is  insoluble  in  water,  and  in  nitric  or  sulphuric  acid,  but 
dissolves  in  hydrochloric  acid,  a  portion  of  it  being  decomposed  into  metal  and 
bichloride.  It  dissolves  more  readily  in  a  solution  of  bichloride  of  platinum. 

Alkalies  decompose  the  chloride,  forming  oxide  of  platinum. 

Its  solution  in  hydrochloric  acid  is  not  precipitated  by  chloride  of  ammonium, 
but  on  carefully  evaporating  the  liquid,  vellow  crystals  are  obtained,  of  the 
formula  PtCl.NH4Cl. 

Similar  compounds  may  be  formed  with  the  chlorides  of  potassium  and 
sodium. 

Chloride  of  platinum,  when  treated  with  ammonia,  gives  rise  to  several  new 
compounds,  the  most  important  of  which  we  shall  briefly  notice. 

AMMONIATED  CHLORIDE  OF  PLATINUM.  Green  Salt  of  Magnus.  PtCl.NH3. 
This  compound  is  formed  when  (proto-)  chloride  of  platinum  is  digested  for  some 
time  with  ammonia  at  a  gentle  heat.  It  is,  however,  more  readily  prepared  as 
follows  :  sulphurous  acid  is  passed  through  solution  of  bichloride  of  platinum 
mixed  with  excess  of  hydrochloric  acid,  until  the  deep  red  liquid  ceases  to  preci- 
pitate a  solution  of  chloride  of  ammonium ;  the  solution  is  then  boiled,  and 
ammonia  gradually  added,  when  the  green  salt  is  precipitated  in  fine  crystalline 
needles,  which  are  insoluble  in  water,  alcohol,  ether,  and  hydrochloric  acid. 

When  the  green  compound  is  heated  with  an  excess  of  ammonia,  it  gradually 
dissolves,  and  the  solution  deposits  yellowish-white  prismatic  crystals,  of  the 
formula  PtCl,2NH3+HO. 

This  last  is  known  as  the  white  compound  of  Reisef,  and  should  be  written 
PtN3H6Cl-4-HO,  since  it  is  the  chloride  of  a  new  radical,1  the  formula  of  which 
is  PtNaET6.  The  water  is  expelled  at  212°  F.,  leaving  the  anhydrous  chloride. 

By  dissolving  the  white  compound  of  Reiset  in  hot  water,  and  decomposing  it 
with  sulphate  of  silver,  chloride  of  silver  is  precipitated,  and  the  filtered  solution, 
on  evaporation,  yields  colorless  crystals,  of  the  formula  PtNaH6O.S03;  these  are 
the  sulphate  of  a  new  base,  PtN3H60,  which  may  be  isolated  by  carefully  decom- 
posing the  sulphate  with  baryta-water,  filtering,  and  evaporating  the  solution  in 
vacuo,  when  white  crystals  are  obtained,  of  the  formula  PtN3H6O.HO. 

This  hydrated  base  bears  a  great  analogy  to  hydrate  of  potassa ;  it  is  deliques- 
cent, has  a  caustic  taste,  reacts  strongly  alkaline  to  test-papers,  and  absorbs 
carbonic  acid  from  the  air ;  it  is  also  capable  of  expelling  ammonia  from  its 
salts. 

1  This  radical  has  been  recently  named  diplatosammonium ;  the  base  corresponding  to  it 
being  termed  diplatosamine. 


408  PLATINUM-BASES. 

A  pretty  complete  series  of  the  salts  of  this  base  has  been  obtained. 

When  it  is  heated  to  230°  F.  (110°  C.),  it  parts  with  ammonia  and  water, 
and  is  converted  into  PtNH30  (oxide  qfplatosammoniurn),  which  is  a  new  base, 
insoluble  in  water;  the  sulphate  of  this  base  has  the  formula  PtNH3O.S03-f-HO; 
the  nitrate  is  represented  by  PtNH3O.N05.  These  salts  are  converted  into  salts 
of  the  base  PtN3H60,  when  dissolved  in  ammonia.  The  chloride  corresponding 
to  this  base,  viz.  PtNH3Cl,  is  isomeric  with  the  green  salt  of  Magnus,  and  may 
be  obtained  by  dissolving  that  compound  in  a  hot  solution  of  nitrate  or  sulphate 
of  ammonia,  when  the  new  salt  crystallizes  out  on  cooling. 

When  the  green  compound  of  Magnus  (PtCl,NH3)  is  heated  with  nitric  acid, 
it  dissolves,  and  the  solution  yields  white  crystals,  which  have  the  formula 
PtCl.N3H6O.N05;  in  this  reaction,  1  equivalent  of  (proto-)  chloride  of  platinum 
has  been  abstracted  from  the  aramoniated  chloride,  and  an  equivalent  of  oxygen 
added ;  the  compound  thus  formed  is  in  fact  the  nitrate  of  another  base  (usually 
termed  Gros's  base,  from  its  discoverer),  PtClN3H60,  which  is  the  oxide  of  a 
radical  PtClN3H6,  isomeric  with  the  chloride  of  Reiset's  radical  PtN3H6.  Neither 
the  radical  nor  the  base  itself  has  been  isolated. 

By  dissolving  the  ammoniated  (proto-)  chloride  of  platinum  in  a  large  excess 
of  nitric  acid,  two  more  nitrates  are  obtained,  having  the  formulae 

Pt3C105N4H13,  2N05,  and  Pt9Cl,04N4Htt.2NO5. 

The  former  of  these  is  deposited  in  needles  as  the  liquid  cools,  and  the  latter 
may  be  obtained  from  the  mother-liquor. 

Other  salts  of  the  base,  PtaC105N4H13  (Raewsky's  base')  have  been  obtained. 

We  have  now  become  acquainted  with  the  three  well-defined  series  exhibited 
in  the  subjoined  table  : — 

Hypothetical  Radical.  Base.  Chloride. 

Reiset's  first  base    .     .    PtN2H6  (PtN3H6)0  (PtN2H6)Cl 

Reiset's  second  base     .     PtNH3  (PtNH3)O  (PtNH8)Ci 

Gros'sbase    .     .     .     PtClN3H6  (PtClN3H6)0  (PtClN3H6)Cl 

(not  isolated) 

But  little  can  be  at  present  made  out  respecting  the  true  constitution  of  these 
very  interesting  compounds. 

BICHLORIDE,  OR  PERCHLORIDE  OF  PLATINUM,  PtCla. 

§  275.  Preparation. — This  salt,  commonly  called  chloride  of  platinum,  is 
prepared  by  dissolving  the  metal  in  a  mixture  of  two  parts  of  hydrochloric  acid 
and  one  part  of  nitric,  evaporating  the  liquid  at  a  gentle  heat  to  the  consistence 
of  a  syrup,  redissolving  in  dilute  hydrochloric  acid,  and  again  evaporating,  to 
expel  excess  of  nitric  acid;  the  syrupy  liquid  solidifies  on  cooling;  care  must  be 
taken  that  it  be  not  overheated.  Platinum-wire  should  not  be  employed  for  this 
purpose,  since  it  dissolves  very  slowly;  pieces  of  platinum  foil  and  old  crucibles 
should  be  dissolved ;  they  must  be  previously  cleaned,  however,  by  boiling  suc- 
cessively with  concentrated  nitric  acid,  with  water,  and  then  with  concentrated 
hydrochloric  acid. 

It  is  often  necessary,  in  the  laboratory,  to  prepare  the  bichloride  of  platinum 
from  platinum  residues,  which  should  always  be  saved  for  this  purpose.  These 
residues  may  contain  a  great  variety  of  substances,  and  the  pure  platinum  must 
be  extracted  from  them  as  follows ;  the  residues,  filters,  &c.,  are  evaporated  to 
dryness  in  a  dish,  then  transferred  to  a  Hessian  crucible,  and  very  strongly 
ignited  with  excess  of  air,  by  which  all  organic  and  volatile  matters  are  expelled; 
the  residue  is  boiled  successively  with  concentrated  hydrochloric  acid,  with  water, 
and  with  concentrated  nitric  acid;  lastly,  again  with  water  (two  or  three  times), 
and  dissolved  in  nitro-hydrochloric  acid;  the  solution  may  be  evaporated,  as 


BICHLORIDE    OF   PLATINUM.  409 

directed  above,  and  if  any  doubt  still  exist  as  to  its  purity,  the  residue  may  be 
dissolved  in  alcohol,  the  solution  filtered,  and  again  evaporated. 

Properties  — The  bichloride  of  platinum  has  a  dark  red-brown  color,  and  does 
not  crystallize;  it  is  deliquescent,  and  very  soluble  in  water  and  alcohol.  When 
heated,  it  leaves,  first,  the  (proto-)  chloride,  and  then  the  metal. 

When  a  solution  of  bichloride  of  platinum  is  mixed  with  concentrated  sulphuric 
acid,  it  gives  a  dark  yellow  precipitate,  which  is  the  anhydrous  bichloride. 

Bichloride  of  platinum  combines  with  many  other  chlorides  to  form  double- 


This  salt  is  a  very  useful  reagent ;  it  is  much  employed  in  the  laboratory 
for  the  precipitation  and  estimation  of  potassium  and  ammonium;  it  serves, 
moreover,  to  convert  the  hydrochlorates  of  the  organic  bases  into  double-salts, 
which  leave  metallic  platinum  when  ignited,  from  the  weight  of  which  we  may 
calculate  the  atomic  weight  of  the  base  under  examination;  since  the  equivalent 
of  platinum  is  very  high,  a  loss  which  would  considerably  influence  other  deter- 
minations little  affects  these,  so  that  the  atomic  weight,  determined  by  experiment, 
not  unfrequently  coincides  exactly  with  that  ascertained  by  calculation. 

Bichloride  of  platinum  is  sometimes  used  in  medicine. 

Bichloride  of  Platinum  and  Chloride  of  Potassium,  KCl.PtCl2,  also  some- 
times called  polassio-chloride  of  platinum,  and  platino-chloride  of  potassium. — 
This  compound  is  obtained  as  a  crystalline  precipitate,  on  mixing  solutions  of  its 
constituent  salts,  or  on  adding  hydrochloric  acid  and  bichloride  of  platinum  to  a 
solution  of  any  salt  of  potassa.  If  the  experiment  be  made  with  a  dilute  solu- 
tion, so  that  the  salt  is  deposited  only  on  standing,  or  if  the  precipitate  be  dis- 
solved in  boiling  water,  and  the  solution  allowed  to  cool,  crystals  of  considerable 
size  may  be  obtained. 

The  crystals  are  yellow  octohedra;  .they  are  decomposed  by  heat,  leaving  a 
mixture  of  chloride  of  potassium  and  metallic  platinum.  This  double  chloride 
requires  144  parts  of  cold  water  for  solution,  but  is  more  soluble  in  boiling  water; 
the  solution  is  neutral.  It  is  insoluble  in  alcohol. 

Potassium  is  generally  estimated  in  this  form. 

Bichloride  of  Platinum  and  Chloride  of  Sodium,  or  Platino-  Chloride  of  Sodi- 
ww,NaCl.PtCla. — This  salt  is  very  soluble  in  water,  and  moderately  so  in  alcohol; 
it  crystallizes  in  yellow  prisms.  It  is  occasionally  employed  medicinally. 

Bichloride  of  Platinum  and  Chloride  of  Ammonium,  Ammonio  chloride  of 
Platinum,  NH4Cl.PtCl3. — The  precipitate  produced  by  solution  of  bichloride  of 
platinum  in  solution  of  chloride  of  ammonium,  or  of  any  salt  of  ammonia,  to 
•which  hydrochloric  acid  has  been  added,  consists  of  this  double  salt. 

It  may  be  crystallized  in  yellow  octohedra  in  the  same  way  as  the  potassium- 
salt.  When  heated,  it  is  decomposed,  leaving  metallic  platinum.  This  salt  is 
nearly  insoluble  in  absolute  alcohol,  one  part  dissolves  in  26,535  parts  of  alcohol 
of  77.5  per  cent.,  and  665  parts  of  alcohol  of  45  per  cent. 

It  will  be  remembered  that  it  is  employed  as  a  source  of  pure  platinum. 

In  this  form,  also,  nitrogen  is  generally  weighed;  and  if  we  compare  its 
equivalent  (223.2)  with  that  of  nitrogen  (14),  we  shall  conceive  the  accuracy 
•with  which  this  element  may  be  determined. 

The  double-salts  formed  by  bichloride  of  platinum  with  the  chlorides  of  bari- 
um, strontium,  magnesium,  and  calcium,  are  soluble  and  crystallizable ;  those 
formed  by  other  metallic  chlorides  are  for  the  most  part  insoluble. 

SULPHIDES  OF  PLATINUM. 

Two  compounds  of  platinum  and  sulphur  are  known,  which  correspond  to  the 
oxides. 

Sulphide  or  Protosulphide  of  Platinum,  PtS,  may  be  prepared  by  beating 
two  parts  of  sulphur  with  one  part  of  finely-divided  platinum,  when  it  forms  a 


410  METALLURGY  OF  PLATINUM. 

gray,  brittle  mass.  It  is  also  obtained  when  the  (proto-)  chloride  of  platinum 
is  decomposed  by  hydrosulphuric  acid  or  an  alkaline  sulphide. 

The  Bisulphide  of  Platinum  is  precipitated  when  sulphuretted  hydrogen  is 
passed  through  a  neutral  or  acid  solution  of  the  binoxide.  It  forms  a  black  pre- 
cipitate, which  loses  half  its  sulphur  when  heated  in  close  vessels.  It  is  insoluble 
in  hydrochloric  and  sulphuric  acids,  but  dissolves  in  concentrated  nitric  acid, 
being  converted  into  sulphate  of  binoxide  of  platinum.  It  dissolves  to  some 
extent,  but  not  readily,  in  the  alkalies  and  alkaline  sulphides,  yielding  sulphur- 
salts,  from  which  the  bisulphide  is  reprecipitated  by  acids. 

§  276.  ALLOYS  OF  PLATINUM. — Iron  is  capable  of  forming,  with  platinum, 
alloys  which  are  malleable,  and  possess  considerable  lustre. 

Copper  and  platinum  form  a  very  brilliant  alloy,  which  is  sometimes  employed 
for  the  specula  of  telescopes. 

Platinum  hardens  silver  in  a  remarkable  manner. 

It  has  already  been  mentioned,  that  if  platinum  be  alloyed  with  a  sufficient 
quantity  of  silver,  it  becomes  soluble  in  nitric  acid. 

Other  alloys  of  platinum  with  lead,  tin,  antimony,  gold,  &c.,  are  known,  but 
possess  no  practical  interest. 

METALLURGY  OF  PLATINUM. 

This  metal  is  always  found  native  in  alluvial  deposits  similar  to  those  in  which 
gold  occurs ;  in  fact,  the  latter  often  accompanies  the  platinum. 

It  is  usually  found  in  small  grains,  but  sometimes  in  masses,  and  is  associated 
with  osmium,  iridium,  palladium,  rhodium,  ruthenium,  gold,  silver,  iron,  copper, 
and  several  foreign  minerals,  such  as  magnetic  oxide  of  iron,  titanic  iron,  chrome 
iron,  pyrites,  &c. 

When  the  ore  (obtained  by  washing  the  sand)  contains  any  considerable  quan- 
tity of  gold,  this  metal  is  extracted  by  amalgamation  (see  p.  399).  The  ore  is 
then  heated  with  somewhat  dilute  aqua  reyia,  as  long  as  anything  is  dissolved 
by  a  fresh  portion  of  this  acid;  since,  during  this  operation,  very  irritating 
vapors  of  osrnic  acid  are  evolved,  it  should  be  performed  under  a  chimney. 
The  solution  will  contain  nearly  all  the  platinum,  whilst  the  residue  contains 
the  greater  part  of  the  iridium  and  osmium,  which  are  not  soluble  in  diluted 
nitre-hydrochloric  acid.  The  solution  is  evaporated  to  a  small  bulk,  and 
mixed  with  chloride  of  ammonium,  which  precipitates  the  platinum  and  a  little 
iridium  as  double  chlorides. 

The  supernatant  liquid,  which  still  contains  a  little  platinum,  is  precipitated 
by  metallic  iron,  and  the  finely-divided  metal  treated  with  dilute  aqua  reyia, 
which  dissolves  only  the  platinum ;  the  solution  is  precipitated  with  chloride  of 
ammonium,  this  precipitate  added  to  the  former,  the  whole  washed,  dried,  and 
ignited  at  a  dull  red  heat;  in  order  to  convert  into  malleable  metal  the  spongy 
platinum  thus  obtained,  it  is  powdered  in  a  wooden  mortar,  mixed  into  a  paste 
with  water,  and  rubbed  through  a  sieve ;  a  wooden  mortar  is  employed,  because 
the  use  of  metal  would  render  some  parts  of  the  platinum  too  compact. 

The  paste  of  platinum  is  introduced  into  a  cylinder  of  brass,  closed  by  a  steel 
plate,  and  compressed  first  with  a  wooden,  and  afterwards  with  a  metallic  piston; 
the  water  is  thus  squeezed  out,  and  some  cohesion  given  to  the  metal ;  it  is  now 
submitted  to  the  action  of  a  powerful  press,  then  heated  to  whiteness,  and  beaten 
into  malleable  platinum  upon  an  anvil;  it  may  then  be  worked  into  wire  or  plate. 

Platinum  is  chiefly  used  for  vessels  serving  the  purposes  of  the  chemist;  it  is 
largely  employed  for  the  stills  in  which  oil  of  vitriol  is  concentrated. 

Platinum  is  also  used  in  porcelain-painting,  for  that  species  of  ware  termed 
silver-lustre.  In  Russia,  this  metal  circulates  in  the  form  of  coin.  It  is  also 
used  for  the  touchholes  of  fowling-pieces;  on  account  of  its  resistance  to  the 
action  of  corrosive  agents. 


PALLADIUM.  411 


PALLADIUM. 

Sym.  Pd.     Eq.  53.3.     Sp.  Gr.  11.5. 

i 

§  277.  Preparation. — This  metal  occurs  in  small  quantity,  associated  with 
native  gold  and  platinum. 

It  is  usually  prepared  from  the  mother-liquor  remaining  after  the  precipitation 
of  platinum,  from  its  solution  in  aqua  regia,  by  means  of  chloride  of  ammonium. 
It  will  be  remembered  that  this  mother  liquor  was  decomposed  by  metallic  iron, 
when  a  black  deposit  is  formed  containing  platinum,  palladium,  rhodium,  iridi- 
um,  gold,  lead,  and  copper.  The  copper  and  lead  are  extracted  by  weak  nitric 
acid,  the  residue  dissolved  in  aqua  regia,  the  solution  neutralized  with  carbonate 
of  soda,  and  a  solution  of  cyanide  of  mercury  added,  which  precipitates  the  pal- 
ladium in  the  form  of  cyanide;  this  latter,  when  ignited,  leaves  spongy  palladium, 
which  may  be  converted  into  the  malleable  metal,  in  the  same  manner  as  platinum. 

Properties. — Palladium  is  one  of  the  hardest  metals.  Its  color  is  intermediate 
between  that  of  platinum  and  silver;  it  is  malleable,  ductile,  and  capable  of  being 
welded  like  platinum.  Palladium  is  very  infusible ;  it  may  be  liquefied  in  the 
flame  of  the  oxyhydrogen  blowpipe,  where  it  throws  off  sparks  like  platinum. 

This  metal  is  unalterable  in  air  at  the  ordinary  temperature ;  when  heated  in 
air,  it  becomes  blue,  from  superficial  oxidation,  but  regains  its  natural  color  as 
the  temperature  rises,  the  oxide  being  decomposed. 

Palladium  is  not  capable  of  decomposing  water  under  any  circumstances; 
concentrated  nitric,  sulphuric,  and  hydrochloric  acids  dissolve  it  to  some  extent, 
but  it  is  much  more  readily  dissolved  by  aqua  regia.  It  combines  directly  with 
chlorine,  sulphur,  carbon,  and  phosphorus,  among  the  non-metallic  elements,  and 
with  most  of  the  metals. 

Fused  potassa  attacks  palladium,  if  air  be  present;  a  mixture  of  potassa  and 
nitre  very  readily  corrodes  it.  It  is  also  attacked  hy  fused  bisulphate  of  potassa. 

Uses. — Palladium  is  sometimes  employed  instead  of  silver  for  the  graduated 
scales  of  philosophical  instruments,  since  it  is  not  tarnished  by  sulphuretted 
hydrogen. 

This  metal,  moreover,  is  used  in  the  construction  of  accurate  balances  and 
chronometers. 

An  alloy  of  palladium,  with  one-tenth  of  silver,  is  employed  by  dentists. 

Palladium  forms  two  oxides  corresponding  to  those  of  platinum. 

OXIDE,  OR  PROTOXIDE  OF  PALLADIUM,  PdO. 

The  anhydrous  (prot-)  oxide  is  obtained  by  gently  heating  the  nitrate  of  palla- 
dium ;  it  forms  a  dark  gray  metallic-looking  powder,  which  is  easily  reduced  by 
heat.  It  dissolves  in  acids,  forming  salts,  but  is  not  acted  on  by  alkalies. 

The  hydrate  is  precipitated  by  adding  an  alkaline  carbonate  to  nitrate  of  palla- 
dium ;  it  has  a  brown  color,  and  is  soluble  both  in  acids  and  alkalies. 

The  salts  of  oxide  of  palladium  have  a  red- brown  color. 

Nitrate  of  Oxide  of  Palladium  is  obtained  by  dissolving  the  metal  in  nitric 
acid ;  the  solution  does  not  deposit  crystals  when  evaporated,  but  if  ammonia  be 
added,  crystals  of  a  double  nitrate  may  be  obtained. 

Binoxide  of  Palladium  (Pd03)  has  not  been  obtained  in  a  pure  state;  when 
the  bichloride  is  decomposed  by  an  alkali  or  an  alkaline  carbonate,  a  brown  pre- 
cipitate is  formed,  which  always  contains  alkali ;  this  precipitate  dissolves  in 
most  acids. 


412  RHODIUM. 

(PROTO-)  CHLORIDE  OF  PALLADIUM,  PdCl. 

This  compound  is  produced  when  the  metal  is  dissolved  in  as  little  nitro- 
hydrochloric  acid  as  possible ;  it  forms  a  red  solution  from  which  crystals  of  the 
same  color  may  be  obtained  by  evaporation ;  it  is  completely  decomposed  by 
heat,  yielding  first  an  oxychloride,  and  afterwards  the  metal.  Chloride  of  palla- 
dium is  sometimes  used  in  analysis  for  separating  iodine  from  chlorine  and  bro- 
mine. This  chloride  forms  double-salts  with  the  chlorides  of  the  alkali-metals. 

The  double  chloride  of  palladium  and  potassium,  PdCl.KCl,  and  that  of 
palladium  and  ammonium,  PdCl.NH4Cl,  are  slightly  soluble  in  water,  and 
insoluble  in  alcohol ;  they  may  be  obtained  in  fine  crystals. 

The  corresponding  sodium  salt,  PdCl.NaCl,  is  deliquescent,  and  soluble  in 
water.1 

BICHLORIDE  OF  PALLADIUM,  PdCla. 

The  bichloride  is  formed  when  the  preceding  compound  is  heated  with  an 
excess  of  aqua  regia,  and  may  be  obtained  as  a  brown  crystalline  mass  by  eva- 
poration in  vacuo.  It  is  very  unstable,  being  decomposed  when  heated,  even  in 
a  state  of  solution,  into  chloride  of  palladium  and  chlorine. 

When  solution  of  bichloride  of  palladium  is  mixed  with  chloride  of  potassium, 
or  chloride  of  ammonium,  a  red  precipitate  of  a  double  chloride  is  produced. 

A  compound  of  palladium  with  carbon  is  formed  when  this  metal  is  heated 
in  the  flame  of  a  spirit-lamp. 

REACTIONS  OF  PALLADIUM. — (Prot )  oxide. — Potassa,  soda,  and  their  car- 
bonates ;  brownish  precipitate,  soluble  in  excess ,  and  reprecipitated  from  solu- 
tion in  the  carbonates  by  boiling. 

Ammonia  and  its  carbonate ;  no  precipitate  except  in  the  chloride,  which 
gives  a  flesh-colored  precipitate  (ammonio-chloride  of  palladium)  soluble  in  large 
excess,  on  standing. 

Hydrosulphuric  acid  and  sulphide  of  ammonium  ;  black  sulphide  of  palladium. 

Sulphate  of  iron  and  (pro(o-)  chloride  of  tin ;  in  concentrated  solutions;  a 
black  precipitate  of  reduced  palladium,  and,  in  the  case  of  tin,  a  green  super- 
natant liquid. 

Iodide  of  potassium;  black  precipitate  of  iodide  of  palladium. 

Cyanide  of  mercury  ;  yellowish- white  precipitate  of  cyanide  of  palladium; 
produced  after  a  time  in  acid  solutions. 

(Binoxide). —  Chlorides  of  potassium  and.  ammonium;  brownish-red  precipi- 
tate of  a  double  salt,  sparingly  soluble  in  water  and  alcohol. 

Solution  of  the  bichloride  of  palladium  evolves  chlorine  when  heated,  and  is 
converted  into  the  (proto-)  chloride. 


RHODIUM. 

Sum.  Rh.     Eq.  52.2.     Sp.  Gr.  10.6. 

§  278.  Preparation. — Rhodium  is  also  found  in  the  ores  of  platinum.  It  is 
extracted  from  them  by  dissolving  the  ore  in  aqua  regia,  precipitating  the  pla- 
tinum by  chloride  of  ammonium,  neutralizing  the  solution  with  carbonate  of 
soda,  adding  cyanide  of  mercury  to  separate  the  palladium,  and  evaporating  the 

1  A  series  of  ammonia-compounds,  similar  to  those  of  platinum,  have  been  obtained 
from  the  chloride  of  palladium. 


CHLORIDES   OF  RHODIUM.  413 

filtered  liquid  to  dryness  with  excess  of  hydrochloric  acid ;  the  residue  is  treated 
with  alcohol,  which  leaves  the  double  chloride  of  rhodium  and  sodium  undissolved, 
as  a  red-brown  powder.  This  salt  is  heated  in  a  bulb-tube  through  which  a 
stream  of  pure  hydrogen  is  passed ;  the  rhodium  is  thus  reduced  to  the  metallic 
state,  and  the  chloride  of  sodium  may  be  washed  away  by  water. 

Properties. — Rhodium  is  a  grayish-white  ductile  metal;  it  is  exceedingly  hard, 
and  one  of  the  most  infusible  of  the  metals ;  the  oxyhydrogen  blowpipe-flame 
only  softens  it. 

This  metal  is  unaltered  in  air  at  the  ordinary  temperature,  but,  at  a  red  heat, 
is  easily  oxidized. 

Pure  rhodium  is  not  attacked  by  acids,  it  even  resists  the  action  of  aqua  regia, 
which  dissolves  it,  however,  when  alloyed  with  other  metals. 

A  mixture  of  potassa  and  nitre  converts  rhodium  into  sesquioxide. 

Rhodium  is  employed,  on  account  of  its  hardness,  for  making  the  nibs  of  gold 
pens. 

When  heated  with  bisulphate  of  potassa,  the  double  sulphate  of  rhodium  and 
potassa  is  formed. 

Two  oxides  of  rhodium  are  known. 

The  Oxide,  RhO,  is  produced  when  the  finely  divided  metal  is  heated  in  air, 
but  it  then  becomes  partially  converted  into  sesquioxide. 

The  Sesquioxide  of  rhodium,  Rh203,  is  formed  when  aqua  regia  acts  upon 
alloys  of  rhodium  with  other  metals. 

It  may  be  prepared  by  fusing  finely  divided  rhodium  with  a  mixture  of  pot- 
assa and  nitre,  and  washing  the  mass,  first  with  water,  then  with  a  dilute  acid. 

It  is  thus  obtained  as  a  black  powder,  which  is  not  decomposed  by  heat. 

Hydrated  sesquioxide  of  rhodium  is  obtained  as  a  yellowish-brown  gelatinous 
precipitate,  when  a  solution  of  the  sesquichloride  is  boiled  with  potassa. 

Sesquioxide  of  rhodium  combines  with  acids,  forming  salts  which  are  red  in 
concentrated,  and  pink  in  diluted  solutions. 

Several  intermediate  oxides  of  rhodium  also  exist. 

It  is  also  capable  of  playing  the  part  of  a  weak  acid,  dissolving  in  alkalies,  and 
forming  salts  termed  rhodiates. 

CHLORIDES  OF  RHODIUM. 

(Proto-^  chloride  of  rhodium^  RhCl,  is  obtained  by  heating  rhodium  in  air, 
and  treating  the  product  with  hydrochloric  acid,  when  the  sesquioxide  which  is 
present  is  dissolved  in  the  form  of  sesquichloride,  and  the  (proto-)  chloride  is 
left  as  an  insoluble  reddish  powder. 

Sesquichloride  of  rhodium,  RhaCl3,  has  a  brownish-black  color,  and  does  not 
crystallize.  It  resists  a  pretty  high  temperature  without  decomposition,  and 
dissolves  in  water  to  form  a  red  solution. 

Sesquichloride  of  rhodium  forms  crystallizable  double-salts  with  the  chlorides 
of  the  alkali-metals  j  these  compounds  are  best  prepared  by  heating,  in  a  current 
of  chlorine,  a  mixture  of  finely-divided  rhodium  with  an  alkaline  chloride. 

The  name  of  rhodium  is  derived  from  the  red  color  of  its  compounds  (£o5o»>, 
a  rose). 

REACTIONS  OF  RHODIUM — (Sesquioxide). — Potassa,  soda,  and  their  carbon- 
ates; yellowish  hydrate,  by  the  former,  on  boiling,  by  the  latter  in  the  cold,  after 
some  time. 

Ammonia  and  its  carbonate;  yellowish  precipitate. 

Hydromlphuric  acid  and  sulphide  of  ammonium  (the  former  after  some 
time)  ;  brown  precipitate. 

(Proto-'}  chloride  of  tin  ;  dark-red  brown  color. 

Iodide  of  potassium;  similar  reaction. 

Chlorides  of  potassium  and  ammonium  ;  pink  precipitates. 


414  IBIDIUM. 

Compounds  of  rhodium  may  easily  be  reduced  to  the  metallic  state  by  heating 
in  an  atmosphere  of  hydrogen;  the  reduced  rhodium  may  be  distinguished  by 
its  insolubility  in  aqua  reyia,  and  its  solubility  in  fused  bisulphate  of  potassa,  to 
which  it  imparts  a  pink  color. 


IRIDIUM. 

Sym.  Ir.     Eq.  99.     Sp.  Gr.  16. 

§  279.  This  metal,  which  has  received  the  above  name  in  consequence  of  the 
various  colors  of  its  compounds,  occurs  in  native  platinum,  generally  in  combina- 
tion with  osmium,  and  its  extraction  will  be  described  in  the  history  of  that 
metal.  An  alloy  of  indium  and  platinum  is  also  found  in  nature,  crystallized 
in  octohedra,  the  specific  gravity  of  which  is  22.3. 

Iridium  is  obtained,  by  calcining  the  ammonio-chloride,  in  a  spongy  state,  but 
it  may  be  rendered  more  compact  by  pressure.  It  has  a  gray  color,  and  its  spec, 
grav.  is  about  16 ;  but  it  is  generally  believed  to  be  even  heavier  than  platinum, 
from  the  high  specific  gravity  of  the  alloy  mentioned  above. 

Iridium  is  neither  malleable  nor  ductile ;  it  has  not  yet  been  fused,  and  is 
oxidized  if  heated  and  allowed  to  cool  in  air.  Like  rhodium,  it  is  not  attacked 
by  acids,  unless  it  be  alloyed  with  platinum,  or  some  other  metal,  when  aqua 
rrgia  dissolves  it.  It  is  oxidized  by  a  mixture  of  potassa  and  nitre,  and  is 
capable  of  direct  combination  with  chlorine.  It  is  also  attacked  by  bisulphate  of 
potassa  at  a  high  temperature. 

Finely  divided  iridium  (indium-Wade)  possesses  properties  similar  to  those  of 
platinum-black. 

Iridium  forms  four  oxides ;  viz :  oxide,  IrO ;  sesquioxide,  Ira03 ;  binoxide, 
IrOa;  teroxide,  Ir03. 

The  oxide  is  prepared  by  decomposing  the  double  chloride  of  iridium  and 
potassium  with  an  alkaline  carbonate,  when  it  is  obtained  as  a  greenish-gray  pre- 
cipitate, which  dissolves  in  acids. 

This  oxide  is  not  decomposed  by  heat,  but  may  be  easily  reduced  by  hydrogen. 
It  is  gradually  oxidized  when  exposed  to  air. 

Sesquioxide  of  Iridium,  Ir303,  is  formed  when  the  metal  is  oxidized  by  nitre, 
or  by  caustic  alkalies.  It  may  be  prepared  by  heating  the  double  chloride  of 
iridium  and  potassium  (IrCl3  KC1)  with  carbonate  of  potassa,  in  an  atmosphere 
of  carbonic  acid,  and  washing  the  residue  with  slightly  acidulated  water  : — 

2(IrCla.KCl)+4(KO.C03)=Ir203+6KCl+0+4COa. 

The  sesquioxide  is  a  black  powder,  which  is  reduced  to  the  (prot-)  oxide  when 
heated;  it  is  insoluble  in  acids,  but  combines  with  alkalies  to  form  brown, 
unstable  compounds,  which  are  little  known. 

The  most  important  oxide  of  iridium  is  the  binoxide,  Ir03,  which  is  produced 
when  solutions  of  the  lower  oxides  are  boiled  in  contact  with  air,  or  with  nitric 
acid. 

When  solution  of  the  sesquichloride  is  heated  with  potassa  in  contact  with  air, 
no  precipitate  is  formed  at  first,  but  oxygen  is  gradually  absorbed ;  the  solution 
becomes  blue,  and  deposits  blue  hydrated  binoxide  of  iridium,  Ir03.2HO. 

This  oxide  resembles  the  binoxide  of  platinum  in  its  chemical  relations ;  its 
solutions  have  a  deep  red-brown  color. 

Teroxide  of  Iridium,  Ir03,  is  obtained  as  a  greenish  precipitate  when  ter- 
chloride  of  iridium  is  decomposed  by  an  alkali. 


OSMIUM.  415 


CHLORIDES  OF  IRIDIUM. 

The  chlorides  of  iridium  correspond  to  the  oxides. 

The  (Proto-)  chloride  is  produced  when  chlorine  is  passed  over  finely  divided 
iridium  at  a  red  heat  ]  it  is  formed  more  readily,  if  the  iridiura  be  mixed  with 
chloride  of  potassium.  It  has  a  dark-green  color,  and  is  insoluble  in  water.  The 
double  chlorides  which  it  forms  with  the  chlorides  of  potassium  and  ammonium 
are  soluble  and  crystallizable. 

Sesquichloride  of  Iridtum,  Ir3Cl3,  is  formed  by  dissolving  the  sesquioxide  in 
hydrochloric  acid }  it  has  a  very  dark  color,  is  deliquescent,  and  uncrystallizable. 
It  combines  with  the  alkaline  chlorides,  forming  soluble  double-salts,  which  are 
decomposed  by  ebullition  into  soluble  salts  of  the  (proto-)  chloride,  and  insoluble 
salts  of  the  bichloride  (which  are  precipitated). 

The  Bichloride  (IrCl2)  is  the  product  of  the  action  of  nitro-hydrochloric  acid 
upon  iridium  (alloyed  with  other  metals),  or  one  of  its  oxides ;  it  is  soluble  in 
water,  and  forms  a  yellowish-red  solution. 

This  chloride  also  combines  with  the  chlorides  of  the  alkali-metals. 

The  double-salt  of  bichloride  of  iridium  and  chloride  of  potassium  is  soluble 
in  water,  and  forms  a  red  solution,  from  which  very  dark  red  octohedra  may  be 
obtained,  having  the  composition  IrCl2.KCl.HO. 

The  corresponding  compound  of  ammonium  is  obtained  as  a  very  dark  brown 
precipitate  when  chloride  of  ammonium  is  added  to  solution  of  bichloride  of 
iridium ;  it  may  be  dissolved  in  boiling  water,  and  crystallized  in  octehedra. 
The  red  color  of  the  ammonio-chloride  of  platinum  is  often  due  to  the  presence 
of  this  salt,  which  is  not  materially  detrimental  to  an  analysis,  since  the  equiva- 
lent of  iridium  is  nearly  the  same  as  that  of  platinum. 

The  precipitate  of  ammonio-chloride  of  iridium  dissolves  in  solution  of  sul- 
phurous acid,  being  converted  into  the  double-salt  of  the  (proto-)  chloride.  . 

Terchloride  of  Iridium,  IrCl3,  is  produced  when  an  oxide  of  iridium  is  dis- 
solved, at  a  gentle  heat,  in  very  concentrated  aqua  reyia. 

It  is  a  very  dark  brown,  deliquescent  substance,  soluble  in  water,  and  capable 
of  forming  double-salts  with  the  alkaline  chlorides. 

The  compounds  of  iridium  with  sulphur  correspond  to  the  oxides  and  chlorides. 

A  carbide  of  iridium  also  exists. 

REACTIONS  OF  IRIDIUM. — (Binoxide). — The  alkalies,  when  added  in  excess  to 
solutions  of  iridium,  produce  a  greenish  color,  becoming  blue  on  exposure  to  air. 

The  carbonates  of  soda  and  of  ammonia,  and  the  alkaline  bicarbonates  ;  simi- 
lar reaction. 

Carbonate  of  potassa  ;  a  brownish-red  precipitate,  redissolved  spontaneously 
after  some  time ;  the  color  of  the  liquid  alters  as  above,  upon  exposure  to  air. 

Hydrosulphuric  acid,  and  sulphide  of  ammonium  ;  brown  precipitate,  soluble 
in  sulphide  of  ammonium. 

(Proto-')  sulphate  of  iron  discolors  the  solution ;  after  some  time,  a  greenish 
precipitate. 

(Proto-)  chloride  of  tin  ;  a  light  brownish  precipitate. 

Chlorides  of  potassium  and  ammonium  ;  dark  brown  precipitates. 


OSMIUM. 

Sym.  Os.     Eq.  99.6.     Sp.  Gr.  10. 

§  280.  This  metal  is  prepared  from  the  alloy  of  iridium  and  osmium  (osm- 
iridium) ,  which  is  found  in  company  with  native  platinum. 


416  OSMIUM. 

Preparation. — The  alloy  is  mixed  with  three  parts  of  nitre,  and  strongly 
heated  for  about  an  hour.  The  fused  mass  (containing  osmic  acid,  Os04,  and 
teroxide  of  iridium)  is  heated  in  a  retort  with  a  large  excess  of  nitric  acid;  a 
considerable  quantity  of  osmic  acid  distils  over,  and  condenses  in  white  crystals 
in  the  receiver.  When  no  more  osmic  acid  passes  off,  which  may  be  known  by 
the  odor,  the  contents  of  the  retort  are  mixed  with  water,  the  oxides  of  iridium 
and  osmium  collected  on  a  filter,  and  dissolved  in  aqua  reyia.  The  solution  is 
then  treated  with  chloride  of  ammonium,  which  precipitates  the  two  metals  as 
double  chlorides ;  these  are  suspended  in  water  and  subjected  to  a  current  of 
sulphurous  acid,  which  reduces  the  bichloride  of  iridium  to  the  state  of  soluble 
(proto-)  chloride,  whilst  the  double  chloride  of  osmium  and  ammonium  is  left, 
and  may  be  reduced  by  a  heating  in  a  current  of  hydrogen. 

The  solution  containing  the  double  chloride  of  iridium  and  ammonium  yields 
crystals  on  evaporation,  and  by  igniting  these,  metallic  iridium  is  obtained. 

Properties. — Osmium  is  a  grayish,  brittle  metal,  of  spec.  grav.  about  10. 
When  precipitated  from  its  solutions,  it  has  often  a  bluish  color.  It  cannot  be 
fused,  nor  volatilized,  if  air  be  excluded. 

Osmium,  in  a  finely  divided  state,  absorbs  oxygen  from  the  air,  and  is  con- 
verted into  osmic  acid ;  it  takes  fire  in  oxygen,  even  at  212°  F.  (100°  C.). 

When  heated  on  platinum  foil  in  the  flame  of  a  spirit-lamp,  it  is  converted 
into  osmic  acid,  which  is  volatile,  and  has  a  characteristic  odor,  whereby  we  are 
enabled  to  recognize  small  quantities  of  osmium. 

Osmium  dissolves  in  nitric  acid,  being  converted  into  osmic  acid. 

The  alkaline  hydrates  and  nitrates,  attack  osmium,  osmiates  being  produced. 

Five  compounds  of  osmium  with  oxygen  are  known,  viz:  OsO,  Os20~,  Os02, 
Os03,0s04. 

Oxide  of  Osmium  (OsO),  is  obtained  as  a  dark  green  precipitate  when  a  solution 
of  the  double  chloride  of  osmium  and  potassium  is  decomposed  by  potassa. 

It  is  easily  reduced  by  hydrogen,  and  dissolves  in  acids,  forming  green  solutions. 

Sesquioxide  of  Osmium  (Os203),  is  only  known  in  combination  with  ammonia, 
and  may  be  obtained  by  gently  heating  osmic  acid  with  that  reagent;  the  com- 
pound has  a  dark  brown  color,  and,  when  boiled  with  solution  of  potassa,  and 
subsequently  washed,  is  very  explosive.  It  dissolves  in  acids,  yielding  yellow 
compounds  which  do  not  crystallize. 

Binoxide  of  Osmium  (Os02). — In  order  to  obtain  this  oxide,  a  current  of 
chlorine  is  passed  over  a  mixture  of  osmium  with  chloride  of  potassium,  when  a 
compound  of  bichloride  of  osmium  with  chloride  of  potassium  is  obtained,  which 
yields  the  binoxide  when  heated  with  carbonate  of  potassa. 

Binoxide  of  osmium  is  black ;  it  dissolves  in  acids,  when  freshly  prepared, 
forming  salts  which  are  little  known. 

Osmious  Acid  (Os03)  is  only  known  iq  combination  ;  when  an  attempt  is 
made  to  isolate  it,  it  is  decomposed  into  osmic  acid  and  binoxide  of  osmium : — 

20s03=0s04+0s0a. 

Osmite  of  potassa  is  obtained  by  decomposing  a  solution  of  the  osmiate  with 
reducing  agents  (alcohol  or  nitrite  of  potassa).  It  forms  rose-colored  crystals, 
soluble  in  water,  but  insoluble  in  alcohol;  its  aqueous  solution  absorbs  oxygen 
from  the  air,  and  yields  osmiate  of  potassa. 

Osmite  of  soda  is  prepared  in  the  same  manner,  and  is  more  soluble  than  the 
osmite  of  potassa. 

OSMIC  ACID,  Os04. — This  acid  may  be  prepared  by  heating  osmium  with 
nitric  acid,  in  a  retort,  when  the  osmic  acid  condenses  in  the  receiver  in  colorless 
prismatic  crystals,  which  fuse  and  volatilize  below  the  boiling  point  of  water, 
yielding  a  vapor  of  a  very  peculiar,  irritating  odor,  which  is  dangerous  to  the 
operator.  Osmic  acid  should  not  be  handled,  for  it  destroys  the  skin.  It  is 


,1  RUTHENIUM.  417 

very  soluble  in  water,  and  its  solution  evolves  vapor  of  osmic  acid  at  the  ordinary 
temperature.  Its  acid  properties  are  feeble,  it  neither  reddens  litmus  nor  decom- 
poses the  carbonates ;  its  salts  are  unstable. 

OSMIUM  AND  CHLORINE. — When  osmium  is  heated  in  a  current  of  chlorine, 
a  chloride  and  a  bichloride  are  obtained;  the  former,  being  less  volatile,  con- 
denses near  to  the  osmium,  whilst  the  latter  is  carried  to  a  greater  distance. 

The  (proto-)  chloride  has  a  green  color,  and  is  soluble  in  water,  but  the  solu- 
tion speedily  decomposes,  with  precipitation  of  metallic  osmium,  hydrochloric 
and  osmic  acids  being  produced. 

The  bichloride  has  an  orange-yellow  color,  is  crystalline,  very  fusible,  and 
deliquescent. 

The  name  of  osmium  has  been  derived  from  oopy,  odor,  in  consequence  of  the 
powerful  odor  of  osmic  acid. 

REACTIONS  OF  OSMIUM  (Binoxide). —  The  alkalies  and  their  carbonates; 
after  some  time  or  on  boiling,  a  black  precipitate. 

Hydrosulphuric  acid  and  sulphide  of  ammonium  ;  brownish-yellow  precipitate. 

Subnitrate  of  mercury  ;  yellowish-white  precipitate. 

Chloride  of  tin  ;  brownish  precipitate. 

All  compounds  of  osmium,  when  boiled  with  excess  of  nitric  acid}  evolve  the 
peculiar  odor  of  osmic  acid. 


RUTHENIUM. 

Sym.  Ru.     Eq.  52.2.     Sp.  Gr.  8.6. 

§  281.  Ruthenium  exists  in  native  platinum,  alloyed  with  osmium  and  iridium. 

Preparation. — In  order  to  extract  it,  the  alloy  is  powdered,  mixed  with  chlo- 
ride of  sodium,  and  heated  to  redness  in  a  current  of  moist  chlorine;  the  mass 
is  extracted  with  water,  and  a  few  drops  of  ammonia  added  to  the  solution,  which 
is  then  gently  heated  ;  a  red-brown  precipitate  is  thus  obtained,  which  is  a  mix- 
ture of  the  oxides  of  ruthenium  and  osmium.  This  precipitate  is  boiled  with 
concentrated  nitric  acid,  to  dryness,  when  all  the  osmium  is  volatilized  in  the 
form  of  osmic  acid ;  the  residue  is  fused  in  a  silver  crucible  with  a  mixture  of 
potassa  and  nitre,  and  the  fused  mass  digested  in  a  closed  flask  with  cold  water 
free  from  air ;  after  several  hours,  the  supernatant  liquid  is  decanted,  and  neu- 
tralized with  nitric  acid,  when  a  black  precipitate  of  sesquioxide  of  ruthenium 
is  obtained ;  this  precipitate  may  be  washed  and  heated  in  a  current  of  hydrogen, 
to  obtain  the  metal. 

Properties. — Ruthenium  much  resembles  iridium ;  it  is  brittle,  infusible,  and 
scarcely  affected  by  aqua  re<jia.  Its  spec.  grav.  is  said  to  be  only  8.6.  Ruthe- 
nium is  oxidized  when  heated  to  redness  in  air;  it  forms  four  oxides. 

The  Oxide  (RuO)  obtained  by  heating  the  chloride  with  carbonate  of  soda  in 
a  current  of  carbonic  acid,  and  washing  the  residue  with  water,  is  a  dark  gray 
powder  with  metallic  lustre;  it  is  insoluble  in  acids,  and  is  reduced  by  hydrogen 
at  the  ordinary  temperature. 

The  Sesquioxide  (Rua03)  is  of  a  dark  brown  color ;  it  is  insoluble  in  water 
and  alkalies,  but  dissolves  in  acids,  giving  yellow  solutions.  These  produce, 
with  sulphuretted  hydrogen,  a  brown  precipitate  of  sesquisulphide  of  ruthenium, 
the  supernatant  liquid  having  a  blue  color. 

Binoxule  of  Ruthenium  (Ru03)  is  obtained  by  boiling  the  sesquisulphide 
with  nitric  acid,  and  decomposing  the  sulphate  of  binoxide  thus  obtained  with 
27 


418  ANALYSIS   OF  PLATINUM-ORES. 

an  alkali.  By  calcining  the  precipitated  hydrate,  the  binoxide  is  obtained  as 
a  greenish-blue  powder  of  metallic  appearance. 

Ruthenic  Acid  (Ru03)  is  only  known  in  combination  with  bases ;  rutheniate 
of  potassa  is  obtained  when  either  of  the  oxides  of  ruthenium  is  heated  with 
nitrate  of  potassa;  it  is  soluble  in  water,  yielding  a  yellow  solution,  from  which 
the  acid  may  be  momentarily  isolated  by  adding  a  stronger  acid,  but  is  soon 
decomposed  into  binoxide  of  ruthenium  and  oxygen. 

Chloride  of  Ruthenium,  RuCl,  obtained  by  heating  the  metal  in  a  current  of 
chlorine,  is  black,  crystalline,  insoluble  in  water  and  acids. 

Sesquichloride  of  Ruthenium,  Ru3Cl3,  is  formed  by  dissolving  the  hydrated 
sesquioxide  in  hydrochloric  acid,  and  evaporating  to  dryness ;  it  has  a  bluish- 
green  color,  and  is  soluble  in  water;  the  aqueous  solution  yields,  with  the  chlo- 
rides of  potassium  and  ammonium,  dark  brown  crystalline  precipitates,  which 
are  double  chlorides. 

The  bichloride,  RuCla,  is  only  known  in  combination  with  chloride  of  potas- 
sium. 

REACTION  OF  RUTHENIUM  (Sesquioxide). — The  alkalies  and  their  car- 
bonates; brown  precipitates,  soluble  in  excess. 

Hydrosulphuric  acid  and  sulphide  of  ammonium  ;  dark  brown  precipitate. 

Chlorides  of  potassium  and  ammonium;  dark  brown  crystalline  precipitates. 

Cyanide  of  mercury  ;  blue  precipitate,  and  blue  solution. 

Nitrate  of  silver ;  black  precipitate,  which  becomes  lighter  on  standing,  the 
supernatant  liquor  acquiring  a  rose  color. 


We  have  now  concluded  the  description  of  the  group  of  metals  found  in  the 
ores  of  platinum,  viz.  platinum,  palladium,  rhodium,  iridium,  osmium,  and 
ruthenium,  and  it  cannot  fail  to  have  been  observed  that  a  remarkable  similarity 
exists  between  these  metals  in  their  infusibility,  and  in  the  disposition  of  their 
chlorides  to  form  double-salts  with  the  chlorides  of  the  alkali-metals. 

Moreover,  a  striking  coincidence  is  observed  in  their  equivalents,  by  which 
we  are  enabled  to  subdivide  them  into  two  classes,  the  first  comprising 

Platinum Eq.  98.7 

Iridium       ....     ;;  V "     99.0 

and  Osmium "     99.6 

Whilst  the  second  includes 

Rhodium Eq.  52.2 

Palladium "      53.3 

and  Ruthenium "      52.2 

The  differences,  it  will  be  perceived,  are  in  all  these  cases  so  slight,  that  pro- 
bably, were  errors  of  analysis  left  out  of  the  question,  they  would  actually  dis- 
appear.1 

>;   #<!:.'•.:•:    '•»:.'  ••:«i(.:;i*;;  t  v|  - '  V.    :  ']'\- 

ANALYSIS  OF  THE  ORES  OF  PLATINUM. 

§  282.  The  complete  analysis  of  the  ores  of  platinum  is  an  operation  of  such 
a  complicated  character,  that  it  would  be  impossible  to  describe  it  here  with  all 
the  details  necessary  for  its  successful  execution.  We  shall  therefore  content 
ourselves  with  giving  a  general  outline  of  the  method  adopted,  which  although 
of  little  practical  utility,  possesses  great  interest  in  the  eyes  of  the  scientific 

1  This  remarkable  circumstance  would  suggest  a  connection  between  these  metals 
similar  to  that  pointed  out  at  p.  152,  between  other  analogous  elements. 


ANALYSIS   OF   PLATINUM-ORES.  419 

chemist,  as  one  of  the  best  examples  of  elaborate  analysis  with   which  we  are 
acquainted. 

The  ores  of  platinum  generally  contain,  besides  that  metal, 


Iron, 

Iridium, 

Copper, 


Rhodium, 

Palladium, 

Osmium. 


It  is  our  intention  merely  to  point  out  the  methods  of  separating  and  esti- 
mating the  rarer  metals  in  this  list. 

About  30  or  40  grains  of  the  ore  are  dissolved  in  aqua  rpgia,  in  a  small 
retort,  to  which  a  carefully-cooled  receiver  is  attached.  The  distillation  is  con- 
tinued until  the  liquid  becomes  syrupy,  and  solidifies  on  cooling.  The  saline 
mass  is  dissolved  in  the  smallest  possible  quantity  of  water,  and  the  solution 
carefully  decanted  into  another  vessel.  The  distilled  acid  is  poured  back  on  to 
the  undissolved  residue,  and  the  distillation  carried  on  to  the  same  point  as 
before. 

The  distillate,  which  contains  the  osmium,  is  diluted  with  water,  and  nearly 
neutralized  with  ammonia.  It  is  poured  into  a  flask,  diluted  so  as  nearly  to  fill 
it,  and  thoroughly  saturated  with  sulphuretted  hydrogen;  after  which  the  flask 
is  closed  with  a  cork,  and  set  aside  for  a  day  or  two,  till  the  precipitate  has  com- 
pletely separated,  leaving  the  solution  clear.  The  clear  liquid  is  drawn  off  with 
a  siphon,  the  sulphide  of  osmium  collected  upon  a  weighed  filter,  washed,  dried, 
and  weighed. 

The  solution  in  the  retort,  and  that  previously  poured  out,  are  mixed  together, 
and  filtered  off  from  the  residue,  which  contains  a  little  osmide  of  iridium,  sand, 
&c.,  which  should  be  weighed. 

The  filtered  solution  is  mixed  with  twice  its  volume  of  alcohol  of  sp.gr.  .0.833, 
and  a  strong  solution  of  chloride  of  potassium  added,  as  long  as  it  produces  any 
precipitate,  which  consists  of  the  potassio-chlorides  of  platinum  and  iridium, 
together  with  small  quantities  of  the  corresponding  compounds  of  rhodium  and 
palladium.  The  precipitate  is  collected  upon  a  filter,  and  washed  with  alcohol 
of  60  per  cent.,  mixed  with  a  small  quantity  of  a  strong  solution  of  chloride 
of  potassium,  until  the  washings  are  no  longer  precipitated  by  sulphuretted  hy- 
drogen. 

The  precipitate  is  then  dried,  mixed  with  its  own  weight  of  carbonate  of  soda, 
and  heated  in  a  porcelain  crucible  till  the  mixture  has  become  black  throughout, 
when  the  platinum  has  been  reduced  to  the  metallic  state. 

The  mass  is  washed  with  water,  and  when  the  greater  part  of  the  saline 
matter  had  been  thus  removed,  the  residue  is  treated  with  dilute  hydrochloric 
acid,  to  dissolve  the  remainder  of  the  alkali,  collected  on  a  filter,  washed,  dried, 
ignited,  and  weighed.  Its  weight  represents  that  of  the  metallic  platinum, 
together  with  the  sesquioxides  of  iridium  and  rhodium.  This  residue  is  now 
fused  with  five  or  six  parts  of  bisulphate  of  potassa,  in  a  platinum  crucible. 
The  mass  is  treated  with  water,  the  residue  (platinum  and  sesquioxide  of  iridium) 
ignited  and  weighed. 

The  solution,  containing  the  rhodium,  is  mixed  with  an  excess  of  carbonate  of 
soda,  evaporated  to  dryness,  and  the  residue  ignited  in  a  platinum  crucible. 

The  ignited  mass  is  treated  with  water,  when  sesquioxide  of  rhodium  remains 
undissolved  \  it  is  collected  on  a  filter,  washed,  ignited  with  the  filter,  and  re- 
duced by  hydrogen. 

The  mixture  of  platinum  and  sesquioxide  of  iridium  is  digested  with  very 
dilute  aqua  regia,  to  remove  the  platinum.  The  mixture  is  allowed  to  subside, 
the  clear  liquid  decanted,  strong  aqua  reyia,  mixed  with  some  chloride  of  sodium, 
poured  over  the  residue,  and  the  whole  evaporated  to  dry  ness  (the  chloride  of 
sodium  is  added  to  convert  the  bichloride  of  platinum  into  a  double  chloride, 


420  TIN. 

and  thus  to  prevent  the  formation  of  any  (proto-)  chloride).  The  mass  ia 
washed,  in  a  filter,  with  a  dilute  solution  of  chloride  of  sodium,  afterwards  with 
dilute  chloride  of  ammonium,  dried,  and  ignited.  The  iridium  is  reduced  by 
hydrogen,  and  weighed.  The  small  quantity  of  iridium  contained  in  the  solu- 
tion is  recovered  by  adding  an  excess  of  carbonate  of  soda,  evaporating  and  ig- 
niting. The  residue  is  washed  with  water,  the  platinum  removed  by  aqua  regia, 
the  residual  sesquioxide  of  iridium  washed,  dried,  reduced  by  hydrogen,  and 
weighed ;  its  weight  is  then  added  to  that  of  the  iridium  previously  obtained. 

The  amount  of  the  platinum  is  obtained  by  difference. 

The  alcoholic  liquid  filtered  from  the  double  chlorides  of  platinum,  iridium,  and 
rhodium,  is  poured  into  a  flask,  perfectly  saturated  with  sulphuretted  hydrogen, 
the  flask  closed,  and  allowed  to  stand  for  twelve  hours  in  a  warm  place.  The 
solution  is  then  filtered,  and  the  alcohol  evaporated,  any  additional  precipitate 
being  added  to  the  former  one. 

The  precipitate  contains  chiefly  the  sulphides  of  palladium,  iridium,  and  rho- 
dium ;  a  little  iridium  and  rhodium  also  remaining  in  the  filtrate. 

The  sulphides  are  roasted  in  a  platinum  crucible  as  long  as  any  sulphurous 
acid  is  evolved ;  the  residue  is  treated  with  concentrated  hydrochloric  acid,  which 
dissolves  a  basic  sulphate  of  binoxide  of  palladium  (together  with  a  basic  sul- 
phate of  copper),  leaving  the  sesquioxide  of  rhodium  and  iridium,  together  with 
a  little  platinum. 

The  hydrochloric  solution  is  mixed  with  chloride  of  potassium  and  a  little  nitric 
acid,  and  evaporated  to  dryness.  The  residue  is  dissolved  in  boiling  water,  and 
the  palladium  precipitated  as  cyanide,  by  solution  of  cyanide  of  mercury;  the 
cyanide  of  palladium,  when  ignited,  leaves  the  metal. 

The  residue  left  by  hydrochloric  acid  is  fused  with  bisulphate  of  potassa,  the 
mass  washed  with  water,  treated  with  aqua  regia  to  remove  a  little  platinum, 
and  the  oxide  of  iridium  which  is  left  may  be  reduced  and  weighed. 

The  rhodium  in  the  solution  of  bisulphate  of  potassa  may  be  determined  ac- 
cording to  the  directions  given  above. 

The  original  filtrate  from  the  precipitate  produced  by  sulphuretted  hydrogen 
is  heated  with  nitric  acid  to  peroxidize  the  iron,  which  is  then  precipitated  by 
ammonia,  washed,  dried,  ignited,  and  weighed.  Since  it  contains  a  little  iridium 
and  rhodium,  it  must  be  reduced  by  hydrogen,  and  dissolved  in  ydrochloric 
acid,  when  those  two  metals  are  left ;  they  are  converted  into  sesqi  oxides  by 
ignition  in  the  open  air,  and  weighed. 

The  filtrate  from  the  sesquioxide  of  iron,  which  still  contains  iridium  and 
rhodium,  is  mixed  with  excess  of  carbonate  of  soda,  evaporated  to  dryness,  and 
the  residue  heated  to  dull  redness;  it  is  afterwards  treated  with  water,  which 
leaves  the  sesquioxides  of  iridium  and  rhodium  undissolved.  These  may  be 
mixed  with  the  sesquioxides  obtained  above,,  and  separated,  as  usual,  by  fusion 
with  bisulphate  of  potassa. 


TIN. 

Sym.  Sn.     Eq.  58.     Sp.  Gr.  7.285. 

§  283.  This  metal  and  its  compounds  deserve  a  considerable  share  of  our 
attention,  since  they  are  applied  to  a  great  many  useful  purposes.  Tin  is  not 
met  with  in  commerce  in  a  state  of  purity;  commercial  tin  generally  contains 
traces  of  lead,  iron,  copper,  arsenic,  and,  sometimes,  antimony,  zinc,  bismuth, 
molybdenum,  tungsten,  and  manganese.  In  order  to  obtain  perfectly  pure  tin, 


TIN.  421 

the  ordinary  metal  is  granulated,  and  dissolved  in  hydrochloric  acid,  and  the 
solution  concentrated  by  evaporation.  It  is  allowed  to  cool  in  a  beaker,  and 
carefully  covered  with  a  layer  of  water ;  a  plate  of  tin  is  then  introduced,  so  as 
to  traverse  the  two  layers  of  liquid,  when  a  feeble  galvanic  current  will  be  ex- 
cited, and  the  pure  tin  will  be  deposited  in  fine  crystals. 

Properties. — Tin  is  a  white  metal,  with  a  very  faint  tinge  of  yellow.  It  is 
one  of  the  softest  and  least  elastic  metals.  The  malleability  of  tin  is  very  con- 
siderable, but,  with  the  exception  of  lead,  it  is  the  least  tenacious  of  common 
metals,  for  a  wire  of  one-tenth  of  an  inch  in  diameter  will  support  only  forty-seven 
pounds.  Tin  has  a  great  tendency  to  crystallize,  and  the  ordinary  forms  of  this 
metal  have  a  remarkably  crystalline  texture,  as  may  be  shown  by  rubbing  the 
surface  with  warm  diluted  nitro-hydrochloric  acid,  when  it  assumes  a  peculiar 
diversified  appearance,  which  is  termed  the  moire  metallique,  and  is  due  to  the 
unequal  reflection  of  light  by  the  facets  of  the  crystals.  When  a  bar  of  tin  is 
bent,  a  peculiar  crackling  sound  is  heard,  caused  by  the  friction  of  the  crystals 
upon  each  other. 

The  fusing  point  of  tin  is  442°.4  F.  (228°  C.).  It  is  very  slightly  volatile,  even 
at  the  highest  temperatures.  When  fused  tin  is  allowed  to  cool  gradually,  it 
crystallizes  in  octohedral  prisms.  If,  when  in  the  fused  state,  it  be  poured  into 
a  warm  iron  mortar,  and  stirred  continually  till  it  cools,  it  may  be  reduced  to 
powder. 

Tin  is  not  altered  by  exposure  to  air  at  the  ordinary  temperature ;  when  fused 
in  air,  it  becomes  covered  with  a  gray  film,  containing  both  oxide  and  binoxide 
of  tin,  and,  at  a  white  heat,  it  burns  in  air,  being  entirely  converted  into  the 
binoxide.  It  is  also  capable  of  decomposing  steam  at  a  red  heat,  binoxide  of 
tin  being  produced,  and  hydrogen  evolved. 

Very  strong  nitric  acid  does  not  act  upon  tin,  but  when  a  little  water  is  added, 
the  metal  is  very  rapidly  oxidized  (with  evolution  of  binoxide  of  nitrogen),  and 
converted  into  metastannic  acid,  Sn5010,  which  is  insoluble  in  water  and  in  nitric 
acid,  so  that  no  tin  is  found  in  solution. 

When  tin  is  treated  with  moderately  strong  nitric  acid,  it  is  oxidized  partly  at 
the  expense  of  the  water,  the  hydrogen  of  which,  in  the  nascent  state,  acting 
upon  the  excess  of  nitric  acid,  or  upon  one  of  the  inferior  oxides  of  nitrogen, 
gives  rise  to  the  production  of  ammonia,  and  hence  nitrate  of  ammonia  is  always 
found  in  the  nitric  solution  of  alloys  containing  tin. 

Tin  dissolves  slowly  in  cold  or  dilute  hydrochloric  acid,  but  much  more  rapidly 
in  the  hot  concentrated  acid,  hydrogen  being  evolved,  and  (proto-)  chloride  of 
tin  formed.  It  has  been  found  that  hydrochloric  acid  holding  a  quantity  of  chlo- 
ride of  tin  in  solution,  attacks  the  metal  much  less  readily  than  the  pure  acid, 
whence  arises  the  difficulty  which  is  experienced  in  dissolving  a  quantity  of  tin 
entirely  in  one  and  the  same  portion  of  hydrochloric  acid. 

Dilute  sulphuric  acid  dissolves  tin  slowly  with  the  aid  of  heat,  hydrogen 
being  evolved;  but  the  hot  concentrated  acid  rapidly  converts  this  metal  into 
sulphate  of  the  (prot-)  oxide,  with  evolution  of  sulphurous  acid. 

The  hydrates  of  potassa  and  soda  act  upon  tin,  at  high  temperatures,  hydrogen 
being  evolved,  and  a  soluble  compound  of  the  alkali  with  metastannic  acid  pro- 
duced. 

Fused  nitre  is  also  capable  of  oxidizing  tin.  This  metal  combines  directly, 
and  often  very  energetically,  with  chlorine,  sulphur,  phosphorus,  &c.  It  also 
forms  alloys  with  many  of  the  metals. 


422  TIN   AND   OXYGEN, 


TIN    AND    OXYGEN. 

(Prot-)  oxide  of  Tin SnO 

Binoxide  (stannic  acid) Sn03 

Metastannic  acid Sn5010. 

Various  intermediate  oxides  of  tin  exist. 

OXIDE  OR  PROTOXIDE  OF  TIN,  SnO. 

§  284.  This  oxide  presents  itself  in  various  forms,  according  to  the  manner  in 
which  it  is  obtained. 

Preparation. — I.  When  a  solution  of  (proto-)  chloride  of  tin  is  precipitated 
by  carbonate  of  ammonia,  and  afterwards  boiled,  the  oxide  is  separated  in  olive- 
colored  crystalline  plates. 

II.  If  an  excess  of  potassa  be  added  to  chloride  of  tin,  the  precipitate  which 
forms  at  first  is  redissolved,  and  if  the  solution  be  evaporated  in  vacuo,  black 
crystals  of  the  oxide  are  deposited.    When  this  modification  is  heated,  it  exhibits 
a  kind  of  decrepitation,  with  apparent  increase  of  volume,  and  is  converted  into 
the  olive-colored  plates. 

III.  By  decomposing  chloride  of  tin  with  excess  of  ammonia,  boiling  the  pre- 
cipitate for  some  minutes  with  the  supernatant  liquid,  and  afterwards  drying  it 
without  washing  away  the  chloride  of  ammonium,  a  bright  red  form  of  the  oxide 
is  obtained,  which  may  be  converted  into  the  olive-colored  variety  by  merely 
rubbing  in  a  mortar. 

Properties. — When  heated  in  air,  oxide  of  tin  burns  like  tinder,  and  is  con- 
verted into  the  binoxide.  It  is  insoluble  in  water,  and  in  alkaline  solutions,  but 
dissolves  readily  in  acids,  forming  salts. 

The  hydrate  (SnO. HO)  is  precipitated  when  chloride  of  tin  is  decomposed  by 
an  alkali,  or  its  carbonate.1  It  forms  a  white  precipitate,  which  absorbs  oxygen 
from  the  air,  and  dissolves  readily  in  acids  and  alkalies. 

When  a  solution  of  this  hydrate  in  an  excess  of  potassa  is  rapidly  boiled,  the 
oxide  is  decomposed  into  metallic  tin,  which  separates,  and  stannic  acid,  which 
combines  with  the  alkali : — 

2SnO+KO=KO.SnOa+Sn. 

The  salts  of  oxide  of  tin  are  not  very  well  known. 

The  sulphate  (SnO.S03)  may  be  prepared  by  dissolvingthe  recently-precipitated 
hydrate  in  hot  dilute  sulphuric  acid,  when  the  new  salt  is  deposited,  on  cooling, 
in  crystalline  plates,  which  are  easily  soluble  in  cold  water,  forming  an  acid  solu- 
tion. When  their  solution  is  heated,  a  basic  sulphate  is  deposited.  The  double- 
salts  which  this  sulphate  forms  with  alkaline  sulphates  are  crystallizable,  and 
more  stable  than  the  sulphate  itself. 

When  the  hydrated  oxide  is  dissolved  in  dilute  nitric  acid,  nitrate  of  oxide  of 
tin  is  formed,  but  on  evaporation,  this  salt  is  decomposed,  binoxide  of  tin  being 
deposited.  When  the  metal  is  treated  with  nitric  acid  of  spec.  grav.  1.114,  a 
solution  of  a  double  nitrate  of  oxide  of  tin  and  oxide  of  ammonium  is  obtained, 
which  deposits  binoxide  of  tin  when  boiled. 

1  According  to  Schaffner,  the  precipitate  produced  by  ammonia  is  a  basic  salt,  and  the 
true  formula  of  the  hydrate  is  2SnO.HO. 


METASTANNIC  ACID.  423 

. 

BINOXIDE  OP  TIN,  STANNIC  ACID. 
Sn03.     Eq.  74. 

§  285.  This  compound  (which  occurs  in  nature  as  tin-stone]  may  be  prepared 
by  decomposing  the  bichloride  of  tin  with  water,1  or  by  adding  an  acid  to  a 
soluble  stannate. 

It  is  thus  obtained  as  a  hydrate,  forming  a  white  gelatinous  precipitate,  which 
is  soluble  in  an  excess  of  acids  and  alkalies  ;  when  dried  in  vacuo,  its  composi- 
tion is  represented  by  Sn03.HO;  when  strongly  heated,  it  is  converted  into  a 
yellow  hard  mass,  said  to  be  metastannic  acid,  Sn5010. 

Binoxide  of  tin  is  sometimes  used  for  polishing,  under  the  name  of  putty- 
powder. 

The  binoxide  of  tin  appears  to  possess  a  decidedly  acid  character,  for  no 
definite  compound  of  this  substance  with  an  acid  has  hitherto  been  obtained, 
whilst,  with  bases,  it  forms  a  series  of  salts  termed  stannates. 

STANNATE  OF  POTASSA  (KG.  SnOa,4Aq)  is  obtained  by  dissolving  stannic  acid 
in  potassa,  or  by  fusing  metastannic  acid  with  this  alkali  in  a  silver  crucible ;  by 
evaporating  the  aqueous  solution  in  vacuo,  the  stannate  may  be  obtained  in  white 
prismatic  crystals,  which  are  very  soluble  in  water,  and  insoluble  in  alcohol. 
The  aqueous  solution  is  strongly  alkaline,  and  decomposes  after  a  time  into  pot- 
assa and  metastannate  of  potassa. 

Almost  all  soluble  salts,  even  those  of  the  alkalies,  cause  a  precipitate  in  solu- 
tion of  stannate  of  potassa. 

STANNATE  OF  SODA  (NaO.Sn03,4Aq)  much  resembles  the  potassa  salt;  it  is 
more  soluble  in  cold  than  in  hot  water,  so  that  its  aqueous  solution  becomes 
turbid  when  boiled. 

The  alkaline  stannates  are  used  as  mordants  in  dyeing  and  calico-printing. 
Stannate  of  soda  is  prepared  on  a  large  scale  by  boiling  sheets  or  scraps  of  tin, 
and  litharge  or  sulphate  of  lead,  with  solution  of  caustic  soda.  The  lead  com- 
pounds yield  their  oxygen  to  the  tin,  and  greatly  facilitate  the  oxidation;  the 
lead-powder  obtained  as  secondary  product  may  be  reoxidized  by  exposure  to  air, 
and  again  employed  for  the  oxidation  of  fresh  quantities  of  tin. 

The  Stannate  of  Oxide  of  Tin  (SnO.Sn03),  or,  as  it  is  sometimes  termed,  ses- 
quioxide of  tin,  is  obtained  by  the  action  of  hydrated  sesquioxide  of  iron  upon 
chloride  of  tin  : — 

Fe203-f2SnCl=Sn203-f2FeCl. 

It  forms  a  yellowish  precipitate,  which  becomes  black  when  heated  in  close  ves- 
sels ;  it  is  soluble  in  ammonia. 

Binoxide  of  tin  is  used  in  the  manufacture  of  opaque  white  glass ;  it  is  also 
employed,  in  conjunction  with  small  quantities  of  sesquioxide  of  chromium,  for 
producing  certain  red  and  lilac  colors,  which  are  employed  for  coloring  earthen- 
ware, and  for  paper-staining. 

METASTANNIC  ACID,  Sn5010. 

This  acid  was  for  a  long  time  regarded  as  a  modification  of  stannic  acid. 

It  is  obtained  as  a  white  powder  by  the  action  of  nitric  acid  upon  tin. 

Metastannic  acid  thus  prepared  is  crystalline ;  when  dried  in  air,  it  has  the 
composition  Sn5010,10HO,  but  loses  5  eqs.  water  at  the  boiling-point;  all  the 
water  may  be  expelled  at  a  higher  temperature.  It  is  completely  insoluble  in 
water,  in  nitric  acid,  and  dilute  sulphuric  acid,  but  dissolves  to  some  extent  in 
concentrated  sulphuric  and  hydrochloric  acids;  tartaric  acid  and  bitartrate  of 
potassa  are  also  capable  of  dissolving  metastannic  acid  to  a  slight  extent. 

1  Daubre'e  has  obtained  very  hard  lustrous  crystals  of  the  binoxide  by  passing  the 
vapor  of  bichloride  of  tin,  mixed  with  steam,  through  a  redhot  porcelain  tube. 


424 


CHLORIDES    OF   TIN. 


Metastannic  acid  dissolves  in  potassa,  forming  a  metastannate  j  "when  freshly 
precipitated  from  its  salts  by  acids,  it  is  soluble  in  ammonia,  but  not  after  boil- 
ing in  the  liquid. 

When  fused  with  alkalies,  metastannic  acid  is  converted  into  a  stannate. 

Metastannate  of  Potassa  (KO.Sii50JO,4Aq)  may  be  obtained  in  the  pure  state 
by  dissolving  some  hydrate  of  potassa  in  the  solution  of  metastannic  acid  in 
potassa,  when  the  metastannate,  being  insoluble  in  an  excess  of  potassa,  is  pre- 
cipitated. 

This  salt  cannot  be  crystallized ;  it  is  very  soluble  in  water,  and  has  a  power- 
ful alkaline  reaction.  It  cannot  be  rendered  anhydrous  without  undergoing 
decomposition;  when  metastannate  of  potassa  is  heated  to  redness,  and  the  mass 
extracted  with  water,  the  potassa  alone  is  dissolved,  and  metastannic  acid  remains. 

The  Metastannate  of  Soda  is  quite  similar. 

Metastannate  of  Oxide  of  Tin  (SnO.Sn5010,4Aq)  is  obtained  as  a  yellow  in- 
soluble substance  by  the  action  of  chloride  of  tin  upon  metastannic  acid  : — 
Sn5Oio_|_SnCl4-HO=SnO,Sn5010+HCl. 

CHLORIDE  OR  FROTOCHLORIDE  OF  TIN,  SnCl. 

§  286.  This  useful  salt  may  be  prepared  in  the  anhydrous  state  by  the  action 
of  hydrochloric  acid  gas  upon  tin  at  a  gentle  heat,  or  by  distilling  powdered  tin 
with  an  equal  weight  of  chloride  of  mercury. 

Thus  obtained,  it  is  a  brilliant  gray  solid,  which  volatilizes  at  a  bright  red 
heat ;  it  takes  fire  in  chlorine,  and  is  converted  into  the  bichloride. 

Hydrated  chloride  of  tin  is  obtained  by  dissolving  the  metal  in  hydrochloric 
acid ;  the  concentrated  acid  should  be  diluted  with  an  equal  bulk  of  water ;  the 
solution  is  decanted  from  the  undissolved  metal,  and  evaporated  to  crystallization. 

It  crystallizes  in  transparent  needles,  having  the  composition  SnCl,2Aq ;  these 
are  somewhat  deliquescent,  and  absorb  oxygen  when  exposed  to  air,  yielding  a 
combination  of  binoxide  and  bichloride  of  tin;  when  heated,  the  crystals  lose 
their  water,  and  a  partial  decomposition  takes  place,  some  hydrochloric  acid 
being  disengaged,  but,  at  a  higher  temperature,  great  part  of  the  salt  may  be 
distilled  unchanged. 

The  chloride  of  tin  is  very  soluble  in  water;  a  large  quantity  of  water,  how- 
ever, decomposes  it,  an  oxy-chloride  of  tin  (SnCl,SnO)  being  deposited. 

Chloride  of  tin  is  a  very  powerful  deoxidizing  agent,  it  reduces  the  metals 
from  the  salts  of  silver,  mercury,  and  gold,  and  brings  oxide  of  copper,  sesqui- 
oxide  of  iron,  and  many  other  oxides  to  a  lower  state  of  oxidation ;  hence  this 
salt  is  often  employed  as  a  reagent;  it  is  also  used  by  dyers,  sometimes  as  a 
mordant,  and  sometimes  to  alter  the  reducible  coloring  matters,  such  as  sesqui- 
oxide  of  iron  and  binoxide  of  manganese.1  Chloride  of  tin  is  also  used  as  an 
antichlore  {see  p.  259). 

The  alkaline  chlorides  form  crystalline  double-salts  with  chloride  of  tin.  It 
absorbs  ammoniacal  gas. 

BICHLORIDE  OR  PERCHLORIDE  OF  TIN. 
{Fuming  Liquor  of  Libavius)  SnCl3. 

Preparation. — This  compound  may  be  prepared  by  the  direct  combination  of 
its  constituents.  A  quantity  of  tinfoil  is  rolled  up,  and  introduced  into  a  tube 

1  For  the  expeditious  determination  of  the  value  of  any  specimen  of  chloride  of  tin,  Penny 
makes  use  of  a  solution  of  bichromate  of  potassa  of  known  strength,  which  is  added  to  the 
liquid  containing  free  hydrochloric  acid,  until  a  portion  tested  with  acetate  of  lead  shows 
that  an  excess  of  chromic  acid  is  present.  The  following  equation  then  gives  the  data  for 
calculating  the  amount  of  chloride  of  tin  present : — 

3SnCl-fK0.2Cr03-f7HCl=3SnC]a-fKCl-fCr2Cl3-f7HO. 


SULPHIDES   OF   TIN.  425 

of  hard  glass,  placed  at  a  very  slight  inclination,  and  connected,  at  the  lower 
end,  with  an  appropriate  receiver,  and  at  the  other  with  an  apparatus  evolving 
dry  chlorine ;  the  tube  should  be  constricted  somewhat  at  the  lower  end,  so  as 
to  form  a  shoulder  upon  which  the  tin  may  rest;  it  is  only  necessary  to  heat  the 
metal  gently  while  the  chlorine  is  passing,  when  combination  ensues,  attended 
with  combustion,  and  the  bichloride  distils  over.  The  product  may  be  freed  from 
excess  of  chlorine  by  agitation  with  a  little  granulated  tin,  and  rectification. 

A  solution  of  the  bichloride  may  be  obtained  by  dissolving  the  metal  in  nitro- 
hydrochloric  acid,  but  a  better  method  consists  in  boiling  granulated  tin  for  a  few 
hours  with  moderately  strong  hydrochloric  acid,  and  passing  chlorine  through 
the  solution  (containing  the  undissolved  tin)  until  it  no  longer  precipitates  solu- 
tion of  (proto-)  chloride  of  mercury  (corrosive  sublimate) ;  the  excess  of  chlorine 
may  then  be  expelled  by  a  slow  evaporation. 

Properties. — When  pure,  bichloride  of  tin  is  a  colorless  liquid,  which  evolves 
suffocating  white  fumes  in  the  air;  its  spec.  grav.  2.28;  it  boils  at  248°  F.  (120° 
C.),  yielding  a  vapor  of  spec.  grav.  9.2.  It  has  a  powerful  affinity  for  water, 
combining  with  it,  with  a  hissing  sound,  to  form  a  hydrate,  which  is  deposited 
in  crystals  of  the  formula  Sn(Jl2-f  5Aq,  which  lose  three  eqs.  water  when  exposed, 
in  vacuOj  over  sulphuric  acid ;  its  aqueous  solution  is  partly  decomposed  by  eva- 
poration, hydrochloric  acid  being  evolved,  and  stannic  acid  deposited.1 

Bichloride  of  tin  is  capable  of  absorbing  sulphuretted  and  phosphuretted  hy- 
drogen. It  combines  also  with  ammonia,  and  with  various  organic  substances. 

This  salt  forms,  with  many  other  chlorides,  compounds  which  may  be  termed 
chlorostannates,  in  which  the  bichloride  of  tin  plays  the  part  of  an  acid. 

The  chlorostaniHites  of  chloride  of  potassium  and  of  chloride  of  ammonium 
are  anhydrous,  and  crystallize  in  octohedra,  having  the  composition,  respectively, 
KCl.SnCl2,  and  NH4Cl.SnCl3;  the  corresponding  compounds  of  the  chlorides 
of  sodium  and  of  the  metals  of  the  alkaline  earths  crystallize  with  5  eqs.  water. 

Bichloride  of  tin  is  used,  to  a  considerable  extent,  in  dyeing. 

TIN  AND  SULPHUR. 

Sulphide  of  tin SnS 

Bisulphide     " SnS3 

SULPHIDE  OR  PROTOSULPHIDE  or  TIN,  SnSa. 

This  substance  is  obtained  by  heating  granulated  tin  with  sulphur,  reducing 
the  mass  to  powder,  and  fusing  it  with  an  additional  quantity  of  sulphur;  thus 
obtained,  it  is  a  brilliant,  dark,  gray,  crystalline  mass.  It  is  precipitated  in  a 
hydrated  state  when  sulphuretted  hydrogen  is  passed  through  a  solution  of  a 
proto-salt  of  tin;  it  is  then  black. 

Sulphide  of  tin  dissolves  in  concentrated  hydrochloric  acid,  with  disengage- 
ment of  sulphuretted  hydrogen  ;  nitric  acid  converts  it  into  metastannic  acid  ; 
it  is  not  soluble  in  sulphide  of  ammonium,  unless  an  excess  of  sulphur  be  pre- 
sent, which  converts  the  sulphide  into  bisulphide. 

This  sulphide  is  a  pretty  powerful  sulphur-base. 

A  sesquisulphide  of  tin,  Sn3S3  (probably  a  compound  of  sulphide  and  bisul- 

1  Lowenthal  found  that  bichloride  of  tin  was  decomposed  by  the  alkaline  sulphates  with 
precipitation  of  the  binoxide  : — 

SnCl2-f-4(NaO.S03)-f4HO=Sn02.2H04-2NaC14-2(NaO.S03,HO.S03). 
Since  a  solution  of  (proto-)  chloride  of  tin  is  not  affected  by  alkaline  sulphates  if  air 
be  excluded,  it  is  proposed  to  employ  these  salts  for  the  detection  of  bichloride  of  tin  in 
the  chloride.      Lowenthal  also  suggests  that  this  reaction  may  be  turned  to  account  in 
dyeing. 


426  METALLURGY   OF  TIN. 

phide),  is  obtained  when  the  sulphide  is  heated  to  dull  redness  with  an  excess 
of  sulphur. 

BISULPHIDE  OF  TIN,  SnS3. 

This  compound,  when  prepared  in  the  dry  way,  is  known  by  the  name  of 
aurum  mudvum,  or  Mosaic  gold,  which  is  used  for  gilding  wood  and  decorating- 
paper;  it  is  commonly  termed  bronze-powder. 

In  order  to  prepare  it,  an  amalgam  is  made  of  12  parts  of  tin  and  6  parts  of 
mercury;  this  is  mixed  with  7  parts  of  flowers  of  sulphur  and  6  of  sal-ammoniac; 
the  mixture  is  then  heated  (in  a  glass  flask  placed  in  a  sand-bath)  to  dull  red- 
ness, until  no  more  white  fumes  are  disengaged  ;  the  bisulphide  is  left  as  a  yellow 
crystalline  layer  at  the  lower  part  of  the  flask ;  in  this  process,  the  sole  use  of 
the  mercury  appears  to  be  to  effect  the  fine  division  of  the  metallic  tin,  thus 
facilitating  its  combination  with  the  sulphur;  the  bisulphide  of  tin  thus  formed, 
however,  is  amorphous,  and  only  becomes  crystalline  after  a  sublimation, 
which  is  promoted  by  the  volatilization  of  the  chloride  of  ammonium;  this 
latter  also  serves  (by  rendering  a  large  amount  of  heat  latent)  to  prevent  the 
temperature  in  the  flask  from  rising  sufficiently  high  to  convert  the  bisulphide 
into  sulphide. 

The  product  of  this  operation  forms  very  light  golden-yellow  hexagonal  plates, 
which  are  attacked  only  by  nitro-hydrochloric  acid. 

Similar  scales  are  obtained  when  a  mixture  of  sulphuretted  hydrogen  and 
vapor  of  bichloride  of  tin  is  passed  through  a  tube  heated  to  dull  redness. 

The  hydrated  bisulphide  is  thrown  down  as  a  light  yellow  precipitate,  when 
sulphuretted  hydrogen  is  passed  through  solution  of  bichloride  of  tin  ;  if  the 
latter  be  not  perfectly  pure,  but  contain,  as  is  often  the  case,  a  trace  of  antimony, 
the  precipitate  will  have  a  dirty  yellow  color.  This  precipitate  dissolves  with 
difficulty  in  concentrated  hydrochloric  acid,  but,  being  a  powerful  sulphur-acid, 
it  is  readily  soluble  in  the  alkaline  sulphides,  or  even  in  the  pure  alkalies  or 
their  carbonates. 

METALLURGY  OF  TIN. 

§  287.  The  only  ore  of  tin,  properly  so  called,  is  the  binoxide,  or  tin-stone, 
which  occurs  in  a  crystalline  form,  often  associated  with  wolfram,  sulphide  of 
molybdenum,  and  arsenical-pyrites.  It  has  usually  a  brown  or  red-brown  color, 
and  is  very  hard. 

Tin  is  also  found  in  Cornwall,  combined  with  sulphur,  in  tin-pyrites,  which 
contains  also  sulphide  of  copper. 

The  metal  is  always  extracted  from  the  binoxide,  which  occurs  sometimes 
associated  with  other  ores  in  veins  (mine-tin),  and  sometimes  as  an  alluvial 
deposit  in  the  beds  of  rivers  (stream-tin). 

The  ore  is  pounded  in  stamping-mills,  and  submitted  to  a  species  of  rough 
levigation,  which  washes  away  the  earthy  matter  and  all  light  impurities;  it  is 
then  roasted,  to  expel  the  sulphur  and  arsenic,  and  mixed  with  about  one-eighth 
of  its  weight  of  small  coal ;  the  mixture  is  heated  in  a  reverberatory  furnace, 
and  the  fused  metal  run  into  moulds. 

Any  considerable  quantity  of  copper  is  removed  from  the  ore,  previously  to 
smelting,  by  exposure  to  air  and  subsequent  treatment  with  sulphuric  acid. 

If  the  ore  contain  wolfram  (tungstate  of  iron  and  manganese),  it  undergoes, 
previously  to  reduction,  a  purification  which  consists  in  fusing  it  with  carbonate 
of  soda,  in  a  reverberatory  furnace,  when  the  tungsten  is  removed  in  the  form  of 
tungstate  of  soda,  which  is  used  by  calico-printers. 

The  pigs  of  tin  thus  obtained  are  sometimes  subjected  to  a  refining  process 
(termed  liquation),  which  consists  in  gradually  remelting  them  on  a  gently  inclined 
hearth,  and  allowing  the  portion  which  first  fuses  to  flow  into  a  large  basin, 


METALLURGY   OP   TIN.  427 

"where  a  mechanical  separation  of  the  remaining  impurities  is  effected,  either  by 
stirring  the  melted  metal  with  billets  of  green  wood  (when  the  gases  evolved  give 
rise  to  considerable  agitation),  or  by  throwing  portions  of  the  metal  repeatedly 
from  a  ladle  raised  to  a  considerable  height  (timing).  The  impurities  are  care- 
fully skimmed  off  from  time  to  time.  The  metal  remaining  on  the  liquation- 
hearth,  which  is  much  less  pure,  constitutes  the  ordinary  block-tin;  the  purer 
kind  is  generally  heated  to  a  temperature  somewhat  exceeding  212°,  and  allowed 
to  fall  from  a  height,  when,  being  brittle,  it  is  divided  into  small  fragments  which 
are  known  in  commerce  as  grain-tin. 

A  process  for  obtaining  very  pure  metal  from  stream-tin,  consists  in  reducing 
the  ore  with  charcoal  in  a  small-blast  furnace  (see  Iron). 

Tin  is  generally  examined  as  to  its  purity  by  fusing  it  at  a  gentle  heat,  and 
observing  its  surface  at  the  moment  of  solidification ;  the  purest  tin  is  whitest, 
most  brilliant,  and  least  crystalline  in  appearance. 

USES  Of  TIN. — Since  this  metal  is  not  easily  affected  by  most  chemical  agents, 
it  serves  very  advantageously  to  protect  the  surface  of  such  as  are  more  easily 
acted  upon,  such  as  copper  and  iron ;  moreover,  it  is  employed,  in  the  state  of 
foil,  for  preserving  substances  from  the  action  of  air,  and  for  silvering  looking- 
glasses;  this  metal  is  also  an  ingredient  of  many  useful  alloys. 

Tinfoil  is  prepared  by  beating  plates  of  the  best  tin  with  a  hammer  till}  they 
are  reduced  to  a  certain  thickness,  when  they  are  cut  up,  laid  upon  each  other, 
and  again  beaten,  the  process  being  repeated  till  they  have  attained  the  required 
extension. 

Tinned  iron,  or  tin-plate,  as  it  is  commonly  called,  consists  of  a  plate  of  iron 
covered  with  a  layer  of  an  alloy  of  that  metal  with  tin,  and,  externally,  with  a 
layer  of  pure  tin ;  the  process  for  manufacturing  tin-plate  is  as  follows :  The 
iron  plates  are  first  thoroughly  cleansed  with  hydrochloric  and  sulphuric  acids, 
then  well  washed  with  water,  and  scoured  with  sand  to  remove  all  trace  of  rust, 
which  would  prevent  the  tin  from  adhering ;  the  plates  are  then  immersed  in  a 
bath  of  melted  tallow,  which  dries  them  thoroughly,  and  are  removed  from  this 
into  a  bath  of  tin,  the  surface  of  which  is  covered  with  tallow,  to  prevent  oxida- 
tion ;  after  being  heated  for  about  an  hour  and  a  half  in  the  melted  metal,  they 
are  taken  out,  drained,  plunged  into  another  bath  of  melted  tin,  and  brushed  to 
remove  the  excess  of  this  metal,  afterwards  again  dipped  to  erase  the  marks  of 
the  brush,  and,  lastly,  immersed  in  the  melted  tallow  to  remove  the  small 
quantity  of  superfluous  tin. 

This  tin-plate  is  exceedingly  durable,  but  if,  by  accident,  the  iron  should  be 
exposed  in  any  part,  it  rusts  very  rapidly,  from  galvanic  action.1 

In  order  to  give  an  internal  coating  of  tin  to  copper  vessels  for  culinary  pur- 
poses, they  are  first  cleaned  very  carefully,  a  quantity  of  sal-ammoniac  strewed 
over  the  surface,  to  protect  it  from  oxidation,  the  vessel  then  made  sufficiently 
hot  to  melt  tin,  which,  either  in  the  pure  state,  or  alloyed  with  a  certain  amount 
of  lead,  is  then  rubbed  over  them. 

Tin  is  the  chief  ingredient  of  the  alloy  known  as  Britannia  metal,  which  con- 
tains, moreover,  antimony,  copper,  and  a  little  lead,  the  proportions  varying 
according  to  the  judgment  of  the  manufacturer. 

The  better  kinds  of  pewter  are  alloys  of  tin  with  small  quantities  of  copper, 
lead,  and  sometimes  antimony  and  bismuth. 

ASSAY  OF  TIN  ORES. — The  assay  of  ores  of  tin  is  attended  with  considerable 
difficulty,  on  account  of  the  affinity  which  exists  between  the  oxides  of  tin  and 
silica. 

The  powdered  ore  is  first  freed,  as  far  as  possible,  from  silicious  gangue,  by 

1  It  has  been  proposed  to  alloy  the  tin  employed  for  this  purpose  with  T'5  of  nickel, 
which  renders  the  coating  more  durable  and  less  easily  fusible. 


428  ANTIMONY. 

roasting  it,  in  an  earthen  crucible,  with  a  little  powdered  charcoal  (to  assist  it  in 
the  expulsion  of  the  arsenic,  &c.),  and  afterwards  roughly  levigated  in  a  porce- 
lain dish,  to  remove  the  lighter  particles.  The  heavier  portion  may  then  be 
boiled  with  nitro-hydrochloric  acid,  to  remove  the  pyrites,  &c.,  water  added,  the 
residue  collected  on  a  filter,  well  washed  and  dried.  It  is  then  removed  from 
the  filter,  and  roasted  in  a  wide  open  crucible,  to  expel  any  sulphur  which  may 
be  left.  The  ore  thus  prepared  is  mixed  with  30  or  40  per  cent,  of  a  mixture 
of  equal  parts  of  borax  and  carbonate  of  soda,  and  reduced  in  a  crucible  lined 
with  charcoal,  at  the  same  temperature  as  that  used  for  an  iron  assay.  The  but- 
ton is  afterwards  extracted  and  weighed. 

A  far  more  accurate  method  of  analyzing  an  ore  of  tin  is  executed  as  fol- 
lows : — 

The  powdered  ore  is  heated  to  redness,  in  order  to  expel  any  water;  it  is  then 
weighed  in  a  small  porcelain  boat,  and  introduced  into  a  tube  of  porcelain,  or 
hard  glass,  through  which  a  stream  of  dry  hydrogen  is  passed.  Tj^e  tube  is 
heated  to  dull  redness  by  a  gas-burner  or  a  charcoal  fire,  when  the  binoxide  of 
tin  is  easily  reduced.  The  reduced  residue  is  allowed  to  cool  in  the  atmosphere 
of  hydrogen,  and  the  tin  dissolved  in  hydrochloric  acid,  with  the  aid  of  a  few 
drops  of  nitric  acid. 

The  weight  of  the  tin  may  then  be  either  directly  ascertained,  by  determining 
it  in  the  solution,  or  by  calculation  from  the  amount  of  silica  left  undissolved, 
which  is  collected,  for  that  purpose,  on  a  filter,  washed,  dried,  ignited,  and 
weighed.  This  latter  method  is  obviously  applicable  only  when  no  other  metal 
but  tin  is  present  in  the  ore. 


ANTIMONY. 

Sym.  Sb.     Eq.  129.     Sp.  Gr.  6.702. 

§  288.  This  metal  is  found  in  commerce  in  a  very  impure  state;  the  regulus 
of  antimony,  as  it  is  termed,  contains  generally  sulphur,  arsenic,  iron,  and  lead. 
Its  purification  is  attended  with  considerable  difficulty. 

Wohler  recommends  that  1  part  of  crude  antimony  be  fused  with  1J  part  of 
nitre  and  £  part  of  carbonate  of  soda,  for  about  an  hour;  the  fused  mass  powdered, 
and  washed  with  boiling  water,  which  leaves  antimoniate  of  soda  undissolved; 
this  may  be  reduced  by  fusion  with  black  flux ;  since  the  metal  thus  obtained 
contains  a  little  potassium,  it  should  be  reduced  to  powder,  and  washed  with 
water  till  the  washings  are  no  longer  alkaline ;  the  pure  metal  is  then  fused  into 
a  globule. 

Liebig  fuses  16  parts  of  powdered  antimony,  in  a  Hessian  crucible,  with  one 
part  of  native  tersulphide  of  antimony,  and  two  parts  of  carbonate  of  soda;  the 
latter  decomposes  the  tersulphide  of  antimony,  producing  sulphide  of  sodium, 
which  combines  with  the  tersulphide  of  arsenic.  ,  The  globule  of  antimony  is 
afterwards  fused  for  two  hours  with  carbonate  of  soda.1 

A  very  efficient  method  of  removing  the  impurities  from  crude  antimony, 
consists  in  dissolving  the  metal  in  a  mixture  of  equal  volumes  of  concentrated 
hydrochloric  acid  and  water,  to  which  moderately  dilute  nitric  acid  (one  part  of 
concentrated  acid  and  two  parts  of  water)  is  added,  by  small  portions  at  a  time; 
the  solution  of  terchloride  of  antimony  thus  obtained  is  largely  diluted  with  wa- 
ter, the  precipitate  (p.  433)  allowed  to  subside,  washed,  first,  by  decantation, 

1  According  to  Bensch,  this  method  is  successful  only  when  the  metal  contains  iron ; 
if  this  be  not  the  case,  he  recommends  the  addition  of  two  per  cent,  of  sulphide  of  iron 
to  the  original  metal.  . 


ANTIMONY  AND  OXYGEN.  429 

and  afterwards  on  a  filter,  and  boiled  with  concentrated  hydrochloric  acid ;  the 
filtered  solution  is  mixed  with  a  very  slight  excess  of  ammonia,  the  precipitate 
well  washed  and  dried;  this  precipitate  may  serve  either  for  the  preparation  of 
other  compounds  of  antimony  (the  tersulphide,  e.  #.)  in  a  pure  state,  or  may  be 
fused  with  black  flux,  when  it  yields  the  pure  metal. 

Properties. — Antimony  is  a  very  brilliant  metal,  of  rather  a  blackish-gray 
color ;  it  is  exceedingly  brittle,  and  may  be  easily  powdered.  In  texture,  it  is 
lamellar  and  highly  crystalline,  the  primitive  form  of  its  crystals  being  the  octo- 
hedron;  it  is  unaltered  by  exposure  to  air  at  the  ordinary  temperature. 

Antimony  fuses  at  about  800°  F.  (427°  C.)>  and  volatilizes  very  perceptibly 
at  a  somewhat  higher  temperature ;  it  is  not,  however,  sufficiently  volatile  to  be 
distilled  like  zinc.  Fused  antimony  crystallizes  on  cooling. 

Heated  in  contact  with  air,  the  metal  becomes  covered  with  a  film  of  crystal- 
lized teroxide  of  antimony,  mixed  with  antimonic  acid  ;  if,  when  strongly  heated, 
the  fused  globule  be  allowed  to  fall  upon  the  ground,  it  is  divided  into  numerous 
smaller  globules,  which  burn  very  brilliantly,  giving  off  white  fumes. 

At  a  red  heat,  antimony  decomposes  water,  being  converted  into  teroxide. 

This  metal  is  readily  oxidized  by  nitric  acid,  being  converted  into  a  white  com- 
pound of  teroxide  of  antimony  with  antimonic  acid,  Sb03,Sb05(=2Sb04  antimo- 
nious  acid).  A  small  quantity  of  antimony  is  always  found  in  the  nitric  solution; 
a  little  nitrate  of  ammonia  is  also  produced  in  this  reaction  (see  p.  129). 

Hydrochloric  acid  acts  very  slowly  upon  antimony,  but  aqua  recjia  dissolves 
it  with  ease. 

It  does  not  decompose  water  in  presence  of  sulphuric  acid,  but  the  concentrated 
acid  converts  it,  with  the  aid  of  heat,  into  sulphate  of  teroxide  of  antimony,  with 
evolution  of  sulphurous  acid. 

ANTIMONY   AND    OXYGEN. 

Suboxide       ....'. Sb304 

Teroxide Sb03 

Antimonic  acid Sb05* 

Some  chemists  also  admit  the  existence  of  an  oxide  of  the  formula  Sb04  (anti- 
monious  acid),  but  we  prefer  to  consider  this  as  a  compound  of  the  teroxide  with 
antimonic  acid. 

§  289.  SUBOXIDE  OF  ANTIMONY  (Sb304)  constitutes  the  film  which  is  formed 
upon  the  surface  of  antimony  exposed  to  the  action  of  moist  air. 

It  may  be  obtained  by  decomposing  a  concentrated  solution  of  tartar-emetic 
(tartrate  of  antimony  and  potassa)  by  a  powerful  galvanic  battery,  when  the 
nascent  hydrogen  of  the  water  reduces  the  teroxide  of  antimony  to  the  state  of 
suboxide  ;  it  is  black,  and  assumes  a  metallic  lustre  when  rubbed.  When  heated, 
it  is  decomposed  into  metal  and  teroxide. 

Hydrochloric  acid  converts  it  into  terchloride  of  antimony,  with  separation  of 
the  metal  : — 

3Sb304+12HCl=12HO+4SbCl3-fSbs. 

TEROXIDE  OF  ANTIMONY,  Sb03  (Sesquioxide  of  Antimony,  Sb203). 

Eq.  153. 

This  oxide  is  formed  when  antimony  is  heated  in  air.  It  is  also  found  in 
nature  as  white  antimony-ore. 

1  The  equivalent  of  antimony  is  sometimes  estimated  at  64.5,  being  the  half  of  129, 
as  we  have  considered  it.  Upon  that  view,  the  above  oxides  would  be  written  with  twice 
the  number  of  equivalents  of  metal ;  thus  teroxide  of  antimony  becomes  a  sesquioxide, 
Sb203,  and  antimonic  acid  is  Sb206. 


430  OXIDES   OP  ANTIMONY. 

The  anhydrous  teroxide  may  be  prepared  in  quantity  by  fusing  antimony  in  a 
capacious  Hessian  crucible,  over  which  another  crucible  (with  a  hole  in  the  bot- 
tom) is  inverted  ;  the  teroxide  will  condense  in  the  uppermost  crucible  in  needle- 
like  crystals,  which  were  formerly  called  argentine  flowers  of  antimony. 

It  is  of  a  pearly-white  color,  and  is  capable  of  crystallizing  in  two  distinct 
forms,  one  of  which  is  a  regular  octohedron,  and  the  other  belongs  to  the  pris- 
matic system  ;  in  this  respect,  it  resembles  arsenious  acid,  with  which  it  is  iso- 
morphous.  When  heated  to  redness,  teroxide  of  antimony  fuses,  and^  at  a  high 
temperature,  sublimes  in  brilliant  needles. 

If  heated  in  contact  with  air,  it  absorbs  oxygen,  and  is  converted  into  the 
antimoniate  of  teroxide  of  antimony,  Sb03.Sb05. 

It  is  easily  reduced  by  hydrogen  or  charcoal  at  a  high  temperature. 

Hydrated  teroxide  of  antimony  (Sb03.HO)  may  be  obtained  by  precipitating 
a  solution  of  the  terchloride  in  dilute  hydrochloric  acid,  with  carbonate  of  potassa 
or  soda  in  slight  excess,  and  digesting  the  precipitate  for  some  time  with  the 
supernatant  liquid. 

The  hydrate  is  readily  soluble  in  acids  and  alkalies,  whence  it  would  appear 
that  the  teroxide  was  capable  of  playing  the  part  of  a  base,  or  of  an  acid,  indif- 
ferently. However,  on  evaporating  the  alkaline  solution,  anhydrous  teroxide  of 
antimony  is  deposited.  -  When  heated,  the  hydrate  assumes  a  yellow  tint. 

When  teroxide  of  antimony  is  fused  with  alkalies,  in  presence  of  oxygen,  the 
latter  is  absorbed,  and  antimoniates  are  produced. 

The  soluble  neutral  salts  of  teroxide  of  antimony  redden  litmus- paper. 

Basic  nitrate  of  teroxide  of  antimony  (2Sb03,N03)  is.  obtained  in  a  crystal- 
line form  when  teroxide  of  antimony  is  dissolved  in  fuming  nitric  acid ;  it  is 
decomposed  by  water,  the  teroxide  being  left  undissolved. 

SULPHATES  OF  TEROXIDE  OP  ANTIMONY. 

The  salts  of  teroxide  of  antimony  present  an  anomaly  similar  to  that  observed 
in  the  case  of  uranium.  The  neutral  salts  of  the  teroxide  do  not  contain,  as 
would  be  expected,  three  equivalents,  but  only  one  equivalent  of  base,  a  circum- 
stance, which  P41igot  explains  by  assuming  the  existence  of  a  radical,  antimonyle 
Sb02  (or  Sb203)  of  which  the  protoxide  would  be  expressed  by  (SbOa)0=Sb03 
(or  by  (SbaOa)0=Sba03). 

Four  sulphates  of  teroxide  of  antimony  have  been  examined  by  this  chemist. 

The  sulphate  of  the  formula  Sb03.4S03  is  obtained  in  crystalline  needles, 
when  oxychloride  of  antimony  is  treated  with  mono-hydrated  sulphuric  acid. 

The  salt  Sb03.2S03  is  deposited  in  small  crystals  from  a  solution  of  the  ter- 
oxide in  Nordhausen  sulphuric  acid. 

When  either  of  these  salts  is  treated  with  hot  water,  the  (neutral)  sulphate, 
Sb03.S03.2HO,  is  obtained. 

The  sulphate  of  the  formula  2Sb03.S03  is  obtained  from  the  residue  left  by 
the  action  of  oil  of  vitriol  upon  metallic  antimony,  by  digesting  it  with  cold  water. 

§  290.  The  highest  oxide  of  antimony,  like  the  binoxide  of  tin,  was  formerly 
considered  capable  of  existing  in  two  distinct  modifications,  but  it  has  been  re- 
cently proved  that  these  are  two  independent  acids,  differing  in  their  capacity  of 
saturation,  and  designated,  respectively,  antimonic  and  metautimonic  acid. 

ANTIMONIC  ACID,  Sb05(Sbfl05). 

This  acid  may  be  obtained  by  the  action  of  strong  nitric  acid  upon  antimony ; 
it  is  then,  however,  generally  combined  with  teroxide  of  antimony;  it  may  be 
prepared  in  the  pure  state  by  decomposing  an  antimoniate  with  dilute  nitric  acid. 

The  acid  thus  prepared  is  hydrated,  having  the  composition  Sb05.5HO;  it  is 


METANTIMONIC  ACID.  431 

white,  slightly  soluble  in  water,  and  capable  of  feebly  reddening  litmus;  it  is 
insoluble  in  dilute  mineral  acids,  but  dissolves  in  potassa  or  ammonia. 

When  heated,  it  assumes  a  pale  yellow  color,  and  is  converted  into  the  anhy- 
drous antimonic  acid,  which,  if  further  heated,  loses  oxygen,  and  is  converted 
into  the  antimoniate  of  teroxide  of  antimony  (Sb03.Sb09). 

Antimonic  acid  combines  with  one  equivalent  of  basic  protoxides,  forming  a 
class  of  salts  termed  antimoniates. 

ANTIMONIATE  OF  POTASSA,  KO.Sb03. 

This  salt  is  prepared  by  gradually  adding  one  part  of  powdered  antimony  to 
four  parts  of  nitre,  fused  in  a  Hessian  crucible  ;  the  fused  mass  is  powdered, 
washed  with  warm  water,  which  removes  the  excess  of  nitre  and  the  nitrite  of 
potassa,  and  leaves  the  anhydrous  antimoniate  of  potassa,  which  is  boiled  for  an 
hour  or  two  with  water,  when  it  becomes  hydrated  and  dissolves,  a  little  bi-anti- 
moniate  of  potassa  (K0.2Sb05)  being  left.  The  clear  liquid,  when  slowly  eva- 
porated, leaves  a  gummy  mass,  of  the  composition  KO.Sb05,5HO. 

Antimoniate  of  potassa  has  an  alkaline  reaction. 

At  320°  F.  (160°  C.)  it  loses  two  equivalents  of  water,  and  becomes  insoluble; 
at  a  higher  temperature  the  whole  of  the  water  is  expelled,  but  the  original  solu- 
ble salt  is  reproduced  by  continued  boiling  with  water. 

Antimoniate  of  potassa  is  less  soluble  in  saline  solutions  than  in  water,  so  that 
many  salts  precipitate  it,  as  a  white  gelatinous  mass,  from  its  aqueous  solution. 

A  solution  of  this  salt  is  easily  decomposed  by  acids,  hydrated  antimonic  acid 
being  precipitated.  When  carbonic  acid  is  passed  into  its  solution,  the  bi-anti- 
moniate,  K0.2Sb05,  is  precipitated. 

The  antimoniates  of  soda  resemble  the  potassa-salts. 

Two  antimoniates  of  ammonia  are  also  known  ;  they  are  insoluble  in  water. 

ANTIMONIATE  OF  TEROXIDE  OF  ANTIMONY,  Sb03.Sb05. — It  has  been  already 
remarked  that  this  substance  was  formerly  regarded  as  an  independent  acid,  re- 
presented by  the  formula  Sb04,  and  termed  antimonious  acid. 

This  compound  is  always  obtained  when  antimonic  acid  is  heated  as  long  as  it 
evolves  oxygen ;  it  may  therefore  be  very  readily  prepared  by  oxidizing  antimony 
with  nitric  acid,  and  strongly  igniting  the  residue,  when  the  antimoniate  remains 
as  a  white  powder,  insoluble  in  water. 

Alkaline  solutions  decompose  it,  dissolving  the  antimonic  acid,  and  leaving  ter- 
oxide of  antimony.  If  it  be  boiled  with  solution  of  bi-tartrate  of  potassa,  the 
teroxide  is  dissolved,  and  antimonic  acid  left. 

METANTIMONIC  ACID,  Sb05. 

This  acid  is  prepared  by  decomposing  the  pentachloride  of  antimony  with 
much  water : — 

SbCl5-f5HO=5HCl-fSb05. 

It  forms  a  white  precipitate,  which  only  differs  from  antimonic  acid  in  con- 
taining four  eqs.  water,  and  in  requiring  two  eqs.  of  a  protoxide  to  form  a  neutral 
salt,  so  that  the  general  formula  of  the  metantirnoniates  is  2MO.Sb05;  this  acid 
is  also  capable  of  producing  a  class  of  acid  salts  pf  the  general  formulzrMO.Sb05, 
isomeric  with  the  neutral  antimoniates. 

An  antimoniate  may  be  converted  into  a  metantimoniate  by  fusing  with  an 
excess  of  base;  and  conversely,  the  latter  into  the  former,  by  removing  one  eq. 
of  base. 

MKTANTIMONIATE  OF  POTASSA  (2KO.Sb05)  is  prepared  by  fusing  antimonic 
acid  with  a  large  excess  of  potassa  in  a  silver  crucible;  the  mass  is  dissolved  in 
a  little  water,  and  the  solution  evaporated  in  vacuoj  when  crystals  of  the  metan- 
timoniate are  obtained. 


432  ANTIMONIURETTED   HYDROGEN. 

Tins  salt  is  deliquescent,  and  very  soluble  in  water,  yielding  an  alkaline  solu- 
tion ;  it  is  soluble  without  decomposition  in  a  liquid  containing  excess  of  potassa, 
but  is  decomposed  by  cold  water  into  potassa  and  bi-metantimoniate  of  potassa, 
whence  the  solution  gives,  with  salts  of  soda,  a  white  crystalline  precipitate  of 
bi-metantimoniate  of  soda. 

BI-METANTIMONIATE  OF  POTASSA  (KO.Sb05)  possesses  some  importance, 
since  it  is  occasionally  used  as  a  test  for  soda;  but,  unfortunately,  it  is  so  liable 
to  furnish  precipitates  in  solutions  containing  traces  of  other  metallic  oxides 
(lime,  baryta,  magnesia,  &c.),  that  little  faith  is  generally  placed  in  its  indi- 
cations. 

This  salt  is  prepared  by  deflagrating  1  part  of  antimony  with  4  parts  of  nitre, 
washing  the  fused  mass  with  warm  water,  and  subsequently  boiling  with  water 
till  as  much  as  possible  has  been  dissolved ;  the  liquid  filtered  from  the  insoluble 
bi-antiraoniate  is  now  evaporated  in  a  silver  capsule  to  a  syrupy  consistence,  a 
few  fragments  of  caustic  potassa  added  (to  convert  the  antimoniate  of  potassa 
into  metantimoniate),  and  the  evaporation  continued  till  a  drop  of  the  liquid 
crystallizes  on  a  glass  plate  ;  on  cooling,  a  crystalline  deposit  is  formed,  which 
consists  of  a  mixture  of  metantimoniate  and  bi-metantimouiate  of  potassa;  this 
is  washed  rapidly  (four  or  five  times)  with  cold  water,  to  remove  the  excess  of 
potassa,  and  to  convert  all  the  metantimoniate  into  bi-metantimoniate,  and  after- 
wards agitated  for  some  time  with  water,  when  enough  t)f  the  bi-metantimoniate 
will  be  dissolved  to  enable  the  filtered  liquid  to  serve  to  detect  very  small  quan- 
tities of  soda.1 

The  bi-metantimoniate  of  potassa,  prepared  as  above,  is  a  white  crystalline 
salt,  having  the  composition  KO.Sb05.7HO;  when  heated,  it  loses  2  eqs.  of 
water,  and  is  converted  into  antimoniate  of  potassa. 

Bi-metantimomate  of  Soda  has  the  formula  NaO.Sb05,7HO;  it  is  very  slightly 
soluble  in  cold,  but  more  soluble  in  boiling  water. 

Metantimoniate  of  Ammonia  is  formed  when  metantimonic  acid  is  dissolved 
in  ammonia;  this  salt  is  soluble  in  water,  but  if  a  few  drops  of  alcohol  be  added 
to  the  solution,  the  bi-metantimoniate  (NH4O.Sb05,6HO)  is  precipitated;  this 
last  salt,  like  the  corresponding  potassa-compound,  is  slightly  soluble  in  water. 

When  kept  for  some  time  (even  in  sealed  tubes)  it  is  transformed  into  anti- 
moniate of  ammonia  (NH4O.Sb05.4HO),  which  is  insoluble  in  water.  The  same 
change  takes  place  immediately  on  heating. 

ANTIMONIURETTED  HYDROGEN. 

§  291.  The  composition  of  this  compound  is  not  certainly  known,  since  it  has 
never  been  obtained  perfectly  free  from  hydrogen ;  it  is,  however,  generally 
represented  as  SbH3.  Antimoniuretted  hydrogen  is  formed  when  antimony  aud 
hydrogen  are  brought  in  contact  in  the  nascent  state;  this  may  be  effected  by 
pouring  a  solution  of  antimony  into  an  apparatus  from  which  hydrogen  is  evolved 
by  zinc  with  dilute  sulphuric  acid;  a  mixture  of  hydrogen  with  antimoniuretted 
hydrogen  is  evolved,  which  is  inodorous,  insoluble  in  water,  and  burns  with  a 
livid  flame,  yielding  water  and  teroxide  of  antimony ;  if  a  porcelain  plate  be 
depressed  into  the  flame,  a  stain  of  finely-divided  antimony  will  be  deposited 
upon  it ;  antimoniuretted  hydrogen  is  decomposed  when  passed  through  a  tube 
heated  with  a  spirit-lamp,  a  shining  mirror  of  metal  being  deposited  immediately 

J  Reynoso  has  described  a  very  ready  method  of  preparing  this  reagent ;  it  consists  in 
precipitating  a  solution  of  terchloride  of  antimony  by  potassa,  redissolving  the  precipitate 
in  an  excess  of  potassa,  and  adding  permanganate  of  potassa  until  the  solution  acquires 
a  pink  color ;  it  is  then  decolorized  by  a  few  drops  of  terchloride  of  antimony,  evaporated, 
and  allowed  to  crystallize ;  the  crystals  of  bi-metautimoniate  of  potassa  are  washed  with 
cold  water.  The  same  process  may  be  employed  for  obtaining  other  metallic  acids,  as 
chromic  and  stannic  acids. 


PENTACHLOEIDE   OP   ANTIMONY. 

before  the  flame.  When  passed  into  solution  of  nitrate  of  silver,  antiraoniuretted 
hydrogen  yields  a  black  precipitate,  the  composition  of  which  is  not  certainly 
known.  Both  the  hydrogen  and  the  metal  are  oxidized  when  the  gas  is  passed 
into  hot  nitric  acid. 

The  production  of  the  hydrogen-compound  of  antimony  is  sometimes  had  re- 
course to  in  the  detection  of  this  metal,  as  will  be  further  explained  hereafter. 

TERCHLORTDE  OP  ANTIMONY,  SbCl3  (sesquichloride,  Sb2Cl3). 

This  compound  was  formerly  known  as  butter  of  antimony,  on  account  of  its 
semi-solid  consistence.  It  may  be  prepared  by  either  of  the  following  me- 
thods : — 

I.  By  passinor  chlorine  (slowly)  over  an  excess  of  metallic  antimony. 

II.  By  distilling  an  intimate  mixture  of  1  part  of  powdered  antimony  and  2 
parts  of  chloride  of  mercury  (corrosive  sublimate). 

III.  By  dissolving  tersulphide  of  antimony  in  hydrochloric  acid  : — 

SbS3+3HCl=SbClg-f-3HS. 

IV.  By  distilling  a  mixture  of  chloride  of  sodium  and  sulphate  of  teroxide  of 
antimony. 

V.  By  dissolving  metallic  antimony  in  hydrochloric  acid,  with  gradual  addi- 
tion of  nitric  acid;  too  large  a  quantity  of  the  latter  must  be  avoided,  since  it  will 
cause  a  precipitation  of  antimoniate  of  teroxide  of  antimony. 

Properties. — Terchloride  of  antimony  is  a  soft,  gray  solid,  which  deliquesces 
when  exposed  to  air ;  it  fuses  at  a  gentle  heat,  and  crystallizes  on  cooling  in 
tetrahedra.  It  volatilizes  at  a  moderately  high  temperature,  yielding  a  vapor 
of  sp.  gr.  8.1.  The  terchloride  dissolves,  without  alteration,  in  a  small  quantity 
of  water,  especially  if  a  little  acid  be  added,  but  a  large  quantity  of  water 
decomposes  it,  with  formation  of  hydrochloric  acid,  and  of  a  white  precipitate, 
known  as  powder  of  Alyaroth,  which  is  an  oxychloride  of  antimony,  having  the 
formula,  SbCl3.2Sb03,HO  :— 

3SbCl,+6HO=SbCl,.2SbOa+6HCl. 

When  a  solution  of  terchloride  of  antimony  in  acidulated  water  is  poured  into 
a  large  quantity  of  water,  a  very  voluminous  white  precipitate  is  formed,  which, 
after  some  time,  contracts  very  considerably,  and  becomes  converted  into  a  col- 
lection of  white  prismatic  needles,  which  are  probably  identical  with  those 
obtained  by  Peligot,  on  adding  hot  water  to  a  hydrochloric  solution  of  the  ter- 
chloride, which  were  found  to  have  the  composition  SbCl3,5Sb03.  The  above 
oxychlorides  are  both  soluble  in  tartaric  acid,  and  are  converted,  by  long  wash- 
ing, into  teroxide  of  antimony. 

Nitric  acid  acts  upon  terchloride  of  antimony,  producing  the  antimoniate  of 
teroxide  of  antimony. 

Terchloride  of  antimony  is  capable  of  absorbing  ammoniacal  gas,  producing 
the  compound,  SbCl3.NH3. 

It  also  combines  with  hydrochloric  acid,  and  forms  double  chlorides  with  those 
of  potassium,  sodium  and  ammonium. 

Terchloride  of  antimony  is  occasionally  used  in  surgery ;  it  also  serves  as  a 
bronze  for  gun-barrels,  upon  which  it  deposits  a  film  of  metallic  antimony. 

PENTACHLORIDE  OF  ANTIMONY,  SbCl5. 

Preparation. — The  pentachloride  is  prepared  by  heating  coarsely-powdered 

antimony  in  a  retort  of  green  glass,  through  which  a  stream  of  dry  chlorine  is 

passed;  the  neck  of  the  retort  is  fitted  into  an  adapter,  which  serves  to  condense 

the  pentachloride ;  the  product  is  to  be  completely  saturated  with  chlorine,  and 

28 


434  ANTIMONY  AND   SULPHUR. 

subsequently  redistilled,  the  first  portions,  which  contain  the  excess  of  chlorine, 
being  rejected. 

Properties. — Pentachloride  of  antimony  is  a  yellowish  liquid,  which  is  volatile, 
and  evolves  thick  white  fumes  when  exposed  to  moist  air;  when  brought  in  con- 
tact with  water,  energetic  action  takes  place,  and  the  pentachloride  is  first  con- 
verted into  a  crystalline  hydrate,  and  subsequently  decomposed  into  hydrochloric 
and  antimonic  acids  : — 

SbCl5+5HO=Sb05+5HCl. 

When  heated,  the  pentachloride  is,  to  some  extent,  decomposed  into  terchloride 
and  free  chlorine. 

Pentachloride  of  antimony  is  capable  of  combining  with  ammonia  and  with 
sulphuretted  hydrogen. 

A  compound  of  pentachloride  of  antimony  with  chloride  of  sulphur  has  been 
obtained  by  the  action  of  chlorine  upon  the  tersulphide  of  antimony;  this  com- 
pound has  the  formula,  SbCl5.3SCl;  it  is  a  white  solid  which  decomposes,  at  a 
slightly  elevated  temperature,  into  chloride  of  sulphur,  chlorine  and  terchloride 
of  antimony. 

Pentachloride  of  antimony  is  frequently  employed  in  the  laboratory  as  a  chlo- 
rinating agent,  since  it  readily  yields  chlorine  to  substances  having  a  great  affinity 
for  it;  thus,  olefiant  gas  (CLH4),  when  passed  through  the  pentachloride,  is  con- 
verted into  Dutch  liquid  (C^H4C13),  and  carbonic  oxide  into  chlorocarbonic  acid, 
the  pentachloride  being  reduced  to  terchloride. 

A  chlorosulphide  of  antimony,  SbCl3S3,  has  been  prepared  by  the  action  of 
hydrosulphuric  acid  upon  pentachloride  of  antimony. 

The  terbromide  of  antimony ,  SbBra,  is  a  colorless  crystalline  solid. 

The  teriodide  is  a  red  solid. 

The  terfluoride  forms  colorless  crystals. 

The  bromide  iodide,  and  fluoride  corresponding  to  antimonic  acid  are  not  known. 


ANTIMONY   AND   SULPHUR. 

Tersulphide  .     .     *  ^fctwjjten***  r*    •     •     SbS8. 
Pentasulphide SbS5. 

TERSULPHIDE  OF  ANTIMONY,  SbS3. 

§  292.  This  sulphide  is  found  pretty  abundantly  in  nature,  and  forms  the 
commonest  ore  of  antimony  (gray  ore  of  antimony].  It  has  a  bluish-gray 
color  and  metallic  lustre;  is  crystallized  in  prismatic  needles,  and  has  the  sp. 
gr.  4.62.  The  native  sulphide  is  generally  associated  with  quartz,  sulphate  of 
baryta,  or  iron-pyrites.  When  heated  in  close  vessels,  it  fuses  easily,  without 
suffering  any  decomposition,1  and  crystallizes  on  cooling.  It  is  volatile,  and  may 
be  sublimed  unchanged.  When  heated  with  access  of  air,  it  is  partially  con- 
verted into  teroxide,  which  remains  in  combination  with  unaltered  tersulphide. 
When  heated  to  redness  in  a  current  of  hydrogen,  it  is  reduced  to  mefallic  anti- 
mony. 

The  tersulphide  of  antimony  dissolves  in  hydrochloric  and  sulphuric  acids, 
with  the  aid  of  heat,  sulphuretted  hydrogen  being  evolved;  it  dissolves  to  a 
considerable  extent  in  nitric  acid,  leaving  a  white  residue. 

This  sulphide  plays  the  part  of  a  sulphur-acid,  dissolving  readily  in  the  alka- 
line sulphides.  It  is  also  soluble  in  the  caustic  alkalies,  producing  compounds 

1  This  property  is  taken  advantage  of  in  order  to  free  the  crude  sulphide  from  gangue. 


SULPHIDES    OF  ANTIMONY. 


435 


of  the  alkali  with  teroxide  of  antimony,  and  of  an  alkaline  sulphide  with  ter- 
sulphide  of  antimony;  thus  : — 

4SbS,  +  4KO=KO.SbOa+8(KS.SbSB). 

Anhydrous  tersulphide  of  antimony  may  be  obtained  artificially,  in  prismatic 
crystals  with  metallic  lustre,  by  fusing  a  mixture  of  sulphur  with  antimoniate  of 
teroxide  of  antimony,  when  sulphurous  acid  is  evolved. 

The  Tiydrated  tersulphide  is  obtained  as  a  fine  orange-red  precipitate,  when 
sulphuretted  hydrogen  is  passed  through  a  solution  of  teroxide  of  antimony  ;  it 
loses  its  water  when  moderately  heated,  assuming  a  dark  gray  color,  and  metallic 
lustre. 

Tersulphide  of  antimony  is  occasionally  used  for  the  preparation  of  pure  hydro- 
sulphuric  acid.  Its  chief  application  is  in  pyrotechny  and  in  the  preparation  of 
detonating  compositions  for  military  purposes.  The  latter  use  depends  upon  its 
combustibility,  and  the  former  upon  the  property  which  it  possesses  of  burning 
with  a  bright  bluish-white  flame. 

The  compounds  known  as  glass  of  antimony,  liver  of  antimony,  and  crocus, 
are  formed  by  roasting  the  native  tersulphide  with  access  of  air.  They  contain 
variable  proportions  of  teroxide  and  tersulphide  of  antimony. 

Glass  of  antimony  contains  about  eight  parts  of  teroxide,  and  one  part  of  ter- 
sulphide ;  it  is  transparent,  and  of  a  reddish-yellow  color. 

Crocus  has  a  similar  color,  but  is  opaque  ;  it  contains  eight  parts  of  teroxide 
and  two  of  tersulphide;  liver  of  antimony  has  an  opaque  brown  color,  and  con- 
tains about  half  its  weight  of  tersulphide  of  antimony. 

These  compounds  are  chiefly  employed  in  veterinary  medicine,  and  in  the 
preparation  of  tartar-emetic. 

PENTASULPHIDE  OF  ANTIMONY,  SbS5  (Sulphantimonic  acid). 

This  sulphide  is  obtained  by  passing  sulphuretted  hydrogen  through  a  solu- 
tion of  pentachloride  of  antimony  in  hydrochloric  acid.  It  forms  a  bright  orange- 
red  precipitate,  which  is  a  hydrate  of  the  pentasulphide ;  when  heated,  it  first 
loses  its  water,  and  afterwards  two  equivalents  of  sulphur,  leaving  the  tersulphide 
of  antimony. 

Pentasulphide  of  antimony  is  a  powerful  sulphur-acid,  and  is  capable  of 
expelling  hydrosulphuric  acid  from  the  hydrosulphates  of  alkaline  sulphides. 

The  sulpliantimoniate  of  sulphide  of  sodium,  3NaS.SbS5,  is  sometimes  employed 
in  medicine;  it  is  prepared  by  intimately  mixing  18  parts  of  tersulphide  of  anti- 
mony, 12  parts  of  carbonate  of  soda  (dry),  13  parts  of  lime,  and  3£  parts  of 
sulphur;  the  mixture  is  well  triturated  for  half  an. hour,  then  digested,  with 
frequent  agitation,  for  two  or  three  days,  in  a  flask  perfectly  filled  with  cold 
water;  the  filtered  solution  is  then  evaporated,  first  on  a  sand-bath,  then  in  the 
receiver  of  an  air-pump,  when  tetrahedral  crystals  are  obtained,  of  the  formula 
3NaS.SbS5.l8HO;  these  are  colorless,  or  slightly  yellow,  and  very  soluble  in 
water;  acids  precipitate  the  sulphantimonic  acid  from  this  solution, 

KERMES  MINERAL. — The  pharmaceutical  compound  known  under  this  name 
is  a  mixture  of  teroxide  and  tersulphide  of  antimony,  which  is  prepared,  either 
by  fusing  tersulphide  of  antimony  with  carbonate  of  soda,  and  boiling  the  fused 
mass  with  much  water,  or  by  boiling  the  finely  powdered  tersulphide  with  car- 
bonate of  soda  and  a  large  quantity  of  water;  in  either  case,  the  liquid,  filtered 
while  hot,  deposits  the  kermes  on  cooling;  this  substance  is  collected  on  a  filter, 
well  washed,  and  dried  at  a  low  temperature. 

The  formation  of  kermes  is  easily  explained ;  the  tersulphide  of  antimony  is 
decomposed  by  the  soda,  yielding  sulphide  of  sodium  and  teroxide  of  antimony, 
which  combines  with  part  of  the  soda  : — 

4NaO  +  SbS3=NaO.Sb03+3NaS; 


436  METALLURGY  OF  ANTIMONY. 

whilst  a  portion  of  unaltered  tersulphide  of  antimony  dissolves  in  the  sulphide 
of  sodium  ;  since  the  compound  of  teroxide  of  antimony  with  soda  is  decomposed 
by  boiling  with  water,  and  tersulphide  of  antimony  is  more  soluble  in  a  hot  than 
in  a  cold  solution  of  sulphide  of  sodium,  a  mixture  of  the  teroxide  and  tersul- 
phide would  of  course  be  deposited  as  the  solution  cools.  The  kermes  generally 
contains  a  small  quantity  of  sulphide  of  sodium,  carried  down  with  the  tersul- 
phide of  antimony,  which  serves  to  account  for  the  variation  of  color  observed  in 
different  specimens  of  this  preparation.  The  crystalline  teroxide  of  antimony 
may  be  recognized  in  kermes  under  the  microscope. 

When  the  mother-liquors  from  which  the  kermes  has  been  deposited  are 
treated  with  dilute  sulphuric  acid,  a  mixture  of  tersulphide  and  pentasulphide  of 
antimony,  known  as  yolden  sulphuret  of  antimony,  is  deposited. 

§  293.  ALLOYS  OF  ANTIMONY. — Antimony  is  capable  of  forming  alloys  with 
many  metals;  it  has  already  been  said  that  this  metal  is  employed  to  harden 
several  useful  alloys. 

An  alloy  of  antimony  and  potassium  is  obtained  by  heating,  in  a  covered  cru- 
cible, for  some  hours,  a  mixture  of  6  parts  of  tartar-emetic  with  1  part  of  nitre, 
when  a  button  containing  a  considerable  quantity  of  antimony  is  obtained,  which 
decomposes  water  at  the  ordinary  temperature,  with  disengagement  of  hydrogen. 

If  the  alloy  be  prepared  in  a  very  fine  state  of  division,  by  calcining,  for  three 
hours,  in  an  earthen  crucible,  a  mixture  of  100  parts  of  tartar-emetic,  and  3 
parts  of  lampblack,  it  will  be  found  capable  of  taking  fire,  with  explosion,  in 
moist  air ;  it  should  therefore  be  allowed  to  cool,  in  a  closed  crucible,  beneath  a 
bell-jar  of  dry  air,  and  must  be  handled  with  great  care. 

An  alloy  of  antimony  with  iron  (Reaumur's  alloy}  may  be  procured  by  fusing, 
at  a  very  high  temperature,  a  mixture  of  7  parts  of  antimony  and  3  of  iron 
filings ;  the  alloy  is  exceedingly  hard,  and  emits  sparks  when  filed. 

METALLURGY  OF  ANTIMONY. 

§  294.  Metallic  antimony,  associated  with  small  quantities  of  silver  and  iron, 
has  been  found  in  nature. 

Antimony  exists  most  frequently  in  combination  with  sulphur,  and  indeed, 
the  only  ore  of  antimony,  in  a  strict  sense,  is  the  gray  ore,  or  native  tersulphide. 

A  mineral  containing  antimony  and  nickel,  and  termed  nickelifcrous  sulphuret 
of  antimony  or  nickel-antimony,  is  known. 

Antimony  is  sometimes,  though  rarely,  found  in  an  oxidized  state  in  white 
ore  of  antimony,  ochre  of  antimony,  and  red  ore,  which  last  appears  to  be  an 
oxy-sulphide. 

The  reduction  of  antimony  from  the  ore  consists  of  two  distinct  processes,  one 
of  which  is  intended  to  separate  the  ore  from  the  gangue,  and  the  other  to  obtain 
the  antimony  in  the  metallic  state. 

The  former  object  is  attained  by  fusing  the  crude  ore  upon  the  inclined  hearth 
of  a  reverberatory  furnace,  when  the  tersulphide  fuses,  and  flows  away  from  the 
gangue  into  appropriate  receptacles. 

The  purified  ore  is  afterwards  roasted  in  a  reverberatory  furnace,  where  it  is 
converted  into  oxy-sulphide  of  antimony  (glass  of  antimony).  This  is  powdered, 
and  mixed  with  1  its  weight  of  charcoal  previously  saturated  with  a  strong  solu- 
tion of  carbonate  of  soda;  on  heating  this  mixture  in  a  crucible,  the  teroxide  of 
antimony  is  reduced  by  the  charcoal,  and  a  portion  of  the  tersulphide,  having 
been  converted  into  teroxide  by  double  decomposition  with  the  soda  of  the  car- 
bonate, is  also  reduced ;  a  quantity  of  regulus  of  antimony  is  found  at  the  bottom 
of  the  crucible,  and,  above  it,  a  slag  containing  tersulphide  and  teroxide  of  anti- 
mony, which  may  be  employed  for  the  preparation  of  kermes  mineral. 

The  tersulphide  of  antimony  was  formerly  reduced  by  iron  at  a  high  tempera- 


ARSENIC.  437 

ture,  but  it  was  found  necessary  to  give  up  this  process,  since  the  metal  obtained 
was  always  alloyed  with  a  large  quantity  of  iron. 

Assay  of  Ores  of  Antimony. — Ores  of  antimony  which  do  not  contain  sulphur 
are  assayed  by  fusion  with  3  parts  of  black  flux,  a  very  high  temperature  being 
avoided,  because  of  the  volatility  of  the  metal.  Care  must  be  taken  that  the 
button  be  not  broken  in  extracting  it  from  the  crucible. 

The  best  method  of  assaying  the  sulphide  of  antimony  consists  in  fusing  it  at 
a  moderate  heat,  in  an  earthen  crucible,  with  4  parts  of  Liebig's  cyanide  of 
potassium. 

It  is  obvious  that  the  volatility  of  the  metal  must  prevent  the  attainment  of 
anything  more  than  an  approximation  to  the  amount  of  antimony  present  in  the 
ore. 

§  295.  Pharmaceutical  Preparations  of  Antimony. — Several  preparations  of 
antimony  are  used  in  medicine. 

The  most  important  of  these  is  tartar-emetic,  the  double  tartrate  of  antimony 
and  potassa,  the  description  of  which  falls  within  the  province  of  organic 
chemistry. 

Antimonium  calcinatum,  or  diaphoretic  antimony,  is  prepared  by  deflagrating 
the  tersulphide  with  3  parts  of  nitre,  and  washing  the  fused  mass  with  water ; 
the  residue  contains  an  acid  antimoniate  of  potassa. 

Antimonii  cinis  (antimony-ash]  is  an  oxy-sulphide,  prepared  by  roasting  the 
tersulphide  in  air. 

The  substance  termed  antimonii  oxydum,  or  antimonii  oxydum  nitro-muriati- 
cum,  is  prepared  by  dissolving  the  tersulphide  in  hydrochloric  or  nitro-hydro- 
chloric  acid,  precipitating  by  water,  and  washing  the  precipitate  as  long  as  the 
washings  have  any  acid  reaction ;  it  consists  of  teroxide  of  antimony  with  a  lit- 
tle terchloride. 


ARSENIC. 

Sym.  As.     Eq.  75.     Sp.  Gr.  5.75. 

§  296.  Although,  in  its  combinations,  this  element  more  nearly  resembles  the 
non-metallic  bodies,  we  have,  according  to  the  usual  custom,  placed  it  among  the 
metals. 

Arsenic  is  rather  widely  diffused  in  nature,  sometimes  in  the  metallic  state,  or 
as  a  sulphide,  but  generally  associated  with  the  ores  of  iron,  nickel,  cobalt,  and 
copper. 

The  mineral  known  as  arsenical  pyrites  (mispickel)  usually  contains  arsenic, 
iron,  and  sulphur,  in  the  proportions  expressed  by  the  formula  FeS2,  FeAsa. 

Red  and  yellow  orpiment  will  be  spoken  of  under  the  sulphides  of  arsenic. 

Preparation. — Arsenic  is  prepared  either  from  mispickel  or  from  arsenious 
acid. 

The  arsenical  pyrites  is  strongly  heated  in  earthen  cylinders,  with  fragments 
of  iron,  which  retain  the  whole  of  the  sulphur,  while  the  arsenic  sublimes  into 
other  cylinders,  serving  as  receivers ;  it  is  purified  by  redistilling  with  a  little 
charcoal. 

In  order  to  obtain  arsenic  from  arsenious  acid,  it  is  only  necessary  to  mix  the 
latter  with  about  twice  its  weight  of  black  flux,  and  to  heat  the  mixture  in  a 
Hessian  crucible,  which  is  covered  with  a  second  crucible,  kept  cool  in  order  that 
the  arsenic  may  be  condensed ;  the  two  crucibles  should  be  luted  together,  a 
small  aperture  being  left  for  the  .escape  of  the  carbonic  oxide. 

Properties. — Arsenic  has  a  steel-gray  color,  and  metallic  lustre ;  it  is  crystal- 


438  ARSENIC  AND  OXYGEN. 

line  in  texture,  and  exceedingly  brittle.  It  is  converted  into  vapor  at  about 
572°  F.  (300°  C.),  without  previously  fusing ;  it  may,  however,  be  fused  in  a 
sealed  tube.  If  the  vapor  of  arsenic  be  allowed  to  condense  slowly,  the  metal 
is  deposited  in  brilliant  rhombohedral  crystals.  The  density  of  the  vapor  of 
arsenic  is  10.39. 

When  exposed  to  air,  arsenic  is  tarnished  and  assumes  a  dull  black  color,  pro- 
bably becoming  covered  with  a  film  of  suboxide ;  when  placed  in  contact  with 
water,  air  being  allowed  free  access,  it  is  gradually  converted  into  arsenious  acid. 

When  heated  in  air,  this  metal  is  oxidized,  and  produces  white  fumes  of 
arsenious  acid,  at  the  same  time  exhaling  a  peculiar  alliaceous  odor,  ascribed  by 
some  to  the  vapor  of  the  metal  itself,  by  others  to  a  suboxide  of  arsenic. 

Arsenic  burns,  when  heated  in  oxygen,  with  a  pale  blue  flame,  producing 
arsenious  acid.  It  is  not  capable  of  decomposing  water  at  any  temperature,  nor 
in  presence  of  acids. 

Arsenic  is  not  attacked  by  hydrochloric  acid,  but  nitric  acid  dissolves  it  readily, 
arsenious  or  arsenic  acid  being  produced,  according  to  the  concentration  of  the 
acid ;  when  the  ordinary  nitric  acid  of  the  laboratory  is  employed,  the  former 
is  usually  found  in  solution.  Chlorine  combines  energetically  with  arsenic,  the 
powdered  metal  taking  fire  spontaneously  in  this  gas. 

Metallic  arsenic, does  not  produce  symptoms  of  poisoning  in  animals  till  a  con- 
siderable period  after  its  administration;  it  is  probably  first  converted  into 
arsenious  acid. 

The  substance  known  as  fly-powder  consists  of  a  mixture  of  metallic  arsenic 
with  arsenious  acid,  and  is  prepared  by  exposing  the  metal  to  air  in  presence  of 
water. 

Arsenic  exhibits  in  its  combinations  a  remarkable  similarity  to  phosphorus ; 
thus,  with  hydrogen,  oxygen,  and  chlorine,  it  forms  compounds  analogous  to 
those  formed  by  that  element. 


ARSENIC  AND  OXYGEN. 

Arsenious  acid As03 

Arsenic  acid        AsO.1 


§  297.  The  existence  of  an  inferior  oxide  is  regarded  as  doubtful ;  some 
chemists  contend  that  the  product  of  the  slow  oxidation  of  arsenic  by  exposure  to 
moist  air,  is  merely  a  mixture  of  metallic  arsenic  and  arsenious  acid;  it  cer- 
tainly yields  these  products  when  subjected  to  heat. 

ARSENIOUS  ACID,  As03  (commonly  called  ARSENIC,  or 
White  Arsenic.^) 

Preparation. — Arsenious  acid  is  prepared  by  roasting  arsenical  pyrites  with 
free  access  of  air,  when  the  arsenic  is  oxidized,  and  the  arsenious  acid  is  condensed 
in  large  chambers. 

It  is  also  obtained  as  a  by-product  in  roasting  certain  ores,  especially  those  of 
tin  and  cobalt. 

The  arsenious  acid  thus  obtained  is  purified  by  sublimation. 

Properties. — Arsenious  acid,  when  freshly  prepared,  forms  transparent  color- 
less, vitreous  masses,  which,  after  some  time,  become  opaque  externally,  the 
opacity  afterwards  extending  throughout  the  mass,  until  it  resembles  a  fragment 
of  porcelain. 

1  The  equivalent  of  arsenic  is  sometimes  considered  as  37.5,  when  arsenious  acid  would 
be  As203,  and  arsenic  acid  As205. 


ARSENIC  AND   OXYGEN.  439 

The  vitreous  and  opaque  varieties  of  arsenious  acid  differ  considerably  in  some 
of  their  properties. 

The  specific  gravity  of  the  vitreous  acid  is  3.74,  that  of  the  opaque  variety 
3.70. 

When  the  vitreous  acid  is  reduced  to  powder,  it  is  converted  into  the  opaque 
variety. 

At  the  ordinary  temperature,  the  vitreous  acid  is  three  times  as  soluble  in 
water  as  that  which  is  opaque. 

Heat  is  capable  of  causing  the  opaque  acid  to  become  vitreous,  while  cold 
reverses  the  change ;  hence,  by  long  boiling  with  water,  the  opaque  acid  is  con- 
verted into  the  vitreous  modification,  and,  as  the  solution  cools,  part  of  the  arse- 
nious acid  in  the  opaque  condition  is  deposited ;  thus  these  two  forms  of  arsenious 
acid  are  generally  found  in  the  same  solution. 

When  vitreous  arsenious  acid  is  dissolved  in  boiling  dilute  hydrochloric  acid, 
it  is  deposited  on  cooling  in  regular  octohedra  of  the  opaque  variety,  the  deposi- 
tion of  each  crystal  being  said  to  be  attended  by  a  flash  of  light,  which  is  not 
the  case  if  the  crystals  be  redissolved  in  hydrochloric  acid,  or  if  the  opaque  variety 
be  originally  employed. 

Arsenious  acid  is  dimorphous,  and  has  been  obtained  by  sublimation  in  thin 
prisms.  It  volatilizes  below  a  red  heat,  without  previously  fusing ;  it  may,  how- 
ever, be  fused,  if  heated  in  a  sealed  tube. 

Vapor  of  arsenious  acid  is  inodorous,  and  has  the  specific  gravity  13.85.  If  it 
be  condensed  in  a  receiver  which  attains  a  pretty  high  temperature,  a  layer  of 
vitreous  arsenious  acid  is  formed,  whilst,  if  deposited  in  a  slow  current  of  air, 
the  acid  is  obtained  in  fine  octohedral  crystals. 

Arsenious  acid  is  sparingly  soluble  in  cold  water,  but,  as  implied  above,  more 
so  in  hot  water;  1000  parts  of  boiling  water  dissolve  about  80  parts  of  arsenious 
acid,  and  the  solution,  after  cooling  to  60°  F.  (15°. 5  C.),  retains  only  30  parts. 
If  water  at  60°  F.  be  mixed  with  arsenious  acid  in  powder,  only  2£  parts  are 
dissolved  by  1000  of  water.1 

The  aqueous  solution  has  a  feeble  acid  reaction  to  test-papers.  It  is  much 
more  soluble  in  hydrochloric  acid.  When  arsenious  acid  is  boiled  with  concen- 
trated hydrochloric  acid,  terchloride  of  arsenic  is  formed  and  volatilized. 

When  boiled  with  nitric  (or  better,  nitro-hydrochloric)  acid,  arsenious  is  con- 
verted into  arsenic  acid.  Solution  of  ammonia  is  capable  of  dissolving  it,  and  of 
depositing  it  again  in  crystals.  Arsenious  acid  is  easily  reduced  to  the  metallic 
state  by  hydrogen  or  carbon  at  a  high  temperature. 

This  acid  is  bibasic,  forming  salts,  which  are  termed  arsenites.  It  is  a  most 
virulent  poison. 

Uses. — Arsenious  acid  is  used  in  the  manufacture  of  glass,  where  it  serves  to 
oxidize  any  (prot-)  oxide  of  iron  which  may  be  present,  converting  it  into  sesqui- 
oxide,  which  does  not  color  the  glass  so  deeply.  It  also  enters  into  the  com- 
position of  various  pigments  and  coloring  matters.  Arsenious  acid  is  extensively 
employed  for  destroying  vermin,  and  for  preventing  the  smut  in  grain. 

§  298.  Arsenite  of  Potassa  (2KO.As03)  is  obtained  by  dissolving  arsenious 
acid  in  solution  of  potassa. 

It  crystallizes  with  difficulty,  and  is  deliquescent ;  its  solution  has  an  alkaline 
reaction.9 

1  The  amount  dissolved,  however,  depends,  to  a  remarkable  extent,  upon  the  duration 
of  the  contact  between  the  arsenious  acid  and  the  water. 

2  According  to  Pasteur,  there  exist  two  other  arsenites  of  potassa,  KO.H0.2As03,  and 
KO.As03. 

Rose  has  obtained  insoluble  arseniates  of  magnesia  and  the  alkalies,  by  fusing  ignited 
arseniate  of  magnesia  and  ammonia  with  alkaline  carbonates. 


440  ARSENIC   ACID. 


ARSENITE  or  COPPER,  2CuO.As03.     (Scheelts  green.) 

This  substance  is  precipitated  in  a  hydrated  state  when  sulphate  of  copper  is 
added  to  a  solution  of  a  neutral  arsenite. 

It  is  prepared  on  the  large  scale  by  dissolving  6£  Ibs.  of  carbonate  of  potassa 
and  2J  Ibs.  of  arsenious  acid  in  3  gallons  of  water,  and  gradually  adding  the 
liquid  to  a  boiling  solution  of  6^  Ibs.  of  sulphate  of  copper  in  9  gallons  of  water, 
with  continual  stirring. 

The  shade  of  color  may  be  modified  by  varying  the  quantity  of  arsenious  acid. 

Arsenite  of  copper  dissolves  readily  in  acids,  and  in  ammonia.  When  heated, 
the  arsenious  acid  is  expelled,  oxide  of  copper  being  left.  It  is  a  very  active 
poison. 

Uses. — Scheele's  green  is  employed  largely  by  paper-stainers,  and  in  oil-paint- 
ing. It  is  also  used  to  a  lamentable  extent  in  coloring  ornaments  of  confectionery, 
and  grave  accidents  frequently  arise  from  this  cause. 

The  pigment  known  as  Schwemfart  green  is  a  compound  of  arsenite  with 
acetate  of  copper,  CuO.A,3(2CuO.As03),  and  is  prepared  by  mixing  together 
boiling  solutions  of  equal  weights  of  arsenious  acid  and  of  acetate  of  copper,  the 
ebullition  being  maintained  for  some  time  after  mixing. 

ARSENIC  ACID,  As05. 

§  299.  Preparation. — Arsenious  acid  is  heated  with  a  considerable  excess  of 
nitric  acid  and  a  small  quantity  of  hydrochloric;  8  parts  of  arsenious  acid  may 
be  dissolved  in  24  parts  of  nitric,  and  2  parts  of  hydrochloric  acid.  The  solution 
is  evaporated  to  a  syrupy  consistence,  and  pretty  strongly  heated,  to  expel  the 
excess  of  acid. 

Properties. — Arsenic  acid  is  a  white  deliquescent  solid ;  when  strongly  heated, 
it  first  fuses,  and  is  decomposed  into  arsenious  acid  and  oxygen.  This  acid  is 
very  soluble  in  water,  but  dissolves  slowly  after  it  has  been  dried;  the  aqueous 
solution  deposits  crystals  if  sufficiently  evaporated,  and  set  aside.  These  crystals 
contain  hydrated  arsenic  acid.  It  is  easily  decomposed  by  deoxidizing  agents ; 
sulphurous  acid  reduces  it  to  arsenious  acid. 

Arsenic  acid  is  tri basic ;  its  salts  much  resemble  those  of  the  tribasic  phos- 
phoric acid  with  which  it  is  isomorphous ;  like  these  latter,  the  arseniates  may 
contain  1  or  2  eqs.  of  basic  water. 

Tribasic  arseniate  of  potassa,  with  3  eqs.  of  fixed  base  (3KO.As05),  is  pre- 
pared by  adding  an  excess  of  potassa  to  arsenic  acid,  and  crystallizes  in  fine 
deliquescent  needles. 

Common  arseniate  of  potassa  (2KO.HO.As05)  is  prepared  by  neutralizing 
potassa  with  arsenic  acid ;  it  is  deliquescent,  and  has  not  been  crystallized. 

Acid  arseniate  of  potassa,  K0.2HO  As05,  may  be  obtained  by  adding  an  ex- 
cess of  arsenic  acid  to  the  preceding  salt ;  it  crystallizes  in  forms  derived  from 
the  octohedron,  and  is  unaltered  in  air. 

The  corresponding  arseniates  of  soda  have  been  obtained. 

The  common  arseniate,  2Na6.HO.As05,  crystallizes  with  26  eqs.  of  water; 
the  crystals  effloresce  in  air. 

Solutions  of  the  arseniates  give,  with  nitrate  of  silver,  a  brick-red  precipitate 
of  the  tribasic  arseniate  of  silver,  3AgO.As05,  the  solution  being  neutral  or  acid 
after  the  reaction,  according  to  the  amount  of  fixed  base  present. 

Arsenic  acid  is  capable  of  forming  insoluble  compounds  with  binoxide  of  tin, 
as  may  be  shown  by  oxidizing  an  alloy  of  tin  and  arsenic  with  nitric  acid,  when 
a  considerable  quantity  of  arsenic  may  be  found  in  the  residue. 


ARSENIC   AND    SULPHUR.  441 

ARSENIURETTED  HYDROGEN,  AsH3. 

§  300.  This  compound  is  prepared  by  dissolving  an  alloy  of  tin  and  arsenic 
in  hydrochloric  acid,  with  the  aid  of  heat;  or  by  acting  upon  zinc  with  dilute 
sulphuric  acid  in  presence  of  arsenic.  The  gas  obtained  by  these  methods  always 
contains  free  hydrogen. 

Properties. — Arseniuretted  hydrogen  is  a  colorless  gas  having  a  sickly  allia- 
ceous odor ;  its  sp.  gr.  is  2.69.  It  may  be  liquefied  at  -22°  F.  (-30°  C.)  It 
is  somewhat  soluble  in  water;  5  vols.  of  water  dissolve  about  1  vol.  of  the  gas. 
Arseniuretted  hydrogen  is  inflammable,  and  burns  with  a  livid  flame,  yielding 
arsenious  acid  and  water ;  if  it  be  burnt  in  a  bell-jar,  with  a  limited  supply  of 
air,  a  brown  deposit  (said  to  be  a  solid  compound  of  arsenic  with  hydrogen)  is 
formed  simultaneously  with  the  above  products.  A  similar  brown  deposit  is 
formed  when  the  gas  is  kept  for  a  long  time  over  water.  '  ,  t 

If  a  porcelain  plate  be  depressed  into  the  flame  of  arseniuretted  hydrogen,  so 
as  partially  to  cut  off  the  supply  of  air,  the  hydrogen  alone  is  oxidized,  and  a 
spot  of  arsenic  is  deposited  upon  the  porcelain. 

This  gas  is  very  readily  decomposed  into  its  elements  by  heat ;  if  the  tube 
through  which  arseniuretted  hydrogen  is  passed  be  heated  to  redness  with  a 
spirit-lamp,  a  lustrous  mirror  of  metallic  arsenic  is  deposited  at  some  distance 
from  the  heated  portion. 

Chlorine  decomposes  arseniuretted  hydrogen  with  great  energy,  emitting  a 
brilliant  light.  The  gas  is  absorbed  by  several  metallic  salts  (sulphate  of  cop- 
per, nitrate  of  silver,  &c.),  producing,  in  some  cases,  dark  precipitates,  the  nature 
of  which  is  not  known  with  certainty. 

It  is  a  very  poisonous  gas,  and  great  care  should  be  taken  not  to  respire  it. 

Arseniuretted  hydrogen  is  sometimes  prepared  in  order  to  furnish  indications 
of  the  presence  of  arsenic  (Marsh's  test) ;  we  defer  the  details  of  the  process 
until  the  detection  of  arsenic  comes  under  consideration. 

TERCHLORIDE  or  ARSENIC,  AsCl8. 

To  prepare  this  substance,  arsenic  is  gently  heated  in  a  retort',  through  which 
a  current  of  dry  chlorine  is  passed;  or  it  may  be  obtained  by  distilling  the  metal 
with  6  parts  of  chloride  of  mercury  (corrosive  sublimate). 

It  is  a  colorless  liquid,  heavier  than  water,  and  boiling  at  270°  F.  (132°  C.) 
The  density  of  its  vapor  is  6.3. 

Terchloride  of  arsenic  is  decomposed  by  water,  yielding  hydrochloric  and 
arsenious  acids  : — * 

AsCl3-f3HO=As03-f3HCl. 

It  is  said  to  be  poisonous. 

No  pentachloride  of  arsenic  has  yet  been  obtained. 

A  compound  of  terchloride  of  arsenic  with  3  eqs.  of  chloride  of  sulphur  has 
been  obtained. 


ARSENIC   AND   SULPHUR. 

Subsulphide As6S 

Bisulphide As83 

Tersulphide AsS3 

Pentasulphide AsS5 

Octodeca-sulphide   ' AsS18 

1  A  hydrated  terchloride  of  arsenic  is  produced  when  the  terchloride  is  mixed  with  a 
small  quantity  of  water,  or  when  arsenious  acid  is  dissolved  in  hydrochloric  acid. 


442  SULPHIDES   OP  ARSENIC. 

§  801.  Sulphide  of  arsenic  (As6S)  is  obtained  by  digesting  realgar  with  a 
concentrated  solution  of  potassa ;  it  is  a  dark  brown  insoluble  substance,  which 
takes  fire  when  moderately  heated  in  air. 

BISULPHIDE  OF  ARSENIC,  RED  ORPIMENT,  REALGAR,  AsS2. 

This  substance  is  found  in  nature  crystallized  in  oblique  rhombic  prisms. 

It  may  be  prepared  by  fusing  1  eq.  of  metallic  arsenic  with  2  eqs.  of  sulphur, 
or  2  eqs.  of  arsenious  acid,  with  5  eqs.  of  sulphur. 

Realgar  is  a  soft  mineral  of  a  fine  brownish-red  color ;  when  heated,  it  fuses, 
and  may  be  sublimed  unchanged.  It  is  insoluble  in  water,  but  dissolves  in 
nitric  acid. 

The  bisulphide  of  arsenic  is  a  sulphur-acid,  forming  salts  with  the  sulphur- 
bases.  When  treated  with  potassa,  it  yields  arsenite  of  potassa,  subsulphide  of 
arsenic,  As6S,  which  is  precipitated,  and  a  soluble  compound  of  bisulphide  of 
arsenic  with  sulphide  of  potassium.  It  is  soluble  in  ammonia. 

Realgar  is  chiefly  employed  as  a  pigment ;  it  is  also  useful  in  pyrotechny ;  the 
well-known  Indian  fire,  which  burns  with  such  a  brilliant  white  light,  is  com- 
posed of  2  parts  of  realgar,  24  parts  of  nitre,  and  7  parts  of  flowers  of  sulphur. 

TERSULPHIDE  OF  ARSENIC,  KING'S  YELLOW,  YELLOW  ORPIMENT, 
SULPHARSENIOUS  ACID,  AsS3. 

The  tersulphide  is  found  in  nature  in  beautiful  crystalline  plates,  of  a  brilliant 
yellow  color,  and  generally  mixed  with  arsenious  acid.  It  may  be  artificially 
obtained  by  distilling  arsenic  or  arsenious  acid  with  sulphur : — 

2As03+S9=2AsS3+3S02; 

or  by  passing  sulphuretted  hydrogen  through  a  solution  of  arsenious  acid  acidu- 
lated with  hydrochloric  acid.  This  precipitate  is  a  hydrate. 

Tersulphide  of  arsenic  has  always  a  fine  yellow  color ;  when  heated  in  close 
vessels,  it  first  fuses,  then  sublimes.  Heated  in  contact  with  air,  it  burns  with 
a  pale  flame,  and  is  converted  into  arsenious  and  sulphurous  acids. 

The  tersulphide  is  scarcely  affected  by  hydrochloric  acid,  but  dissolves  readily 
in  nitric  acid  and  in  ammonia. 

It  is  a  powerful  sulphur-acid;  the  alkalies  and  their  carbonates  (the  latter 
with  evolution  of  carbonic  acid)  dissolve  it,  forming  arsenites  and  sulpharsenites: — 

5KO  +  2AsS3=3KS.AsS3+2KO.As03. 

Of  course,  it  dissolves  easily  in  alkaline  sulphides.  Tersulphide  of  arsenic  is 
poisonous.  It  is  used  in  dyeing ;  in  order  to  fix  orpiment  and  realgar  in  the 
fibre  of  the  fabric,  they  are  dissolved  in  ammonia,  and  thus  applied ;  as  the  sol- 
vent evaporates,  the  coloring  matter  is  precipitated. 

PENTASULPHIDE  OF  ARSENIC,  SULPHARSENIC  ACID,  AsS5. 

This  compound  may  be  prepared  by  treating  with  hydrosulphuric  acid  a  solution 
of  arsenic  acid  mixed  with  hydrochloric  acid ;  however,  since  the  precipitate  does 
not  deposit  till  after  a  considerable  period,  it  is  more  convenient  to  saturate  a 
solution  of  arseniate  of  potassa  (2KO.HO.As05)  with  sulphuretted  hydrogen, 
and  to  decompose  the  resulting  sulpharseniate  of  sulphide  of  potassium  (2KS, 
AsS5)  with  hydrochloric  acid : — 

2KO.HO  AsO.+7HS=8HO  +  2KS.AsS5; 
2KS.AsS5+2HCl=2KCl+2HS+AsS5. 

Pentasulphide  of  arsenic  is  a  yellow  solid,  which  fuses  a  little  above  the 
boiling-point  of  water,  and  acquires  a  reddish  color;  it  may  be  sublimed  un- 
changed. 


ARSENIDES.  443 

The  pentasulphide  much  resembles  the  tersulphide  in  solubility,  but  is  a  more 
powerful  sulphur-acid ;  it  expels  carbonic  acid  from  alkaline  carbonates,  hydro- 
sulphuric  acid  from  the  hydrosulphates  of  alkaline  sulphides,  and  forms  well- 
defined  sulphur-salts. 

There  exist  sulpharseniates  of  the  sulphides  of  potassium,  sodium,  and  ammo- 
nium, containing  respectively  6,  2,  and  3  eqs.  of  the  sulphide  of  either  of  these 
metals,  in  combination  with  sulpharsenic  acid ;  they  are  prepared  by  passing 
sulphuretted  hydrogen  through  the  arseniates  with  1,  2,  and  3  equivalents  of  fixed 
base. 

Octodeca-sulphide  of  Arsenic. — Berzelius  obtained  a  sulphide  of  arsenic  of  the 
formula  AsS18,  by  precipitating  with  alcohol  a  neutral  solution  of  sulpharseniate 
of  sulphide  of  potassium,  filtering,  and  evaporating  two-thirds  of  the  alcohol 
added,  when  the  new  compound  was  obtained  in  brilliant  yellow  crystals. 

ARSENIC  WITH  METALS. — Arsenic  combines  directly  with  several  metals;  the 
arsenide  of  manganese,  formed  by  the  combination  of  its  elements  at  a  red  heat, 
is  a  hard  gray  substance  with  metallic  lustre.  It  burns  in  air  with  a  bluish  flame 
and  alliaceous  odor ;  it  may  be  represented  by  Mn2As. 

Arsenic  and  iron  are  capable  of  combining  in  several  proportions,  forming 
compounds  which  are  harder,  more  brittle,  and  more  fusible  than  iron  itself. 

The  arsenides  of  iron  are  found  in  nature.  The  compound  FeAs  occurs  in 
some  specimens  of  iron-pyrites. 

Fe2As3  usually  constitutes  the  mineral  termed  arsenical  iron. 
FeAsa  exists  in  mispickel,  the  composition  of  which  may  be  expressed  by 
FeS2,FeAsa. 

Arsenides  of  nickel,  having  the  composition  NiAs  and  NiAs2,  are  natural  pro- 
ducts. 

Subarsenide  of  cobalt,  having  the  composition  Co3As2,  is  obtained  when  arse- 
niate  of  cobalt  is  reduced  by  hydrogen. 

Several  compounds  of  arsenic  and  cobalt  exist  in  the  mineral  kingdom ;  the 
chief  of  these  are  CoAs  and  CoaAs3.  The  latter  loses  arsenic  when  heated  in 
close  vessels. 

In  the  natural  sesqui- arsenide  of  cobalt,  part  of  the  latter  is  often  replaced  by 
iron  and  nickel. 

Pure  gray  cobalt-ore  (Tunaberg  cobalt)  may  be  expressed  by  the  formula 
CoAsa.CoS3. 

Cobalt-glance  contains  CoAs.CoS2. 

Arsenic  and  Copper. — A  very  small  quantity  of  arsenic  suffices  to  bleach 
copper  and  to  render  it  brittle,  as  may  be  seen  by  heating  this  metal  in  the  vapor 
of  arsenic. 

A  compound  of  the  formula  Cu4As  (white  tombac),  is  obtained  when  copper- 
filings  are  heated  with  an  equal  weight  of  arsenic.  Cu3As  is  prepared  by  the 
action  of  arseniuretted  hydrogen  upon  a  salt  of  copper.1 

Arsenic  and  Tin. — Tin  is  rendered  harder,  less  malleable,  and  highly  crystal- 
line when  alloyed  with  a  small  quantity  of  arsenic  (see  speculum-metal,  p.  389). 
These  metals  may  be  made  to  unite  directly  in  almost  any  proportion,  forming 
gray  brittle  compounds,  less  fusible  than  tin,  and  easily  oxidized  by  roasting. 
When  they  are  treated  with  hydrochloric  acid,  a  mixture  of  hydrogen  and  arse- 
niuretted hydrogen  is  disengaged,  and  a  little  arsenic  liberated  at  the  same  time. 
Pharmaceutical  Preparations  of  Arsenic. — Some  compounds  of  arsenic  are 
occasionally  used  in  medicine  and  surgery. 

The  arsenical  caustic  employed  in  cancer  is  prepared  by  fusing  arsenious  acid 
with  tersulphide  of  antimony. 

1  Condurrite  is  a  mixture  of  suboxide  of  copper,  arsenious  acid,  and  the  residue  of  the 
mineral  by  the  alteration  of  which  it  has  been  originally  formed;  according  to  Blyth,  the 
original  mineral  would  have  the  formula  Cu6As. 


444  TUNGSTEN. 

Arsenious  acid  in  the  pure  state,  is  also  sometimes  made  use  of,  but  it  is  more 
generally  employed  in  the  form  of  "  liquor  arsenicatis,"  which  is  a  solution  of 
arsenite  of  potassa,  prepared  by  dissolving  arsenious  acid  in  carbonate  of  potassa. 

The  sulphides  of  arsenic  have  also  been  employed  as  external  applications. 


TUNGSTEN. 

Sym.  W.     Eq.  95.     Sp.  Gr.  17.6. 

§  302.  This  metal,  which  is  by  no  means  very  abundant  in  nature,  is  found 
chiefly  in  the  mineral  wolfram,  which  contains  tungstic  acid  in  combination  with 
the  oxides  of  iron  and  manganese. 

Preparation. — Tungsten  may  be  obtained  by  reducing  tungstic  acid  with  dry 
hydrogen  at  a  high  temperature,  when  the  metal  is  left  in  a  finely-divided  state. 

It  is  procured  in  a  coherent  (but  not  fused)  mass,  by  strongly  heating  tungstic 
acid  in  a  crucible  lined  with  charcoal. 

Properties. — This  metal  has  a  dark  gray  color,  and  a  metallic  lustre  when 
rubbed ;  its  hardness  is  very  considerable ;  it  is  not  affected  by  air  at  the  ordi- 
nary temperature,  but,  when  heated  to  redness,  is  oxidized,  and  converted  into 
tungstic  acid.  It  is  not  volatile,  and  nearly  infusible.  It  is  not  affected  by 
water  at  the  ordinary  temperature,  but  at  high  temperatures  decomposes  it,  liberat- 
ing hydrogen,  and  forming  tungstic  acid. 

Hydrochloric  and  dilute  sulphuric  acids  do  not  act  upon  this  metal ;  concen- 
trated sulphuric  acid,  with  the  aid  of  heat,  oxidizes  it;  nitric  acid  readily  con- 
verts it  into  tungstic  acid. 

When  fused  with  hydrated  alkalies,  it  is  converted  into  a  tungstate,  hydrogen 
being  disengaged  ;  fused  nitrate  of  potassa  converts  it  into  tungstate  of  potassa. 

Tungsten  combines  directly  with  chlorine,  but  not  with  sulphur. 


TUNGSTEN  AND  OXYGEN. 

Binoxide  of  tungsten W09. 

Tungstic  acid       W03. 

An  intermediate  oxide  also  exists. 

<  .  •  ..  •.  .-',"",,•     s>.f 

BINOXIETE  OF  TUNGSTEN,  W0a. 

This  oxide  may  be  obtained  by  reducing  tungstic  acid  with  hydrogen  at  a 
carefully  regulated  temperature,  or  by  moistening  that  compound  with  hydro- 
chloric acid,  and  placing  it  in  contact  with  zinc. 

A  better  method  consists  in  fusing  1  part  of  wolfram  with  2  parts  of  carbo- 
nate of  soda,  in  a  platinum  crucible,  extracting  the  tungstate  of  soda  from  the 
fused  mass  with  water,  mixing  the  solution  with  J  part  of  chloride  of  ammonium, 
evaporating  to  dryness,  and  calcining  the  residue ;  a  mixture  of  chloride  of  sodium 
with  binoxide  of  tungsten  is  thus  obtained,  from  which  the  former  may  be  ex- 
tracted with  water ;  the  binoxide  should  be  digested  with  a  little  potassa  to 
remove  the  last  traces  of  tungstic  acid. 

Binoxide  of  tungsten  is  a  dark  brown  powder,  insoluble  in  water  and  acids ; 
when  boiled  with  solution  of  potassa,  it  yields  tungstate  of  potassa,  hydrogen 
being  disengaged.  When  heated  in  air,  binoxide  of  tungsten  is  converted  into 
tungstic  acid. 


COMPOUNDS   OP  TUNGSTEN.  445 

Binoxide  of  tungsten  is  an  indifferent  oxide. 

A  compound  of  this  oxide  with  soda,  having  the  formula  NaO.SWC^,1  is  ob- 
tained when  acid  tungstate  of  soda  is  reduced,  at  a  red  heat,  by  hydrogen ;  if 
the  resulting  mass  be  treated  with  water,  neutral  tungstate  of  soda  is  dissolved, 
and  the  new  compound  is  obtained  in  brilliant,  yellow  cubical  crystals  ;  it  should 
be  washed,  first  with  hydrochloric  acid,  -then  with  an  alkali,  to  free  it  from 
tungstic  acid. 

This  compound  is  remarkable  (among  soda-compounds)  for  its  insolubility  in 
water  and  acids. 

TUNGSTIC  ACID,  W03. 

This  acid  is  generally  prepared  from  the  mineral  wolfram,  which  may  be  re- 
presented by  the  general  formula  FeO,W03  -f-  MnO,WO3,  the  proportions  of 
the  two  tungstates  varying  in  different  specimens. 

This  mineral  forms  dark  brown  quadrilated  prisms,  with  considerable  lustre. 

In  order  to  prepare  tungstic  acid,  wolfram  is  treated  with  nitre-hydrochloric 
acid,  which  dissolves  the  oxides  of  iron  and  manganese,  leaving  tungstic  acid ; 
the  residue  is  collected  on  a  filter,  well  washed,  and  treated  with  ammonia,  which 
dissolves  the  tungstic  acid,  leaving  behind  any  silicious  matters  which  may  be 
present. 

The  tungstate  of  ammonia  may  be  crystallized  from  this  solution,  and  heated 
in  air,  when  tungstic  acid  is  left. 

Tungstic  acid  is  a  solid  of  a  straw-yellow  color ;  when  heated,  it  is  converted 
into  a  blue  intermediate  oxide^  W02,W03,  which  is  always  the  product  of  a  par- 
tial reduction  of  this  acid. 

Tungstic  acid  is  insoluble  in  water  and  acids ;  when  prepared  by  the  above 
method,  it  is  not  easily  soluble  in  alkalies,  but  if  it  be  obtained  by  decomposing 
an  alkaline  tungstate  with  hydrochloric  acid,  it  dissolves  readily  in  solutions  of 
the  fixed  alkalies  and  of  ammonia. 

Tungstic  acid  is  capable  of  existing  in  several  modifications,  which  bear  to 
each  other  a  relation  similar  to  that  between  stannic  and  inetastannic  acids.3 

Only  the  tungstates  ofpotassa,  soda,  and  ammonia  are  soluble  in  water.  These 
salts  are  composed  of  single  equivalents  of  acid  and  base. 

The  tungstates  are  decomposed  by  acids,  being  converted,  first  into  acid  tung- 
states, and  ultimately  into  pure  tungstic  acid. 

Solutions  of  the  neutral  tungstates  of  the  alkalies  are  not  precipitated  by  sul- 
phuretted hydrogen,  a  soluble  sulphur-salt  being  produced. 

When  tungstic  acid,  or  a  tungstate,  is  placed  in  contact  with  hydrochloric  acid 
and  zinc,  the  blue  intermediate  oxide  of  tungsten  is  obtained. 

The  tungstates  of  soda  and  lime  have  recently  been  applied  in  dyeing. 

Tungstic  acid  combines  with  the  strong  mineral  acids,  forming  sparingly-soluble 
compounds. 

CHLORIDES  OF  TUNGSTEN. 

The  bichloride  (WC12)  is  obtained  by  passing  chlorine  over  tungsten  heated  in 
a  tube;  it  forms  small  dark  red  needles,  which  are  very  fusible  and  volatile;  it 
is  decomposed  by  water. 

The  terchloride  (WC18),  also  red,  crystalline,  and  decomposed  by  water,  is 
formed  when  sulphotungstic  acid  is  heated  in  a  current  of  chlorine.  Its  vapor 
has  a  red-brown  color. 

When  chlorine  is  passed  over  tungstic  acid,  an  oxychloride  is  obtained,  of  the 
formula  WOaCi ;  it  forms  yellow  needles. 

1  Wright  has  obtained  this  compound  by  the  action  of  other  reducing  agents  upon  bi- 
tungstate  of  soda;  he  assigns  to  it  the  formula  W02.W03,NaO.W03. 

2  Laurent,  Ann.  Ch.  Phys.  [3]  xxi.  54. 


446  MOLYBDENUM  AND  OXYGEN. 


SULPHIDES  OF  TUNGSTEN. 

Tungstic  acid,  which  has  not  been  calcined,  dissolves  in  the  hydrosulphates  of 
alkaline  sulphides,  forming  sulphur-salts,  from  which  acids  precipitate  the  tersul- 
phide  of  tungsten,  or  sutphotunystic  acid,  WS3;  this  compound  has  a  brown  color, 
and  loses  sulphur  when  heated,  leaving  black  bisulphide  of  tungsten. 

Two  phosphides  of  tungsten  have  recently  been  obtained  by  Wohler.  The 
compound  W8Pa  is  a  dark  gray  powder,  prepared  by  heating  tungsten  in  vapor 
of  phosphorus.  The  other  phosphide,  W4P,  is  obtained  in  brilliant  prisms,  by 
reducing  a  mixture  of  tungstic  and  phosphoric  acids,  at  a  very  high  temperature, 
in  a  crucible  lined  with  charcoal. 

REACTIONS  OF  TUNGSTEN  {Tungstic  acid). — Sulphuric,  nitric,  and  hydro- 
chloric  acids;  white  precipitate,  insoluble  in  excess,  but  soluble  in  ammonia. 
These  precipitates  are  soluble,  to  a  slight  extent,  in  water. 

Hydrosulphuric  acid',  in  neutral  solutions,  no  precipitate,  but  if  the  solution 
be  afterwards  mixed  with  an  acid,  a  brown  precipitate  is  formed,  which  is  soluble 
in  sulphide  of  ammonium. 

Reducing  agents,  such  as  chloride  of  tin,  zinc,  in  presence  of  an  acid,  &c.,  pro- 
duce a  fine  blue  color. 

With  a  bead  of  phosphorous  salt;  in  the  outer  flame,  a  colorless  or  pale  yellow 
glass,  becoming  blue  in  the  inner  flame.  If  iron  be  present,  a  blood-red  bead  is 
obtained  in  the  inner  flame,  but  the  blue  color  is  produced  on  the  addition  of  a 
minute  quantity  of  metallic  tin. 


MOLYBDENUM. 

Sym.  Mo.  JEq.  46.  Sp.  Gr.  8.62. 

§  303.  This  metal  is  of  rare  occurrence  in  nature,  in  the  form  either  of  bisul- 
phide (molybdena~),  or  of  molybdate  of  lead. 

It  may  be  obtained  by  heating  molybdic  acid  to  redness  in  a  stream  of  hydro- 
gen, or  by  exposing  it,  in  a  crucible  lined  with  charcoal,  to  the  strongest  heat  of 
a  forge.  The  metal  is  obtained  by  the  latter  method,  in  masses  having  the  ap- 
pearance of  dead  silver,  which  acquire  a  lustre  when  rubbed.  It  is  very  infusible. 

When  exposed  to  air  (especially  if  reduced  by  hydrogen),  it  is  oxidized;  if 
heated  to  redness  in  air,  it  is  converted  first  into  a  brown  oxide,  then  into  a  blue 
intermediate  oxide,  and  lastly  into  white  molybdic  acid.  Molybdenum  decom- 
poses steam  at  a  high  temperature. 

Dilute  sulphuric  and  hydrochloric  acids  do  not  attack  it,  but  nitric  acid 
oxidizes  it  rapidly,  and  converts  it  into  molybdic  acid ;  nitre-hydrochloric  acid  is 
the  best  solvent  of  molybdenum. 


MOLYBDENUM    AND   OXYGEN. 

(Prot-)  oxide     .     .     .     ^;/4;^-*-.     MoO 
Binoxide Mo03 

Molybdic  acid        .     .  .>.•;  '>:«"#  -  v   .     .     Mo03 

OXIDE  OF  MOLYBDENUM,  MoO. 

Oxide  or  protoxide  of  molybdenum,  may  be  prepared  by  dissolving  a  molyb- 
date in  an  excess  of  hydrochloric  acid,  and  introducing  some  metallic  zinc ;  the 


MOLYBDIC   ACID.  447 

color  passes,  as  the  reduction  proceeds,  through  different  shades  of  blue  and 
brown,  and  finally  becomes  black,  when  the  solution  contains  chloride  of  molyb- 
denum, from  which  the  hydrated  oxide  is  precipitated  by  adding  an  excess  of 
potassa. 

Hydrated  oxide  of  molybdenum  is  brown,  insoluble  in  the  caustic  alkalies,  but 
soluble  in  carbonate  of  ammonia.  It  oxidizes  rapidly  when  exposed  to  air. 

This  oxide  dissolves  in  acids,  forming  salts. 

When  heated  in  vacua,  it  loses  water,  and  is  afterwards  converted,  with  sud- 
den incandescence,  into  a  modification  which  is  insoluble  in  acids. 

BINOXIDE  OF  MOLYBDENUM,  Mo03. 

This  oxide  is  obtained  in  the  anhydrous  state  by  calcining  molybdate  of  am- 
monia, or  a  mixture  of  molybdate  of  soda,  with  chloride  of  ammonium,  with 
exclusion  of  air ;  it  then  forms  a  red-brown  crystalline  powder. 

In  order  to  obtain  the  hydrate,  a  solution  of  molybdic  acid  in  hydrochloric 
acid  is  digested  with  copper,  and  the  solution,  then  containing  bichloride  of 
molybdenum  and  chloride  of  copper,  decomposed  with  excess  of  ammonia,  which 
precipitates  the  hydrated  binoxide  of  molybdenum.1 

This  substance  is  very  similar  in  appearance  to  hydrated  sesquioxide  of  iron; 
it  is  oxidized  by  exposure  to  air.  Binoxide  of  molybdenum  is  a  basic  oxide. 

MOLYBDIC  ACID,  Mo03. 

This  acid  (which  occurs  native  as  molybdic  ochre)  is  prepared  by  dissolving 
the  native  bisulphide  of  molybdenum  in  nitro- hydrochloric  acid,  evaporating  to 
dryness,  extracting  the  molybdic  acid  from  the  residue  by  treatment  with  am- 
monia, crystallizing  the  molybdate  of  ammonia  from  the  solution,  and  either 
separating  the  molybdic  acid  by  hydrochloric  acid,  or  by  calcining  the  salt  with 
access  of  air. 

Molybdic  acid  (which  has  not  been  ignited)  forms  a  white  mass;  it  may  be 
obtained  in  lustrous  needles.  When  heated  in  close  vessels,  it  fuses,  and  be- 
comes yellow ;  if  heated  in  a  current  of  air,  it  sublimes  easily,  in  a  crystalline 
state.  It  is  sparingly  soluble  in  cold,  but  more  soluble  in  hot  water;  the 
solution  reddens  litmus-paper.  This  acid  expels  carbonic  acid  from  alkaline 
carbonates. 

Reducing  agents,  as  zinc,  (proto-)  sulphate  of  iron,  &c.,  decompose  molybdic 
acid,  producing  a  blue  intermediate  oxide,  the  composition  of  which  is  expressed 
by  the  formula  Mo03.4Mo03.  This  compound  is  soluble  in  water,  and  is  pre- 
cipitated from  the  solution  by  chloride  of  ammonium.  It  is  easily  oxidized,  even 
on  exposure  to  air,  and  converted  into  molybdic  acid.  Acids  dissolve  it,  forming 
blue  solutions,  which  are  decolorized  by  potassa. 

A  green  intermediate  oxide  (Mo02.2Mo03)  is  formed  by  the  direct  combination 
of  its  proximate  constituents. 

The  neutral  molybdates  have  the  general  formula  MO.Mo03;  the  molybdates 
of  the  alkalies  are  colorless,  crystallizable,  and  soluble. 

The  other  molybdates  are,  for  the  most  part,  insoluble. 

If  the  solution  of  a  molybdate  be  not  too  dilute,  the  molybdic  acid  may  be 
precipitated  by  stronger  acids;  the  precipitate  is  soluble  in  excess  of  acid. 

Molybdic  acid  exhibits  a  peculiar  deportment  towards  phosphoric  acid,  which 
has  been  applied  in  testing  for  this  latter.  When  a  solution  of  molybdic  acid 
is  mixed  with  excess  of  ammonia,  some  phosphate  of  soda  added,  and  afterwards 
an  excess  of  nitric  acid,  a  yellow  precipitate  is  obtained,  which  was  found  by 

1  According  to  Kobell,  a  sesquioxide,  and  not  a  binoxide,  is  obtained  in  this  case;  he 
doubts  the  existence  of  a  biuoxide. 


448  CHLORIDES   OF   MOLYBDENUM. 

Sonnenschein  to  contain  about  3  per  cent,  of  phosphoric  acid,  and  86  per  cent, 
of  molybdic  acid,  together  with  molybdate  of  ammonia  and  water ;  the  precipi- 
tate is  insoluble  in  dilute  acids,  but  soluble  in  alkalies  and  their  carbonates. 
Arsenic  acid  does  not  yield  a  similar  precipitate,  unless  the  liquid  be  heated  to 
boiling. 

CHLORIDES  OF  MOLYBDENUM. 

The  (profo-")  chloride  is  obtained  by  dissolving  the  hydrated  (prot-)  oxide  in 
hydrochloric  acid. 

Bichloride  of  molybdenum,  MoCl2,  is  obtained  when  molybdenum  is  heated  in 
chlorine ;  it  forms  a  red  vapour,  which  condenses  into  crystals  resembling  iodine, 
and  is  easily  soluble  in  water. 

A  soluble  oxy-chloride  of  molybdenum,  of  the  formula  Mo02Cl,  has  been  pre- 
pared by  heating  binoxide  of  molybdenum  in  chlorine. 

Bisulphide  of  molybdenum  (MoSa)  is,  as  already  mentioned,  found  native ;  it 
has  a  lead-gray  color,  and  much  resembles  graphite;  it  is  not  affected  by  a 
moderate  heat  in  closed  vessels,  but  is  converted  into  molybdic  acid  by  roasting. 

Nitric  acid  converts  it  into  molybdic  acid.  Boiling  concentrated  sulphuric 
acid  attacks  it,  producing  a  blue  solution,  and  evolving  sulphurous  acid. 

Two  other  sulphides  of  molybdenum  exist,  having  the  formulas  MoS3  and 
MoS4. 

REACTIONS  OF  MOLYBDENUM. — {Protoxide.} — The  alkalies;  a  brownish- 
black  precipitate,  insoluble  in  excess. 

The  alkaline  carbonates;  brownish-black  precipitates,  slightly  soluble  in 
excess  of  the  fixed  alkaline  carbonates,  but  more  easily  soluble  in  excess  of 
carbonate  of  ammonia,  from  which  solution  the  oxide  is  reprecipitated  upon 
boiling. 

•Hydrosulphuric  acid  and  sulphide  of  ammonium  (the  former  not  immedi- 
ately) ;  brown  precipitates,  soluble  in  sulphide  of  ammonium. 

(Binoxide.') — The  alkalies;  dark-brown  precipitates,  insoluble  in  excess. 

The  alkaline  carbonates  ;  light-brown  precipitates,  soluble  in  excess. 

Hydrosulphuric  acid  and  sulphide  of  ammonium  (the  former  after  a  time)  ', 
brown  precipitates,  soluble  in  sulphide  of  ammonium. 

Ferrocyanide  and  ferricyanide  of  potassium;  brown  precipitates. 

(^Molybdic  acid.} — Hydrochloric  and  nitric  acids  ;  in  moderately  concentrated 
solutions,  white  precipitates,  soluble  in  excess. 

Hydrosulphuric  acid ;  in  acid  solutions,  a  brown  precipitate,  the  supernatant 
liquid  being  green.  If  the  solution  is  dilute,  a  green  color  only  is  obtained. 
The  addition  of  a  very  small  quantity  of  sulphuretted  hydrogen  colors  the 
solution  blue. 

Sulphide  of  ammonium,  after  some  time,  renders  solutions  of  alkaline  molyb- 
dates  of  a  golden-yellow  color,  and  acids  precipitate  brown  tersulphide  of 
molybdenum. 

Chloride  of  tin;  a  greenish-blue  precipitate,  or,  in  dilute  solutions,  a  blue 
coloration. 

Tin,  zinc,  and  copper  ;  in  acid  solutions,  a  blue  coloration,  afterwards  becoming 
green,  and  finally  brown. 

With  a  bead  of  microcosmic  salt;  in  the  inner  blowpipe-flame,  a  green  bead, 
the  color  of  which  is  fainter  in  the  outer  flame;  with  borax  in  the  inner  flame,  a 
brownish-red  bead. 


TELLURIUM  AND  OXYGEN.  449 


TELLURIUM. 

Hi 

Sym.  Te.     Eq.  64.2.     Sp.  Gr.  6.2. 

§  304.  This  very  rare  element  presents  so  great  an  analogy  to  sulphur  and 
selenium  that  it  is  often  classed  among  the  non-metallic  bodies. 

Tellurium  was  originally  discovered  in  certain  Transylvanian  gold  ores,  in 
combination  with  gold,  silver,  copper,  and  lead;  it  has  been  more  recently  found 
in  combination  with  bismuth. 

Preparation. — The  telluride  of  bismuth  is  heated  to  bright  redness,  with  an 
equal  weight  of  carbonate  of  potassa  and  charcoal;  the  bismuth  is  reduced,  while 
the  tellurium  is  converted  into  telluride  of  potassium,  which  dissolves  when  the 
fused  mass  is  treated  with  water;  when  this  (purplish-red) solution  is  exposed  to 
air,  the  tellurium  is  deposited,  and  may  be  purified  by  washing  with  a  little  acid. 

Properties — Tellurium  has  a  silvery  lustre;  in  texture  it  is  crystalline  and 
brittle.  It  fuses  at  about  the  same  temperature  as  antimony,  crystallizes  easily 
from  a  fused  state,  and  appears  to  be  isomorphous  with  antimony  and  arsenic. 
Tellurium  volatilizes  at  a  high  temperature.  Whenr  heated  in  air,  it  burns  with 
a  bright-blue  flame. 

It  dissolves  unchanged  in  concentrated  sulphuric  acid,  imparting  to  it  a  purple- 
red  color.  When  heated  with  solutions  of  the  alkalies,  it  yields  tellurides  and 
tellurites. 


TELLURIUM  AND   OXYGEN. 

Tellurous  acid .     TeOa. 

Telluric  acid Te03. 

TELLUROUS  ACID,  Te03. 

This  acid  is  obtained  when  tellurium  is  burnt  with  free  access  of  air.  It  may 
be  prepared  by  oxidizing  the  metal  with  nitric  acid,  or  by  decomposing  bichloride 
of  tellurium  with  water,  when  the  acid  is  deposited  in  octohedra. 

Tellurous  acid  is  a  white,  crystalline,  fusible  powder,  capable  of  sublimation, 
and  insoluble  in  water  and  acids  ;  it  dissolves  in  alkalies,  forming  tellurites,  from 
which  acids  precipitate  the  hydrated  tellurous  acid ;  this  hydrate  is  soluble  in 
hydrochloric  acid,  and  expels  the  carbonic  acid  when  heated  with  solutions  of 
alkaline  carbonates. 

TELLURIC  ACID,  Te03. 

Telluric  acid  is  prepared  by  passing  chlorine,  to  saturation,  into  a  solution  of 
tellurite  of  potassa,  mixed  with  excess  of  potassa ;  the  solution  of  tellurate  of 
potassa  thus  obtained  is  precipitated  by  chloride  of  barium,  and  the  tellurate  of 
baryta  decomposed  with  sulphuric  acid. 

The  hydrated  telluric  acid  crystallizes  in  six-sided  prisms,  containing  three  eqs. 
of  water,  and  is  soluble;  when  moderately  heated  it  loses  two  eqs.  of  water, 
and  at  a  higher  temperature,  becomes  anhydrous  and  insoluble ;  if  heated  still 
further,  it  loses  oxygen,  and  is  converted  into  tellurous  acid. 

If  a  solution  of  a  tellurate  be  acidulated  with  hydrochloric  acid,  and  heated 
with  sulphurous  acid,  a  black  precipitate  of  tellurium  is  formed. 

The  tellurates  evolve  oxygen  when  heated,  leaving  tellurites.     They  are  de- 
composed even  by  acetic  acid. 
29 


TITANIUM. 

TELLURETTED  HYDROGEN.     HYDROTELLURIC  ACID,  HTe. 

This  compound  is  obtained  by  decomposing  telluride  of  potassium  or  of  iron 
with  hydrochloric  acid. 

It  is  a  colorless  gas,  having  an  odor  like  that  of  sulphuretted  hydrogen ;  its 
specific  gravity  is  5.12. 

Telluretted  hydrogen  is  soluble  in  water ;  the  solution  is  decomposed  by  the 
oxygen  of  the  air,  and  yields  a  brown  precipitate  of  tellurium.  It  is  inflammable, 
and  deposits  tellurium  when  burnt.  It  acts  upon  solutions  of  metallic  oxides 
like  hydrosulphuric  acid. 

CHLORIDE  OF  TELLURIUM  (TeCl)  obtained  by  strongly  heating  the  metal  in 
a  feeble  current  of  chlorine,  is  a  black  solid  ;  its  vapor  is  violet-colored. 

Water  decomposes  the  chloride  into  bichloride  and  metal. 

The  bichloride  (TeCla)  is  prepared  by  gently  heating  tellurium  in  an  excess  of 
chlorine ;  it  is  a  white,  crystalline,  volatile  solid,  soluble  in  water. 

A  bisulphide  and  a  tersulphide  of  tellurium  are  known ;  the  latter  is  very  un- 
stable. These  sulphides  are  sulphur-acids. 

The  tellurides  of  the  metals  are  very  similar  to  the  sulphides  and  selenides. 
The  alkaline  tellurides  have  a  reddish-brown  color,  and  yield  red  solutions. 
When  a  telluride  is  boiled  with  nitric  acid,  tellurous  acid  is  formed,  the  other 
metal  being  converted  into  a  nitrate. 

REACTIONS  OP  TELLURIUM  (Tellurous  acid). — Alkalies  and  their  carbo- 
nates ;  white  precipitate,  soluble  in  excess. 

Bydrosulphuric  acid,  in  acid  solutions,  brown  precipitate,  soluble  in  the  alka- 
line sulphides. 

Reducing  agents,  e.  g.  sulphurous  acid,  chloride  of  tin,  zinc,  &c. ',  black  pre- 
cipitate. 

(Telluric  Acid.) — Hydrosulphuric  acid,  in  acid  solutions,  black  precipitate, 
soluble  in  alkaline  sulphides. 

Reducing  agents ;  same  result  as  with  tellurous  acid. 


TITANIUM. 

(Although  the  reactions  of  this  metal  would  entitle  it  to  a  place  in  the  third 
group,  it  so  much  resembles  tin,  in  the  general  characters  of  its  compounds,  that 
we  have  deferred  giving  its  history  until  that  metal  had  been  described.) 

Sym.  Ti.     JBq.  25.     Sp.  Gr.  5.3. 

§  305.  Titanium  is  a  rare  metal,  which,  in  its  compounds,  very  much  resem- 
bles tin. 

It  is  found  in  nature  chiefly  in  the  minerals  rutile,  anatase,  brookite,  and 
titanic  iron. 

Rutile,  brookite,  and  anatase,  are  almost  entirely  composed  of  titanic  acid. 

Titanic  iron  ores  contain  titanate  of  iron  mixed  with  more  or  less  oxide  of  iron. 

Titanite,  or  sphene,  is  a  compound  of  titanate  and  silicate  of  lime. 

Preparation. — The  following  process  is  that  generally  adopted  for  the  prepa- 
ration of  titanium. 

A  mixture  of  finely-powdered  rutile  with  twice  its  weight  of  carbonate  of 
potassa  is  fused  in  a  platinum  crucible;  the  fused  mass  is  powdered,  and  treated 
with  dilute  hydrofluoric  acid,  which  converts  it  into  a  sparingly-soluble  titano- 
fluoride  of  potassium  (a  double-fluoride  of  titanium  and  potassium).  This  com- 
pound is  ignited  to  expel  all  traces  of  water,  and  heated  in  a  covered  platinum 


TITANIUM   AND   OXYGEN.  451 

crucible  with  potassium ;  when  the  violent  reaction  has  terminated,  the  mass  is 
allowed  to  cool  and  treated  with  water,  which  dissolves  the  fluoride  of  potassium, 
leaving  only  the  titanium. 

Properties. — Titanium  thus  obtained  is  a  dark  green,  infusible,  amorphous 
powder.  When  heated  in  air,  it  burns  vividly,  and  is  converted  into  titanic 
acid.  When  heated  with  oxide  of  lead  or  of  copper,  it  is  also  converted  into 
titanic  acid  with  vivid  incandescence. 

Titanium  decomposes  water  even  at  the  boiling-point,  producing  titanic  acid. 

This  metal  is  dissolved  by  hot  hydrochloric  acid,  with  disengagement  of  hydro- 
gen.1 When  fused  with  a  mixture  of  hydrate  and  nitrate  of  potassa,  it  is  con- 
verted into  titanate  of  potassa. 


TITANIUM  AND  OXYGEN. 

Oxide  of  titanium TiO 

Sesquioxide     "         Ti20y 

Titanic  acid  TiO.,, 


OXIDE,  OR  PROTOXIDE  OF  TITANIUM,  TiO. 

This  oxide  is  obtained  when  titanic  acid  is  heated  with  potassium.  It  has  a 
black  color,  and  is  infusible ;  when  heated  in  air,  it  is  converted  into  titanic 
acid.  Oxide  of  titanium  dissolves  slowly  in  acids  and  alkalies;  it  forms  a  blue 
hydrate,  which  absorbs  oxygen  from  the  air,  and  decomposes  water. 

SESQUIOXIDE  OP  TITANIUM,  Ti303. 

When  titanic  acid  is  reduced  by  hydrogen  at  a  high  temperature,  toe-  sesqui- 
oxide  is  obtained  as  a  black  powder.  The  hydrate  falls  as  a  gelatinous  brown 
precipitate  when  sesquichloride  of  titanium  is  decomposed  by  alkalies ;  when  ex- 
posed to  air,  it  absorbs  oxygen,  becoming  black,  then  blue,  and  lastly  white, 
being  converted  into  titanic  acid. 

Sesquioxide  of  titanium  possesses  basic  characters ;  it  dissolves-  in  sulphuric 
acid,  forming  a  violet  solution. 

TITANIC  ACID,  TiOa. 

Titanic  acid,  as  before  mentioned,  is  found  nearly  pure  in  rutile,  which  con- 
tains generally  1  or  2  per  cent,  of  oxide  of  iron. 

Rutile  is  isomorphous  with  native  binoxide  of  tin,  and,  like  that  mineral,  is 
not  attacked  by  acids. 

Anatase,  also  nearly  pure  titanic  acid,  forms  fine  blue  crystals. 

Brookite  forms  opaque  prismatic  crystals,  and  contains  very  little  iron. 

Preparation. — In  order  to  obtain  perfectly  pure  titanic  acid,  finely-powdered 
rutile  is  fused,  at  a  very  high  temperature,  with  2  or  3  times  its  weight  of  chlo- 
ride of  barium.  The  fused  mass  is  powdered  and  treated  with  hot  water,  which 
dissolves  the  excess  of  chloride  of  barium,  leaving  a  residue  of  titanate  of  baryta 
and  sesquioxide  of  iron ;  this  residue  is  boiled  with  concentrated  sulphuric  acid, 
the  greater  excess  of  the  latter  expelled  by  heat,  and  the  residue  treated  with 
water;  the  whole  of  the  baryta  is  left  as  insoluble  sulphate,  whilst  the  solution 
contains  the  titanic  acid  in  combination  with  sulphuric  acid,  together  with  sul- 
phate of  sesquioxide  of  iron ;  a  little  sulphuretted  hydrogen  is  passed  through 
the  solution,  to  remove  any  tin  which  might  be  present,  and  the  acid  is  then 
neutralized  with  ammonia,  which  precipitates  the  titanic  acid  colored  with  a  little 

1  Wohler. 


452 


CHLORIDES   OF   TITANIUM. 


sulphide  of  iron ;  the  supernatant  liquor  is  decanted  from  the  precipitate,  and 
the  latter  digested  with  a  solution  of  sulphurous  acid,  which  removes  the  sul- 
phide of  iron  in  the  form  of  hyposulphite,  and  leaves  the  titanic  acid  in  a  state 
of  purity. 

Properties. — The  hydrate  (Ti03.HO)  in  appearance  much  resembles  alumina; 
it  is  distinguished  by  a  remarkable  tendency  to  pass  through  filters;  it  is  soluble 
in  some  acids  (e.  g.  hydrochloric),  but  not  readily  in  alkalies. 

The  acid  solutions  deposit  most  of  the  titanic  acid  when  boiled.  When  dried, 
hydrated  titanic  acid  becomes  insoluble  in  all  acids  except  concentrated  sulphuric ; 
it  assumes  a  yellow  color  when  heated,  and  becomes  white  again  on  cooling. 

Anhydrous  titanic  acid  is  infusible,  fixed,  and  insoluble;  it  reddens  blue  litmus. 
"When  titanic  acid  is  fused  with  alkalies,  it  forms  masses  which  crystallize  on 
cooling,  and  are  decomposed  by  water  into  insoluble  and  highly  acid  titanates, 
whilst  but  little  titanic  acid  is  found  in  solution. 

NITRIDES  OF  TITANIUM. — When  bichloride  of  titanium  is  treated  with  dry 
ammonia,  it  forms  a  white  compound,  which,  when  heated  in  a  stream  of 
ammoniacal  gas,  leaves  a  residue  of  brilliant  purple  scales  of  nitride  of  titanium, 
having  the  formula  Ti3Na.  When  this  compound  is  heated  in  a  current  of  hydro- 
gen, yellow  lustrous  scales  are  obtained,  the  composition  of  which  is  Ti5N3. 

If  titanic  acid  be  heated  in  a  porcelain  tube  through  which  dry  ammonia  is 
passed,  it  is  converted  into  a  violet  powder,  which  is  a  third  nitride  of  titanium, 
TiN. 

In  the  furnaces  in  which  iron-ores  containing  titanium  are  smelted,  crystals 
are  sometimes  found,  which  were  formerly  thought  to  be  metallic  titanium,  but 
have  been  recently  shown  to  be  represented  by  the  formula  TiCy.3Ti3N.  This 
most  curious  compound  forms  coppery-red  cubical  crystals,  which  volatilize  at  a 
high  temperature,  and  are  so  hard  as  to  scratch  quartz. 

The  nitrides  of  titanium  are  remarkable  for  their  stability,  resisting  a  high 
temperature  without  decomposition. 

CHLORIDES  OF  TITANIUM. 

Sesquichloride  of  Tifamum,  Ti2Cl3,  is  obtained  by  passing  through  a  tube 
heated  to  redness,  a  current  of  hydrogen  saturated  at  212°.  F.  (100°  C.)  with 
vapor  of  bichloride  of  titanium,  when  crystals  of  the  sesquichloride  condense  upon 
the  cooler  parts  of  the  tube  : — 

2TiCl3+ H=TiaCl3 + HC1. 

This  compound  forms  dark  violet  scales,  which  deliquesce  when  exposed  to 
air,  forming  a  violet  liquid.  It  is  a  most  powerful  dechlorinating  (or  deoxidiz- 
ing) agent ;  it  precipitates  the  noble  metals  from  their  solutions,  reduces  the 
higher  oxides  of  iron  and  copper,  and  is  even  said  to  be  capable  of  separating 
sulphur  from  sulphurous  acid. 

Bichloride  of  Titanium,  TiCl3,  is  prepared  by  passing  chlorine  over  a  mixture 
of  titanic  acid  and  carbon  at  a  red  heat.  It  forms  a  colorless  liquid,  very  similar 
to  bichloride  of  tin  ;  it  fumes  in  the  air,  and  boils  at  275°  F.  (135°  C.)  In  its 
behavior  with  water  it  much  resembles  the  bichloride  of  tin  ;  with  a  small 
quantity  it  combines,  forming  a  crystalline  compound,  which  is  decomposed  by 
a  larger  quantity  into  hydrochloric  acid  and  titanic  acid ;  this  latter  is  partly 
dissolved  by  the  hydrochloric  acid,  but  is  reprecipitated  on  boiling. 

Bisulphide  of  Titanium  (TiS3)  is  formed  by  passing  through  a  tube  heated 
to  redness,  a  mixture  of  sulphuretted  hydrogen  and  vapor  of  bichloride  of 
titanium. 

It  forms  brilliant  yellow  scales,  very  similar  to  aurum  musivum  (bisulphide 
of  tin),  which  are  decomposed  by  moist  air,  evolving  sulphuretted  hydrogen  ; 
when  heated  in  air,  bisulphide  of  titanium  is  converted  into  sulphurous  and 


TITANIUM.  453 

titanic  acids ;  hydrochloric  acid  decomposes  it  with  disengagement  of  hydro- 
sulphuric  acid. 

REACTIONS  OF  TITANIUM  (Sesquioxide^. — Alkalies  and  their  carbonates; 
dark  brown  precipitates  gradually  decomposing  water,  becoming  black,  blue,  and 
finally  white. 

Sulphide  of  ammonium,  a  similar  precipitate. 

Solutions  of  gold,  silver,  and  mercury  are  reduced  to  the  metallic  state. 

(Titanic  Acid.) — Alkalies  and  alkaline  carbonates;  white  precipitate,  insolu- 
ble in  excess. 

Sulphide  of  ammonium;  a  similar  precipitate. 

Oxalic  acid;  white  precipitate  (if  the  solution  do  not  contain  too  much  hy- 
drochloric acid). 

Metallic  zinc  ;  in  presence  of  free  acid,  a  blue  solution  which  deposits,  after  a 
time,  a  blue  precipitate,  becoming  white  on  standing. 

With  a  bead  of  phosphorus-salt,  in  the  inner  flame,  a  bead  which  is  yellow 
while  hot,  and  becomes  violet  on  cooling ;  in  the  outer  flame  the  bead  is  ren- 
dered colorless.  If  iron  be  present,  the  bead  produced  in  the  inner  flame  as- 
sumes a  brown-red  color  on  cooling ;  the  blue  color  may  then  be  produced  by 
an  addition  of  tin. 


454  MERCURY. 


METALS  OF  THE  FIFTH  GROUP. 


MERCURY.1 

(  Quicksilver.*) 

Sym.  Hg.     Eq.  100.     Sp.  Gr.  13.595. 

§  306.  THIS  is  the  only  metal  which  is  not  solid  at  ordinary  temperatures. 

The  mercury  of  commerce  is  never  perfectly  pure,  as  may  be  seen  by  scatter- 
ing a  little  upon  a -smooth  plate  of  glass,  when,  instead  of  forming  small  spher- 
oidal globules,  as  is  the  case  with  the  pure  metal,  it  gives  pyriform  drops  which 
leave  a  gray  trace  where  they  roll  along  the  glass. 

When  mercury  is  very  impure,  it  is  subjected  to  distillation,  the  iron  bottles 
in  which  it  is  imported  being  used  as  retorts ;  but  since  this  process  is  very 
rarely  executed  in  laboratories,  we  shall  not  enter  into  details  respecting  it. 

The  simplest  process  for  purifying  mercury  from  the  lead  and  tin  which  the 
commercial  metal  usually  contains,  consists  in  stirring  it  in  a  Wedgwood  or  por- 
celain dish,  with  a  mixture  of  nitric  acid  and  two  volumes  of  water ;  the  con- 
tents of  the  dish  are  heated  to  about  130°  F.  (54°. 5  C.)  for  several  hours,  with 
frequent  agitation ;  the  foreign  metals,  being  more  easily  oxidized  than  the  mer- 
cury, are  dissolved  by  the  acid,  while  that  metal  is  left  in  a  state  of  purity ;  the 
supernatant  liquid  is  removed  by  decantation,  the  mercury  well  washed  with 
water,  and  dried,  first  with  blotting-paper,  and  afterwards  by  a  gentle  heat. 
Should  it  be  found  that  the  mercury  is  still  impure,  the  treatment  with  nitric 
acid  may  be  repeated. 

Properties. — Pure  mercury  has  a  slightly  bluish-white  color  and  a  brilliant 
lustre.  It  solidifies  at  a  temperature  of— 40°  F.  (-40°  C.),  which  may  be  ob- 
tained with  solid  carbonic  acid  and  ether,  or  more  easily  with  pounded  ice  and 
crystallized  chloride  of  calcium.  If  it  be  slowly  solidified,  the  metal  crystallizes 
in  octohedra.  Solid  mercury  much  resembles  lead  and  tin  in  malleability  and 
tenacity ;  its  specific  gravity  is  13.39,  showing  that,  like  water,  mercury  expands 
in  the  act  of  solidifying. 

This  metal  boils  at  about  660°  F.  (349°  C.)  yielding  a  transparent  vapor  of 
sp.  gr.  6.976. 

Mercury  suffers  a  very  considerable  expansion  by  heat;  and  since,  between  the 

1  Mercury  and  lead,  although  often  occurring,  in  the  course  of  analysis,  under  the 
fourth  group,  are  here  placed  by  the  side  of  silver,  because  mercury  forms  a  subchloride 
which,  like  chloride  of  silver,  is  insoluble  in  water ;  and  the  chloride  of  lead,  though  not 
absolutely  insoluble,  is  most  frequently  precipitated  together  with  the  chloride  of  silver 
and  subchloride  of  mercury.  We  seize  this  opportunity  of  repeating  the  caution  given  in 
the  outset,  that  this  classification  should  only  be  regarded  as  an  arbitrary  division,  in- 
tended to  facilitate  the  subsequent  study  of  analysis,  and  not  as  founded  upon  any  close 
analogies  in  the  chemical  relations  of  the  metals  composing  individual  groups.  The  other 
methods  of  arranging  the  metals  (according  to  their  affinity  for  oxygen,  or  their  power  of 
decomposing  water),  although  more  strictly  philosophical,  have  appeared  to  us  to  possess 
less  practical  utility  than  the  division  which  we  have  adopted. 


MERCURY  AND   OXYGEN.  455 

freezing  and  boiling-points  of  water,  its  expansion  is  nearly  proportional  to  the 
amount  of  heat  which  it  receives,  it  is  very  useful  for  thermometric  purposes. 
The  expansion  suffered  by  this  metal  between  32°  F.  and  212°  F.  amounts  to 
0.018153  of  its  volume  at  32°. 

That  mercury  volatilizes  even  at  ordinary  temperatures,  is  shown  by  the  con- 
densation of  minute  globules  of  the  metal  in  the  vacuum  of  the  barometer.  It 
appears,  however,  that  the  properties  of  vapor  of  mercury  differ  from  those  of 
ordinary  vapors,  for  it  is  found  that  if  a  leaf  of  gold  be  suspended  in  a  bottle 
containing  a  small  quantity  of  mercury  at  a  rather  low  temperature,  only  that 
portion  of  the  gold  which  is  nearest  to  the  mercury  becomes  whitened,  the  upper 
part  retaining  its  yellow  color,  showing  that  the  atmosphere  of  mercurial  vapor 
is  limited  to  a  small  space  above  the  surface  of  the  metal.1 

When  mercury  is  boiled  with  water,  a  considerable  quantity  of  the  metal 
passes  over  with  the  steam. 

Perfectly  pure  mercury  evinces  no  attraction  for  surfaces  of  glass  or  porcelain, 
so  that  in  vessels  made  of  these  materials,  the  mercury  assumes  a  convex  sur- 
face ;  but  if  4^^  of  lead  be  dissolved  in  it,  the  surface  is  plane  :  this  circumstance 
is  turned  to  advantage  in  the  graduation  of  glass  tubes  with  the  aid  of  mercury. 

When  mercury  is  violently  agitated  with  saline  solutions,  it  is  divided  into 
numerous  minute  globules,  which  are  reunited  with  some  difficulty.  Mercury 
is  capable  of  retaining,  mechanically,  small  quantities  of  air  and  water,  from 
which  it  can  be  freed  only  by  continued  ebullition. 

This  metal  is  not,  to  any  extent,  and  it  is  questionable  whether  it  be  in  the 
least,  affected  by  exposure  to  air  at  the  ordinary  temperature ;  when  heated  to  a 
temperature  approaching  its  boiling-point,  for  some  hours,  in  a  long-necked  flask, 
with  free  access  of  air,  it  is,  to  a  considerable  extent,  converted  into  small  red 
crystals  of  oxide  of  mercury.  This  experiment  must  always  possess  a  peculiar 
interest,  since,  in  the  hands  of  Lavoisier,  it  gave  rise  to  the  discovery  of  the 
composition  of  atmospheric  air. 

Mercury  does  not  decompose  water  at  any  temperature. 

Nitric  acid  dissolves  mercury  even  at  the  ordinary  temperature,  but  very  rapidly 
when  heated,  producing  nitrate  of  the  suboxide,  or  of  the  oxide,  according  as 
the  metal  or  the  acid  is  in  excess. 

Hydrochloric  acid  does  not  act  upon  mercury ;  hydriodic  and  hydrosulphuric 
acids  convert  it,  respectively,  into  subiodide  and  subsulphide  of  mercury,  hydro- 
gen being  set  free. 

Dilute  sulphuric  acid  has  no  action  upon  mercury,  but  the  concentrated  acid, 
with  the  aid  of  heat,  converts  it  into  a  sulphate  of  one  of  its  oxides,  sulphurous 
acid  being  disengaged.  Mercury  combines  directly  with  chlorine,  bromine, 
iodine,  sulphur,  and  with  many  of  the  metals,  especially  with  potassium,  sodium, 
zinc,  copper,  gold,  tin,  and  lead.  Its  compounds  with  the  metals  are  termed 
amalgams. 

Mercury  exerts  a  powerful  action  upon  the  animal  economy,  and  materially 
injures  the  health  of  workmen  engaged  in  employments  where  this  metal  is 
largely  used. 

MERCURY  AND  OXYGEN. 

Suboxide Hg2O 

Oxide2 HgO 

1  Karsten  has  found  that  the  volatilization  of  mercury  is  perceptible  even  at  tempera- 
tures below  32°. 

2  The  equivalent  of  mercury  was  formerly  considered  by  some  chemists  as  200,  when 
the  suboxide  of  mercury  was  regarded  as  a  protoxide,  HgO,  and  the  present  protoxide 
was  looked  upon  as  a  binoxide,  Hg08. 


456  MERCURY  AND   OXYGEN. 


SUBOXIDE  OF  MERCURY,  BLACK  OXIDE,  HgaO. 

§  307.  Preparation. — The  black  oxide  may  be  prepared  by  decomposing  pre- 
cipitated subchloride  of  mercury  with  cold  potassa,  light  being  excluded.  It  is 
also  obtained  as  a  black  precipitate  when  a  solution  of  a  salt  of  suboxide  of  mer- 
cury is  decomposed  by  potassa,  but  is  then  almost  always  mixed  with  metallic 
mercury  (arising  from  the  decomposition  of  a  part  of  the  suboxide),  as  may  be 
seen  by  examining  the  precipitate  with  a  lens,  or  by  triturating  it  in  a  mortar, 
when  the  metal  accumulates  into  globules. 

Properties. — Suboxide  of  mercury  is  a  weak  base ;  it  has  a  black  color  and  is 
exceedingly  unstable,  being  decomposed  by  exposure  to  light,  or  to  a  slightly 
elevated  temperature,  into  oxide  of  mercury  and  free  metal : — 

Hg30=Hg04-Hg; 
this  speaks  strongly  in  favor  of  its  being  a  suboxide. 

The  soluble  neutral  salts  of  suboxide  of  mercury  have  an  acid  reaction. 

NITRATE  or  SUBOXIDE  OP  MERCURY,  SUBNITRATE  OP  MERCURY, 
PROTONITRATE  or  MERCURY,  HgaO.N05. 

This  salt  is  prepared  by  acting  upon  a  slight  excess  of  mercury  with  nitric 
acid,  in  the  cold ;  it  is  also  formed  when  peroxide  of  nitrogen  (N04)  acts  upon 
metallic  mercury. 

This  nitrate  forms  fine  colorless  crystals  of  the  formula  HgaO.N05  -f-  2  Aq, 
which  dissolve  in  nitric  acid,  but  are  decomposed  by  water  into  a  basic  nitrate, 
2Hg3O.N05,  which  is  precipitated,  and  an  acid  nitrate  which  passes  into  solution. 

The  same  basic  nitrate  is  deposited  in  oblique  rhombic  prisms  of  the  formula 
2Hg2O.N05-f  HO,  when  the  neutral  nitrate  is  dissolved  in  a  small  quantity  of 
hot  water  or  nitric  acid,  and  the  solution  allowed  to  cool.  When  the  neutral 
nitrate  is  heated,  a  yellow  basic  compound  is  produced,  the  composition  of  which 
is  expressed  by  the  formula  Hg30.2HgO.N05. 

When  a  very  large  excess  of  mercury  is  acted  on  by  nitric  acid  in  the  cold, 
crystals  of  a  basic  nitrate  are  deposited,  having  the  composition  3Hg20,2N05 
-f-8Aq.  This  salt  may  readily  be  distinguished  from  the  neutral  salt  by  triturat- 
ing in  a  mortar  with  a  little  chloride  of  sodium ;  the  neutral  salt  remains  white, 
but  the  basic  compound  gives  a  black  color,  from  the  separation  of  suboxide  of 
mercury. 

The  compound  known  as  liydrargyri  precipitatum  nigrum,  or  Hannemann's 
soluble  mercury,  is  prepared  by  adding  very  dilute  ammonia  to  a  solution  of  the 
nitrate  of  suboxide  of  mercury  in  dilute  nitric  acid,  as  long  as  a  gray  precipitate 
is  formed.  This  gray  precipitate,  which  is  the  compound  in  question,  varies  in 
composition,  but  is  generally  considered  as  a  combination  of  ammonia  with  a 
basic  nitrate  of  suboxide  of  mercury,  2HgaO.N05,NH3. 

SULPHATE  or  SUBOXIDE  OF  MERCURY,  SUBSULPHATE  OF  MERCURY. 

HgaO.S03. 

When  dilute  sulphuric  acid  is  added  to  a  solution  of  nitrate  of  suboxide  of 
mercury,  this  sulphate  is  precipitated  as  a  white  crystalline  powder.  It  may 
also  be  obtained  by  gently  heating  an  excess  of  mercury  with  concentrated  sul- 
phuric acid. 

Sulphate  of  suboxide  of  mercury  is  very  sparingly  soluble  in  water ;  it  crys- 
tallizes in  prisms;  a  small  quantity  of  alkali  decomposes  it,  producing  an  inso- 
luble basic  salt. 

The  chromate  of  suboxide  of  mercury  (HgaO.Cr03)  is  precipitated  when  chro- 


OXIDE   OF   MERCURY.  457 

mate  of  potassa  is  added  to  nitrate  of  suboxide  of  mercury.     It  has  an  orange- 
red  color,  and  leaves  a  residue  of  pure  sesquioxide  of  chromium  when  ignited. 

OXIDE,  OR  PROTOXIDE,  OF  MERCURY,  RED  OXIDE. 
HgO.     Eq.  108. 

§  308.  Preparation.  —  I.  This  oxide  is  formed,  as  already  mentioned,  when 
mercury  is  heated  for  some  time,  near  its  boiling-point,  in  contact  with  air;  the 
minute  crystalline  scales  thus  formed,  were  termed  by  the  old  chemists  precipi- 
tatum  per  se. 

II.  The  red  oxide  of  mercury  is  generally  obtained  by  calcining  the  nitrate  at 
a  moderate  heat;  it  is  then  commonly  called  nitric  oxide  of  mercury. 

The  external  appearance  of  the  oxide  thus  obtained  depends  upon  that  of  the 
nitrate.  Nitrate  of  mercury  in  powder  yields  a  pulverulent  oxide  of  an  orange 
yellow  color;  when  the  nitrate  is  in  crystals,  a  crystalline  oxide  is  obtained; 
the  red  crystalline  oxide  of  commerce  is  prepared  by  heating  minute  crystals  of 
nitrate  of  mercury. 

III.  When  an  excess  of  potassa  is  added  to  a  solution  of  chloride  of  mercury 
(corrosive  sublimate),  a  yellow  amorphous  precipitate   of  oxide  of  mercury  is 
obtained  ;  this  should  be  collected  upon  a  filter,  and  well  washed  with  boiling 
water  till  the  washings  leave  no  residue  on  evaporation. 

Properties.  —  We  have  seen  that  oxide  of  mercury  is  capable  of  existing  in  two 
states,  in  one  of  which  it  is  yellow,  in  the  other,  red;  these  manifest,  also,  some 
difference  in  their  chemical  properties;  thus,  the  yellow  modification  combines 
with  oxalic  acid  in  the  cold,  which  is  not  the  case  with  the  red  variety;  again, 
an  alcoholic  solution  of  corrosive  sublimate  converts  the  yellow  oxide  into  a 
black  oxychloride,  while  the  red  oxide  is  not  affected  by  it. 

Oxide  of  mercury  is  slightly  blackened  by  exposure  to  light,  being  decomposed 
to  some  extent.  When  heated,  oxide  of  mercury  assumes  a  dark  brown,  nearly 
black  color,  but  regains  its  original  color  on  cooling;  a  heat  somewhat  below 
redness  resolves  it  into  its  elements. 

Oxide  of  mercury  is  slightly  soluble  in  water,  the  solution  has  an  alkaline 
reaction  to  very  delicate  color-tests  ;  it  combines  readily  with  most  acids,  forming 
definite  salts.  The  soluble  neutral  salts  redden  litmus.  It  is  a  powerful  oxid- 
izing agent,  and  is  often  employed  as  such  in  the  laboratory;  it  will  be  remem- 
bered that  oxide  of  mercury  is  employed  to  convert  chlorine  into  hypochlorous 
acid.  It  is  also  used  to  complete  the  incineration  of  organic  substances,  and  to 
reconvert  any  sulphides,  produced  in  the  process  of  incineration,  into  sulphates. 

OXY-AMIDIDE   OF   MERCURY,    AMMONIATED   OXIDE   OF   MERCURY. 

3HgO.HgNH3. 

When  oxide  of  mercury  (especially  the  yellow  modification)  is  treated  with 
ammonia,  a  compound  is  produced,  which  is  represented  by  some  chemists  as  an 
ammoniated  oxide  of  mercury,  4HgO.NH3  2HO,  and  by  others  as  a  hydrated 
oxy-amidide  of  mercury,  3HgO.HgNH3+3HO.  This  latter  view  seems  to 
account  more  satisfactorily  for  the  various  changes  which  this  substance  under- 
goes. 

This  base  has  a  yellow  color,  and  is  decomposed  by  exposure  to  light  ;  it  de- 
crepitates when  rubbed  in  a  mortar.  When  exposed  for  a  long  time  in  vacua 
over  quicklime,  or  when  heated  to  266°  F.  (130°  C.),  its  loses  its  water,  becom- 
ing 3HgO.HgNH2,  which  has  a  brown  color. 

It  is  insoluble  in  water  and  alcohol.  The  hydrated  oxy-amidide  of  mercury 
is  not  decomposed  by  solution  of  potassa  in  the  cold,  but,  when  heated  with  it, 
disengages  ammonia;  the  anhydrous  compound  only  disengages  ammonia  when 
fused  with  hydrate  of  potassa. 


UNIVERSITY  / 

*****  j 


458  SALTS   OF    MERCURY. 

The  basic  characters  of  the  oxy-amidide  of  mercury  are  very  well  marked;  it 
absorbs  carbonic  acid  from  the  air,  and  disengages  ammonia  from  ammoniacal 
salts. 

It  combines  readily  with  oxygen-acids;  the  following  are  examples  of  the 
salts  thus  formed  : — 

Sulphate  (3HgO.HgNHa)S03. 
Carbonate  (3HgO.HgNHa)CO, 
Nitrate  (3HgO.HgNH3NOJ-f  HO. 

When  treated  with  hydrogen  acids,  it  gives  rise  to  water  and  to  salts  of  the 
radicals  of  these  acids. 

Two  chlorides  exist,  having,  respectively,  the  formulae  2HgO.HgCl.HgNHa, 
and  3HgCl.HgNH2;  the  iodide  corresponds  to  the  former  of  these  chlorides. 

NITRATE  OP  OXIDE  OP  MERCURY,  HgO.N05. 

This  salt  may  be  prepared  by  dissolving  mercury  or  oxide  of  mercury  in 
excess  of  nitric  acid,  with  the  aid  of  heat ;  if  an  attempt  be  made  to  crystallize 
the  salt  in  the  ordinary  way  from  this  solution,  a  basic  salt  will  be  obtained, 
but  by  dissolving  ox!de  of  mercury  in  excess  of  nitric  acid,  so  as  to  obtain  a 
syrupy  liquid,  and  "exposing  this  to  a  refrigerating  mixture,  crystals  may  be 
obtained,  of  the  formula  HgO.N05,2HO. 

If  the  solution  of  this  nitrate  be  evaporated,  crystals  are  deposited,  of  the 
formula  2HgON05-f  2HO;  this  basic  salt  may  also  be  obtained  by  digesting  the 
solution  of  the  neutral  nitrate  with  an  excess  of  recently  precipitated  oxide  of 
mercury. 

These  salts  are  decomposed  by  water,  yielding  a  basic  nitrate  having  the  com- 
position 3HgO.N05,HO;  by  continued  washing  with  boiling  water,  this  basic 
salt  is  converted  into  the  red  oxide  of  mercury.  The  basic  salt  is  remarkable  for 
its  difficult  solubility  in  nitric  and  sulphuric  acids. 

When  solution  of  nitrate  of  oxide  of  mercury  is  digested  with  metallic  mer- 
cury, the  latter  is  gradually  dissolved,  nitrate  of  suboxide  of  mercury  being 
produced. 

By  adding  ammonia  to  a  solution  of  nitrate  of  oxide  of  mercury,  a  white  pre- 
cipitate is  obtained  which  appears  to  be  the  nitrate  of  the  oxy-amidide  of 
mercury  mentioned  above. 

SULPHATE  OF  OXIDE  OP  MERCURY,  HgO.S03. 

The  sulphate  is  obtained,  as  a  white  crystalline  powder,  by  boiling  mercury 
with  an  excess  of  concentrated  sulphuric  acid,  until  the  latter  begins  to  pass  off 
in  vapor;  on  the  large  scale,  the  boiling  is  carried  to  dryness,  in  order  to  expel 
excess  of  acid. 

Sulphate  of  oxide  of  mercury  crystallizes  in  white  deliquescent  needles;  when 
treated  with  cold  water  it  is  decomposed,  a  yellow  basic  salt  being  produced, 
which  is  known  as  turbith  mineral,  and  a  highly  acid  salt  being  dissolved.  The 
formula  of  turbith  mineral  is  3HgO.S03;  it  is  converted  into  oxide  of  mercury 
by  long  boiling  with  water. 

Sulphate  of  oxide  of  mercury  is  employed  for  the  preparation  of  corrosive 
sublimate. 

When  sulphate  of  oxide  of  mercury  is  treated  with  an  excess  of  ammonia,  it 
produces  the  sulphate  of  oxy-amidide  of  mercury. 

Sulphate  of  mercury  is  capable  of  forming  crystalline  compounds  by  direct 
combination  with  different  proportions  of  ammonia. 

Two  basic  carbonates  of  oxide  of  mercury  having  the  formulas,  respectively, 
4HgO.C03  and  3HgO.COa,  are  obtained  as  red- brown  precipitates  by  adding  a 


MERCURY  AND  CHLORINE.  459 

solution  of  nitrate  of  oxide  of  mercury  to  solutions  of  carbonate  and  bicarbonate 
of  potassa  employed  in  excess. 

NITRIDE  OF  MERCURY,  Hg3N. 

§  309.  This  compound  has  been  obtained  by  passing  a  stream  of  ammoniacal 
gas  over  precipitated  red  oxide  of  mercury,  as  long  as  the  ammonia  is  absorbed, 
and  afterwards  heating  the  compound  in  an  oil-bath  to  266°  F.  (130°  C.), 
whilst  the  stream  of  ammonia  is  still  maintained,  until  no  more  water  is 
formed : — 

3HgO-fNH3=3HO-f-Hg3N. 

The  product  is  washed  with  a  little  very  dilute  nitric  acid  to  remove  the  excess 
of  oxide  of  mercury. 

Nitride  of  mercury  is  a  dark-brown  powder,  which  detonates  when  heated ;  it 
is  insoluble  in  water,  and  dissolves  slowly  in  the  dilute  acids,  producing  salts  of 
ammonia  and  of  oxide  of  mercury ;  it  is  so  unstable  that  it  detonates  even  when 
struck. 

SUBCHLORIDE  OF  MERCURY,  CALOMEL,  Hg3Cl. 

Preparation. — The  simplest  method  of  preparing  the  subchloride  of  mercury, 
consists  in  decomposing  a  solution  of  subnitrate  of  mercury  with  chloride  of 
sodium,  when  a  slightly  yellowish-white  precipitate  is  formed,  which  must  be 
collected  upon  a  filter  and  well  washed  : — 

Hg2O.N05+NaCl=Hg2Cl-r-NaO.N05. 

It  may  also  be  prepared  by  intimately  mixing  the  chloride  of  mercury  (corro- 
sive sublimate)  with  1  eq.  of  metallic  mercury,  with  addition  of  a  little  water, 
drying  the  mixture  thoroughly,  and  subliming  it : — 

HgCl  +  Hg=HgaCl. 

A  more  convenient  method  is  to  sublime  a  mixture  of  sulphate  of  suboxide  of 
mercury  and  chloride  of  sodium : — 

HgaO.S03  -f  NaCl=NaO.S03  +  Hg.Cl. 

Since,  however,  it  is  very  difficult  to  obtain  the  sulphate  of  suboxide  of  mer- 
cury in  a  state  of  perfect  purity,  it  is  customary  to  replace  it  by  a  mixture  of 
sulphate  of  the  oxide  with  1  eq.  of  metallic  mercury. 

The  following  is  the  prescription  of  the  London  Pharmacopeia  for  the  pre- 
paration of  calomel : — 

2  parts  of  mercury  are  dissolved,  with  the  aid  of  heat,  in  3  parts  of  concen- 
trated sulphuric  acid,  and  the  solution  evaporated  to  dryness : — 

Hg+2(HO.S03)=HgO.S03-f2HO+SOa. 

The  residue  of  sulphate  of  oxide  of  mercury  is  intimately  mixed  with  2  more 
parts  of  mercury,  and  the  mixture  afterwards  triturated  with  1£  parts  of  chloride 
of  sodium  until  globules  are  no  longer  visible;  the  whole  is  then  sublimed  in 
an  appropriate  vessel;  the  production  of  the  subchloride  of  mercury  is  thus 
represented : — 

HgO  .SO.+ Hg-fNaCl=Hg3Cl-f  NaO.S03. 

The  calomel  thus  prepared,  however,  is  always  more  or  less  contaminated  with 
corrosive  sublimate,  which,  being  exceedingly  poisonous,  must  always  be  entirely 
removed  from  the  calomel  before  its  employment  medicinally ;  the  removal  of 
the  corrosive  sublimate  is  effected  by  washing  the  calomel  with  water  until  the 
washings  are  no  longer  tinged  by  sulphuretted  hydrogen. 

For  medicinal  purposes,  the  calomel  is  obtained  in  a  very  finely  divided  state, 
by  subliming  it  into  chambers  sufficiently  large  to  allow  it  to  condense  before 
coming  in  contact  with  the  walls. 


460  CHLORIDE    OF   MERCURY. 

Pure  calomel  should  leave  no  residue  when  heated  on  platinum  ;  when  agitated 
with  hot  water,  and  filtered,  the  solution  should  give  no  precipitate  or  coloration 
with  sulphuretted  hydrogen  or  solution  of  potassa. 

Properties. — Subchloride  of  mercury  is  not  absolutely  white;  in  large  masses 
it  has  a  yellow  tint.  It  may  be  crystallized,  by  careful  sublimation,  in  four- 
sided  prisms  with  tetrahedral  summits.  It  is  slowly  decomposed  by  exposure  to 
light,  into  mercury  and  chloride  of  mercury,  assuming  a  gray  color.  It  is 
readily  converted  into  vapor  by  a  moderate  heat,  and  fuses  at  or  near  its  point 
of  volatilization. 

Subchloride  of  mercury  is  almost  totally  insoluble  in  water;  concentrated 
nitric  acid,  with  the  aid  of  heat,  dissolves  it,  producing  chloride  of  mercury,  and 
nitrate  of  the  oxide.  When  boiled  with  hydrochloric  acid,  it  is  decomposed 
into  chloride  of  mercury  and  metal,  which  separates.  The  alkalies  convert  it 
into  black  suboxide  of  mercury.  Alkaline  chlorides,  especially  in  presence  of 
organic  matters,  are  said  to  be  capable  of  decomposing  it  into  metallic  mercury 
and  chloride  of  mercury,  which  would  help  to  throw  some  light  upon  its  thera- 
peutic action. 

Calomel  dissolves  in  solution  of  chlorine,  being  converted  into  corrosive  subli- 
mate. 

Ammoniacal  gas  is  absorbed  by  Subchloride  of  mercury,  a  compound  being  pro- 
duced, of  the  formula  HggCl,NH8. 

When  calomel  is  treated  with  liquefied  ammonia,  a  gray  compound  is  produced, 
having  the  composition  Hg3Cl.HgNH3,  which  is  therefore  a  double  compound  of 
amidide  and  Subchloride  of  mercury. 

CHLORIDE  OF  PROTOCHLORIDE  OF  MERCURY,  CORROSIVE  SUBLIMATE. 

HgCl. 

§  310.  Preparation. — The  chloride  of  mercury  may  be  prepared  by  dissolving 
mercury  in  nitro-hydrochloric  acid,  and  evaporating  the  solution  to  crystallization. 
It  is,  however,  obtained  on  the  large  scale  by  heating  a  mixture  of  sulphate  of 
oxide  of  mercury  and  chloride  of  sodium  : — 

HgO.S03+NaCl=NaO.S03  +  HgCl. 

2  parts  of  mercury  are  dissolved  in  3  parts  of  sulphuric  acid,  with  the  aid  of 
heat,  the  solution  evaporated  to  dryness,  and  the  residue  mixed  with  1?  parts  of 
chloride  of  sodium. 

Since  the  sulphate  of  oxide  of  mercury  often  contains  sulphate  of  the  sub- 
oxide,  some  calomel  might  be  produced  in  the  above  process ;  to  avoid  this,  3 
part  of  binoxide  of  manganese  is  often  added  to  the  above  ingredients. 

The  mixture  is  introduced  into  a  large  glass  flask,  which  is  then  imbedded  in 
sand  up  to  the  neck ;  the  sand-bath  is  furnished  with  a  hood  to  carry  off  the 
mercurial  vapors  which  may  escape ;  a  gradual  heat  is  applied  at  first  to  expel 
all  moisture ;  the  sand  is  then  removed  so  as  to  leave  the  upper  part  of  the  flask 
uncovered,  and  the  heat  increased ;  the  chloride  of  mercury  sublimes,  and  con- 
denses on  the  cool  part  of  the  flask ;  when  the  sublimation  has  been  continued 
for  8  or  10  hours,  the  heat  is  considerably  increased  in  order  to  fuse  the  chloride 
partially,  thus  rendering  it  more  compact ;  the  flasks,  when  cold,  are  broken  up, 
and  the  sublimate  removed. 

Properties. — Corrosive  sublimate  occurs  in  commerce  in  the  form  of  transpa- 
rent colorless  masses,  possessing  considerable  lustre,  and  bearing  evidence  of  a 
crystalline  texture;  the  density  of  this  substance  is  6.5.  It  fuses  at  about  509° 
F.  (265°  C.),  and  boils  at  563°  F.  (295°  C.),  yielding  a  colorless  vapor,  which 
condenses  in  colorless  octohedra  upon  a  cold  surface. 

Corrosive  sublimate  dissolves  in  f  6  parts  of  boiling  and  in  3  parts  of  cold 
water ;  its  aqueous  solution  has  an  acid  reaction,  and  when  exposed  to  light, 


MERCURY   AND   CHLORINE.  461 

becomes  more  strongly  acid,  and  deposits  a  white  precipitate  of  subchloride  of 
mercury.  It  is  much  more  soluble  in  alcohol  and  ether  than  in  water ;  1  part 
of  chloride  of  mercury  dissolves  in  2£  parts  of  cold  alcohol,  and  in  1J  of  boiling 
alcohol ;  3  parts  of  cold  ether  also  dissolve  1  part  of  this  substance.  If  an 
aqueous  solution  of  corrosive  sublimate  be  agitated  with  ether,  the  latter  removes 
the  greater  part  of  the  salt,  which  may  be  obtained  by  evaporation. 

Chloride  of  mercury  crystallizes  from  its  solutions  in  a  right  rhombic  prism, 
or  some  form  derived  from  it. 

Hydrochloric  and  nitric  acids  readily  dissolve  chloride  of  mercury,  without 
alteration. 

The  fixed  alkalies  and  their  carbonates,  when  not  added  in  excess  to  a  solution 
of  corrosive  sublimate,  give  red-brown  precipitates,  which  are  oxychlorides  of 
mercury. 

Ammonia  produces,  in  solution  of  chloride  of  mercury,  a  white  precipitate,  to 
which  we  shall  recur  presently. 

We  have  seen  that  when  triturated  with  metallic  mercury,  the  chloride  passes 
into  subchloride. 

Corrosive  sublimate  is  entirely  precipitated  from  its  solutions  by  albumen, 
which  forms  with  it  a  perfectly  insoluble  compound ;  hence  the  use  of  the  white 
of  egg  as  an  antidote  in  cases  of  poisoning  by  corrosive  sublimate.  This  property 
of  forming  insoluble  compounds  with  albumen  and  organic  substances  of  a  simi- 
lar nature,  may  perhaps  explain  the  powerful  antiseptic  qualities  of  corrosive 
sublimate,  which  lead  to  its  employment  for  the  preservation  of  wood,  of  ana- 
tomical preparations,  &c. 

Chloride  of  mercury  forms  a  great  many  crystallizable  double-salts  with  other 
metallic  chlorides. 

Three  double  chlorides  of  potassium  and  mercury  are  known  to  exist;  their 
formulae  are  the  following : — 

KCl,HgCl  +  HO 
KCl,2HgCl-fHO 
KCl,4HgCl+4HO. 

The  double  chloride  of  ammonium  and  mercury  has  the  composition 
NH4Cl,HgCl+HO. 

Chloride  of  mercury  combines  with  the  bichromates  of  potassa  and  ammonia, 
forming  crystallizable  double  compounds.     The  double  compound  with  bichro- 
mate of  potassa  has,  according  to  Millon,  the  formula,  HgCl,K0.2Cr03,  whilst 
those  with  bichromate  of  ammonia  were  found  by  Richmond  and  J.  Abel  to  be 
HgCl,NH40.2Cr03-fHO 
HgCl,3(NH40.2Cr03). 

Uses. — Chloride  of  mercury  is  frequently  used  in  the  laboratory,  either  as  a 
reagent,  or  in  order  to  obtain  some  of  the  volatile  metallic  chlorides;  thus,  it 
will  be  recollected  that  bichloride  of  tin  is  prepared  by  distilling  a  mixture  of 
metallic  tin  with  corrosive  sublimate. 

The  employment  of  this  substance  for  preserving  wood  and  anatomical  prepa- 
rations has  been  mentioned  above ;  the  preservative  liquid  known  as  Goadly's 
solution  is  composed  as  follows : — 

Bay  salt 4  oz. 

Alum ....*.  2  oz. 

Corrosive  sublimate* 2  grs. 

Water 2  pts. 

This  solution  is,  however,  somewhat  objectionable  for  the  preservation  of  sub- 
stances actually  under  dissection,  since  the  knives  are  much  corroded  both  by 
the  alum  and  by  the  mercury-salt. 


462  WHITE   PRECIPITATE. 


OXYCHLORIDES   OP   MERCURY. 

When  chlorine  is  allowed  to  act  upon  an  excess  of  oxide  of  mercury  (as  in 
the  preparation  of  hypochlorous  acid,  see  p.  137),  an  insoluble  substance  is  pro- 
duced, varying  in  color  from  brick-red  to  black,  which  is  composed  of  one  or 
more  oxychlorides  of  mercury. 

Three  such  compounds  may  be  prepared,  either  by  the  above  method,  or  by 
boiling  solution  of  corrosive  sublimate  with  oxide  of  mercury,  or  lastly,  by  de- 
composing the  solution  of  corrosive  sublimate  with  alkalies  or  alkaline  carbon- 
ates in  different  proportions,  but  always  in  too  small  quantity  to  decompose  the 
whole  of  the  chloride.  These  oxychlorides  are  insoluble  in  water. 

A  white,  somewhat  soluble  oxychloride,  of  the  formula  2HgCl.HgO,  always 
accompanies  the  oxychloride  obtained  by  the  action  of  chloride  of  mercury  upon 
the  oxide  at  high  temperatures ;  the  formula  of  this  compound  is  HgC1.2HgO ; 
it  may  be  either  amorphous  or  crystalline,  red,  purple,  or  black ;  if  black,  it 
yields  the  red  oxide  of  mercury  when  decomposed  by  alkalies,  but  in  the  other 
states,  it  gives  the  yellow  oxide. 

The  oxychloride  of  the  formula  HgCl.SHgO  may  be  also  amorphous  or  crys- 
talline, and  varies  in  color  from  brownish-yellow  to  dark  brown ;  it  always  yields 
the  yellow  oxide  of  mercury. 

HgC1.4HgO  resembles  the  preceding,  but  always  yields  the  red  oxide  when 
decomposed. 

A  compound  of  the  formula  HgCl.GHgO  has  also  been  obtained. 

AMIDO-CHLORIDE  (OR  CHLORAMIDIDE)  OP  MERCURY. 
WHITE  PRECIPITATE.     HgC^HgNH,/ 

This  compound  is  prepared  by  decomposing  solution  of  corrosive  sublimate 
with  an  excess  of  ammonia  : — 

2HgCl  +  2NH3=NH4Cl+HgCl,HgNH3. 

It  is  a  fine  white  amorphous  powder;  when  heated  to  about  680°  F.  (360°  C.) 
it  evolves  ammonia,  and  yields  a  sublimate  of  ammoniated  subchloride  of  mer- 
cury, 2HgaCl,NH? ;  the  residue,  which  is  insoluble  in  water,  and  unchanged  by 
boiling  with  alkalies,  has  a  composition  corresponding  with  the  formula  HgaCl,- 
HgjN  (that  is,  a  double  compound  of  nitride  and  subchloride  of  mercury). 

At  a  higher  temperature,  this  compound  evolves  nitrogen,  and  leaves  a  residue 
of  subchloride  of  mercury. 

Amido-chloride  of  mercury  is  insoluble  in  water,  but  soluble  in  mineral  acids; 
it  is  also  soluble  in  free  ammonia  in  the  presence  of  the  sulphate,  nitrate,  and 
acetate  of  ammonia,  so  that  this  reagent  does  not  produce  a  precipitate  in  solu- 
tions of  salts  of  oxide  of  mercury,  containing  a  sufficient  quantity  of  free  sul- 
phuric, nitric,  or  acetic  acid.  When  boiled  with  water,  amido-chloride  of  mer- 
cury is  partly  decomposed,  assuming  a  yellow  color. 

White  precipitate  becomes  yellow  when  treated  with  potassa,  ammonia  being 
evolved. 

When  ammonia  is  added  to  a  very  large  excess  of  chloride  of  mercury,  a  com- 
pound is  precipitated,  which  is  expressed  by  the  formula  3HgCl.  HgNH0,  and 
will  be  recognized  as  the  chloride  corresponding  to  the  oxyamidide  of  mercury, 

1  This  compound  might  also  be  considered  to  be  the  chloride  of  di-mcrcurammoniumt 

.  N  {ikl CL 

Wagner's  experiments  have  disposed  him  to  regard  it  as  a  compound  of  chloride  of 
mercury  with  mercuramine,  HgCl,N  •<  »i 


IODIDE    OF    MERCURY.  463 

3HgO.HgNH2.  By  increasing  the  proportion  of  ammonia,  the  other  chloride 
(2HgO.HgCl.HgNH3)  of  this  series  may  be  obtained. 

Various  compounds  of  amidide  of  mercury  (HgNHa)  with  salts  of  oxide  of 
mercury,  have  been  obtained  by  the  action  of  ammonia  upon  those  salts. 

The  preceding  compounds  are  interesting  as  forming  one  of  the  chief  supports 
of  the  amidogen- theory  of  the  constitution  of  ammoniacal  salts. 

§  311.  The  Bromides  of  Mercury  correspond  in  nearly  all  respects  to  the 
chlorides. 

The  sub-bromide  Hg3Br,  is  white,  volatile,  and  insoluble. 

The  bromide  HgBr,  is  soluble  and  crystallizable. 

A  black  compound  of  sub-bromide  with  amidide  of  mercury,  Hg3Br.HgNH2, 
is  obtained  by  treating  the  former  with  ammonia. 

An  oxybromide,  HgBr.3HgO,  is  also  known. 

SUBIODIDE  OP  MERCURY  (HgMI)  may  be  formed  by  triturating  iodine  with 
excess  of  mercury  and  a  little  alcohol ;  it  is  precipitated  when  an  excess  of  ni- 
trate of  suboxide  of  mercury  is  added  to  iodide  of  potassium. 

It  has  a  dirty  green  color,  and  may  be  fused  and  sublimed  without  change,  if 
rapidly  heated  ;  when  heated  slowly,  however,  it  is  decomposed  into  mercury 
and  iodide  of  mercury  ;  the  alkaline  iodides  cause  it  to  undergo  the  same  decom- 
position, and  dissolve  the  iodide  formed. 

IODIDE  OP  MERCURY,  Hgl. 

Preparation. — This  most  beautiful  substance  may  be  prepared  by  triturating 
equal  equivalents  of  mercury  and  iodine  with  a  little  alcohol,  when  the  subiodide 
is  formed  at  the  same  time.  It  is  also  easily  obtained  by  adding  chloride  of 
mercury  to  a  solution  of  iodide  of  potassium,  when  it  is  precipitated  at  first  of  a 
very  light  color,  which  quickly  passes  into  a  brilliant  scarlet;  in  this  experiment, 
the  proportions  employed  must  be  carefully  attended  to,  since  the  iodide  is  solu- 
ble in  an  excess  of  either  reagent. 

Properties. — Iodide  of  mercury  ordinarily  presents  a  splendid  scarlet  color, 
which  is  somewhat  injured  by  exposure  to  light ;  when  heated,  it  fuses  easily  to 
a  red  liquid,  which  afterwards  sublimes  in  brilliant  yellow  crystals.  The  vapor 
of  iodide  of  mercury  is  colorless,  and  is  the  heaviest  gaseous  substance  known ; 
its  specific  gravity  is  15.68. 

The  yellow  crystals  gradually  assume  a  scarlet  color  if  left  to  themselves,  but 
if  rubbed  with  a  hard  body,  they  undergo  this  change  immediately.  Iodide  of 
mercury  is  a  dimorphous  substance;  the  primitive  form  of  the  red  modification 
is  the  square-based  octohedron,  while  the  crystals  of  the  yellow  variety  are  de- 
rived from  the  right  rhombic  prism. 

Iodide  of  mercury  is  very  slightly  soluble  in  water,  requiring  150  parts  in  the 
cold;  it  dissolves  in  alcohol,  with  the  aid  of  heat,  forming  a  colorless  solution, 
from  which,  if  slowly  cooled,  the  iodide  is  deposited  in  the  red  modification ; 
whereas,  by  rapid  cooling,  the  yellow  variety  is  obtained.  It  dissolves  very  rea- 
dily in  solution  of  iodide  of  potassium,  forming  a  colorless  solution ;  the  best 
method  of  crystallizing  the  iodide  of  mercury  consists  in  dissolving  it,  with  the 
aid  of  heat,  to  saturation,  in  solution  of  iodide  of  potassium,  which  deposits  it, 
on  cooling,  in  fine  scarlet  crystals. 

Iodide  of  mercury  is  capable  of  combining  with  several  other  iodides,  and  with 
some  chlorides. 

An  intermediate  iodide  of  mercury,  of  the  formula  Hg3T.2HgI,  is  obtained  as 
a  yellow  precipitate  when  nitrate  of  suboxide  of  mercury  is  precipitated  by  a 
solution  of  iodide  of  potassium  containing  free  iodine. 

An  oxy-iodide  of  mercury,  of  the  formula  HgL3HgO,  has  been  obtained. 
When  this  compound  is  exposed  to  the  action  of  dry  ammonia,  water  is  formed, 
together  with  a  red-brown  compound,  HgNH3.HgI.2HgO. 


464  MERCUEY  AND  SULPHUR. 

MERCURY  AND  SULPHUR. 

Subsulphide Hg2S. 

Sulphide HgS. 

SUBSULPHIDE  OP  MERCURY,  Hg3S. 

§  312.  This  compound  may  be  obtained  by  gradually  adding  a  solution  of  a 
salt  of  suboxide  of  mercury  to  a  solution  of  an  alkaline  sulphide  ;  it  is  a  black 
precipitate  which  is  exceedingly  unstable,  being  decomposed,  even  when  heated 
under  water,  into  metallic  mercury  and  the  sulphide. 

SULPHIDE  OP  MERCURY,  CINNABAR,  VERMILION,  HgS. 

This  sulphide  exists  in  the  mineral  kingdom,  and  is,  in  fact,  the  chief  ore  of 
mercury.1 

Preparation. — Sulphide  of  mercury  is  obtained  as  a  black  precipitate  by  the 
action  of  sulphuretted  hydrogen,  or  a  soluble  sulphide,  upon  a  solution  of  a  salt 
of  oxide  of  mercury. 

There  are  several  methods  of  obtaining  vermilion  on  the  large  scale. 

I.  When  15  parts  of  sulphur  are  moderately  heated  with  95  parts  of  mercury, 
a  black  compound  is  formed,  which  is  known  as  Ethiops  mineral,  and  consists  of 
a  mixture  of  sulphide  of  mercury  with  an  excess  of  sulphur;  this  mixture  is 
subjected  to  sublimation,  when  the  sulphide  is  obtained  pure ;  when  finely  pow- 
dered with  a  little  water,  this  sulphide  forms  the  vermilion  of  commerce. 

II.  The  most  beautiful  vermilion,  however,  is  obtained  in  the  moist  way,  by 
the  action  of  solutions  of  the  higher  alkaline  sulphides  upon  the  black  sulphides 
of  mercury.    300  parts  of  mercury  and  114  parts  of  sulphur  are  rubbed  together 
in  a  mortar  for  two  or  three  hours ;  75  parts  of  hydrate  of  potassa  and  400  parts 
of  water  are  then  added,  and  the  whole  kept  for  some  hours  at  about  122°  F. 
(50°  C.)>  when  the  original  black  sulphide  assumes  a  fine  red  color. 

The  theory  of  this  operation  is  scarcely  yet  explained  in  a  satisfactory  manner. 

III.  If  ordinary  cinnabar  be  reduced  to  powder  and  heated  for  some  time  to 
about  122°  F.  (50°  C.)  with  a  solution  of  liver  of  sulphur,  it  is  converted  into  a 
fine  specimen  of  vermilion. 

IV.  At  Idria,  where  the  extraction  of  mercury  from  its  ores  is  extensively 
carried  on,  vermilion  is  manufactured  by  a  method  similar  to  the  first  of  those 
given  above.     100  parts  of  mercury  and  18  of  sulphur  are  introduced  into  small 
wooden  casks  which  revolve  upon  a  horizontal  axis ;  these  casks  are  allowed  to 
rotate  for  three  or  four  hours,  when  the  mercury  is  converted  into  black  sulphide, 
which  acquires  a  fine  red  color  when  sublimed  and  reduced  to  powder. 

Properties. — Cinnabar,  in  its  native  state,  is  often  associated  with  the  sulphides 
of  iron  and  copper ;  it  is  found  sometimes  in  amorphous  masses,  sometimes  crys- 
tallized in  six-sided  prisms,  and  varying  in  color  from  a  dark  brown  to  a  bright 
red  ;  it  is  occasionally  transparent ;  it  is  brittle,  and  has  the  sp.  gr.  8.098.  When 
heated  in  close  vessels,  cinnabar  sublimes,  without  previously  fusing,  and  con- 
denses again  in  six-sided  prisms.  If  roasted  in  air,  it  burns,  evolving  sulphurous 
acid  and  vapors  of  metallic  mercury. 

Sulphide  of  mercury  is  insoluble  in  water ;  it  dissolves  only  to  a  slight  extent 
in  hydrochloric  or  nitric  acid,  but  readily  in  aqua  regia. 

When  fused  with  alkalies  or  their  carbonates,  cinnabar  loses  its  sulphur,  and 
metallic  mercury  escapes;  lime  effects  a  similar  reduction. 

'          : 

1  Cinnabar  has  been  found  in  a  Tery  pure  state  in  California. 


AMALGAMS.  465 

If  sulphide  of  mercury  be  heated  with  oxide  of  mercury,  the  sulphur  is  oxidized 
at  the  expense  of  the  latter,  and  the  mercury  of  both  compounds  is  separated  in 
the  metallic  state : — 

HgS  +  2HgO==Hg3-fSOa. 

Carbon,  hydrogen,  copper,  iron,  tin,  zinc,  &c.,  are  capable  of  reducing  sulphide 
of  mercury  at  a  high  temperature. 

The  sulphide  of  mercury,  in  the  nascent  state,  is  capable  of  combining  with 
many  of  the  salts  of  oxide  of  mercury,  to  form  white  compounds,  which  are  ob- 
tained by  adding  a  very  small  quantity  of  sulphuretted  hydrogen  to  a  solution  of 
one  of  the  salts  in  question  ;  thus,  if  the  sulphate  of  oxide  of  mercury  be  treated 
with  a  small  quantity  of  sulphuretted  hydrogen,  a  white  precipitate  is  obtained, 
having  the  composition  HgO  SO3-f  2HgS.  Nitrate  of  oxide  of  mercury  yields 
a  similar  compound.  When  the  chloride  of  mercury  is  thus  treated,  the  formula 
of  the  white  precipitate  is  HgCl-f-2HgS.  These  precipitates  are  all  converted 
into  black  sulphide  of  mercury  when  treated  with  an  excess  of  hydrosulphuric 
acid. 

Vermilion  is  sometimes  adulterated  with  minium,  colcothar,  brickdust,  dra- 
gon's blood  or  realgar;*  the  first  three  are  left  behind  when  the  specimen  is 
heated;  the  realgar  may  be  detected  by  heating  the  vermilion  with  yellow  sul- 
phide of  ammonium,  and  testing  the  filtered  solution  with  excess  of  hydrochloric 
acid,  which  would  precipitate  yellow  pentasulphide  of  arsenic.  The  presence  of 
dragon's  blood  will  be  known  by  the  empyreumatic  odor  evolved  on  heating,  and 
by  the  red  color  which  the  specimen  imparts  to  alcohol. 


AMALGAMS. 

§  313.  Mercury  does  not  generally  combine  with  those  metals,  such  as  iron, 
manganese,  nickel,  and  cobalt,  the  fusing-points  of  which  are  very  high ;  we 
find,  however,  an  exception  to  this  rule  in  platinum,  which,  in  a  finely  divided 
state,  is  capable  of  amalgamating  with  mercury.  The  amalgams  themselves  are 
solid,  but  dissolve  very  readily  in  an  excess  of  mercury;  their  fusing-points  are 
very  low.  All  amalgams  are  decomposed  by  heat,  their  mercury  being  volatilized. 

At  a  slightly  elevated  temperature,  mercury  combines  energetically  with  potas- 
sium and  sodium,  forming  compounds  which  readily  decompose  water,  the  light 
metal  being  oxidized  and  dissolved,  whilst  the  mercury  separates. 

These  amalgams  are  employed  for  the  preparation  of  the  amalgam  of  ammo- 
nium (for  the  properties  of  which  we  refer  to  p.  135). 

It  is  said  that  the  amalgams  of  potassium,  sodium,  and  ammonium,  crystallize 
in  cubes  at  a  low  temperature. 

An  amalgam  of  iron  has  been  obtained  by  Joule,  by  precipitating  that  metal 
upon  mercury  by  the  electrotype  process. 

Mercury  readily  unites  with  zinc ;  when  a  plate  of  the  latter  metal  is  well 
cleaned  with  an  acid,  and  rubbed  with  mercury,  a  very  brilliant  amalgam  is 
formed  upon  its  surface ;  zinc  plates  are  thus  treated  when  employed  in  the 
galvanic  battery,  in  order  to  protect  them  in  some  measure  from  the  action  of 
the  acid,  since  the  latter  acts  much  more  slowly  upon  the  amalgam  than  upon 
zinc  itself.1 

An  amalgam  of  2  parts  of  zinc  and  5  of  mercury  is  used  for  the  rubbers  of 
electrical  machines. 

1  Zinc  plates  may  also  be  amalgamated  by  rubbing  them  with  a  solution  of  chloride  of 
mercury  acidified  with  hydrochloric  acid. 

According  to  Rose,  the  mercury  precipitated  by  zinc  from  acid  solutions  of  the  sulphate 
and  nitrate  does  not  combine  with  the  zinc. 

30 


466  AMALGAMS. 

Bismuth  also  combines  very  easily  with  mercury ;  an  alloy  of  1  part  of  bis- 
muth with  4  of  mercury,  when  shaken  in  a  perfectly  clean  and  dry  glass  vessel, 
coats  the  surface  with  a  brilliant  metallic  film,  giving  it  the  aspect  of  a  mirror. 

Gold  is  immediately  attacked  by  mercury ;  if  a  plate  of  gold  be  brought  in 
contact  with  traces  even  of  mercury-vapor,  its  surface  is  whitened.  If  it  be 
rubbed  with  mercury,  it  becomes  exceedingly  brittle. 

Mercury  is  capable  of  dissolving  a  large  quantity  of  gold  without  losing  its 
white  color  or  its  fluidity ;  when  saturated  with  gold  it  is  semisolid,  and  has  a 
slightly  yellow  color ;  if  the  liquid  amalgam  be  squeezed  in  a  chamois  leather, 
the  mercury  which  passes  through  is  found  to  contain  very  little  gold,  whilst  the 
white  pasty  amalgam  left  on  the  filter  is  composed  of  about  2  parts  of  gold  and 
1  part  of  mercury. 

Powdered  gold,  which  is  employed  in  painting,  is  prepared  by  dissolving  1 
part  of  that  metal  in  8  parts  of  mercury,  and  distilling  the  amalgam,  when  the 
finely  divided  gold  is  left. 

Mercury  is  not  capable  of  acting  upon  compact  platinum,  only  on  the  spongy 
metal  j  when  the  amalgam  of  platinum  is  treated  with  nitric  acid,  it  dissolves, 
forming  nitrate  of  oxide  of  mercury  and  nitrate  of  binoxide  of  platinum  ;  it  will 
be  recollected  that  platinum  itself  is  not  attacked  by  nitric  acid. 

An  amalgam  of  copper  in  which  the  proportion  of  the  metals 'is  represented 
by  the  formula  CuHg,  has  been  obtained  by  Joule,  by  retaining  mercury  in  con- 
tact with  the  negative  pole  of  a  galvanic  battery  under  solution  of  sulphate  of 
copper,  until  that  metal  was  fully  saturated  with  copper. 

The  amalgams  of  tin  possess  some  practical  importance,  since  one  of  them  is 
employed  for  silvering  looking-glasses. 

Mercury  dissolves  T^  its  weight  of  tin  without  much  loss  of  fluidity ;  when 
the  latter  metal  amounts  to  £  the  weight  of  the  mercury,  the  amalgam  is  soft 
and  crystalline. 

The  silvering  of  looking-glasses  with  an  amalgam  of  tin  is  thus  effected.  A 
sheet  of  tinfoil  is  smoothly  spread  upon  a  perfectly  horizontal  table,  and  its 
surface  well  rubbed  with  mercury ;  a  thin  layer  of  this  metal  is  then  poured 
uniformly  over  it,  and  the  plate  of  glass  slid  on  to  it  in  such  a  way  that  its 
edge  shall  carry  before  it  all  the  impurities  upon  the  surface  of  the  mercury ; 
the  glass  is  then  weighted,  and  the  table  slightly  inclined,  to  allow  the  superflu- 
ous mercury  to  run  off  as  It  is  expressed;  after  some  days,  the  amalgam  is  found 
firmly  adhering  to  the  glass ;  this  amalgam  is  composed  of  about  4  parts  of  tin 
and  1  of  mercury. 

Lead  and  mercury  are  exceedingly  prone  to  enter  into  combination. 

An  amalgam  of  silver,  AgHg3,  has  been  found  in  nature,  crystallized  in 
dodecahedra. 

Silver  and  mercury  combine  directly  in  almost  all  proportions ;  as  in  the  case 
of  gold,  the  liquid  amalgams  of  silver,  when  strained,  are  separated  into  very 
rich  solid,  and  very  poor  liquid  amalgams ;  a  continued  red  heat  is  required  to 
expel  the  last  traces  of  mercury  from  an  amalgam  of  silver. 

An  amalgam  of  15  parts  of  silver  with  85  of  mercury,  is  sometimes  used  for 
silvering  copper  and  brass. 

By  submitting  amalgams  of  various  metals,  in  a  suitable  apparatus,  to  a  pres- 
sure of  60  tons  per  square  inch  of  surface,  Joule  has  succeeded  in  expelling  the 
excess  of  mercury  from  them,  and  has  obtained  definite  amalgams,  of  which  the 
formula)  are  PtHga,  AgHg3,  CuHg,  FeHg,  ZnaHg,  Pb3Hg,  Sn7Hg.* 

1  Oookewitt  has  examined  certain  definite  amalgams,  to  which  he  has  assigned  the 
formulae  AuHg4,  BiHg,  PbHg,  Cd2Hg5,  Ag5Hg)6,  AgHg2,  AgHg3,  and  AgHg4. 


METALLURGY   OF   MERCURY.  467 


METALLURGY  OF   MERCURY. 

§  314.  Mercury  is  sometimes  found  native  in  small  globules  disseminated 
throughout  certain  bituminous  strata  in  the  neighborhood  of  cinnabar. 

Cinnabar,  the  sulphide  of  mercury,  has  been  previously  mentioned  as  the 
chief  ore  of  this  metal. 

Subchloride  of  mercury  is  sometimes  found  in  the  mineral  kingdom ;  it  is 
commonly  termed  horn-mercury^  and  is  occasionally  crystallized  in  four-sided 
rectangular  prisms. 

An  iodide  of  mercury  has  been  found  in  Mexico. 

EXTRACTION  OF  MERCURY. — The  extraction  of  mercury  is  exceedingly  simple, 
in  consequence  of  the  great  volatility  of  the  metal. 

At  Idria  and  Almaden,  where  the  metal  is  chiefly  extracted,  the  cinnabar  is 
roasted,  with  free  access  of  air,  in  reverberatory  furnaces  of  a  particular  construc- 
tion; the  sulphur  is  oxidized  and  converted  into  sulphurous  acid,  while  the  mer- 
cury passes  off  in  vapor,  and  is  condensed,  either  by  passing  through  a  long 
series  of  earthenware  adapters,  or  in  brick  chambers  of  considerable  size;  if  any 
of  the  sulphide  passes  over  unchanged,  it  is  moulded  into  bricks  with  clay,  or 
placed  in  saucers,  and  again  roasted  with  the  next  charge  of  ore. 

Mercury  is  also  sometimes  extracted  by  distilling  the  ore  with  iron  or  lime; 
in  the  latter  case,  sulphide  of  calcium  and  sulphate  of  lime  are  formed  : — 
4HgS+4CaO=3CaS  +  CaO.S03+Hg4. 

If  the  ore  itself  contain  a  sufficient  amount  of  limestone,  as  is  sometimes  the 
case,  it  is  only  requisite  to  moisten  it  with  a  little  water,  and  to  distil  it.  In 
any  other  case,  the  ore  is  mixed  with  a  certain  amount  of  slaked  lime.  The 
distillation  is  effected  in  iron  retorts.1 

ASSAY  OF  THE  ORES  OF  MERCURY. — The  determination  of  mercury  in  a 
specimen  of  cinnabar  is  effected  by  mixing  100  grs.  with  4  or  5  parts  of  dry 
carbonate  of  soda  and  about  10  parts  of  quicklime,  heating  the  mixture  in  a 
hard  glass  tube  placed  in  a  combustion-furnace,  and  collecting  the  mercury  which 
distils  over;  this  may  be  washed  with  water  by  decantation,  to  remove  any  par- 
ticles of  lime,  dried  in  the  water-bath,  and  weighed.  It  will  be  found  advan- 
tageous to  place  a  little  bicarbonate  of  soda  at  the  closed  end  of  the  tube,  so  that 
by  heating  it  at  the  conclusion  of  the  operation,  carbonic  acid  may  be:  evolved, 
to  sweep  away  all  mercury -vapors  out  of  the  tube. 

PHARMACEUTICAL  PREPARATIONS  OF  MERCURY. — Mercury  in  various  forms 
of  combination  is  frequently  used  in  medicine. 

The  red  or  nitric  oxide,  as  it  is  termed,  is  sometimes  applied  externally.  The 
suboxide  has  also  been  used. 

Calomel  is  the  principal  form  in  which  mercury  is  administered  medicinally, 
and  since  it  is  termed  by  some  chemists  the  chloride,  and  by  others  the  sub- 
chloride  of  mercury,  it  would  be  well  if  its  common  name  (calomel)  were  always 
retained  in  prescriptions,  since  a  mistake  between  the  two  chlorides  would  be 
almost  inevitably  fatal. 

1  Violette  recommends  the  application  of  high-pressure  steam  to  the  purification  of 
mercury ;  he  allows  the  steam  to  pass  first  through  an  iron  worm,  in  which  its  tempera- 
ture is  raised  to  about  700°  F.,  and  then  conducts  it  into  an  iron  retort,  in  which  is 
inclosed  the  vessel  containing  the  mercury;  the  delivery-pipe,  from  which  the  steam 
issues,  dips  into  the  mercury. 

The  metal  is  thus  raised  to  the  proper  temperature  for  distillations  and  the  resulting 
vapor  rapidly  removed  from  the  retort  by  the  steam,  passing  into  an  ordinary  condensiug- 
apparatus.  This  process  appears  to  present  many  advantages  over  the  ordinary  process 
of  distillation. 


468  LEAD. 

Corrosive  sublimate  (bichloride  of  mercury),  in  small  doses,  is  an  important 
remedial  agent. 

White  precipitate,  or  hydrargyri  ammonio-chloridum,  is  used  as  an  external 
application. 

Turbifh  or  turpelh  mineral,  hydrargyri  oxydum  sulphuricum,  see  p.  458,  is 
seldom  employed. 

The  sulphide  and  the  two  iodides  of  mercury  are  found  in  the  preparations  of 
the  Pharmacopoeia. 

Several  preparations  of  mercury  are  employed  medicinally,  which  are  obtained 
by  triturating  metallic  mercury  with  various  substances  which  have  no  chemical 
action  upon  it,  until  globules  of  metal  are  no  longer  visible;  examples  of  these 
are  seen  in  blue  pill,  blue  ointment,  hydrargyrum  cum  cretd,  &c.  It  is  yet 
undecided  in  what  form  the  mercury  exists  in  these  preparations,  some  chemists 
asserting  that  they  contain  the  metal  itself,  and  others  maintaining  that  it  is 
present  in  the  form  of  suboxide;  the  former  opinion,  namely,  that  the  metal  is 
present  in  a  very  finely  divided  state,  seems  the  most  feasible,  for  it  is  difficult 
to  believe  that  a  substance  which  has  so  feeble  an  affinity  for  oxygen  at  the  ordi- 
nary temperature  should  be  oxidized  during  the  short  period  occupied  by  the 
trituration ;  perhaps  only  a  part  of  the  mercury  is  present  in  the  form  of 
suboxide. 

Sal-alembroth  is  a  mixture  of  corrosive  sublimate  with  an  equal  weight  of 
chloride  of  ammonium,  which  dissolves  more  readily  in  water  than  pure  corrosive 
sublimate,  in  consequence  of  the  formation  of  a  double-salt. 


LEAD. 

Sym.  Pb.     Eq.  103.7.     Sp.  Gr.  11.445. 

§  315.  The  metal  now  before  us  is  of  great  importance,  because  both  itself 
and  its  compounds  are,  and  have  been  from  remote  antiquity,  applied  to  many 
useful  purposes.  The  metallurgy  of  lead  will,  as  usual,  be  discussed  at  the  end 
of  the  section. 

Preparation  of  Pure  Lead. — In  order  to  obtain  this  metal  in  a  state  of  purity, 
nitrate  of  lead  is  calcined  to  expel  the  nitric  acid,  and  the  residual  oxide  of  lead 
fused  in  a  Hessian  crucible  lined  with  charcoal,  when  a  button  of  pure  metal  is 
obtained. 

Or  precipitated  sulphate  of  lead  may  be  reduced  by  charcoal  or  nascent 
hydrogen  (p.  172). 

Properties. — Lead  has  a  bluish-gray  bolor,  and  when  freshly  cut,  considerable 
lustre.  It  is  exceedingly  soft,  may  be  easily  scratched  with  the  nail,  or  cut  with 
a  knife,  and  leaves  a  dark  trace  upon  paper.  Lead  is  very  malleable,  and  may 
be  beaten  into  thin  leaves,  but  these  arc  easily  split,  from  the  imperfect  tenacity 
of  the  metal ;  for  the  same  reason  it  cannot  be  drawn  out  into  very  fine  wire ;  a 
wire  of  Jj  inch  in  diameter  will  not  support  more  than  20  Ibs. 

Exposed  to  air,  lead  is  soon  tarnished,  probably  becoming  covered  with  a  film 
of  suboxide. 

If  lead  be  prepared,  in  a  very  finely  divided  state,  it  will  be  pyrophoric. 

The  lead-pyrophorus  is  made  by  heating  the  dry  tartrate  of  lead1  in  a  glass 

1  The  tartrate  of  lead  is  prepared  by  mixing  solution  of  tartaric  acid  with  a  slight 
excess  of  ammonia,  evaporating  to  neutrality,  and  precipitating  with  acetate  of  lead ;  the 
precipitate  is  washed  with  cold  water. 


LEAD   AND   OXYGEN.  469 

tube  (closed  at  one  end,  and  constricted  near  the  open  end,  so  as  to  be  readily 
sealed)  as  long  as  any  fumes  are  evolved;  the  tube  is  then  sealed  with  the  blow- 
pipe flame.  If  the  extremity  of  this  tube  be  broken  off,  and  the  mixture  of 
finely  divided  lead,  with  carbon,  be  scattered  into  the  air,  it  burns  with  a  red 
flash. 

Heated  in  close  vessels,  lead  fuses  at  about  635°  F.  (335°  C.),  and  emits  per- 
ceptible vapors  at  a  red  heat;  however,  it  is  not  sufficiently  volatile  to  be  dis- 
tilled. If  fused  lead  be  allowed  to  cool  slowly,  it  crystallizes  in  octohedra. 

Lead  is  often  deposited  in  crystals,  when  slowly  precipitated  from  its  solutions 
by  various  metals;  the  so-called  Saturn' s-tree  is  obtained  by  suspending  a  bundle 
of  zinc-turnings  in  a  solution  of  acetate  of  lead,  acidified  with  acetic  acid,  when 
the  crystals  of  lead  are  deposited  upon  the  zinc,  giving  it  a  pretty  arborescent 
appearance. 

When  fused  in  air,  lead  oxidizes  rapidly,  becoming  covered  first  with  an  iri- 
descent pellicle,  and  subsequently  with  a  yellow  powder,  which  is  litharge,  or 
(prot-)  oxide  of  lead;  at  a  red  heat  the  litharge  fuses,  and  must  be  removed 
from  the  surface,  if  a  continuous  oxidation  be  required. 

Lead  is  capable  of  dissolving  a  certain  amount  of  oxide  of  lead,  which  ren- 
ders it  harder,  hence  the  alteration  in  physical  properties  which  the  metal  suffers 
when  long  fused  in  contact  with  air. 

Pure  lead  is  not  affected  by  perfectly  pure  water  (free  from  air),  at  the  ordi- 
nary temperature ;  but  if  air  be  present,  the  metal  is  oxidized  at  its  expense, 
and  the  oxide  thus  formed  combines  with  the  carbonic  acid  accompanying  the 
air,  to  form  a  basic  carbonate  of  lead,  which  is  deposited  as  a  coating  of  minute 
crystals  upon  the  metal.  The  water  will  then  be  found  to  contain  lead ;  but  if 
saline  matters  (especially  such  as  may  yield  insoluble  lead-compounds,  above  all, 
the  sulphates)  be  present  in  considerable  quantity,  no  lead  will  be  found  in  solu- 
tion, for  a  film  of  an  insoluble  lead-salt  (e.  g.  the  sulphate)  will  be  formed  upon 
the  surface  of  the  metal,  and  will  protect  it  from  further  oxidation. 

Lead  decomposes  steam  slowly,  at  a  white  heat,  litharge  being  formed.  It 
does  not  decompose  water  in  presence  of  acids. 

Lead  is  scarcely  attacked  by  hydrochloric  or  dilute  sulphuric  acid;  concen- 
trated sulphuric  acid  dissolves  it,  with  the  aid  of  heat,  as  sulphate  of  lead,  sul- 
phurous acid  being  evolved : — 

Pb+2(HO.S03)=PbO.S03  +  S03-f2HO. 

Concentrated  nitric  acid  acts  but  slowly  upon  lead,  a  film  of  nitrate  of  lead, 
insoluble  in  that  acid,  being  formed;  dilute  nitric  acid,  especially  if  heated,  dis- 
solves the  metal  rapidly,  as  nitrate. 


LEAD    AND    OXYGEN.     . 

Siboxide Pb30 

Oxide PbO 

Binoxide Pb03 

Intermediate  oxides  also  exist. 

SUBOXIDE  OF  LEAD,  PbaO. 

§  316.  This  oxide  is  supposed  by  some  chemists  to  compose  the  dark  film 
which  forms  upon  the  surface  of  lead  when  exposed  to  air. 

The  suboxide  may  be  prepared  by  heating  oxalate  of  lead  (PbO.Ca03),  in  an 
oil-bath,  to  about  572°  F.  (300°  C.),  as  long  as  any  gas  (carbonic  acid  and  car- 
bonic oxide)  is  disengaged : — 

2(PbO.C308)=PbaO+3COa+CO. 


470  OXIDE   OF   LEAD. 

Suboxide  of  lead  is  a  black  powder;  when  heated  in  close  vessels  to  a  tem- 
perature exceeding  700°  F.  (370°  C.)j  it  is  decomposed  into  metallic  lead  and 
oxide  of  lead. 

If  heated  in  air,  it  burns,  and  is  converted  into  the  oxide. 

Suboxide  of  lead  is  insoluble  in  water ;  acids  and  alkalies  decompose  it  into 
oxide  of  lead,  which  dissolves,  and  metallic  lead. 

OXIDE,  OR  PROTOXIDE,  OF  LEAD,  PbO.     Eq.  111.7. 
MASSICOT  (the  oxide  which  has  not  been  fused). 
LITHARGE  (crystalline  oxide  obtained  by  fusion). 

Preparation. — Some  details  relating  to  the  preparation  of  this  compound  upon 
a  large  scale  will  necessarily  be  given  when  we  describe  the  reduction  of  lead 
from  its  ores;  suffice  it  for  the  present  to  say  that  it  is  produced  by  the  oxida- 
tion of  lead  in  air,  under  the  influence  of  a  high  temperature. 

Pure  oxide  of  lead  may  be  obtained  by  strongly  heating  the  nitrate. 

By  dissolving  oxide  of  lead  in  caustic  soda,  and  slowly  evaporating  the  solu- 
tion, white  dodecahedral  crystals  are  obtained. 

When  hydrated  oxide  of  lead  is  boiled  with  a  quantify  of  potassa  insufficient 
to  dissolve  it,  it  is  converted  into  a  brownish-yellow,  crystalline  anhydrous  oxide, 
which  becomes  of  a  pale  yellow  color  when  heated. 

If  a  solution  of  caustic  soda  be  boiled  with  an  excess  of  litharge,  the  clear 
liquid  deposits,  on  cooling,  rose-colored  nearly  cubical  crystals  of  oxide  of  lead ; 
if  these  be  heated  to  dull  redness,  and  allowed  to  cool  slowly,  they  remain  red, 
but  if  suddenly  cooled,  become  yellow. 

Properties. — From  what  we  have  said  above,  it  will  be  seen  that  the  physical 
properties  of  the  oxide  of  lead  differ  much  according  to  the  method  of  preparation ; 
thus  it  may  vary  in  color  from  white  to  red  or  yellow  ;  all  these  varieties  occur 
in  the  litharge  of  commerce,  which  often  contains  traces  of  silver,  and  occasion- 
ally of  copper.  The  different  varieties  of  the  oxide  give,  when  powdered,  a  pro- 
duct having  the  ash-gray  color  of  litharge. 

Oxide  of  lead,  as  obtained  by  the  calcination  of  the  nitrate,  has  a  yellow  color, 
which  becomes  darker,  and  ultimately  brownish-red  on  heating;  it  fuses  at  an 
intense  red  heat,  and  is  somewhat  volatile  at  a  very  high  temperature.  On  cool- 
ing from  the  fused  state,  it  crystallizes  in  shining  plates  (litharge).  The  true 
primitive  form  of  oxide  of  lead  appears  to  be  the  octohedron  with  a  rhombic 
base. 

When  exposed  to  air,  it  slowly  absorbs  carbonic  acid.  Heated  in  air  to  about 
572°  F.  (300°  C.)  it  absorbs  oxygen,  and  is  converted  into  minium,  a  compound 
of  oxide  with  binoxide  of  lead. 

Oxide  of  lead  is  slightly  soluble  in  pure  water;  about  7000  parts  of  the  latter 
take  up  1  part  of  oxide  of  lead ;  the  solution  has  an  alkaline  reaction.  The 
presence  of  a  small  quantity  of  saline  matter  hinders  the  solution  of  the  oxide. 
Water  holding  sugar  in  solution  is  capable  of  dissolving  a  considerable 
quantity. 

Oxide  of  lead  is  a  powerful  base,  forming  numerous  well-defined  salts.  The 
soluble  neutral  salts  have  an  acid  reaction.  It  is  also  capable  of  dissolving  in 
alkaline  solutions,  forming  compounds,  some  of  which  are  crystallizable,  and 
have  received  the  name  of  plumbites,  though  the  powerful  basic  properties  of  the 
oxide  of  lead  appear  to  forbid  the  supposition  that  it  should  ever  be  capable  of 
playing  the  part  of  an  acid ;  these  are  more  probably  double  compounds  similar 
to  those  which  we  occasionally  see  formed  between  powerful  bases. 

Oxide  of  lead  is  very  easily  reduced  by  hydrogen  or  carbon,  with  the  aid  of 
heat.  Silicic  acid,  at  a  high  temperature,  readily  combines  with  oxide  of  lead ; 


NITRATE   OF  LEAD.  471 

hence  litharge  should  not  be  fused  in  earthen  crucibles,  since  it  corrodes  them 
rapidly. 

Oxide  of  lead  is  isoraorphous  with  baryta  and  lime,  which,  indeed,  in  many 
of  its  chemical  relations,  it  much  resembles. 

Uses. — Litharge  is  employed  in  preparing  white-lead,  in  the  manufacture  of 
glass,  and  in  glazing  some  kinds  of  earthenware.  A  compound  of  litharge  with 
lime  is  sometimes  used  for  dyeing  the  hair  of  a  purplish-black  color ;  the  color 
is  due  to  the  production  of  sulphide  of  lead  from  the  sulphur  existing  in  hair. 

It  is  also  an  important  reagent  in  assaying. 

Hydrated  oxide  of  lead,  PbO.HO,  is  obtained  as  a  white  crystalline  precipi- 
tate when  a  solution  of  a  lead  salt  is  decomposed  by  a  caustic  alkali ;  it  is  easily 
dehydrated  by  heat,  and  dissolves  in  the  alkalies. 

NITRITE  OF  LEAD,  PbO.N03. — This  salt  is  prepared  by  passing  carbonic  acid 
through  an  aqueous  solution  of  basic  nitrite  of  lead,  filtering  off  the  carbonate  of 
lead  which  is  precipitated,  and  evaporating  the  solution,  when  yellow  prismatic 
crystals  of  the  nitrite  are  deposited. 

Nitrite  of  lead  is  employed  for  preparing  other  nitrites  by  double  decompo- 
sition. 

Basic  nitrite  of  lead,  4PbO.N03,HO,  is  obtained  by  boiling  a  solution  of  ni- 
trate of  lead  for  a  considerable  period  with  an  excess  of  metallic  lead.  It  is  a 
crystalline  salt  of  a  pink  color;  its  solution  has  a  very  alkaline  reaction. 

Another  basic  nitrite,  2PbO.N03,HO,  is  deposited  in  yellow  needles  when 
the  salt  2PbO.N04  is  boiled  with  metallic  lead. 

NITRATE  OF  LEAD,  PbO.N05. 

Preparation. — In  order  to  prepare  this  salt,  metallic  lead,  the  oxide,  or  its 
carbonate  is  dissolved  in  nitric  acid,  and  the  solution  allowed  to  crystallize. 

Properties. — Nitrate  of  lead  crystallizes  in  hard  anhydrous  octohedra,  which 
are  sometimes  transparent  and  sometimes  opaque.  They  are  unalterable  by  ex- 
posure to  air.  When  heated,  nitrate  of  lead  decrepitates,  fuses,  and  is  decom- 
posed into  oxide  of  lead,  which  remains  behind,  whilst  peroxide  of  nitrogen  and 
oxygen  are  evolved  : — 

PbO.N05=PbO  +  N04-fO. 

Nitrate  of  lead  is  somewhat  sparingly  soluble  in  water,  1  part  of  the  salt  re- 
quiring about  7  parts  of  cold  water ;  it  is  more  soluble  in  hot  water.  This  salt 
is  almost  insoluble  in  nitric  acid;  hence,  when  alloys  containing  lead  are  treated 
with  that  solvent,  a  considerable  quantity  of  water  should  be  added  after  the 
oxidation  is  completed,  in  order  to  insure  the  solution  of  the  nitrate  of  lead. 

Nitrate  of  lead  is  used  in  the  laboratory  for  the  preparation  of  peroxide  of 
nitrogen  ;  it  is  also  occasionally  employed  as  a  reagent. 

Three  basic  nitrates  of  lead  have  been  obtained. 

PbO.N05,PbO.HO  is  obtained  in  colorless  crystals  when  a  solution  of  nitrate 
of  lead  is  boiled  with  oxide  or  carbonate  of  lead,  and  the  filtered  liquid  allowed 
to  cool. 

PbO.N05,3(PbO.HO)  is  produced  when  the  neutral  nitrate  is  treated  with  a 
slight  excess  of  ammonia ;  if  digested  with  a  large  excess  of  ammonia,  the  hy- 
drated  oxide  of  lead  is  obtained. 

The  other  nitrate  contains  6  eqs.  PbO,  and  is  prepared  by  partially  decom- 
posing the  neutral  nitrate  with  ammonia. 

Two  compounds  of  nitrate  with  nitrite  of  lead  are  known;  they  are  prepared 
by  dissolving  lead  in  a  solution  of  the  nitrate. 

If  a  very  dilute  solution  of  nitrate  of  lead  be  digested  at  about  158°  F.  (70° 
C.)  with  a  quantity  of  metallic  lead  in  the  proportion  of  1  eq.  for  each  equiva- 
lent of  nitrate,  the  metal  is  gradually  dissolved,  forming  a  yellow  solution,  which, 


472  SULPHATE    OF   LEAD. 

on  cooling,  deposits  brilliant  yellow  plates  having  the  composition  2PbO.N05, 
2PbO.N03-f-2HO. 

2(PbO.N03)-fPb3=2PbO.N05,2PbO.N03. 

When  treated  with  strong  acids,  these  crystals  evolve  red  vapors. 

If,  in  the  above  experiment,  3  eqs.  of  lead  be  employed  for  every  2  eqs.  of 
the  nitrate,  the  solution  deposits  crystals  of  an  orange  salt,  much  less  soluble 
than  the  yellow  compound,  and  having  the  composition  4PbO,N05,3PbO.NO3 
+3HO. 

Those  chemists  who  regard  the  compound  NO4  as  hyponitric  acid,  consider 
these  basic  salts  as  hyponit rates  of  lead,  having  the  formula,  respectively,  2PbO. 
N04-f  HO,  and  7Pb0.2N04-f  3HO;  but  this  view  is  contradicted  by  the  cir- 
cumstance that  when  acted  on  by  alkalies,  these  compounds  yield  mixtures  of 
nitrates  and  nitrites. 

SULPHATE  OF  LEAD,  PbO.SOs. 

This  salt  is  found  in  nature  crystallized  in  translucent  oetohedra,  called  by 
mineralogists  lead-vitriol. 

Preparation. — A  solution  of  nitrate  or  acetate  of  lead  is  precipitated  by  dilute 
sulphuric  acid,  the  precipitate  washed,  first  by  decantation,  afterwards  upon  a 
filter,  till  the  washings  have  no  longer  an  acid  reaction. 

A  large  quantity  of  sulphate  of  lead  is  obtained  as  a  by-product  in  the  prepa- 
ration of  acetate  of  alumina  (for  dyeing),  by  decomposing  sulphate  of  alumina 
with  acetate  of  lead. 

Properties. — Sulphate  of  lead  is  a  white  solid;  it  is  the  only  sulphate  of  a 
heavy  metallic  oxide  which  is  not  decomposed  by  a  high  temperature ;  it  is  very 
sparingly  soluble  in  water,  and  in  dilute  sulphuric  acid ;  it  is  soluble,  however, 
to  a  considerable  extent,  in  concentrated  sulphuric  acid,  and  is  precipitated  on 
adding  water.  It  is  also  very  perceptibly  soluble  in  concentrated  and  diluted 
nitric  acid;  hydrochloric  acid,  with  the  aid  of  heat,  dissolves  it  in  the  form  of 
chloride  of  lead,  which  is  deposited  on  cooling,  while  free  sulphuric  acid  is  found 
in  the  solution ;  it  is  insoluble  in  alcohol. 

Sulphate  of  lead  is  decomposed  and  dissolved  by  the  fixed  caustic  alkalies  ;* 
when  boiled  with  carbonates  of  potassa  and  soda,  it  yields  insoluble  carbonate  of 
lead  and  alkaline  sulphates.  The  decomposition  is  more  easily  effected  by  fusion  ; 
the  soluble  sulphides  also  decompose  sulphate  of  lead. 

The  reduction  of  sulphate  of  lead  is  easily  effected  by  carbon,  hydrogen,  or 
carbonic  oxide,  at  a  high  temperature. 

When  strongly  heated  with  an  excess  of  carbon,  it  is  reduced  to  sulphide  of 
lead,  but  if  gradually  heated,  sulphurous  acid  is  disengaged,  and  subsulphide  of 
lead,  PbaS,  remains;  2(PbO.S03)-f  C3=3CO  +  S08+PbaS. 

If  sulphate  of  lead  be  heated  with  only  so  much  carbon  as  is  required  to  re- 
duce the  oxide  of  lead,  and  to  convert  the  sulphuric  acid  into  sulphurous,  metallic 
lead  is  obtained ;  but  if  half  this  quantity  be  employed,  we  obtain  the  oxide  of 
lead,  the  sulphur  being  disengaged  in  the  form  of  sulphurous  acid. 

Sulphate  of  lead  may  be  reduced  to  the  metallic  state  by  zinc,  in  presence  of 
water  acidulated  with  sulphuric  or  hydrochloric  acid,  when  the  nascent  hydrogen 
is  probably  the  true  reducing  agent ;  this  reaction  is  sometimes  turned  to  ad- 
vantage in  preparing  pure  lead  for  cupellation. 

A  partial  decomposition  is  suffered  by  sulphate  of  lead  when  ^strongly  heated 
in  an  earthen  crucible,  a  little  silicate  of  lead  being  formed. 

The  reduction  of  sulphate  of  lead  may  be  effected  by  strongly  heating  it  in 

1  According  to  Kiihn,  when  ammonia  acts  upon  freshly  precipitated  sulphate  of  lead, 
the  compound  2PbO.S03  is  produced. 


CARBONATE   OF   LEAD.  473 

contact  with  sulphide  of  lead ;  if  1  eq.  of  the  sulphate  be  heated  with  1  eq.  of 
sulphide,  all  the  lead  is  reduced  : — 

PbO.S03-fPbS=2S03+Pba; 
when  2  eqs.  of  sulphate  are  employed,  two-thirds  of  the  lead  remain  as  oxide  : — 

2(PbO.S03)  +  PbS=3S03+2PbO-f.Pb; 

We  shall  hereafter  see  these  reactions  turned  to  account  in  the  reduction  of  lead 
from  its  ores. 

CARBONATE  OF  LEAD,  CERUSE,  WHITE  LEAD,  PbO,COa. 

§  317.  The  carbonate  of  lead  (lead-spar  or  white-lead-ore)  is  found  native, 
generally  associated  with  galena;  it  occurs  in  transparent  crystals,  having  the 
same  form  as  those  of  arragonite,  and  possessed  of  the  property  of  double  re- 
fraction. 

The  action  of  air,  containing  aqueous  vapor  and  carbonic  acid,  upon  metallic 
lead,  gives  rise  to  the  production  of  an  incrustation,  often  of  considerable  thick- 
ness, which  is  composed  of  carbonate  and  hydrated  oxide  of  lead ;  the  formation 
of  this  crust  is  much  promoted  by  the  presence  of  organic  matters  (which  yield 
carbonic  or  other  acids  by  their  decomposition).  This  corrosion  of  lead  has  been 
observed  to  be  particularly  active  in  situations  where  portions  of  lead-roofing  are 
exposed  to  the  action  of  the  vitiated  air  issuing  from  a  crowded  apartment. 
Pieces  of  lead  (e.g.  bullets)  which  have  been  cast  in  moulds  smeared  with  oil, 
have  been  known  to  become  coated  with  carbonate,  even  in  a  few  weeks.  The 
presence  of  unstable  organic  matters  in  most  river  and  well-waters,  will  help  to 
explain  their  rapid  action  upon  leaden  cisterns.  It  is  remarkable  that  (as  in  the 
rusting  of  iron)  when  the  superficial  conversion  of  lead  into  carbonate  has  once 
commenced,  it  proceeds  with  comparative  rapidity  throughout  the  mass,  perhaps 
because  a  voltaic  couple  is  formed  by  the  metal  and  its  coating  of  carbonate. 

Preparation. — On  the  small  scale,  it  is  prepared  by  precipitating  a  solution  of 
acetate  of  lead  with  excess  of  carbonate  of  soda ;  the  precipitate  is  collected  on 
a  filter,  and  washed. 

For  the  purposes  of  the  arts,  carbonate  of  lead  is  manufactured  by  decompos- 
ing the  tribasic  acetate  of  lead  with  carbonic  acid : — 

3PbO.A+2C02=2(PbO.C03)+PbOA; 

this  principle  may  be  carried  out  in  various  ways. 

The  old  (Dutch)  process  consists  in  suspending  rolls1  of  sheet  lead  in  earthen 
pots,  into  which  a  small  quantity  of  inferior  vinegar  is  poured ;  this  is  not  per- 
mitted to  come  in  contact  with  the  lead ;  the  pot  is  then  partially  covered  with  a 
sheet  of  lead,  and  several  thus  prepared  are  arranged  in  alternate  layers  with 
dung  or  spent  tan,  and  completely  buried  in  a  heap  of  the  same  refuse,  so  con- 
structed as  to  admit  of  a  free  passage  of  air.  After  some  weeks,  the  heap  is 
destroyed,  when  the  metal  is  found  coated  with  a  thick  incrustation  of  white- 
lead,  which  must  be  detached,  washed,  ground  into  a  paste  with  water  and  dried 
in  porous  earthen  pots  at  a  moderate  heat. 

The  theory  of  this  process  is  very  simple ;  the  lead,  in  contact  with  air  and 
vapors  of  acetic  acid,  is  oxidized  and  converted  into  tribasic  acetate  of  lead,  which 
is  decomposed  by  the  carbonic  acid  disengaged  in  the  fermentation  of  the  heaps, 
yielding  carbonate  and  neutral  acetate  of  lead  (see  the  above  equation)  ;  the  latter 
is  capable  of  combining  with  a  fresh  portion  of  oxide  of  lead,  thus  reproducing 
the  tribasic  acetate,  again  to  undergo  the  same  process;  thus,  a  very  small 
quantity  of  vinegar  would  suffice  to  produce  a  very  considerable  quantity  of  car- 

1  Gratings  of  lead  are  now  generally  employed  instead  of  rolls.  These  are  made  of  the 
purest  lead  to  be  found  in  commerce. 


474  WHITE   LEAD. 

bonate  of  lead ;  a  little  acetate  of  lead  of  course  remains  in  the  white  lead  at 
the  end  of  the  process,  but  is  removed  by  washing ;  moreover,  the  carbonate, 
when  formed,  always  combines  with  more  or  less  hydrated  oxide  of  lead.  The 
operation  is  considerably  accelerated  by  the  heat  disengaged  in  the  fermentation 
of  the  heap,  causing  the  production  of  large  quantities  of  acetic  acid  vapor  in 
the  pots. 

This  process  had  been  in  use  for  a  very  long  time  before  it  was  discovered 
that  it  might  be  carried  out  in  a  far  simpler  manner  by  boiling  an  excess  of 
litharge  with  acetic  acid,  and  passing  a  current  of  carbonic  acid  through  the 
tribasic  acetate  of  lead  thus  obtained,  when  carbonate  of  lead  is  precipitated, 
carrying  with  it  a  variable  amount  of  hydrated  oxide,  and  a  solution  of  neutral 
acetate  produced,  which  needs  only  to  be  boiled  with  more  litharge,  in  order  to 
reproduce  the  tribasic  acetate.  The  carbonic  acid  employed  for  this  purpose  is 
usually  that  produced  in  the  combustion  of  the  fuel  used  for  the  boilers.  Occa- 
sionally, the  process  is  modified  by  passing  the  carbonic  acid  over  litharge  moist- 
ened with  acetic  acid,  or  with  a  weak  solution  of  acetate  of  lead. 

It  is  sometimes  objected,  however,  that  the  white  lead  prepared  by  these  new 
processes  has  not  so  good  a  body  as  the  old  product. 

The  white  lead  of  commerce  always  contains  a  considerable  quantity  of  hydrat- 
ed oxide  of  lead ;  the  analyses  of  many  specimens  of  this  product  have  shown 
that  it  is  generally  a  basic  carbonate  of  the  formula  2(PbO.C02),PbO.HO;1 
other  specimens  have  been  found  to  correspond  to  the  formula  3(PbO.COa), 
PbO.HO. 

Properties. — Carbonate  of  lead  is  a  white  substance,  which  is  easily  decom- 
posed by  heat  into  carbonic  acid  and  (prot-)  oxide  of  lead,  which,  if  not  too 
strongly  heated,  absorbs  oxygen,  and  is  converted  into  minium  (red  lead).  It  is 
insoluble  in  water,  but  dissolves  in  solution  of  carbonic  acid,  and  in  all  acids 
which  form  soluble  compounds  with  its  base ;  carbonate  of  lead  is  also  soluble  in 
the  fixed  alkalies. 

Sulphuretted  hydrogen  easily  decomposes  carbonate  of  lead,  ultimately  con- 
verting it  into  black  sulphide  of  lead ;  hence  arises  the  dark  color  acquired  by 
lead-paints  when  exposed  to  a  foul  atmosphere. 

Carbonate  of  lead  is  a  very  powerful  poison. 

Uses. — Great  use  is  made  of  this  compound  in  painting,  and  it  is  hence  an 
important  article  of  commerce.  It  is  sometimes  adulterated  with  sulphate  of 
lead,  sulphate  of  baryta,  chalk,  and  plaster  of  Paris.  To  detect  these  impurities, 
the  specimen  should  be  heated  with  an  excess  of  acetic  acid  ;  the  solution  saturat- 
ed with  sulphuretted  hydrogen,  filtered,  and  tested  for  lime  with  oxalic  acid ; 
the  production  of  a  precipitate  indicates  adulteration  with  chalk.  The  residue 
left  by  acetic  acid  may  contain  sulphate  of  baryta,  sulphate  of  lead,  and  sulphate 
of  lime  (plaster  of  Paris) ;  it  should  be  washed,  and  boiled  with  dilute  hydro- 
chloric acid,  which  dissolves  the  last  two ;  a  part  of  the  (hot)  solution  may  be 
set  aside  to  cool,  when  crystals  of  chloride  of  lead  will  be  deposited  if  any  sul- 
phate has  been  dissolved  by  the  hydrochloric  acid ;  the  other  portion  may  be 
mixed  with  excess  of  ammonia  and  sulphide  of  ammonium,  the  sulphide  of  lead 
filtered  off,  and  the  solution  tested  for  lime  with  oxalate  of  ammonia ;  the  pres- 
ence of  sulphate  of  baryta  will  be  known  by  the  insolubility  of  the  residue  after 
repeatedly  boiling  with  dilute  hydrochloric  acid.3 

1  This  compound  is  also  obtained  when  an  alkaline  carbonate  is  added  to  a  boiling  solu- 
tion of  a  lead-salt. 

2  When  the  white  lead  is  mixed  with  oil,  it  becomes  more  difficult  to  ascertain  the  exact 
nature  of  the  adulterations,  since  the  methods  which  must  be  adopted  in  order  to  destroy 
the  oil  (viz.,  either  incineration,  or  boiling  with  hydrochloric  acid,  and  gradually  adding 
chlorate  of  potassa)  will  alter  to  a  great  extent  the  forms  of  combination  in  which  the 
substances  exist,  and  the  analyst  must  content  himself  with  merely  identifying  the  differ- 


CHROMATES   OF   LEAD.  475 

Carbonate  of  lead  is  employed  for  glazing  cards,  which  consequently  become 
black  when  exposed  to  sulphuretted  hydrogen  ;  in  fact,  cards  covered  with  carbo- 
nate of  lead  will  indicate  very  small  quantities  of  this  gas. 

In  chemical  investigations  carbonate  of  lead  is  sometimes  employed  to  remove 
sulphuric  or  hydrosulphuric  acid  from  solutions  or  gases  ;  for  the  former  pur- 
pose it  is  better  to  prepare  it  expressly,  and  to  keep  it  in  a  moist  state  till  re- 
quired for  use. 

Compounds  of  sulphate  of  lead  with  1  and  3  eqs.  of  carbonate  of  lead  form 
minerals  called,  respectively,  lanarkite  and  leadliilMte. 

Silicic  acid  and  oxide  of  lead  enter  into  the  composition  of  various  kinds  of 
glass  ;  the  silicates  of  lead  are  easily  fusible,  especially  if  they  contain  a  large 
amount  of  base  ;  in  the  latter  case,  the  silicate  has  a  yellow  or  brown  color, 
whilst,  if  the  silica  predominate,  it  is  colorless. 

CHROMATES  or  LEAD.    NEUTRAL  CHROMATE  OF  LEAD.     CHROME-YELLOW. 

PbO.Cr03. 

This  chromate  is  found  (though  rarely)  in  the  mineral  kingdom,  as  red-lead- 
ore  of  Siberia  ;  it  is  crystallized  in  prisms.  It  is  formed  by  the  action  of  chro- 
mate of  potassa  on  sulphate  or  carbonate  of  lead,  in  the  cold. 

Preparation.  —  It  is  prepared  by  decomposing  acetate  of  lead  with  chromate 
of  potassa,  when  it  falls  as  a  fine  yellow  precipitate:  — 


the  tint  of  the  precipitate  varies  with  the  temperature  at  which  it  is  formed,  and 
according  to  the  state  of  neutrality  of  the  solutions  ;  these  latter  are  employed 
in  a  rather  dilute  state,  to  avoid  the  formation  of  a  crystalline  compound  which 
appears  to  be  a  double-salt. 

Properties.  —  Chromate  of  lead  has  a  very  fine  yellow  color;  when  heated,  its 
color  changes  to  a  red-brown;  it  fuses  at  a  red  heat  into  a  grayish-brown  mass, 
and  subsequently  evolves  oxygen,  and  is  converted  into  a  mixture  of  sesquioxide 
of  chromium  and  a  basic  chromate  of  lead  :  — 

4(PbO.Cr03)-2(2PbO.CrOs)+Cra03+03. 

Chromate  of  lead  is  insoluble  in  water,  sparingly  soluble  even  in  nitric  acid, 
but  readily  so  in  potassa. 

Uses.  —  It  is  employed,  to  a  great  extent,  in  painting  arid  calico-printing  ;  the 
commercial  chromate  is  sometimes  mixed  with  sulphate  of  lime,  which  improves 
its  color. 

Chromate  of  lead  is  very  much  used  in  the  analysis  of  organic  substances  ; 
when  heated  to  bright  redness  with  compounds  containing  carbon  and  hydrogen, 
it  readily  oxidizes  these  elements,  converting  them  into  carbonic  acid  and  water, 
forms  in  which  their  weight  may  be  conveniently  determined  ;  if  sulphur  be  pre- 
sent, it  remains  behind  as  sulphate  of  lead,  which  is  a  great  advantage  in  the  use 
of  chromate  of  lead  instead  of  oxide  of  copper,  for  combustion.  Previously  to 
being  used  for  this  purpose,  the  chromate  is  fused,  in  order  to  expel  all  traces  of 
moisture. 

BIBASIC  CHROMATE  OF  LEAD.    BICHROMATE  OR  SUBCHROMATE  OF  LEAD. 

2PbO.CrO3. 

This  salt  is  always  formed  when  the  neutral  chromate  is  treated  with  a  quan- 
tity of  alkali  insufficient  to  decompose  it;  it  is  also  deposited  in  red  crystals 

ent  acids  and  bases  ;  the  quantities  of  these  will,  however,  guide  him  in  his  conclusions 
as  to  the  really  important  adulteration.  Probably,  by  powerful  pressure  in  blotting-paper, 
between  hot  iron  plates,  the  oil  might  be  so  far  extracted  as  to  allow  of  the  application  of 
the  ordinary  method  of  testing. 


476  BINOXIDE   OP   LEAD. 

when  carbonic  acid  is  passed  through  a  solution  of  oxide  of  lead  and  chromate  of 
lead  in  caustic  potassa. 

A  product  having  a  very  beautiful  red  color,  is  obtained  by  gradually  adding 
chromate  of  lead  to  fused  nitre,  allowing  the  basic  chromate  to  subside,  pouring 
off  the  supernatant  fused  mass,  and  rapidly  washing  the  basic  salt;  the  potassa 
of  the  nitre  here  abstracts  one-half  of  the  chromic  acid  from  the  neutral  lead-salt. 

The  fine  red  color  of  this  basic  chromate  renders  it  useful  in  calico-printing ; 
it  is  usually  produced  by  immersing  the  stuff,  previously  printed  with  the  neutral 
chromate  in  a  bath  of  lime-water  (or  other  weak  alkaline  liquor),  which  converts 
the  chromate  into  dichrornate. 

A  sesqui-basic  chromate  of  lead  (3Pb0.2Cr03)  occurs  in  nature  as  melano- 
chroite. 

BINOXIDE  or  LEAD,  PUCE  OXIDE  OP  LEAD,  PLUMBIC  ACID,  PEROXIDE  OP 

LEAD,  Pb03. 

§  318.  This  oxide  is  found  in  the  mineral  kingdom  as  heavy  lead-ore;  it  is 
formed  when  the  (prot-)  oxide  of  lead  is  treated  with  very  powerful  oxidizing 
agents  ;  thus,  if  litharge  be  gently  heated  with  one-fourth  of  its  weight  of  chlo- 
rate of  potassa,  and  the  fused  mass  washed  with  boiling  water,  binoxide  of  lead 
is  left ;  again,  it  may  be  obtained  by  suspending  the  (prot-)  oxide  in  water,  and 
passing  a  current  of  chlorine,  or,  equally  well,  by  treating  a  solution  of  acetate  of 
lead  with  an  alkaline  hypochlorite ;  in  this  way,  it  is  sometimes  obtained  in  a 
crystalline  state. 

The  following,  however,  is  the  best  method  of  preparing  the  binoxide  of  lead. 

Minium  (red-lead),  in  fine  powder,  is  boiled  with  an  excess  of  dilute  nitric 
acid,  the  mixture  being  constantly  stirred;  the  solution  (containing  nitrate  of 
lead)  is  decanted,  the  residue  (binoxide  of  lead)  boiled  with  water,  and  washed 
until  the  washings  are  no  longer  affected  by  hydrosulphuric  acid  ;  it  is  then  dried 
in  a  water- bath. 

Properties. — Binoxide  of  lead  has  a  dark  purplish-brown  color;  the  native 
variety  forms  iron-black,  lustrous,  six-sided  prisms.  When  heated,  it  is  easily 
decomposed,  evolving  oxygen,  and  yielding,  first,  an  intermediate  oxide,  and 
ultimately  litharge. 

It  is  insoluble  in  water  and  in  acids  in  the  cold ;  nitric  acid  (as  we  have  seen) 
is  incapable  of  dissolving  it,  even  with  the  aid  of  heat;  if  it  be  heated  with  sul- 
phuric acid,  it  parts  with  half  of  its  oxygen,  being  reduced  to  (prot-)  oxide  of 
lead,  which  combines  with  the  acid : — 

PbOa-fHO.S03=PbO.SO3+O-fHO; 

hydrochloric  acid  converts  it  into  chloride  of  lead,  with  evolution  of  chlorine : — 
Pb02+2HCl=PbCl+2HO  +  Cl. 

Binoxide  of  lead  is  a  powerful  oxidizing  agent ;  it  eagerly  absorbs  sulphurous 
acid,  with  great  disengagement  of  heat,  and  is  converted  into  sulphate  of  lead  : — 
Pb03+S03=PbO.S03. 

This  property  renders  it  useful  in  the  laboratory  for  removing  sulphurous  acid 
from  gaseous  mixtures,  especially  in  organic  analysis. 

When  amrnoniacal  gas  is  passed  over  the  binoxide  of  lead,  the  latter  is  par- 
tially reduced,  water  and  nitrate  of  ammonia  being  formed. 

Binoxide  of  lead  is  capable  of  combining  with  bases  to  form  definite,  and,  in 
some  cases,  crystallizable  salts  termed  plumbates. 

The  plumbate  of  potassa  is  prepared  by  fusing  plumbic  acid  with  hydrate  of 
potassa  in  a  silver  crucible  ;  it  dissolves  in  a  boiling  alkaline  solution,  and  may 
be  crystallized  in  colorless  cubes,  the  formula  of  which  is  KO.PbOa.3HO;  water 
decomposes  this  salt,  and  plumbic  acid  is  precipitated. 


CHLORIDE    OF   LEAD.  477 


MINIUM,  RED  LEAD,  PLUMBATE  OF  OXIDE  OF  LEAD. 

This  substance  varies  in  composition  according  to  the  circumstances  under 
which  it  is  obtained. 

When  a  solution  of  oxide  of  lead  in  potassa  is  added  to  plumbate  of  potassa, 
a  yellow  precipitate  of  hydrated  minium  is  formed. 

Preparation. — Minium  is  prepared  on  the  large  scale  by  heating  lead  in  a 
reverberatory  furnace  to  a  temperature  insufficient  to  fuse  the  oxide  which  is 
formed,  and  subsequently  heating  this  oxide  (massicot),  with  free  access  of  air, 
to  a  temperature  not  exceeding  572°  F.  (300°  C.),  when  it  is  converted  into 
minium ;  the  roasting  is  generally  repeated  two  or  three  times  before  the  oxida- 
tion is  complete. 

The  massicot  obtained  by  heating  ordinary  impure  lead  in  air  varies  in  quality; 
the  product  first  formed  contains  the  oxides  of  those  metals  which  are  more 
readily  oxidizable  than  lead,  whilst  that  last  obtained  is  contaminated  with  those 
metals  which  are  less  easily  oxidized,  such  as  copper  and  silver;  the  massicot 
produced  in  the  middle  of  the  process  is  the  purest,  and  is  preferred  for  the 
manufacture  of  minium. 

If  the  lead  employed  should  contain  any  manganese,  permanganate  of  lead 
will  be  found  in  the  minium. 

An  orange  variety  of  minium  is  obtained  by  gently  heating  carbonate  of  lead 
in  air. 

Properties. — The  minium  obtained  by  heating  massicot  in  air  till  no  further 
increase  of  weight  is  observed,  has  the  composition  2PbO.Pb02,  and  this  formula 
would  appear  to  represent  the  true  minium,  the  others  being  probably  mixtures 
of  this  substance  with  oxide  of  lead,  which  is  dissolved  out  by  acetate  of  lead, 
or  by  potassa,  the  above  compound  being  left.  Crystals  of  minium  which  were 
accidentally  formed  in  a  furnace,  were  found  to  contain  3PbO.Pb03 ;  and 
Mulder  has  recently  assigned  this  formula  to  the  greater  number  of  specimens 
of  minium.  A  specimen  of  minium  analyzed  by  Berzelius  contained  PbO. 
Pb02;  the  same  compound  was  obtained  by  Winkelblech,  by  adding  hypo- 
chlorite  of  soda  to  a  solution  of  oxide  of  lead  in  potassa. 

All  the  intermediate  oxides  of  lead,  however,  possess  a  more  or  less  intense 
red  color;  they  evolve  oxygen  when  strongly  heated,  leaving  the  (prot-)  oxide 
of  lead. 

When  treated  with  acids,  the  miniums  behave  just  as  combinations  of 
the  oxide  and  binoxide  of  lead  would  be  expected  to;  thus  nitric  acid  leaves 
binoxide  of  lead  undissolved;  hydrochloric  acid  yields  free  chlorine,  &c. 

Uses. — Minium  is  employed  largely  in  the  arts,  being  the  commonest  red 
mineral  color.  It  is  also  used  in  the  fabrication  of  glass,  where  the  oxygen 
which  it  disengages  when  heated  serves  to  remove  any  carbonaceous  matters 
which  may  accidentally  be  present. 

The  red-lead  of  commerce  is  sometimes  adulterated  with  earthy  substances 
(brickdust)  and  colcothar. 

CHLORIDE  OF  LEAD,  PbCl. 

§  319.  This  chloride,  which  is  found  native  as  horn-lead,  may  be  formed  by 
the  direct  combination  of  its  elements  at  a  red  heat. 

It  is  prepared  by  decomposing  a  concentrated  solution  of  a  lead-salt  with 
hydrochloric  acid  or  a  soluble  chloride,  when  chloride  of  lead  is  precipitated. 

It  has  a  white  color,  and  readily  fuses  when  heated;  at  a  high  temperature, 
it  is  capable  of  volatilization.  Fused  chloride  of  lead  resolidifies  into  a  gray 
horny  mass,  known  by  the  ancients  as  horn-lead. 

Chloride  of  lead  is  very  sparingly  soluble  in  water;   1  part  of  the  salt  requires 


478  SULPHIDE   OF   LEAD. 

135  parts  of  cold,  and  33  of  boiling  water;  it  is  more  soluble  in  hydrochloric 
and  nitric  acids;  it  is  deposited  from  its  solutions,  on  cooling,  in  hexahedral 
prisms.  It  is  insoluble  in  alcohol. 

The  alkalies  and  their  carbonates,  added  in  small  proportion,  convert  it  into 
oxychloride  of  lead,  while  a  larger  quantity  decomposes  it  entirely. 

OXYCHLORIDES   OP   LEAD. 

When  chloride  of  lead  is  heated  in  air  till  no  more  fumes  are  evolved,  the 
compound  PbCl,PbO  is  formed.1 

Oxide  and  chloride  of  lead  appear  to  be  capable  of  combining  in  several  pro- 
portions ;  hence  the  composition  of  the  compound  commonly  called  oxychloride 
is  variable,  but  the  most  general  formula  appears  to  be  PbCl.TPbO.  Two  oxy- 
chlorides  exist  in  nature,  having  the  composition  PbO.PbCl,  and  2PbO.PbCl 
(mendipite). 

The  oxychloride  of  lead  is  prepared  either  by  fusing  1  part  of  the  chloride 
with  6  or  8  parts  of  litharge,  by  heating  10  parts  of  litharge  with  7  of  sal- 
ammoniac,  or  by  boiling  with  water  a  mixture  of  litharge  and  \  its  weight  of 
chloride  of  sodium,  when  a  white  hydrated  oxychloride  is  formed,  which  assumes 
a  yellow  color  on 'calcination. 

A  method  recently  introduced  for  the  preparation  of  the  oxychloride  consists 
in  decomposing  the  chloride  with  lime-water. 

The  compound  obtained  by  the  first  process  varies  in  composition  according 
to  the  proportions  employed;  that  obtained  by  the  second,  has  the  formula 
PbC1.7PbO.  The  third  process  yields  PbC1.3PbO.HO. 

Oxychloride  of  lead  (PbC1.7PbO)  has  a  fine  golden-yellow  color,  and  is  very 
fusible ;  when  resolidifying,  it  crystallizes  in  octohedra. 

It  is  used  as  a  pigment  under  various  names,  such  as  mineral  yellow.  Turner's 
yellow,  Paris  yellow. 

Bromide  of  Lead  resembles  the  chloride. 

Iodide  of  Lead  (PbT)  is  obtained  in  fine  lustrous  yellow  scales  on  mixing 
boiling  solutions  of  iodide  of  potassium  and  acetate  of  lead,  and  allowing  the 
mixture  to  cool. 

Iodide  of  lead  forms  double-salts  with  the  alkaline  iodides;  it  also  gives  a 
crystalline  compound  with  chloride  of  ammonium. 

A  blue  oxy-iodide  of  lead  exists. 

SULPHIDE,  OR  SULPHURET,  OF  LEAD,  PbS. 

§  320.  This  sulphide  occurs  abundantly  in  nature,  in  the  form  of  galena, 
which  is  almost  the  only  ore  of  lead  worth  smelting. 

There  are  two  varieties  of  galena,  the  compact  and  micaceous,  differing  in 
their  external  appearance,  the  latter  presenting  numerous  small  facets  which 
sparkle  in  the  light ;  this  variety  often  contains  a  considerable  quantity  of  silver, 
and  is  then  termed  argentiferous  galena. 

Galena  has  a  dark  gray  color,  and  metallic  lustre;  its  specific  gravity  is  7.585, 
and  the  primitive  form  of  its  crystals  is  the  cube.  Galena  fuses  at  a  higher 
temperature  than  lead,  and  may  be  volatilized  in  a  current  of  gas;  it  loses  a 
little  sulphur  when  strongly  heated.  If  heated  in  air,  galena  is  converted  into  a 
mixture  of  oxide  and  sulphate  of  lead,  sulphurous  acid  being  evolved. 

Dilute  sulphuric  and  hydrochloric  acids  have  scarcely  any  action  upon  the 

1  Pattinson  has  proposed  this  compound  in  a  hydrated  state  as  a  substitute  for  white- 
lead  ;  he  prepares  it  by  decomposing  a  hot  solution  of  chloride  of  lead  with  lime-water, 
when  a  white  precipitate  is  produced,  the  formula  of  which  is  PbCl.PbO.HO. 


METALLURGY   OF   LEAD.  479 

sulphide  of  lead;  concentrated  sulphuric  acid  converts  it  into  sulphate  of  lead, 
with  evolution  of  sulphurous  acid : — 

PbS+4(HO.S03)=PbO.S03-f4S03+3HO; 
it  is  also  attacked  by  long  boiling  with  concentrated  hydrochloric  acid. 

When  treated  with  concentrated  nitric  acid,  sulphide  of  lead  is  entirely  con- 
verted into  the  insoluble  sulphate;  whereas,  if  dilute  nitric  acid  be  employed, 
part  of  the  sulphide  is  converted  into  sulphate,  while  the  remainder  is  decom- 
posed, nitrate  of  lead  being  found  in  solution,  and  sulphur  separated. 

The  alkalies  and  alkaline  earths,  when  fused  with  sulphide  of  lead,  give  rise 
to  a  separation  of  metallic  lead,  the  sulphur  combining  with  the  alkali- metal, 
which  parts  with  its  oxygen  to  a  portion  of  the  sulphide  of  lead ;  a  slag  is  thus 
formed  containing  sulphate  of  lead,  sulphide  of  lead,  and  the  sulphide  of  an 
alkali-metal. 

Many  substances  are  capable  of  oxidizing  a  part  of  the  sulphur  contained  in 
sulphide  of  lead,  thus  causing  a  separation  of  metallic  lead.  In  this  way,  a 
certain  quantity  of  nitre,  when  fused  with  sulphide  of  lead,  separates  a  portion 
of  metal.  The  oxides  of  iron,  manganese,  and  copper  have  the  same  effect. 

When  steam  is  passed  over  sulphide  of  lead  at  a  high  temperature,  the  oxygen 
is  converted  into  sulphurous  acid,  and  the  hydrogen  into  hydrofulphuric  acid, 
metallic  lead  being  eliminated. 

Sulphide  of  lead  may  also  be  reduced  (as  is  effected  on  the  large  scale  in  the 
smelting  of  lead-ores)  by  fusion  with  2  eqs.  of  litharge  : — 
PbS  +  2PbO=Pbs-fS02. 

Hydrogen,  iron,  copper,  zinc,  and  tin  are  capable  of  reducing  sulphide  of  lead 
at  a  high  temperature. 

Sulphide  of  lead  may  be  obtained  artificially  by  fusing  sulphur  with  metallic 
lead,  or  by  the  action  of  sulphuretted  hydrogen  upon  a  solution  containing  that 
metal ;  in  the  latter  case,  it  forms  a  black  precipitate. 

A  red  compound  of  chloride  with  sulphide  of  lead  is  precipitated  when  sul- 
phuretted hydrogen  is  passed  into  a  solution  of  chloride  of  lead  in  hydrochloric  acid. 

Selenide  of  Lead  (PbSe)  occurs  associated  with  the  sulphide  in  certain  lead- 
mines  ;  it  much  resembles  galena,  with  which  it  is  isomorphous.  Selenide  of 
lead  is  employed  as  a  source  of  selenium. 

Lead  is  capable  of  combining  with  almost  all  other  metals,  but  since  these 
compounds  are  not  of  a  very  definite  character,  we  shall  only  consider  them, 
with  reference  to  their  practical  utility,  in  the  section  devoted  to  the  technical 
history  of  lead. 

METALLURGY   OF   LEAD. 

§  321.  Lead  occurs  in  nature  in  a  variety  of  combinations,  of  which  the 
following  are  the  most  important : — 


f  Prnt  ^  n^rlp     5  Pure'  and  in  combination 

(.trot-)  oxide  j  }    witb  alumina. 

Minium 

Oxychloride 

(pure,  and  associated  with  other 
Sulphide,  <     metallic  sulphides,  as  those  of 


Sulphate 
Selenide 
Telluride 


^    silver  and  antimony. 


Arseniate  (mixed  with  chloride  of  lead) 

Phosphate  "  " 

Arsenide 

Carbonate  (with  lead-ore) 
Carbonate  (mixed  with  chloride) 

Chr  ornate 

Vanadiate  , 

Tunystate 


Molybdate,  &c. 

We  have  already  remarked  that  the  metal  is  almost  invariably  extracted  from 
the  sulphide. 


480  METALLURGY   OP  LEAD. 

EXTRACTION  OP  LEAD. — Galena  is  sometimes  reduced  by  iron,  at  a  high 
temperature,  in  a  reverberatory  furnace,  but  far  more  commonly  by  the  method 
of  reaction,  as  it  is  termed,  in  which  the  following  chemical  changes  are  taken 
advantage  of: — 

1.  When  sulphide  of  lead  is  roasted  in  air,  it  is  converted  into  sulphate  of 
lead:— 

PbS+O4±=PbO.S03. 

2.  Sulphide  of  lead,  in  contact  with  3  eqs.  of  sulphate  of  lead  at  a  high 
temperature,  is  decomposed  according  to  the  equation : — 

3(PbO.S03)-fPbS=4PbO+4S03. 

3.  The  sulphide^  heated  with  1  eq.  of  sulphate  of  lead,  yields  sulphurous  acid 
and  the  metal : — 

PbO.S03-fPbS=Pb3-f2S03. 

4.  1  eq.  of  sulphide  of  lead  with  2  eqs.  of  the  oxide,  also  yield  the  metal : — 

PbS+2PbO=Pb3  +  SOa. 

After  the  galena  has  been  freed  from  gangue,  it  is  broken  up  into  small  frag- 
ments, and  roasted  on  the  hearth  of  a  reverberatory  furnace  fed  with  coal;  the 
ore  is  frequently  stirred  with  a  rake  to  expose  fresh  portions  to  the  oxidizing 
action.  Since  the,  rapid  current  of  air  which  traverses  the  hearth  is  liable  to 
carry  away  a  considerable  quantity  of  lead  (and  silver),  several  condensing 
chambers  are  arranged  between  the  furnace  and  the  chimney,  to  avoid  loss  from 
this  cause. 

When  the  roasting  has  been  continued  for  a  sufficient  period,  the  temperature 
is  raised  considerably,  when  the  oxide  and  sulphate  of  lead  react  upon  the  unal- 
tered sulphide,  causing  a  separation  of  metallic  lead,  and  of  a  very  fusible  sub- 
sulphide.  The  fire  is  now  damped,  and  some  quicklime  thrown  on  to  the  fused 
mass ;  this  causes  the  solidification  of  the  slag  (by  forming  a  less  fusible  silicate 
of  lime),  and  allows  the  lead  to  be  drawn  off  into  the  pig-moulds.  The  slag  is 
smelted  in  another  operation,  either  alone,  or  together  with  a  fresh  charge  of 
ore. 

The  lead  thus  obtained  often  contains  enough  silver  to  pay  for  extraction, 
which  is  effected  either  by  cupelling  it  directly,  or  after  subjecting  it  to  a  refin- 
ing process.  This  latter  is  always  had  recourse  to  when  less  than  ToW  °^ 
silver  is  present. 

The  refining  process  (Pattinson's)  consists  in  fusing  the  metal,  and  allowing 
it  to  cool  in  an  iron  pot,  stirring  it  from  time  to  time  with  an  iron  rod;  a  por- 
tion of  the  lead  (containing  comparatively  little  silver)  is  soon  deposited  in  crys- 
tals, which  may  be  removed  with  a  perforated  ladle ;  by  repeating  this  process, 
both  with  the  liquid  and  solid  portions,  the  lead  is  separated  into  two  products, 
the  one  so  poor  in  silver  that  it  may  be  sent  into  the  market,  and  the  other 
sufficiently  rich  to  be  purified  by  cupellation,  wherein  the  superior  oxidability  of 
lead  is  taken  advantage  of  in  order  to  separate  it  from  the  silver. 

The  cupel  from  which  this  process  derives  its  name  is  a  shallow  cup,  made  of 
well-burnt  bone-ashes  rammed  into  an  iron  frame;  the  cupelling-furnace  is  a 
reverberatory  furnace,  the  arch  of  which  is  formed  by  a  movable  dome  of  iron ; 
an  opening  (for  removing  the  litharge)  is  made  near  the  edge,  on  one  side  of  the 
cupel,  and  opposite  to  this  are  one  or  two  tuyere  pipes,  through  which  air  may 
be  forced  over  the  surface  of  the  metal. 

The  lead  is  introduced  into  the  cupel,  through  the  arch  of  the  furnace,  in  a 
melted  state,  and  a  fresh  supply  added  as  it  diminishes  in  quantity;  when  the 
metal  is  brought  to  a  full  red  heat,  a  blast  of  air  is  directed  over  its  surface ;  a 
black  film  of  suboxide  (?)  is  first  formed,  and  removed  by  the  workman;  by  and 
by,  the  heat  is  increased,  and  the  surface  of  the  lead  becomes  covered  with 


ALLOYS   OP   LEAD.  481 

litharge,  which  fuses,  and  is  removed  from  the  surface,  partly  by  the  action  of 
the  blast  air,  partly  by  the  aid  of  a  workman;  the  first  litharge  is  impure  (page 
470),  and  is  collected  separately ;  the  operation  is  continued,  the  stream  of  air 
being  gradually  increased,  until  the  oxidation  of  the  lead  is  completed;  the 
litharge  obtained  in  the  latter  part  of  the  process  being  received  separately,  since 
it  contains  a  considerable  quantity  of  silver;  the  last  portions  of  the  litharge  are 
absorbed  by  the  cupel.  The  termination  of  the  process  is  indicated  by  two 
appearances  in  the  residual  mass  of  metal ;  this  mass  has  been  hitherto  main- 
tained at  a  more  brilliant  temperature  than  the  surrounding  parts  of  the  cupel, 
in  consequence  of  the  heat  evolved  during  the  oxidation  of  the  lead,  but  this 
being  completed,  the  metal  assumes  the  same  temperature  and  aspect  as  the 
cupel  itself;  again,  towards  the  end  of  the  operation,  the  film  of  litharge  gradu- 
ally becoming  thinner,  presents  the  phenomenon  of  iridescence,  and  finally 
vanishes  entirely.  The  workman  observing  these  appearances,  pours  a  quantity 
of  water  on  to  the  metal,  and  removes  the  disk,  which  consists  of  silver  contain- 
ing about  y'g  of  lead,  which  is  separated  from  it  by  a  method  to  be  described 
hereafter  (.see  Extraction  of  Silver). 

This  mass  of  silver  sometimes  presents  a  very  peculiar  appearance,  as  of  ar- 
borescent branches,  sometimes  of  considerable  length,  springing  from  its  upper 
(convex)  surface  (sprouting)  ;  this  is  caused  by  the  remarkable  property  pos- 
sessed by  silver,  of  absorbing,  when  in  the  fused  state,  a  quantity  of  oxygen, 
which  escapes,  throwing  up  portions  of  the  metal,  as  the  mass  cools. 

The  litharge  obtained  in  the  cupelling  process  is  reduced  by  heating  with 
charcoal. 

Another  method  of  desilverizing  lead  consists  in  fusing  it  with  metallic  zinc, 
which  is  found  to  be  capable  of  removing  the  silver  from  argentiferous  lead. 
The  zinc  is  afterwards  separated  by  distillation,  and  the  silver  (containing  a  little 
lead)  refined  by  cupellation. 

The  uses  of  lead  are  too  familiar  to  require  especial  notice;  this  metal  should 
never  be  employed  for  culinary  utensils,  since,  in  contact  with  air,  and  even  weak 
acids,  it  is  easily  dissolved ;  the  injurious  properties  of  some  kinds  of  cider  sre 
said  to  be  due  to  their  having  been  kept  in  leaden  vats. 

It  would  be  well  if  this  metal  were  never  employed  for  water-cisterns  (or  even 
for  water-pipes),  since  there  is  always  some  danger  of  dissolving  a  portion  of  the 
lead,  and  as  it  is  a  cumulative  poison,  the  smallest  quantity  repeatedly  taken 
into  the  system  might  seriously  affect  the  health. 

/ 
ALLOYS  or  LEAD. 

§  322.  Lead  is  capable  of  forming  alloys  with  most  other  metals.  A  very 
small  proportion  entirely  destroys  the  malleability  of  yold,  platinum,  and  silver. 

The  alloys  of  lead  and  tin  are  harder  and  more  fusible  than  the  latter  metal. 
The  most  fusible  of  these  alloys  is  that  containing  3  eqs.  of  tin  to  1  eq.  of  lead, 
which  fuses  at  367°  F.  (186°  C.),  considerably  below  the  fusing-point  of  either 
of  these  metals. 

An  alloy  of  equal  weights  of  lead  and  tin  constitutes  plumbers'  solder. 

Certain  inferior  kinds  of  pewter  are  alloys  of  lead  with  80  or  90  per  cent, 
of  tin. 

The  alloy  used  for  lining  the  chests  in  which  tea  is  imported  contains  9  parts 
of  lead  and  1  of  tin.1 

Type-metal  is  composed  of  4  parts  of  lead  and  1  part  of  antimony ;  a  little 
bismuth  is  sometimes  added. 

1  Crookewitt  has  obtained  alloys  of  lead  and  tin  to  which  he  assigns  the  formulae  Sn?- 
Pb,  SnPb,  and  SnPba.     He  also  mentions  alloys  of  copper  and  lead,  having  the  composi- 
tion Cu2Pb3  and  CuPb. 
31 


482  SILVER. 

Shots  are  made  from  an  alloy  of  lead  with  from  0.3  to  0.8  per  cent,  of  arsenic, 
which  causes  the  drops  of  metal  to  assume  a  spherical  form.  The  workmen 
judge  when  the  necessary  proportion  of  arsenic  has  been  added  by  the  form  of 
the  shots;  too  large  a  quantity  of  this  metal  renders  them  lenticular,  whilst  they 
are  pyriform  if  enough  arsenic  be  not  added. 

The  fused  metal  is  poured  through  a  kind  of  sieve,  which  divides  it  into  drops 
of  various  sizes,  and  allowed  to  fall  from  a  considerable  height  into  water.  The 
sieve  is  lined  with  the  matter  which  is  scraped  off  the  surface  of  fused  lead  at 
the  commencement  of  oxidation.  The  shots  are  afterwards  sorted,  and  polished 
in  revolving  boxes  with  a  little  plumbago. 

ASSAY  OF  GALENA. — In  order  to  determine  the  amount  of  lead  contained  in 
any  specimen  of  this  ore,  300  grs.,  in  powder,  are  fused  with  450  grs.  of  black 
flux  (see  p.  99)  and  80  or  90  grs.  of  small  iron  nails,  in  a  Hessian  crucible,  at  a 
bright  red  heat.  The  sulphur  is  abstracted,  partly  by  the  iron,  partly  by  the 
alkali  of  the  flux,  and  a  button  of  metallic  lead  is  found  at  the  bottom  of  the 
crucible;  the  latter  is  broken  after  the  fusion,  the  button  withdrawn,  flattened 
under  a  hammer,  to  ascertain  that  it  contains  no  iron  nails,  and  weighed. 

In  this  process,  a  certain  quantity  of  lead  passes  into  the  slag,  but  the  result 
is  sufficiently  accurate  for  most  practical  purposes. 

The  assay  of  ores  of  lead  which  are  free  from  sulphur  and  arsenic  may  be 
effected  by  fusing  them  with  carbonate  of  soda  and  charcoal. 


SILVER. 

.  Ag.     Eq.  108.1.     Sp.  Gr.  10.474. 

§  323.  This  very  beautiful  and  important  metal  is,  like  gold,  pretty  widely 
diffused,  though  in  ,small  quantities.1  The  description  of  its  ores  will  be  left  for 
our  subsequent  consideration. 

Preparation. — Standard  silver  is  always  alloyed  with  a  certain  quantity  of 
copper,  which  we  may  separate  by  dissolving  the  alloy  in  dilute  nitric  acid,  with 
the  aid  of  heat,  and  adding  solution  of  chloride  of  sodium  as  long  as  any  preci- 
pitate is  formed  ;  the  silver  is  thus  precipitated  as  chloride,  and  the  copper  re- 
mains in  solution.  The  chloride  of  silver  is  well  washed  by  decantation  as  long 
as  the  washings  give  the  slightest  blue  tinge  with  excess  of  ammonia;  it  is  then 
dried,  and  reduced  by  either  of  the  following  methods  :  1,  By  fusing  in  a  Hes- 
sian crucible  with  an  excess  of  carbonate  of  soda ;  2,  by  fusing  with  70  per  cent, 
of  chalk  and  4  or  5  per  cent,  of  charcoal ;  or,  3,  by  moistening  with  dilute  hy- 
drochloric acid,  and  placing  in  contact  with  a  plate  of  zinc  for  some  hours,  then 
withdrawing  the  zinc,  and  washing  the  reduced  metal  by  decantation  with  dilute 
hydrochloric  acid  (till  the  washings  are  no  longer  precipitated  by  ammonia  and 
sulphide  of  ammonium),  and  subsequently  with  water. 

The  first  two  methods  yield  a  compact  globule  of  silver,  the  last  gives  the 
metal  in  spongy  masses  easily  reduced  to  powder  when  dried. 

A  very  ready  method  of  obtaining  pure  silver  from  the  solution  of  standard 
silver  in  nitric  acid  consists  in  evaporating  the  latter  nearly  to  dry  ness,  to  expel 
excess  of  acid,  diluting  largely  with  water,  and  immersing  a  plate  of  copper  (a 
clean  penny  answers  the  purpose),  which  precipitates  the  silver  in  a  fine  crystal- 
line powder;  when  no  more  metal  is  precipitated,  the  copper  is  withdrawn,  and 

1  In  general,  those  ores  which  consist  of  oxides  or  salts  are  not  so  rich  in  silver  as  the 
sulphides ;  among  the  latter,  iron-pyrites  contains  the  least,  and  galena,  zinc-blende,  and 
copper-pyrites,  the  most  silver. 


SILVER.  483 

t 

the  reduced  silver  washed  by  decantation  till  the  washings  are  no  longer  tinged 
by  ammonia. 

This  method  is  very  useful  for  obtaining   pure  silver  in  order  to  prepare  the 
nitrate,  and,  if  carefully  executed,  it  will  be  found  that  the  metal  is  perfectly 
free  from  copper.     Even  should  a  little  copper  be  found  in  it,  digestion  in  ammo- 
-  nia  will  effect  its  removal. 

Properties. — Pure  silver  has  a  dazzling  white  color,  and  is  capable  of  a  higher 
lustre  than  any  other  metal.  From  what  has  been  stated  above,  it  will  be  seen 
that  it  presents  itself  in  different  forms  according  to  the  method  of  preparation. 
When  reduced  by  other  metals  at  the  ordinary  temperature,  it  forms  spongy 
masses,  composed  of  crystalline  grains  which  may  easily  be  welded  together. 
When  precipitated  from  its  solutions  by  reducing  agents,  it  either  forms  a  gray 
spongy  mass,  or  a  beautiful  silvery  coating  upon  the  sides  of  the  vessel.  When 
obtained  by  sharply  heating  one  of  its  salts,  it  presents  a  most  beautiful  dull 
white  appearance ;  in  any  of  these  forms,  however,  it  is  recognized  by  the  re- 
splendent lustre  which  it  acquires  when  burnished. 

The  specific  gravity  of  silver  is  10.4743;  by  hammering,  however,  it  may  be 
increased  to  10.542. 

Silver  is  harder  than  gold,  but  not  so  hard  as  copper ;  it  is  more  malleable 
and  ductile  than  any  other  metal,  except  gold,  being  capable  of  extension  into 
leaves  of  0.00001  inch  in  thickness,  and  of  being  drawn  out  into  the  very  finest 
wires.  It  surpasses  gold  in  tenacity,  but  is  inferior  to  iron,  copper,  and  plati- 
Dumj  a  silver  wire,  j\  inch  in  diameter,  will  sustain  a  weight  of  250  Ibs.  Silver 
fuses  at  a  bright  red  heat,  approaching  to  whiteness,  and  may  be  volatilized  to 
some  extent  at  very  high  temperatures,  especially  in  a  current  of  air  or  other 
gas ;  it  volatilizes  rapidly  when  heated  in  the  oxyhydrogen  blowpipe-flame,  in- 
the  focus  of  a  burning-glass,  or  between  the  charcoal  points  of  a  powerful  gal- 
vanic battery. 

Silver  may  be  crystallized  from  a  state  of  fusion,  in  cubes  or  oetohedra. 

Fused  silver  is  capable  of  absorbing  mechanically  22  volumes  of  oxygen,  which 
is  evolved  when  the  metal  solidifies,  producing  the  peculiar  arborescence  alluded 
to  in  the  description  of  the  process  of  cupellation.  The  presence  of  a  small  quan- 
tity of  copper  prevents  this  phenomenon. 

Silver  is  not  affected  by  dry  or  moist  air ;  it  is  tarnished,  however,  in  an 
atmosphere  containing  sulphuretted  hydrogen,  which  it  decomposes,  becoming 
coated  with  a  film  of  sulphide  of  silver,  which  may  be  easily  removed  by  a  little 
solution  of  cyanide  of  potassium.  Silver  does  not  decompose  water  at  any  tem- 
perature. 

Dilute  sulphuric  acid  does  not  act  upon  silver,  the  concentrated  acid,,  with  the 
aid  of  heat,  dissolves  it  in  the  form  of  sulphate  : — 

Ag+2(HO.S03)=AgO.S03-f2HO+S03. 

Dilute  hydrochloric  acid  does  not  attack  silver,  but  hot  concentrated  hydro- 
chloric acid  converts  it,  especially  if  finely  divided,  to  some  extent,  into  chloride, 
which  dissolves  in  the  acid,  and  is  precipitated  on  dilution  ;  the  action  of  this 
acid  upon  silver  is,  however,  very  slow. 

Nitric  acid  dissolves  silver  very  rapidly,  binoxide  of  nitrogen  being  disen- 
gaged : — 

Ag3+4(HO.NOs)=3(AgO.N05)-HHQ+N03. 

Phosphoric  acid  attacks  silver  only  in  the  dry  way. 

The  caustic  alkalies  and  their  nitrates  do  not  attack  this  metal  at  a  red  heat ; 
silver  crucibles  are  therefore  often  useful  in  the  laboratory ;  they  should  not  be 
heated  over  a  powerful  gas-burner,  lest  they  be  fused ;  the  heat  of  a  common 
spirit-lamp  is  generally  sufficient. 

When  silver  is  kept  in  contact  for  a  length  of  time  with  common  salt  in  a  state 


484  SILVER  AND    OXYGEN. 

of  fusion,  a  considerable  quantity  of  chloride  of  silver  is  produced ;  the  sodium 
being  oxidized  by  the  air.  Vessels  of  silver  are  also  attacked  when  solutions  of 
alkaline  chlorides  are  boiled  in  them  for  a  long  time,  air  having  access. 

A  solution  of  sulphate  of  sesquioxide  of  iron  is  capable  of  dissolving  silver  at 
a  high  temperature  : — 

Ag+Fe303.3S03=AgO.S08+2(FeO.S03); 

when  the  solution  cools,  the  silver  is  deposited  in  minute  crystals,  sulphate  of 
sesquioxide  of  iron  being  reproduced. 

When  finely  divided  silver  is  heated  with  the  higher  oxides  of  copper,  lead, 
and  manganese,  it  reduces  them  to  their  lowest  state  of  oxidation. 

Silver  is  attacked  slowly  by  chlorine,  bromine,  and  iodine;  it  combines  directly 
with  sulphur,  selenium,  and  phosphorus,  and  with  many  metals. 


SILVER   AND   OXYGEN. 

Suboxide  .     .  <T'T^'*/C . ;:.  Vv    .     .     .     .     Ag30 

Oxide AgO 

Binoxide ''.     .     .     .  v.^,1.  ,  .     AgOa 

SUBOXIDE  or  SILVER,  AgaO. 

§  324.  When  citrate  of  silver  is  heated  to  the  boiling-point  of  water  in  a  cur- 
rent of  hydrogen,  half  the  oxygen  of  the  base  is  abstracted,  and  citrate  of  sub- 
oxide  of  silver  produced;  this  salt  dissolves  in  water,  forming  a  brown  solution, 
from  which  potassa  throws  down  a  black  precipitate  of  suboxide  of  silver. 

This  suboxide  is  very  unstable,  it  is  readily  decomposed  by  heat ;  hydrochloric 
acid  converts  it  into  brown  subchloride  of  silver;  all  other  acids  decompose  it 
into  oxide  and  metallic  silver. 

OXIDE  OR  PROTOXIDE  OF  SILVER. 
AgO.     Eq.  116.1. 

Preparation. — This  oxide  is  prepared  by  decomposing  solution  of  nitrate  of 
silver  with  an  excess  of  potassa;  a  grayish-brown  hydrate  is  precipitated,  which, 
when  well  washed  and  dried,  either  in  vacua  or  at  a  temperature  of  140°  F. 
(60°  C.)  becomes  anhydrous. 

Properties. — Oxide  of  silver  is  a  dark  brown  powder,  which  is  slowly  reduced 
by  exposure  to  light;  a  moderate  heat  decomposes  it  into  its  elements. 

This  oxide  is  somewhat  soluble  in  water;  the  solution  has  a  feeble  alkaline 
reaction  to  reddened  litmus.  Oxide  of  silver  is  a  powerful  base,  and  dissolves 
readily,  even  in  weak  acids,  forming  well-defined  salts,  which  are  neutral  to  test- 
papers.  Since  the  greater  number  of  these  salts  are  neutral  in  constitution, 
easily  purified,  and  decomposed  by  heat,  leaving  metallic  silver,  they  are  very 
frequently  made  use  of  for  determining  the  atomic  weights  of  their  acids,  a  de- 
termination which  is  capable  of  great  accuracy,  from  the  high  equivalent  of 
silver. 

Oxide  of  silver  dissolves  readily  in  ammonia,  if  this  reagent  be  added  to  the 
liquid  in  which  the  oxide  is  precipitated;  but  if  the  oxide  of  silver  be  washed 
and  treated  with  ammonia,  it  forms  a  fulminating  compound,  which  we  shall 
revert  to  presently. 

When  heated  with  vitreous  fluxes  (glass,  e.  g.)  oxide  of  silver  combines  with 
them,  producing  a  yellow  color. 

Oxide  of  silver  forms  a  compound  with  oxide  of  lead;  when  a  solution  of  a 
salt  of  silver  is  mixed  with  excess  of  a  lead-salt,  and  the  mixture  decomposed  by 
potassa,  a  yellow  precipitate  is  formed,  containing  Ag0.2PbO. 


NITRATE   OF   SILVER.  485 

FULMINATING  SILVER.1 — The  composition  of  fulminating  silver  is  still  un- 
certain. '>  'mr" 

It  may  be  regarded  either  as  a  nitride  of  silver,  Ag3N  (and  this  opinion  is  the 
most  prevalent)  produced  according  to  the  equation  : — 

3AgO-{-NH3=3HO  +  Ag3N; 
as  an  amidide  of  silver,  Ag.NHa, 

AgO+NH3=HO+AgNH3; 

or  lastly,  as  a  compound  of  oxide  of  silver  with  ammonia;  on  either  view  its 
explosive  powers  would  be  explained  by  the  instability  of  the  compound,  and 
the  sudden  evolution  of  a  permanent  gas. 

Preparation. — Recently  precipitated  oxide  of  silver,  still  moist,  is  placed  in 
contact  with  a  little  concentrated  ammonia  for  some  hours;  a  great  part  is  dis- 
solved, and  a  black  compound  remains,  which  must  be  thrown  on  a  filter,  and 
allowed  to  dry  spontaneously;  very  small  quantities  should  be  prepared  at  once. 

It  may  also  be  obtained  by  dissolving  nitrate  of  silver  in  ammonia,  and  adding 
potassa  in  excess. 

Properties. — Fulminating  silver  is  sometimes  crystalline;  when  dry,  it  ex- 
plodes with  the  least  touch ;  even  under  water  it  detonates  if  rubbed  with  a  hard 
body,  or  heated.  When  acted  on  by  acids,  it  yields  silver-salts  and  salts  of 
ammonia. 

Fulminating  silver  is  sometimes  employed  for  making  detonating  balls. 

§  325.  NITRITE  OF  SILVER  (AgO.N03)  is  formed  when  nitrate  of  silver  is 
heated  moderately  above  its  fusing  point. 

It  is  prepared  by  precipitating  a  solution  of  crude  nitrite  of  potassa  with 
nitrate  of  silver;  it  may  be  purified  by  dissolving  in  hot  water  and  crystallizing. 
It  forms  fine  yellow  needles,  sparingly  soluble  in  cold  water,  but  soluble  in  hot 
water ;  when  the  solution  is  long  boiled,  the  nitrite  of  silver  is  partly  reduced. 

It  is  employed  for  the  preparation  of  other  nitrites  by  double  decomposition. 

NITRATE  OF  SILVER  {Lunar  Caustic). 
AgO.N05.     JE^.  170.1. 

Preparation. — Since  this  is  the  most  important  of  the  salts  of  silver,  there 
exist  several  methods  of  preparing  it. 

I.  The  simplest  of  these  consists  in  dissolving  pure  silver  in  dilute  nitric  acid, 
with  the  aid  of  heat,  and  evaporating  to  crystallization. . 

II.  Nitrate  of  silver  is,  however,  more  frequently  prepared  from   standard 
silver,  which  is  alloyed  with  copper.     Ordinary  coin,  for  example,  is  dissolved 
in  dilute  nitric  acid,  the  solution  evaporated  to  dryness  in  a  porcelain  dish,  and 
the  residue  heated  nearly  to  redness ;  the  nitrate  of  silver  fuses  without  change, 
but  the  nitrate  of  copper  is  decomposed,  evolving  peroxide  of  nitrogen  and  oxy- 
gen, and  leaving  the  black  oxide  of  copper;  a  small  portion  of  the  mass  is 
removed  from  time  to  time,  dissolved  in  water,  the  solution  filtered,  and  tested 
with  excess  of  ammonia;  when  this  reagent  ceases  to  produce  a  blue  color,  the 
process  is  completed,  and  if  the  residue  be  treated  with  water,  the  solution  will 
yield,  on  evaporation,  crystals  of  pure  nitrate  of  silver. 

III.  Another  method  of  separating  the  oxide  of  copper  from  the  nitric  solu- 
tion consists  in  displacing  it  by  oxide  of  silver. 

The  nitric  solution  of  the  coin  is  evaporated  to  dryness,  to  expel  excess  of 
acid,  and  the  residue  is  redissolved  in  water;  }  of  the  solution  is  separated  and 
precipitated  with  excess  of  potassa ;  the  precipitated  oxides  of  silver  and  copper 

1  This  compound  must  not  be  confounded  with  fulminate  of  silver,  which  is  a  combina- 
tion of  oxide  of  silver  with  a  peculiar  acid,  the  fulminic  (Cya02). 


486 


HYPOSULPHITE   OP    SILVER. 


are  washed  with  cold  water,  and  boiled  with  the  remaining  %  of  the  solution, 
when  the  whole  of  the  oxide  of  copper  is  precipitated,  the  oxide  of  silver  taking 
its  place. 

IV.  The  nitric  solution  of  the  coin  may  also  be  diluted  and  precipitated  by 
metallic  copper,  the  precipitated  silver  being  afterwards  washed  and  dissolved  in 
nitric  acid. 

V.  It  is  frequently  necessary  to  prepare  nitrate  of  silver  from  the   silver- 
residues  in  the  laboratory ;  these  should  be  entirely  precipitated  by  hydrochloric 
acid,  and  the  chloride  well  washed  and  reduced  by  one  of  the  methods  given  for 
the  preparation  of  pure  silver  (.see  p.  482). 

The  salt  obtained  by  either  of  the  above  processes  is  purified  by  recrystalliz- 
ation,  and  dried  on  filter-paper  in  a  dark  place. 

Lunar  caustic  of  commerce  is  fused  and  cast  into  sticks. 

Properties. — Nitrate  of  silver  crystallizes  in  colorless  square  tables,  which  are 
anhydrous ;  when  heated  they  fuse,  and  resolidify,  on  cooling,  to  a  crystalline 
mass ;  a  higher  temperature  expels  part  of  their  oxygen,  leaving  nitrite  of  silver, 
which  is  reduced  to  the  metallic  state  when  further  heated. 

Nitrate  of  silver  dissolves  in  an  equal  weight  of  cold,  and  in  much  less  boil- 
ing water ;  its  aqueous  solution  is  neutral.  Alcohol  also  dissolves  it  to  a  con- 
siderable extent. 

Light  does  not  affect  nitrate  of  silver  unless  organic  matter  be  present,  when 
the  salt  is  reduced.  Nitrate  of  silver  corrodes  the  skin,  producing  black  stains, 
which  may  be  removed  with  iodide  or  cyanide  of  potassium  ;  it  also  produces  a 
black  mark  (probably  metallic  silver  in  a  finely  divided  state)  upon  linen,  and  is 
hence  employed  in  most  permanent  inks. 

When  boiled  with  finely  divided  metallic  silver,  the  nitrate  appears  to  yield 
compounds  similar  to  those  obtained  by  the  analogous  method  from  nitrate  of 
lead. 

Nitrate  of  silver,  fused  in  a  current  of  chlorine,  yields  chloride  of  silver,  oxygen, 
and  anhydrous  nitric  acid  : — 

AgO.NOs+Cl=AgCl-fO+N05. 

Dry  nitrate  of  silver  absorbs  ammoniacal  gas,  producing  a  compound  of  the 
formula  AgO.N05,3NH3,  which  is  soluble  in  water,  and  easily  decomposed  by 
heat,  ammonia  being  evolved. 

If  nitrate  of  silver  be  dissolved  in  excess  of  ammonia,  and  the  solution  evapo- 
rated, crystals  are  obtained,  of  the  formula  AgO.N05,2NH3  (ammonio-nitrate 
of  silver). 

Uses. — Nitrate  of  silver  is  largely  used  in  the  laboratory  for  the  precipitation 
of  acids,  and  as  a  source  of  most  of  the  other  silver-salts.  It  is  also  employed 
both  internally  and  externally  in  medicine.  The  small  sticks  used  by  the  sur- 
geon are  often  black  externally,  from  the/  reduction  of  the  silver  by  contact  with 
metal  or  paper;  sometimes,  even,  this  black  color  extends  throughout  the  mass, 
and  may  then  be  due  to  the  presence  of  a  little  oxide  of  copper.  It  is  also 
employed  in  photography. 

HYPOSULPHITE  OF  SILVER,  AgO.Sa03 — This  salt  possesses  some  slight  in- 
terest, because  some  of  its  compounds  are  produced  when  the  alkaline  hyposul- 
phites are  employed  for  fixing  Daguerreotype  pictures  by  removing  the  unaltered 
silver  compound  from  the  surface  of  the  plate. 

Hyposulphite  of  silver  is  obtained  as  a  white  precipitate  by  adding  a  dilute 
solution  of  hyposulphite  of  potassa  to  a  slight  excess  of  a  dilute  solution  of 
nitrate  of  silver;  the  precipitate  is  very  slightly  soluble  in  cold  water,  and  be- 
comes black  on  exposure  to  light,  being  decomposed  into  sulphide  of  silver  and 
sulphuric  acid;  it  forms  compounds  with  other  hyposulphites,  which  possess 
greater  stability. 


CHLORIDE   OF   SILVER.  487 

The  affinity  of  oxide  of  silver  for  hyposulphurous  acid  is  so  great,  that  it  is 
capable  of  decomposing  the  alkaline  hyposulphites,  separating  half  of  their  bases, 
and  forming  soluble  double  hyposulphites,  which  are  characterized  by  their  re- 
markably sweet  taste.  These  double  hyposulphites  may  also  be  obtained  by  dis- 
solving chloride  of  silver  in  the  alkaline  hyposulphites,  and  precipitating  the 
double-salts  by  alcohol. 

SULPHATE  OP  SILVER,  AgO.S03. — The  sulphate  may  be  prepared,  either  by 
precipitating  a  concentrated  solution  of  nitrate  of  silver  by  sulphate  of  soda,  or 
by  dissolving  silver  in  concentrated  sulphuric  acid,  when  the  sulphate  is  deposited 
on  cooling. 

Sulphate  of  silver  crystallizes  in  brilliant  colorless  prisms,  which  are  decom- 
posed only  at  a  high  temperature ;  it  is  sparingly  soluble  in  cold  water,  but  more 
so  in  hot  water ;  it  dissolves  to  a  greater  extent  in  concentrated  sulphuric  acid, 
and  is  precipitated  on  dilution. 

Sulphate  of  silver  dissolves  in  hot  ammonia;  the  solution,  on  cooling,  deposits 
crystals  of  the  formula  AgO.S03,2NH3. 

When  calcined  with  carbon,  sulphate  of  silver  yields  a  mixture  of  metal  and 
sulphide. 

Carbonate  of  Silver  (AgO.C02)  is  obtained  by  double  decomposition.  It  is 
white,  insoluble,  and  easily  decomposed  by  heat. 

BINOXIDE  OR  PEROXIDE  or  SILVER,  AgOa. 

When  a  very  dilute  solution  of  nitrate  of  silver  is  decomposed  by  the  galvanic 
current,  dark  gray  lustrous  needles  of  binoxide  of  silver  are  deposited  around 
the  positive  pole. 

Binoxide  of  silver  is  insoluble  in  water,  and  is  decomposed  by  a  temperature 
exceeding  the  boiling-point.  It  is  an  indifferent  oxide,  and  therefore  evolves 
oxygen  when  treated  with  oxygen-acids,  and  chlorine  with  hydrochloric  acid, 
salts  of  silver  being  produced.  When  'treated  with  ammonia,  the  hydrogen  of 
the  latter  reduces  the  binoxide  to  (prot-)  oxide,  nitrogen  being  disengaged. 

CHLORIDE  OP  SILVER,  AgCl. 

§  326.  The  chloride  of  silver  is  found  in  nature  crystallized  in  cubes  (horn- 
silver)  •  it  is  purely  white,  lustrous,  and  translucent,  becoming  violet  or  brown 
by  exposure  to  light. 

Chloride  of  silver  may  be  obtained  artificially  by  precipitating  a  solution  of 
nitrate  of  silver  with  hydrochloric  acid  or  a  soluble  chloride,  stirring  well,  and 
washing  the  precipitate  by  decantation.  Thus  obtained  it  forms  a  white  pre- 
cipitate, which  accumulates  into  curdy  masses  when  stirred,  especially  if  a  little 
free  nitric  acid  be  present. 

When  exposed  to  light  it  becomes  violet,  and  ultimately  black;  diffused  day- 
light effects  this  slowly,  but  in  sunlight  the  change  takes  place  very  speedily. 
The  alteration  of  chloride  of  silver  by  exposure  to  light  is  said  to  be  due  to  a  , 
disengagement  of  chlorine,  and  a  reduction  of  the  chloride  to  a  subchloride, 
Ag3Cl,  for  it  does  not  take  place  in  an  atmosphere  of  chlorine,  or  under  nitric 
acid,  and  if  it  be  exposed  in  a  moist  state  to  the  action  of  sunlight  in  a  stop- 
pered bottle,  a  strong  smell  of  chlorine  is  perceived  after  24  hours. 

Chloride  of  silver,  when  heated,  becomes  gradually  darker  in  color,  and  fuses 
at  500°  F.  (260°  C.)  into  a  brown  oily  liquid,  which  solidifies,  on  cooling,  to  a 
mass  much  resembling  horn  in  external  characters,  and  hence  termed  by  the 
ancients  horn-silver.  Fused  chloride  of  silver  volatilizes  to  a  slight  extent  when 
further  heated ;  it  cannot  be  decomposed  by  heat. 

Earthen  crucibles  are  speedily  penetrated  by  chloride  of  silver  in  a  state  of 
fusion. 


488  CHLORIDE   OF   SILVER. 

This  chloride  is  completely  insoluble  in  water,  and  in  nitric  acid.  Boiling 
concentrated  hydrochloric  acid  dissolves  it  to  a  slight  extent,  and  deposits  it  in 
octohedra  when  evaporated  ;  the  chloride  of  silver  may  also  be  precipitated  from 
the  solution  by  water.  Concentrated  sulphuric  acid  decomposes  it  slowly. 

Caustic  potassa  and  soda  decompose  chloride  of  silver  at  the  temperature  of 
ebullition,  forming  alkaline  chlorides  and  oxide  of  silver;  if  a  little  sugar  be 
added  in  this  experiment,  its  carbon  will  be  oxidized  at  the  expense  of  the  oxide 
of  ^ilver,  carbonate  of  potassa  being  formed,  and  the  silver  reduced  to  the  metallic 
state : — 

24AgO+CiaH1A1=12C03+llHO-fAg24; 

Cane-sugar  t 
this  method  is  sometimes  employed  for  the  reduction  of  chloride  of  silver. 

It  is  also  reduced  when  fused  with  the  alkaline  and  earthy  carbonates  : — 
AgCl+NaO.C03=Ag+NaCl+0-fCOa. 

Chloride  of  silver  is  very  commonly  reduced  by  fusing  with  chalk  and  char- 
coal, which  latter  would  tend  to  facilitate  the  decomposition  by  appropriating  the 
oxygen  of  the  lime  : — 

AgCl  +  CaO.C02-f-C3=Ag+CaCl-f3CO. 

Ammonia  readily  dissolves  chloride  of  silver,  forming  a  colorless  solution 
which  deposits  minute  crystals  of  the  chloride  when  evaporated,  either  spontane- 
ously or  with  the  aid  of  heat.  If  very  concentrated  ammonia  be  employed,  the 
solution  deposits  a  compound  of  chloride  of  silver  with  ammonia. 

Chloride  of  silver  absorbs  \\  eq.  of  dry  ammoniacal  gas,  with  evolution  of 
heat,  producing  a  compound  which  gradually  gives  up  its  ammonia  spontaneously, 
and  with  rapidity  when  very  gently  heated,  so  that  it  produces  a  sensation  of 
great  cold  when  placed  upon  the  skin.  It  will  be  remembered  that  this  com- 
pound is  used  for  the  preparation  of  liquefied  ammonia. 

Boiling  solutions  of  the  chlorides  of  potassium,  sodium,  barium,  strontium, 
and  calcium,  are  capable  of  dissolving  chloride  of  silver,  forming  crystallizable 
double  compounds  which  are  decomposed  even  by  water,  but  much  more  readily 
by  concentrated  nitric  acid. 

Chloride  of  silver  dissolves  also  in  solution  of  cyanif  e  of  potassium,  forming 
a  crystallizable  double  compound.1 

Pure  carbon  is  not  capable  of  decomposing  chloride  of  silver  unless  water  be 
present,  when  hydrochloric  acid  and  carbonic  oxide  are  formed  : — 
AgCl+HO-fC=Ag+HCl-fCO; 

common  charcoal,  therefore,  is  capable  of  reducing  the  chloride  at  a  high  tem- 
perature. 

Iron  and  zinc  decompose  chloride  of  silver,  even  at  the  ordinary  temperature, 
especially  in  presence  of  free  hydrochloric  acid,  when  the  nascent  hydrogen  is 
probably  the  reducing  agent. 

Copper,  tin,  and  lead,  reduce  chloride  of  silver  in  the  dry  way. 

Mercury  partially  decomposes  it,  forming  an  amalgam  of  silver. 

The  property  possessed  by  chloride  of  silver  of  blackening  by  exposure  to 
light,  is  turned  to  advantage  for  the  production  of  photographic  pictures ;  the 
paper  is  washed,  in  a  dark  room,  first  with  a  silver-solution,  and  subsequently 
with  chloride  of  sodium,  which  produces  a  film  of  chloride  of  silver ;  the  paper 
is  placed  in  a  camera  until  the  lights  of  the  picture  have  sufficiently  changed 
the  chloride  of  silver,  and  the  object  is  then  fixed  by  washing  (in  a  darkened 

1  Liebig  has  recently  found  that  chloride  of  silver  is  soluble,  to  a  considerable  extent, 
in  solution  of  nitrate  of  mercury  (HgO.N06),  and  may  be  obtained  in  crystals  from  such 
a  solution. 


SULPHIDE  or  SILVER.  489 

room)  with  a  solution  of  hyposulphite  of  soda,  which  dissolves  the  unaltered 
chloride.1 

BROMIDE  OF  SILVER  (AgBr)  is  occasionally  found  native.  It  may  be  pre- 
pared in  the  same  way  as  the  chloride,  which,  in  almost  every  respect,  it  resem- 
bles; it  is,  however,  less  soluble  in  ammonia  than  the  chloride,  and  disengages 
bromine  vapors  when  heated  in  an  atmosphere  of  chlorine.  Bromide  of  silver 
is  easily  blackened  by  light. 

A  compound  of  the  formula  2AgBr.3AgCl  has  been  found  native  (embolite.} 

IODIDE  OF  SILVER,  Agl. 

This  compound  has  also  been  found  in  the  mineral  kingdom.  It  is  obtained 
as  a  yellowish  precipitate  when  a  solution  of  an  iodide  is  added  to  nitrate  of  sil- 
ver. Iodide  of  silver  is  very  similar  to  the  chloride  and  bromide ;  when  heated, 
it  fuses,  assuming  a  dark  red  color,  and  again  becomes  yellow  on  cooling ;  it  is 
slowly  blackened  when  exposed  to  light  ;  the  iodide  of  silver,  however,  is  very 
nearly  insoluble  in  ammonia.  Chlorine  and  bromine  decompose  it,  liberating 
iodine.  Hydrochloric  acid  converts  it  into  chloride  of  silver.  Iodide  of  silver 
is  soluble  in  solution  of  iodide  of  potassium ;  the  solution,  when  evaporated, 
yields  crystals  of  a  double-salt  having  the  formula  Agl.KI. 

FLUORIDE  OF  SILVER  (AgF),  obtained  by  dissolving  oxide  or  carbonate  of 
silver  in  hydrofluoric  acid,  is  very  soluble  in  water. 

SULPHIDE  OF  SILVER,  AgS. 

The  sulphide  of  silver  is  found  native,  and,  in  fact,  constitutes  the  chief  ore 
of  silver ;  it  is  generally  associated  with  other  sulphides,  especially  those  of  lead 
and  antimony.  Pure  sulphide  of  silver  is  known  to  mineralogists  as  silver-glance. 

Red  Silver-ore  is  a  double  sulphide  of  silver  and  antimony,  having  the  compo- 
sition 3AgS.SbS3;  the  antimony  in  this  ore  may  be  replaced  by  arsenic. 

Preparation. — Sulphide  of  silver  may  be  obtained  by  passing  sulphuretted 
hydrogen  through  a  solution  containing  silver,  when  it  falls  as  a  black  precipitate. 

Properties. — Native  sulphide  of  silver  is  sometimes  amorphous,  sometimes 
crystallized  in  cubes  or  octohedra;  it  has  a  metallic  lustre,  and  sp.  gr.  7.2;  it  is 
remarkably  soft  and  malleable,  so  that  medals  may  even  be  struck  from  it;  sul- 
phide of  silver  is  more  fusible  than  the  metal. 

When  roasted  in  air,  sulphide  of  silver  yields  sulphurous  acid  and  metallic 
silver;  it  is  dissolved  by  boiling  nitric  acid  (thougn  slowly  when  in  its  native 
state)  ;  when  boiled  with  concentrated  hydrochloric  acid,  it  is  converted  into 
chloride  of  silver,  hydrosulphuric  acid  being  evolved;  concentrated  sulphuric 
acid,  with  the  aid  of  heat,  converts  it  into  sulphate  of  silver,  sulphurous  acid 
being  disengaged. 

Sulphide  of  silver  is  reduced  by  hydrogen,  and  by  most  of  the  metals  at  a 
moderately  elevated  temperature. 

Chloride  of  copper  and  chloride  of  sodium  convert  the  sulphide  into  chloride 
of  silver;  this  change  is  likewise  effected  when  the  sulphide  is  mixed  with  iron- 
pyrites,  sulphate  of  copper,  and  common  salt,  and  the  mixture  exposed  to  the 
action  of  air.  These  reactions  are  taken  advantage  of  occasionally  in  the  ex- 
traction of  silver  from  its  ores 

Sulphide  of  silver  is  a  sulphur-base,  and  combines  with  many  sulphur-acids, 
such  as  those  of  antimony  and  arsenic.  Many  of  these  compounds  are  found 
in  nature. 

CARBIDES  OF  SILVER. — Though  no  definite  combinations  of  silver  with  carbon 

1  Iodide  and  bromide  of  silver  are  now  generally  employed  for  light  pictures,  and  more 
particularly  in  the  Daguerreotype  process. 


490  METALLURGY   OF    SILVER. 

have  been  obtained  directly,  the  compounds  AgC  and  AgC3  have  been  produced 
by  igniting,  respectively,  the  cuininate  and  the  inaleate  of  silver. 

These  carbides  are  black,  insoluble,  and  infusible ;  when  heated  in  air,  they 
smoulder,  and  leave  a  residue  of  metallic  silver. 

The  alloys  of  silver  will  be  described  in  the  technical  history  of  the  metal. 


METALLURGY    OF    SILVER. 

§  327.  This  metal  occurs  in  a  native  state,  crystallized  in  cubes,  or  forms 
derived  therefrom  ;  native  silver  is  generally  alloyed  with  other  metals,  especially 
with  gold,  arsenic,  and  antimony,  and  is  often  disseminated  through  galena  and 
copper-ores. 

The  greater  part  of  the  silver  found  in  nature  is  in  the  state  of  sulphide 
(brittle  silver-ore),  as  we  have  more  fully  explained  in  another  place. 

It  has  also  been  mentioned  that  silver  sometimes  occurs  in  the  form  of  chloride 
(horn-silver). 

Carbonate  of  silver  has  also  been  found  in  the  mineral  kingdom. 

The  ores,  from  which  the  metal  is  chiefly  extracted,  are  the  sulphide,  the  an- 
timonial  sulphide,  the  native  alloy  of  silver  and  antimony,  and  the  chloride  of 
silver. 

EXTRACTION  OF  SILVER. — The  processes  for  the  extraction  of  silver  from  its 
ores  may  be  conveniently  divided  into — 1.  Those  in  which  the  silver  is  obtained 
as  a  by-product,  the  chief  object  being  to  obtain  another  metal  with  which  it  is 
associated;  and,  2.  Those  in  which  the  extraction  of  silver  is  the  main  object  of 
the  process. 

Those  methods  which  belong  to  the  first  class  are  involved  in  the  treatment  of 
argentiferous  lead  and  copper-ores ;  the  former  has  been  already  noticed  in  the 
history  of  these  metals. 

When  copper-ores  contain  a  sufficient  amount  of  silver  to  pay  for  extraction, 
they  are  smelted  as  usual,  when  an  argentiferous  copper  is  obtained ;  this  is 
fused  with  three  parts  of  lead,  the  resulting  alloy  cast  into  disks,  which  are 
subjected  to  liquation,  i.  e.  placed  upon  a  hearth  and  gradually  heated,  so  that 
the  greater  part  of  the  lead  containing  the  silver  may  fuse  and  flow  off,  leaving 
a  porous  mass  of  copper,  alloyed  with  lead  and  a  very  small  quantity  of  silver. 
The  argentiferous  lead  is  then  subjected  to  cupellation. 

When  the  extraction  of  the  silver  from  its  ores,  properly  so  called,  is  to  be 
effected,  the  process  of  amalgamation  is  brought  into  use,  which  depends  upon 
the  affinity  of  silver  for  mercury. 

There  are  two  processes  of  amalgamating  silver-ores,  one  of  which  is  carried 
out  in  Europe  (chiefly  at  Freiberg),  the  other  principally  in  America,  where  fuel 
is  less  easily  obtained. 

Since  these  processes  involve  somewhat  different  reactions,  we  shall  give  a 
brief  description  of  each  separately. 

The  ore  which  is  worked  at  Freiberg  contains  sulphide  of  silver,  associated 
with  much  iron-pyrites,  with  other  metallic  sulphides  and  an  earthy  gangue. 

A  mixture  of  different  specimens  of  ore  is  made,  containing,  at  most,  0.0025 
of  silver,  and  0.35  of  iron-pyrites. 

The  ore  is  now  mixed  with  one- tenth  of  common  salt,  and  roasted  in  a  reverbera- 
tory  furnace;  the  sulphides  of  iron  and  copper  are  thus  converted  into  sulphates, 
which  are  afterwards  partly  decomposed,  sulphurous  acid  being  evolved,  and  the 
oxides  of  iron  and  copper  left ;  the  sulphide  of  silver  is  also  converted  into  sul- 
phate by  the  sulphates  of  iron  and  copper;  these  three  sulphates  are  decomposed 
by  contact  with  chloride  of  sodium  at  a  high  temperature,  sulphate  of  soda  being 
formed,  together  with  the  chlorides  of  iron,  copper,  and  silver. 


METALLURGY   OF    SILVER.  491 

The  roasted  ore  is  now  ground  in  mills  to  a  very  fine  powder,  and  introduced 
into  strong  casks  made  to  revolve  around  a  horizontal  axis ;  in  these  casks  the 
ore  is  agitated  for  an  hour  with  water  and  a  quantity  of  clean  iron.  The  finely 
divided  chloride  of  silver  is  reduced  to  the  state  of  metal,  the  iron  being  converted 
into  chloride;  probably  the  presence  of  the  common  salt  in  solution  assists  this 
effect  by  dissolving  the  chloride  of  silver,  and  thus  presenting  it  to  the  iron  in  a 
finely  divided  condition.  The  copper  and  lead  are  also  reduced  by  the  iron. 

The  charge  for  each  of  the  revolving  casks  is  generally  about  1120  pounds  of 
roasted  ore,  33  gallons  of  water,  and  112  pounds  of  fragments  of  iron.  560 
pounds  of  mercury  are  then  introduced  into  each  cask,  and  the  turning  repeated 
for  about  eighteen  hours.  The  silver,  lead,  and  copper  are  dissolved  by  the  mer- 
cury, forming  an  amalgam,  which  is  accumulated  by  filling  the  casks  with  water, 
and  again  turning  for  some  time,  and  afterwards  drawn  off. 

This  amalgam  is  strained  through  strong  linen  cloths,  which  separate  the  ex- 
cess of  mercury,  leaving  upon  the  strainer  a  solid  amalgam  containing  about 
82.35  per  cent,  of  mercury. 

The  mercury  is  separated  either  by  distilling  the  amalgam  in  iron  cylinders 
provided  with  eondensing-tubes  dipping  into  water,  or  by  placing  it  in  shallow 
iron  trays  arranged  one  above  the  other,  and  covered  with  an  iron  dome  standing 
over  water ;  the  dome  is  heated  to  redness,  when  the  mercury  rises  in  vapor  from 
the  trays,  and  condenses  in  the  water. 

The  residual  metal  contains  usually  about  70  per  cent,  of  silver,  and  28  of 
copper,  with  traces  of  lead,  nickel,  arsenic,  antimony,  and  mercury.  It  is  re- 
fined by  cupellation. 

The  silver  obtained  by  cupelling  lead  on  the  large  scale  (as  described  at  p. 
480)  is  refined  by  a  second  cupellation  on  a  smaller  scale,  which  is  continued 
until  the  surface  of  the  fused  metal  remains  perfectly  bright. 

In  the  American  process  of  amalgamation  the  roasting  is  omitted,  from  the 
scarcity  of  fuel,  and  the  silver  is  converted  into  chloride,  by  mixing  the  ore  in  a 
very  finely  divided  state  with  chloride  of  sodium  and  roasted  copper-pyrites  (ses- 
quioxide  of  iron  and  sulphate  of  copper),  together  with  a  sufficient  quantity  of 
water.  The  chloride  of  sodium  and  sulphate  of  copper  suffer  mutual  decompo- 
sition, yielding  sulphate  of  soda  and  chloride  of  copper,  which  acts  upon  the 
sulphide  of  silver  in  the  ore,  producing  sulphide  of  copper  and  chloride  of  silver.1 
If  the  chloride  of  copper  be  in  excess,  a  quantity  of  lime  is  added,  in  order  to 
decompose  it,  lest  a  loss  of  mercury  should  be  occasioned  by  its  conversion  into 
subchloride  at  the  expense  of  the  chloride  of  copper. 

Mercury  is  now  added  to  the  mass,  in  the  proportion  of  6  or  8  parts  for  every 
part  of  silver  to  be  extracted ;  the  chloride  of  silver,  dissolved  in  the  solution  of 
chloride  of  'sodium,  is  reduced  by  the  mercury,  part  of  which  is  converted  into 
subchloride,  while  the  remainder  dissolves  the  silver. 

The  amalgam  is  then  treated  as  described  in  the  former  process. 

In  order  to  extract  the  silver  from  very  poor  ores,  they  are  fused  with  iron- 
pyrites,  and  the  argentiferous  sulphide  of  iron  thus  obtained  is  first  roasted,  and 
then  smelted  together  with  lead-ores,  when  argentiferous  lead  is  obtained,  from 
which  the  silver  is  separated  as  usual. 

In  some  parts  of  Mexico,  the  following  methods  are  substituted  for  the  amal- 
gamation process  : — 

I.  The  ores  are  roasted  with  common  salt,  the  resulting  chloride  of  silver  ex- 
tracted from  the  mass  by  means  of  a  solution  of  common  salt,  and  the  silver 
precipitated  by  metallic  copper. 

II.  The  sulphides  are  converted  into  sulphates  by  roasting,  the  mass  treated 
with  water,  and  the  solution  precipitated  by  copper. 

1  According  to  Karsten,  subchloride  of  copper  is  formed  and  sulphur  separated  in  the 
free  state. 


492  USES   OP   SILVER. 

§  328.  TECHNICAL  HISTORY  OF  SILVER. — The  beauty  of  this  metal,  and  its 
property  of  resisting  the  action  of  air  and  of  weak  acids,  render  it  particularly 
valuable  for  the  fabrication  of  ornaments  and  of  domestic  utensils. 

We  have  already  adverted  to  the  use  of  some  silver-compounds  in  medicine; 
the  nitrate  is  the  chief  form  in  which  this  metal  is  employed  ;  it  has  been  re- 
marked, in  patients  under  treatment  with  this  remedy,  that  exposure  to  light 
causes  their  skin  to  assume  a  purple  color  (from  reduction  of  silver  ?).  The 
oxide  and  chloride  of  silver  are  also  occasionally  employed ;  the  solution  termed 
"  liquor  aryenti  muriatico-ammoniati"  is  prepared  by  dissolving  the  chloride  in 
ammonia,  and  partially  neutralizing  the  latter  with  hydrochloric  acid. 

Pure  silver  is  far  too  soft  for  any  useful  purpose ;  it  is  therefore  usually  alloyed 
with  a  certain  quantity  of  copper.  These  two  metals  will  combine,  when  fused 
together,  in  all  proportions.  The  alloys  thus  formed  are  less  malleable,  harder, 
and  more  elastic  than  silver  itself;  they  are  white,  unless  they  contain  a  con- 
siderable quantity  of  copper.  The  color  of  these  alloys  is  generally  improved 
at  the  surface  by  heating  in  air  and  immersing  the  metal  in  dilute  sulphuric 
acid,  which  dissolves  out  the  oxide  of  copper,  leaving  a  superficial  film  of  nearly 
pure  silver. 

The  density  of  the  alloys  of  copper  and  silver  is  rather  higher  than  would  be 
inferred  from  the  respective  densities  of  the  two  metals.  When  these  alloys 
are  fused  and  allowed  to  cool  slowly,  the  metals  separate  to  some  extent,  in  con- 
sequence of  the  difference  in  their  fusing  points,  and  the  cooled  mass  is  therefore 
not  homogeneous.  If  more  than  T\j-  of  copper  be  present,  the  alloy  oxidizes  when 
exposed  to  air  (and  its  use  for  culinary  purposes  would  therefore  be  attended 
with  danger).  When  heated  in  air,  the  copper  is  gradually  separated  as  oxide, 
the  remaining  alloy  becoming  richer  in  silver.  The  greater  part  of  the  copper 
may  also  be  separated  as  sulphide,  by  heating  the  alloy  with  a  quantity  of  sul- 
phur insufficient  to  combine  with  the  whole. 

The  alloy  used  in  the  silver  coinage  of  England,  and  for  most  articles  of  do- 
mestic use,  contains  11.1  parts  of  silver  and  0.9  parts  of  copper. 

The  older  specimens  of  standard  silver,  dating  from  a  period  before  the  intro- 
duction of  the  method  of  parting  with  sulphuric  acid  (see  p.  899),  contain  a 
small  quantity  of  gold,  which  is  left  behind  as  a  dark  purple  powder  on  boiling 
the  alloy  with  nitric  acid. 

Gold  and  silver  may  also  be  made  to  unite  in  all  proportions,  but  the  metals 
separate  to  some  extent  when  the  fused  alloy  is  allowed  to  cool  slowly.  The 
density  of  the  alloys  of  gold  and  silver  is  nearly  what  would  be  predicted.  They 
are  more  fusible  than  gold,  and  are  superior  in  hardness  and  elasticity  to  either 
of  their  constituent  metals.  Alloys  of  gold  and  silver  are  frequently  employed 
for  ornamental  purposes. 

In  order  to  confer  the  beauty  of  silver  upon  articles  of  inferior  cost,  the  baser 
metals  are  often  coated  with  silver  by  different  processes,  the  most  interesting  of 
which  we  proceed  to  mention. 

Plating,  properly  so  called,  consists  in  covering  plates  of  copper  with  silver; 
to  effect  this,  the  surface  of  the  copper  is  well  cleaned,  and  washed  over  with  a 
solution  of  nitrate  of  silver,  which  deposits  a  thin  film  of  that  metal  upon  its 
surface ;  a  plate  of  silver,  rather  larger  than  the  copper,  is  then  applied  to  the 
latter,  and  its  edges  folded  down  over  those  of  the  copper ;  the  two  are  then 
heated  to  dull  redness  and  passed  between  rollers. 

Electro-plating  is  effected  by  depositing  a  film  of  silver  upon  the  surface  of 
the  articles,  by  means  of  the  galvanic  battery,  from  a  solution  of  cyanide  of  silver 
in  cyanide  of  potassium ;  an  outline  of  the  process  will  be  found  in  the  section 
upon  gilding  (p.  400). 

The  silvering  upon  glass,  which  has  of  late  years  acquired  considerable  im- 
portance as  an  ornamental  art,  is  effected  by  reducing  the  silver  from  a  solution 


TANTALUM,    ETC.  493 

by  means  of  essential  oils  (or  grape-sugar),  the  carbon  and  hydrogen  of  which 
readily  abstract  the  oxygen  from  the  oxide  of  silver,  and  cause  the  precipitation 
of  the  metal. 

A  solution  of  nitrate  of  silver  is  mixed  with  carbonate  of  ammonia  and  a  little 
ammonia,  and  with  a  considerable  quantity  of  alcohol;  to  this  mixture  are  added 
solutions  of  oil  of  cassia  and  oil  of  cloves  in  alcohol ;  the  glass  to  be  silvered, 
having  been  thoroughly  freed  from  grease,  the  liquid  is  heated  in  it  to  about 
104°  F.  (40°  C.),  for  two  or  three  hours ;  the  deposit  is  then  formed  upon  the 
sides,  and  is  washed,  dried,  and  varnished. 

For  the  analysis  of  alloys  of  silver,  we  refer  to  Quantitative  Analysis,  Special 
Methods. 

Analysis  of  Ores  of  Silver. — The  amount  of  silver  in  the  ordinary  ores,  where 
it  is  associated  with  lead,  copper,  and  sulphur,  can  scarcely  be  determined  by  the 
wet  process. 

Such  ores  are  usually  assayed  by  reducing  the  copper  or  lead  to  the  metallic 
state  (see  pp.  389  and  482)  and  submitting  the  button  to  cupellation  (see  p. 
401). 

In  principle,  the  assay  of  silver  ores,  therefore,  is  very  similar  to  that  of  auri- 
ferous ores  (see  p.  402). 


TANTALUM    OR   COLUMBIUM,    NIOBIUM,    PELO- 
PIUM,   AND   ILMENIUM. 

§  329.  These  very  rare  metals  have  been  extracted  from  certain  minerals 
known  as  tantaliles  and  yttro-tantalites. 

TANTALUM  (Ta)  is  obtained  by  decomposing  the  chloride,  at  a  red  heat,  with 
ammonia.  It  is  a  black,  infusible  powder,  which  assumes  a  metallic  lustre  when 
burnished.  Heated  in  air,  it  burns,  and  is  converted  into  tantalic  acid. 

Two  oxides  of  tantalum  exist ;  the  (prot-)  oxide,  TaO,  and  tantalic  acid,  Ta303. 

The  oxide  is  obtained  by  reducing  tantalic  acid  in  a  crucible  lined  with  char- 
coal. It  is  a  very  hard,  gray,  indifferent  substance,  insoluble  in  acids. 

Tantalic  acid  may  be  prepared  by  decomposing  the  sesquichloride  of  tantalum 
with  water  containing  a  little  ammonia ;  it  is  a  white,  infusible  substance,  which 
becomes  yellow  when  heated ;  tantalic  acid  dissolves  in  hydrochloric  and  hydro- 
fluoric acids.  Hydrated  tantalic  acid  reddens  litmus,  and  is  soluble  in  potassa. 
Its  salts  are  called  tantalates. 

Sesquichloride  of  tantalum  (Ta3Cl3)  is  obtained  in  yellow  prisms,  by  heating 
a  mixture  of  tantalic  acid  and  carbon  in  a  current  of  chlorine.  It  is  fusible  and 
volatile. 

Sesquisulphide  of  tantalum  (Ta2S3)  forms  a  gray  powder  with  metallic  lustre, 
obtained  by  heating  tantalic  acid  in  hydrosulphuric  acid. 

NIOBIUM  (Nb)  is  obtained  in  a  similar  manner  to  tantalum.  It  is  a  black 
powder,  which  is  converted  into  niobic  acid  when  heated  in  air;  it  is  insoluble  in 
nitric  acid  and  in  aqua  reyia,  but  may  be  dissolved  by  a  mixture  of  nitric  and 
hydrofluoric  acids. 

Niobic  acid  (Nb03?)  may  be  obtained  by  decomposing  the  (ter?)  chloride  of 
niobium  with  water;  it  is  a  white  powder,  slightly  soluble  in  hydrochloric  acid; 
when  fused  with  alkaline  carbonates,  it  yields  the  alkaline  niobates. 

Chloride  of  niobium  is  prepared  like  sesquichloride  of  tantalum;  and  is  vola- 
tile. 

Sulphide  of  niobium  is  a  black,  crystalline  substance,  prepared  by  heating 
niobate  of  soda  in  a  current  of  hydrosulphuric  acid. 


494 


PHYSICAL  PROPERTIES  OF  METALS. 


PELOPIUM  (Pe)  is  prepared  like  the  preceding  metals,  and  much  resembles 
tantalum. 

Pelopic  acid  (Pe03?)  is  prepared  by  decomposing  the  chlorine  compound  with 
water;  it  is  very  similar  to  tantalic  acid,  and  is  more  soluble  in  hydrochloric  acid 
than  niobic  acid.  Its  salts  are  termed  pelopiates. 

Chloride  and  sulphide  of  pelopium  resemble  the  corresponding  compounds  of 
niobium,  and  are  obtained  in  a  similar  manner. 

ILMENIUM1  has  been  found  by  Hermann,  in  place  of  tantalum,  in  the  yttro- 
tantalite  of  Siberia ;  it  is  described  as  very  similar  to  the  preceding  metals. 

The  hydrate  of  ilmenic  acid  is  insoluble  in  hydrochloric  acid. 

Extraction  of  tantalum,  niobium,  and  pelopium,  from  tantalites  and  yttro-tan- 
talites. — These  minerals  contain  tantalic,  niobic,  pelopic,  and  tungstic  acids,  in 
combination  with  lime,  oxide  of  iron,  oxide  of  uranium,  and  yttria.  The  follow- 
ing is  the  method  employed  by  Berzelius  for  extracting  the  tantalic,  niobic,  and 
pelopic  acids. 

One  part  of  the  finely  divided  mineral  is  fused,  in  a  platinum  crucible,  with  6 
or  8  parts  of  bisulphate  of  potassa.  The  mass  is  powdered,  and  the  soluble  sul- 
phates extracted  by  repeatedly  boiling  with  water;  the  residue  which  contains  the 
tantalic,  niobic,  and  pelopic  acids,  is  digested  with  sulphide  of  ammonium,  which 
dissolves  any  tungstic  and  stannic  acids,  and  converts  the  iron  into  sulphide. 
The  residue  is  washed,  and  boiled  with  concentrated  hydrochloric  acid  till  it  be- 
comes white ;  in  order  to  free  it  from  silica,  it  is  dissolved  in  hydrofluoric  acid, 
the  solution  mixed  with  sulphuric  acid,  evaporated  to  dryness,  and  ignited  as 
long  as  it  loses  weight,  when  all  the  silica  is  expelled  as  terfluoride  of  silicon. 
The  three  acids  contained  in  the  mixture  are  separated  by  a  laborious  method 
founded  upon  the  different  volatility  of  the  corresponding  chlorides. 

§  330.  In  the  following  table,  the  chief  physical  properties  of  the  metals  in 
common  use  are  expressed  in  such  a  manner  as  readily  to  admit  of  comparison. 

Their  tenacity  is  represented  by  the  greatest  weight  which  can  be  supported  by 
a  wire  of  T'F  inch  in  diameter;  their  malleability,  ductility,  and  fusibility  are 
indicated,  in  each  case,  by  a  number  denoting  its  rank  in  the  series;  thus,  the 
numbers,  1,  1,  and  6,  affixed  to  gold,  show  this  metal  to  be  the  most  malleable 
and  ductile,  and,  with  two  exceptions,  the  least  fusible. 


Name. 

Sp.  gr. 

Tenacity. 

Malleability. 

Ductility. 

Fusibility. 

7.7 

705 

8 

4 

7 

6.9 

26 

7 

6 

3 

8.8 

385 

3 

5 

5 

Gold     

19.3 

191 

1 

1 

6 

Platinum        «... 

21.0 

361 

5 

3 

8 

Tin                 .... 

7.3 

47 

4 

7 

1 

11.5 

20 

6 

8 

2 

Silver  

10.5 

250 

2 

2 

4 

1  The  existence  of  this  metal  has  been  denied  by  Rose. 


ANALYTICAL  CHEMISTRY. 


QUALITATIVE  ANALYSIS. 


INTRODUCTION. 

§  331.  THE  term  analysis  implies  the  resolution  of  compound  bodies  into  their 
components,  and  is  distinguished  as  proximate  or  ultimate  analysis,  according 
as  the  substance  under  examination  is  resolved  into  its  proximate  constituents,  or 
into  its  elements  ;  thus,  the  proximate  analysis  of  sulphate  of  potassa  consists  in 
the  resolution  of  this  salt  into  sulphuric  acid  and  potassa,  which  are  its  proximate 
constituents ;  whereas,  it  would  be  the  object  of  an  ultimate  analysis  to  decompose 
it  into  sulphur,  oxygen,  and  potassium,  which,  since  they  are  elements,  are  the 
limits  beyond  which  analysis  cannot  proceed. 

Hence,  the  importance  of  this  branch  of  our  subject  will  be  apparent  to  all ; 
in  fact,  analysis  may  be  esteemed  the  basis  of  all  chemical  science ;  and,  indeed, 
this  branch  of  knowledge  is  sometimes  defined  as  that  which  teaches  the  compo- 
sition of  all  kinds  of  matter;  and  analysis,  as  above  explained,  is  the  operation 
by  which  the  composition  is  ascertained. 

The  separation  of  the  constituents  of  compound  bodies  is  effected  by  converting 
either  the  constituent  to  be  separated,  or  that  other  portion  of  the  compound 
from  which  we  intend  to  separate  it,  into  a  form  different  from  that  which  it 
originally  possessed ;  thus,  in  the  analysis  of  the  inferior  oxides  of  nitrogen,  the 
oxygen  is  separated  by  metallic  copper,  with  which  it  enters  into  combination, 
and  the  yas  is  thus  separated  in  the  form  of  a  solid  (oxide  of  copper);  again, 
oxygen  may  be  separated  from  the  oxide  of  copper,  in  the  analysis  of  this  sub- 
stance, by  means  of  hydrogen,  which,  at  a  high  temperature,  converts  the  oxygen 
into  steam,  thus  removing  it,  in  a  gaseous  form,  from  its  solid  combination. 

Precipitation,  however,  is  most  frequently  employed  for  the  separation  of  sub- 
stances from  each  other.  This  operation  consists  in  the  conversion  of  one  con- 
stituent part  of  a  liquid  into  a  solid  form,  when  it  maybe  separated  by  mechanical 
means;  this  may  be  effected  either  by  changing  the  chemical  nature  of  the  con- 
stituent to  be  separated,  or  that  of  the  liquid  in  which  this  constituent  is  dissolved ; 
the  first  method  is  illustrated  by  the  separation  of  baryta  from  the  nitrate  by  the 
addition  of  sulphuric  acid,  which  converts  the  baryta  into  an  insoluble  sulphate, 
whilst  the  second  mode  of  precipitation  is  had  recourse  to  in  the  separation  of 
oxide  of  copper  from  the  sulphate  by  the  addition  of  potassa,  which  converts  the 
sulphuric  acid  (in  which  the  oxide  of  copper  was  dissolved)  into  sulphate  of 
potassa,  and  a  solution  of  this  salt  being  incapable  of  dissolving  the  oxide  of  cop- 
per, this  latter  is  precipitated. 

From  these  examples,  it  will  be  seen  that  a  knowledge  of  the  operation  of 
affinities  under  various  conditions  is  of  very  great  service  to  the  analytical  chemist, 
who  should  also  be  acquainted  with  the  chemical  relations  of  the  most  common 
acids,  bases,  and  salts,  which  he  will  apply  in  the  course  of  analysis,  and  it  is 


496  QUALITATIVE   ANALYSIS. 

therefore  almost  indispensable  to  acquire  a  pretty  good  knowledge  of  general 
chemistry  before  entering  upon  the  study  of  analysis ;  and  although  one  who 
has  not  thus  qualified  himself  may  attain  to  great  readiness  in  the  application  of 
this  instrument  of  investigation,  and  great  familiarity  with  the  systematic  coarse 
marked  out  for  him,  he  will  find  that  every  case  not  provided  for  in  the  general 
rules  will  be  fraught  with  difficulties  which  are  insuperable  to  one  whose  whole 
knowledge  consists  only  in  a  mechanical  familiarity  with  a  certain  routine  of  pro- 
cesses and  manipulations,  and  is  not  founded,  as  it  should  be,  upon  a  correct 
acquaintance  with  the  properties  of  the  elementary  forms  of  matter  and  of  their 
various  combinations. 

Qualitative  analysis  shows  us  merely  the  nature  of  the  component  parts  of  a 
substance,  whilst  the  determination  of  their  quantity  is  the  object  of  a  quantita- 
tive, analysis;  of  course,  a  quantitative  analysis  must  be  preceded  by  a  qualita- 
tive ;  we  must  know  what  the  ingredients  are,  before  we  attempt  to  ascertain 
their  amount. 

The  method  to  be  pursued  in  the  study  of  qualitative  analysis  is,  obviously,  to 
acquaint  ourselves,  first,  with  the  properties  of  those  substances  the  detection 
and  separation  of  which  we  have  in  view;  then  to  ascertain  how  far  these  proper- 
ties are  modified,  when  the  various  substances  exist  together  in  a  compound  or 
mxiture;  and  lastly,  to  deduce  from  these  observations  methods  of  effecting  their 
separation.  And  here  we  may  remind  the  reader  of  the  difference  between  testing 
and  analysis  ;  we  test  for  any  particular  substance  by  eliciting  some  property 
peculiar  to  itself,  such  as  a  change  of  color  or  production  of  some  peculiar  odor, 
which  would  not  afford  us  any  assistance  in  the  separation  of  such  bodies,  i.  e.  in 
the  analysis  of  their  combinations. 

Great  caution  is  obviously  essential  to  successful  analysis ;  it  is  well  to  bring 
the  greatest  amount  of  evidence  to  support  the  presence  of  any  substance,  by 
eliciting  as  many  as  possible  of  the  properties  of  that  substance ;  and  we  must, 
above  all,  beware  of  jumping  to  conclusions,  as  it  is  termed,  by  accepting  a  chain 
of  evidence  in  which  a  few  links  are  wanting,  because  we  imagine  that  the  impro- 
bability of  our  mistaking  the  body  in  question  is  greater  than  the  confirmation 
which  the  presence  of  these  links  would  afford.  We  must  also,  by  dint  of  long 
practice  in  the  analysis  of  bodies  of  known  composition,  learn  to  assign  to  each 
indication  its  own  proper  weight,  and  no  more  ;  otherwise,  by  exaggerating  its 
value,  we  are  in  danger,  either  of  inferring  the  presence  of  any  substance  from 
proof  which  is  really  insufficient,  or  of  setting  it  down  as  absent  upon  the  testi- 
mony of  a  reaction,  the  failure  of  which  ought  to  be  ascribed  to  some  modifying 
cause  with  which  we  may  be  unacquainted. 

Thus,  too  much  reliance  should  not  be  placed  upon  the  color  and  appearance 
of  precipitates,  which  may  be  influenced  by  a  great  variety  of  causes ;  but  we 
should  rather  learn  to  recognize  them  by  their  chemical  relations,  their  solubility, 
insolubility,  &c.,  which  characters  are  generally  as  constant  as  the  others  are 
liable  to  change. 

The  chemical  analyst,  especially  at  the  commencement  of  his  studies,  generally 
finds  it  advantageous  to  note  down  each  step  taken,  with  its  result,  and  the  con- 
clusion drawn  from  it;  such  notes  not  only  enable  him  to  discover  and  retrieve 
any  error  into  which  he  may  have  fallen,  but,  if  preserved,  are  very  useful  for 
reference  and  comparison. 


APPARATUS    USED   IN   QUALITATIVE    ANALYSIS. 

§  332.  The  apparatus  requisite  for  the  practice  of  qualitative  analysis  is  very 
simple;  the  following  list  comprises  all  those  instruments  with  which  the  student 
should  provide  himself  at  the  commencement. 


APPARATUS   USED   IN   QUALITATIVE   ANALYSIS. 


497 


Two  or  three  dozen  of  German  test-tubes, 
and  stand  with  draining  pegs;  brush 
for  cleaning  the  tubes. 

A  test-tube  holder.     (Fig.  70.) 

A  few  glass  funnels  capable  of  containing 
from  eight  ounces  to  half  an  ounce. 

A  selection  of  Berlin  dishes,  and  of  Ber- 
lin crucibles  (Fig.  71)  with  covers.1 

Small  Jlitsks  of  German  glass,  holding 
from  four  to  eight  ounces. 

Glass  rod  and  tube  of  various  sizes. 

A  washing-bottle  containing  about  six- 
teen ounces.  (Fig.  72.) 

A  spirit-lamp.     (Fig.  73.) 

A  few  German  beakers,  from  one  to 
sixteen  ounces. 

A  pestle  and  mortar  of  Berlin  or  of 
Wedgwood  ware. 

Fig.  70. 


Small  sand-tray. 

Watch-glasses. 

Cork-borers  (Fig.  74),  round  and  trian- 
gular files,  scissors. 

Cork-rasp,  spatula. 

A  number  of  the  best  corks. 

A  few  lengths  of  small  vulcanized  tub- 
ing. 

Small  crucible-tongs. 

A  few  iron  spoons  ;  iron  wire  triangles 
for  supporting  crucibles,  &c. 

Black's  blowpipe. 

Platinum  wire  and  foil. 

Small  retort-stand. 

Good  filtering-paper. 

Blue  and  red  litmus-papers. 

Sulphuretted  hydrogen  apparatus.  (Fig. 
75.) 


Fig.  71. 


Fig.  72. 


Fig.  74. 


Fig.  75. 


Meissen  ware  may  be  substituted  for  these. 


498  APPARATUS   USED   IN    QUALITATIVE   ANALYSIS. 

The  particulars  to  be  attended  to  in  the  selection  of  these  different  apparatus, 
as  well  as  the  precautions  in  their  use,  have  been  in  great  measure  described 
already;  we  need  therefore  only  subjoin  here  a  few  remarks,  especially  relating 
to  the  use  of  the  apparatus  in  qualitative  analysis. 

The  most  convenient  test-tubes  will  be  found  to  be  about  six  inches  in  length, 
and  about  three-fourths  of  an  inch  in  diameter;  they  should  be  made  of  very 
thin  German  glass,  and  furnished  with  a  smooth  lip,  but  no  spout.  A  few 
wider  tubes  will  also  be  found  useful  for  boiling  liquids.  The  test-tubes  should 
be  thoroughly  cleaned,  after  use,  by  brushing;  they  should  then  be  rinsed  with 
distilled  water,  and  inverted  upon  the  draining-pegs. 

The  funnels  should  be  plain,  not  ribbed,  and  the  sides  should  form,  as  nearly 
as  possible,  an  angle  of  45°  with  the  stem. 

The  Berlin  crucibles  should  be  of  uniform  thickness,  and  provided  with  light 
covers;  in  capacity,  they  should  vary  from  one  to  four  fluidrachms,  the  latter 
size  being  the  most  useful. 

Porcelain  dishes  for  qualitative  analysis  should  vary  in  size,  from  one  pint  to 
half  an  ounce ;  they  should  be  nearly  hemispherical  in  shape,  and  should  have 
a  spout  to  pour  from ;  it  is  better  to  have  them  glazed  within  and  without. 
These  dishes  are  often  required  to  stand  the  application  of  a  red  heat,  and,  in 
this  respect,  the  Berlin  ware  is  much  preferable  to  any  other. 

Theyfa.s&s  employed  in  analysis  should  be  very  thin,  flattened  at  the  bottom, 
and  provided  with  a  lip  like  that  of  a  test-tube ;  such  flasks  should  be  heated  on 
a  sand-bath. 

Glass  rod  is  very  useful  for  making  stirrers;  for  this  purpose,  the  rod  (which 
should  be  rather  thin)  is  cut  into  lengths  varying  from  three  to  twelve  inches, 
the  ends  of  which  are  rounded  in  the  outer  blowpipe-flame. 

The  characters  by  which  glass  tubing  should  be  selected,  have  been  already 
mentioned;  the  most  convenient  size  for  use  in  analysis  has  an  internal  diameter 
of  about  one-sixth  of  an  inch ;  some  English  tube  should  be  provided  for  bend- 
ing, and  a  few  lengths  of  German  glass  for  reduction  tubes,  &c. 

In  a  former  page,  we  have  described  the  washing-bottle  in  ordinary  use  (p.  92); 
the  one  here  figured  may  be  used  with  hot  water. 

The  beakers  should  be  without  a  punty-mark,  very  thin  and  uniform;  they 
should  be  heated  on  a  sand-bath,  never  by  the  bare  flame. 

A  small  mortar  of  Berlin  porcelain,  capable  of  containing  about  eight  ounces, 
will  be  found  most  useful. 

The  watch-glasses  should  be  made  of  thin,  well-annealed  glass;  they  will 
generally  bear  heating  upon  the  sand-bath,  but  rarely  over  the  flame. 

The  crucible-tongs  in  general  use  are  made  of  iron,  but  it  is  very  advantageous 
to  have  them  tipped  with  platinum,  although  they  become  then  very  much  more 
expensive.  The  ordinary  iron  tongs  should. not  be  employed  for  lifting  dishes 
containing  liquids  likely  to  corrode  the  iron,  and  thus  to  become  contaminated 
with  this  metal. 

An  iron  retort-stand  with  three  or  four  movable  brass  rings,  from  two  to  four 
inches  in  diameter,  serves  to  support  funnels,  dishes,  and  crucibles;  the  latter 
should  never  be  supported  directly  by  the  ring  of  the  retort-stand,  always  upon 
a  triangle. 

Qualitative  filtering-paper  should  be  moderately  strong,  and  should  allow 
liquids  to  pass  pretty  rapidly;  when  boiling  dilute  hydrochloric  acid  is  poured 
through  a  filter  made  of  this  paper,  it  should  take  up  no  alumina  or  earthy 
phosphate  (which  may  be  precipitated  from  the  acid  solution  by  excess  of  am- 
monia), nor  any  traces  of  lime  (detected  by  adding  ammonia  in  excess,  and 
oxalate  of  ammonia,  which  would  produce  a  white  precipitate). 

The  blue  and  red  litmus-papers  should  be  made  of  opaque  very  thinly  sized 
paper,  not  too  strongly  tinted. 


REAGENTS   USED   IN   QUALITATIVE   ANALYSIS. 


499 


The  sulphuretted  hydrogen  apparatus  consists  of  a  generating  bottle  (capable 
of  containing  about  twelve  ounces)  furnished  with  a  funnel-tube  for  adding  the 
acid,  and  with  a  tube  bent  at  right  angles,  connected,  by  means  of  caoutchouc, 
with  a  second  glass  tube  which  conveys  the  gas  to  the  bottom  of  a  small  bottle, 
containing  a  little  water  to  free  it  from  mechanically  suspended  impurities;  from 
this  wash-bottle,  another  tube  proceeds,  which  is  bent  twice  at  right  angles;  to 
the  disengaged  extremity  of  this  tube,  there  is  attached,  by  a  connector,  a  straight 
piece  of  tube,  which  serves  to  convey  the  gas  into  any  solution  through  which 
we  intend  to  pass  it. 


REAGENTS   USED   IN   QUALITATIVE  ANALYSIS. 

§  333.  The  reagents  employed  in  qualitative  analysis  come  next  under  con- 
sideration. 

Reagents  are  the  substances  employed  by  the  analyst  in  ascertaining  the  nature 
of  a  body  under  examination ;  they  are  usually  divided  into  general  and  special 
reagents ;  the  former  designation  is  commonly  applied  to  those  substances  which 
are  used  to  separate  bodies  into  different  groups,  and  the  latter,  to  those  employed 
to  distinguish  the  members  of  these  groups  from  each  other.  We  shall,  however, 
give  a  wider  sense  to  the  term  general  reagents,  and  employ  it  to  denote  all  those 
which  are  frequently  used  in  analysis,  whilst  the  special  reagents  are  such  as  are 
only  used  to  detect  individual  substances. 

The  general  reagents  are  most  conveniently  arranged  over  the  working-table 
within  reach  of  the  operator,  whilst  the  special  reagents  may  be  placed  in  any 
other  part  of  the  laboratory. 

In  the  following  list,  we  have  adopted  this  division  into  general  and  special 
reagents ;  and  it  may  be  remarked  that  comparatively  small  quantities  of  the 
special  reagents  are  employed,  unless  otherwise  mentioned. 


GENERAL  REAGENTS. 


In  solution. 


1.  Concentrated  sulphuric  acid  (HO.S03). 

2.  Dilute  "  " 

3.  Concentrated  hydrochloric  acid  (HC1) 

4.  Dilute  "  " 

5.  Concentrated  nitric  acid  (HO.N05) 

6.  Dilute  "         " 

7.  Acetic  acid  (HO.C4H303=HO.T). 

8.  Tartaric  acid  (2HO.C8H4010=2HO.f]. 

9.  Hydrosulphuric  acid  (HS). 

10.  Potassa  (KO.HO). 

11.  Ferrocyanide  of  potassium  (K2Cy3Fe= 

K2Cfy). 

12.  Carbonate  of  soda  (NaO.C02). 


13.  Phosphate  of  soda  (2NaO.HO.POs). 

14.  Ammonia  (NH40). 

15.  Sesquicarbonate  of  ammonia  (2NEL0.3 

C02). 

16.  Oxalate  of  ammonia  (NH4O.C203). 

17.  Chloride  of  ammonium  (NH4C1). 

18.  Sulphide  of  ammonium  (NH4S). 

19.  Chloride  of  barium  (BaCl). 

20.  Lime  (CaO.HO). 

21.  Sulphate  of  lime  (CaO.S03). 

22.  Chloride  of  calcium  (CaCl). 

23.  Sesquichloride  of  iron  (Fe2Cl8). 


In  the  solid  state. 


24.  Nitrate  of  potassa  (KO.NOS). 

25.  Carbonate  of  potassa  and  soda   (KO. 

COa-f.NaO.C02). 

26.  Cyanide  of  potassium  (KC4N=KCy). 


27.  Carbonate  of  soda  (NaO.C02). 

28.  Biborate  of  soda  (Na0.2BOJ. 

29.  Hydrate  of  lime  (CaO.HO). 


500 


REAGENTS    USED   IN   QUALITATIVE   ANALYSIS. 


SPECIAL  REAGENTS. 

In  solution. 


1.  Sulphurous  acid  (S02). 

2.  Oxalic  acid  (HO.C203=HO.O). 

3.  Hydrofluosilicic  acid  (3HF.2SiFg). 

4.  Sulphate  of  potassa  (KO.S03). 

5.  Bichromate  of  potassa  (KO.iiCr03). 

6.  Acetate  of  potassa  (KO.A)  [in  consider- 

able quantity]. 

7.  Ferricyanide  of  potassium  (K,CyfiFe,>= 

K3Cfdy). 

8.  Sulphite  of  ammonia   (NH4O.S02)   [in 

considerable  quantity], 

9.  Baryta  (BaO.HO)  [in  considerable  quan- 

tity]. 


10.  Sulphate  of  magnesia  (MgO. SO,). 

11.  Nitrate  of  cobalt  (CoO.NO-). 

12.  Sulphate  of  manganese  (MnO.S03). 

13.  Acetate  of  lead  (PbO.~A). 

14.  Sulphate  of  copper  (CuO.S03). 

15.  Chloride  of  mercury  (HgCl). 

16.  Chloride  of  tin  (SnCl). 

17.  Bichloride  of  platinum  (PtCl2). 

18.  Nitrate  of  silver  (AgO.NO.)  [in  consider- 

able quantity]. 

19.  Alcohol  (C4H602). 

20.  Ether  (C4H50). 

21.  Solution  of  indigo  (C,6H4N02). 


In  the  solid  state. 


22.  Chlorate  of  potassa  (KO.C105). 

23.  Phosphate  of  soda  and  ammonia  (NaO. 

NH4O.HO.P05). 

24.  Hydrate  of  baryta  (BaO.HO). 

25.  Dry  chloride  of  calcium  (CaCl). 

26.  Carrara  marble  (CaO.C02). 

27.  Sulphate  of  iron  (FeO.S03). 


28.  Binoxide  of  manganese  (Mn02). 

29.  Granulated  zinc  (Zn). 

30.  Copper  foil  or  wire  (Cu). 

31.  Starch  (C12H,00,0). 

32.  Sulphur  (IS). 

33.  Sulphide  of  iron  (FeS). 


It  is  obvious  that  these  reagents  should  all  be  perfectly  pure,  but  since,  in 
many  cases,  it  is  exceedingly  difficult  to  procure  the  substances  in  a  state  of  abso- 
lute purity,  it  is  allowable  to  employ  them,  although  slightly  contaminated,  pro- 
vided that  the  impurities  are  known  to  the  operator,  and  are  not  such  as  will 
interfere  with  the  particular  use  of  the  reagent  in  question. 

Since  this  subject  possesses  great  practical  importance,  we  shall  now  proceed 
to  consider  the  particular  impurities  to  which  each  reagent  is  liable,  and  the  man- 
ner of  testing  for  them  ;  noticing,  at  the  same  time,  the  general  use  to  which  the 
reagent  is  applied,  unless  this  has  been  referred  to  in  a  previous  section. 

GENERAL  REAGENTS  EMPLOYED  IN  SOLUTION. 

Concentrated  Sulphuric  Acid. — The  ordinary  oil  of  vitriol  sold  by  operative 
chemists  is  sufficient  for  most  purposes ;  it  should  be  colorless,  and  free  from 
nitric  acid,  which  may  be  ascertained  by  diluting  it  with  an  equal  volume  of 
water,  allowing  the  mixture  to  become  nearly  cool,  and  adding  a  crystal  of  sul- 
phate of  iron;  if  the  liquid  be  allowed  to  remain  perfectly  at  rest  for  some 
minutes,  a  brown  halo  will  form  around  the  crystal  if  the  least  trace  of  nitric 
acid  is  present. 

Perfectly  pure  (distilled)  sulphuric  acid  is  necessary,  however,  for  some  pur- 
poses; this  should  be  tested  especially  for  sulphate  of  lead,  nitric  acid,  and  arse- 
nious  acid. 

The  presence  of  sulphate  of  lead  may  be  readily  ascertained  by  mixing  the 
acid  with  three  or  four  times  its  volume  of  water,  when  this  impurity  would  be 
thrown  down  as  a  white  precipitate. 

Nitric  acid  may  be  tested  for  as  above. 

Arsenious  acid  should  be  sought  by  Marsh's  test,  which  will  be  described 
hereafter;  this  is  not  a  common  impurity  of  sulphuric  acid  at  the  present  day. 

Dilute  sulphuric  acid  is  prepared  by  mixing,  in  a  beaker,  one  measure  of  the 
concentrated  acid  with  six  measures  of  water. 

Sulphuric  acid,  in  the  concentrated  state,  is  chiefly  used  for  evolving  sul- 


GENERAL   REAGENTS.  501 

phuretted  hydrogen,  and  for  decomposing  certain  salts,  for  which  purposes  it 
need  not  be  absolutely  pure.  The  dilute  acid  is  generally  used  for  precipitating 
lead,  baryta,  &c.,  and  should  therefore  be  free  from  all  impurities. 

Concentrated  hydrochloric  acid  should  have  a  specific  gravity  of  about  1.20, 
and  must  be  perfectly  colorless.  The  impurities  most  likely  to  occur  in  con- 
centrated hydrochloric  acid  are  sulphate  of  soda,  sulphurous  acid,  free  chlorine, 
and  chloride  of  iron,  which  latter  usually  imparts  a  yellow  tint  to  the  acid.  The 
sulphate  of  soda  may  be  detected  by  diluting  the  acid  with  four  or  five  measures 
of  water,  and  adding  chloride  of  barium,  when  a  white  precipitate  of  sulphate  of 
baryta  will  make  its  appearance.  The  presence  of  sulphurous  acid  may  be  ascer- 
tained by  boiling  the  acid  with  a  few  drops  of  pure  nitric  acid,  which  converts 
the  S03  into  S03,  diluting  with  much  water,  and  adding  chloride  of  barium. 

If  the  hydrochloric  acid  contains  free  chlorine,  it  will  decolorize  solution  of 
indigo. 

Iron  may  be  tested  for  by  adding  an  excess  of  ammonia  to  the  acid,  and  then 
a  drop  of  sulphide  of  ammonium,  which  will  produce  a  greenish-black  precipitate 
or  tinge,  due  to  sulphide  of  iron. 

Pure  hydrochloric  acid  should  leave  no  residue  when  evaporated  on  platinum. 

One  measure  of  hydrochloric  acid  should  be  mixed  with  two  measures  of 
water,  for  the  preparation  of  the  dilute  acid. 

Hydrochloric  acid  is  generally  employed  where  a  free  mineral  acid  is  required, 
the  nature  of  which  is  a  matter  of  indifference,  since  it  is  not  liable  to  alter 
bodies  by  oxidation,  like  nitric  acid,  nor  to  form  insoluble  compounds,  like  sul- 
phuric acid;  thus  it  is  very  frequently  employed  as  a  solvent  in  analysis,  and 
should  therefore  be  absolutely  pure. 

Concentrated  nitric  acid  used  in  analysis  has  a  specific  gravity  of  1.48  to 
1.50.  It  is  liable  to  contain  inferior  oxides  of  nitrogen  (N03  and  N04),  sul- 
phates of  potassa  and  soda,  and  chlorine. 

The  lower  oxides  of  nitrogen  impart  a  red  or  yellow  color  to  the  acid,  and,  for 
most  purposes,  are  not  objectionable. 

The  sulphates  of  potassa  and  soda  may  be  detected  by  diluting  largely  with 
water,  and  testing  with  chloride  of  barium. 

If  the  acid  contains  chlorine,  it  will  give  a  white  precipitate  of  chloride  of 
silver,  upon  addition  of  solution  of  nitrate  of  silver. 

Pure  nitric  acid  should  leave  no  residue  on  platinum. 

Dilute  nitric  acid  is  a  mixture  of  one  measure  of  the  concentrated  acid  with 
two  measures  of  water. 

Nitric  acid  is  generally  used  as  an  oxidizing  agent,  and  but  rarely  as  a  simple 
solvent;  for  the  latter  purpose  the  dilute  acid  is  generally  employed. 

Acetic  Acid. — The  ordinary  acetic  acid  of  the  druggists  is  sufficiently  strong 
for  most  purposes.  It  should  be  tested  for  sulphuric  acid  with  chloride  of 
barium,  and  for  sulphurous  acid  with  the  same  reagent,  after  having  been  boiled 
with  a  little  nitric  acid,  and  diluted  with  water;  pure -acetic  acid  must  not  be 
discolored  by  hydrosulphuric  acid,  and  should  volatilize  entirely  when  heated. 
Acetic  acid  is  generally  used  in  analysis,  where  a  vegetable  acid  is  required. 

Tartaric  acid  of  commerce  is  sufficiently  pure  for  the  purposes  of  analysis;  it 
should  be  used  in  the  form  of  a  cold  saturated  solution,  prepared  by  agitating 
the  crystals  with  water,  and  allowing  them  to  remain  in  contact  with  the  latter 
till  no  more  is  dissolved ;  this  solution  decomposes  after  some  days,  depositing 
white  flocks,  which,  however,  do  not  interfere  materially  with  the  applications 
of  the  reagent. 

Hydrosulphuric  acid  is  merely  a  saturated  aqueous  solution  of  the  washed 
gas;  this  reagent  should  be  kept  in  bottles  nearly  filled  with  it,  and  well  stopped, 
since  it  is  rapidly  oxidized  by  contact  with  air;  it  should  be  freshly  prepared 
every  two  or  three  days.  Hydrosulphuric  acid  is  one  of  the  most  useful  gene- 


502  GENERAL  REAGENTS. 

ral  reagents,  since,  by  precipitating  sulphides  of  various  colors,  it  enables  us  to 
recognize  many  metals  with  great  facility. 

Potassa  is  very  difficult  to  obtain  perfectly  pure,  and  although,  strictly  speak- 
ing, none  but  pure  potassa  should  be  used  in  analysis,  it  is  very  far  too  costly 
for  ordinary  purposes,  and  we  therefore  generally  content  ourselves  with  such  as 
contains  but  a  small  amount  of  impurity. 

The  ordinary  impurities  of  solution  of  potassa  are  silica,  alumina,  carbonic 
acid,  sulphuric  acid,  hydrochloric  acid,  and  oxide  of  lead.1 

Silica  may  be  detected  in  solution  of  potassa,  by  adding  an  excess  of  hydro- 
chloric acid,  evaporating  to  dryness,  and  heating  the  residue  with  dilute  hydro- 
chloric acid,  when  flakes  of  silica  will  remain  insoluble  ;  if  alumina  is  present,  it 
will  be  precipitated  by  ammonia  from  the  hydrochloric  solution  filtered  from  the 
silica. 

The  carbonic  acid  will  be  indicated  by  the  effervescence  which  takes  place 
when  the  solution  of  potassa  is  mixed  with  excess  of  hydrochloric  acid ;  a  small 
quantity  of  carbonic  acid  is  not  objectionable  in  most  of  the  applications  of  potassa. 

The  solution,  mixed  with  excess  of  hydrochloric  acid,  may  be  tested  for  sul- 
phuric acid  with  chloride  of  barium. 

The  presence  of  hydrochloric  acid  may  be  shown  by  acidulating  with  nitric 
acid,  and  testing  with  nitrate  of  silver. 

Oxide  of  lead  may  be  tested  for  with  hydrosulphuric  acid,  which  will  furnish 
a  black  precipitate  of  sulphide  of  lead. 

Good  potassa  should  contain  only  small  quantities  of  silica,  alumina,  sulphuric 
acid,  and  hydrochloric  acid,  should  effervesce  but  slightly  with  acids,  and  should 
be  free  from  oxide  of  lead. 

The  analyst  should  also  have  a  small  store  of  pure  potassa  (alcohol-potassa, 
as  it  is  termed),  for  cases  in  which  it  is  desirable  to  test  for  silica  and  alumina 
with  great  minuteness. 

Potassa  is  chiefly  used  for  dissolving  certain  metallic  oxides  (for  example, 
alumina  and  oxide  of  zinc),  and  thus  separating  them  from  others  which  are 
insoluble  in  this  alkali. 

Ferrocyanide  of  Potassium. — This  salt,  as  it  is  found  in  commerce,  may  be 
employed  as  a  reagent ;  one  part  of  the  crystals  is  dissolved  in  ten  parts  of  water. 
It  is  used  as  a  special  test  for  iron,  copper,  &c. 

The  carbonate  of  soda  employed  in  analysis  should  be  perfectly  pure;  it  is 
liable  to  be  contaminated  with  sulphuric  acid,  chlorine,  silica,  hydrate  of  soda, 
alumina,  and  lime.  Its  aqueous  solution  may  be  tested  for  sulphuric  acid  with 
chloride  of  barium,  after  addition  of  an  excess  of  hydrochloric  acid ;  for  chlorine 
with  nitrate  of  silver,  after  adding  excess  of  nitric  acid ;  for  silica,  by  evaporat- 
ing the  solution,  mixed  with  hydrochloric  acid  in  excess,  to  dryness,  and  redis- 
solving  in  dilute  hydrochloric  acid,  when  flakes  of  silica  would  be  left  behind ; 
alumina  may  be  precipitated  from  the  acid  solution  thus  obtained,  by  ammonia, 
and  lime  will  then  be  indicated  by  oxalate  of  ammonia. 

If  sulphide  of  sodium  be  present,  the  aqueous  solution  will  give  a  somewhat 
gray  precipitate  with  acetate  of  lead,  which  should  throw  down  white  carbonate 
of  lead  only,  if  the  specimen  be  perfectly  pure. 

In  order  to  ascertain  whether  any  hydrate  of  soda  is  present  in  a  specimen  of 
the  carbonate,  the  aqueous  solution  of  the  latter  is  mixed  with  solution  of  chlo- 
ride of  barium,  as  long  as  any  precipitate  is  produced ;  this  precipitate  of  car- 
bonate of  baryta  is  rapidly  filtered  off,  and  a  piece  of  reddened  litmus- paper 
immersed  in  the  filtrate ;  if  the  latter  evince  an  alkaline  reaction,  it  is  a  proof  of 
the  presence  of  hydrate  of  soda  in  the  original  solution. 

1  This  last  impurity  is  avoided  if  the  potassa  be  kept  in  bottles  of  German  glass,  which 
contains  no  lead,  instead  of  in  those  of  ordinary  flint-glass. 


GENERAL  REAGENTS.          '  503 

The  solution  of  carbonate  of  soda  for  use  in  analysis  is  best  prepared  by  dis- 
solving the  salt  in  so  much  warm  water  that  the  solution  shall  be  saturated 
when  cold. 

Carbonate  of  soda  is  in  frequent  use  for  neutralizing  acid  solutions  where  it  is 
desirable  to  avoid  the  introduction  of  ammonia,  and  for  decomposing  certain 
salts  which  are  insoluble  in  water,  and  would  be  destroyed  if  dissolved  in  acids. 

Phosphate  of  soda  is  met  with  in  commerce  of  sufficient  purity  for  analytical 
purposes;  one  part  of  the  crystals  may  be  dissolved  in  six  parts  of  water. 

Solution  of  phosphate  of  soda  should  be  kept  in  bottles  of  German  glass,  since 
it  acts  upon  common  flint-glass,  giving  rise  to  an  opaque  precipitate  of  phosphate 
of  lead. 

Ammonia  is  one  of  the  most  important  reagents  in  the  laboratory;  it  is  pre- 
pared of  suitable  strength  by  mixing  the  solution  of  ammonia  of  sp.  gr.  0.87 
with  an  equal  volume  of  water.  Solution  of  ammonia  is  very  seldom  impure ; 
it  may  contain  chloride  of  ammonium,  carbonate  of  ammonia,  and  sometimes 
traces  of  lime;  the  chlorine  may  be  detected  by  adding  excess  of  nitric  acid  and 
nitrate  of  silver;  the  carbonic  acid  will  produce  a  turbidity  in  solution  of  chlo- 
ride of  calcium,  and  the  lime  will  be  indicated  by  a  white  precipitate  on  addition 
of  oxalate  of  ammonia.  Pure  ammonia  should  leave  no  residue  on  evaporation. 

Ammonia  is  constantly  employed  to  precipitate  metallic  oxides  from  their 
salts,  and  for  neutralizing  solutions  previously  to  analysis ;  it  is  therefore  highly 
important  that  it  be  perfectly  pure. 

Sesquicarbonate  of  ammonia,  in  solution,  is  prepared  by  agitating  the  com- 
mercial sesquicarbonate,  broken  into  small  fragments,  with  cold  water,  as  long 
as  any  of  the  salt  is  dissolved. 

The  sesquicarbonate  of  ammonia  is  liable  to  contain  bicarbonate,  which  consti- 
tutes the  opaque  white  crust  seen  on  the  surface  of  the  former  salt  after  exposure 
to  the  air;  it  also  sometimes  contains  a  little  oxide  of  iron,  which  will  give  a 
greenish-black  tinge  with  sulphide  of  ammonium. 

Sesquicarbonate  of  ammonia  should  leave  no  residue  when  heated  on  platinum. 
This  reagent  is  chiefly  used  in  the  separation  of  tin,  antimony,  and  arsenic,  and 
in  the  precipitation  of  the  alkaline  earths. 

Oxalate  of  ammonia  is  used  as  a  special  test  for  lime;  a  cold  saturated  solu- 
tion may  be  prepared  for  this  purpose,  by  agitating  the  crystals  with  water  as 
long  as  any  of  the  salt  is  dissolved. 

Chloride  of  ammonium,  as  met  with  in  commerce,  is  not  sufficiently  pure  for 
analytical  purposes,  since  it  contains  a  considerable  quantity  of  iron;  one  recrys- 
tallization  generally  purifies  it  sufficiently.  This  salt  should  volatilize  perfectly 
on  platinum,  and  should  not  give  any  tinge  of  sulphide  of  iron  upon  addition  of 
sulphide  of  ammonium. 

Sulphide  of  ammonium  is  very  extensively  employed  in  analysis  for  separating 
certain  classes  of  metallic  oxides. 

When  freshly  prepared,  sulphide  of  ammonium  is  colorless,  but  after  some 
time,  it  becomes  yellow  in  consequence  of  an  absorption  of  oxygen  from  the  air ; 
thus : — 

2NH4S  +  0=NH4S2+HN3+HO. 

Since  this  NH4S3  (bisulphide  of  ammonium)  is  frequently  useful,  and  very 
rarely  objectionable,  it  is  better  to  employ  the  light  yellow  sulphide  of  ammo- 
nium as  a  reagent. 

Sulphide  of  ammonium  should  not  give  any  precipitate  with  solution  of  sul- 
phate of  magnesia,  nor  leave  any  fixed  residue  when  evaporated  on  platinum ; 
the  yellow  sulphide,  when  mixed  with  excess  of  hydrochloric  acid,  should  give  a 
perfectly  white  precipitate  of  sulphur. 

Chloride  of  barium  is  liable  to  a  very  dangerous  impurity,  chloride  of  lead, 
which  may  be  detected  by  the  black  tinge  produced  by  hydrosulphuric  acid;  it 


504    GENERAL  REAGENTS  EMPLOYED  IN  THE  SOLID  FORM. 

may  be  purified  easily  by  recrystallization,  or  the  lead  may  be  precipitated  by 
hydrosulphuric  acid,  the  solution  evaporated  till  the  excess  of  this  reagent  has 
been  expelled,  and,  after  separating  the  precipitated  sulphur  by  filtration,  evapo- 
rated to  crystallization.  A  cold  saturated  solution  of  chloride  of  barium  is  most 
convenient  for  ordinary  use. 

This  reagent  is  largely  employed  in  the  detection  of  the  acids;  its  purity  from 
lead  is  therefore  matter  of  importance. 

Lime-water  is  very  useful  in  the  detection  of  carbonic  acid;  it  is  prepared  by 
shaking  freshly  slaked  lime  with  cold  distilled  water,  allowing  the  excess  of  lime 
to  subside,  and  decanting  the  clear  liquor,  which  should  be  kept  in  well-stoppered 
bottles,  since  it  is  very  liable  to  absorb  carbonic  acid  from  the  air.  Its  alkaline 
reaction  may  serve  to  indicate  its  strength. 

Sulphate  of  Lime. — The  solution  of  this  salt  is  prepared  by  boiling  an  excess 
of  precipitated  sulphate  of  lime  with  water,  which  dissolves  very  little  of  it,  and 
filtering.  It  is  used  to  distinguish  between  baryta  and  strontia. 

Chloride  of  Calcium  is  largely  used  in  the  detection  of  the  acids ;  its  solution 
should  be  prepared  by  dissolving  the  crystals  in  three  parts  of  water.  The  solu- 
tion of  chloride  of  calcium  should  not  be  precipitated  by  ammonia,  which  would 
throw  down  alumina,  nor  by  sulphate  of  lime,  which  would  indicate  baryta  and 
strontia. 

SesquicTiloride  of~  iron  should  not  have  a  powerful  acid  reaction,  and  should 
yield  a  permanent  precipitate  when  stirred  with  a  glass  rod  dipped  in  solution  of 
ammonia;  it  should  contain  no  (proto-)  chloride  of  iron,  which  is  indicated  by 
the  production  of  a  blue  precipitate  on  adding  solution  of  ferricyanide  of  potas- 
sium to  the  highly  diluted  sesquichloride.  The  solution  should  be  diluted  till  of 
a  somewhat  light  sherry  color ;  it  is  used  in  the  detection  of  certain  acids,  espe- 
cially of  phosphoric  acid. 

GENERAL  KEAGENTS  EMPLOYED  IN  THE  SOLID  FORM. 

Nitrate  of  potassa  of  commerce  should  be  purified  by  recrystallization.  It  is 
liable  to  contain  sulphate  of  potassa  and  chloride  of  potassium ;  the  presence  of 
the  former  will  be  indicated  by  chloride  of  barium,  that  of  the  latter  by  nitrate  of 
silver.  The  crystals  should  be  powdered,  and  dried  at  a  gentle  heat. 

Carbonate  of  Potassa  and  Soda — This  reagent  consists  of  a  mixture  of  equiva- 
lent weights  of  the  two  carbonates  (about  four  parts  of  dried  carbonate  of  potassa 
and  three  of  dried  carbonate  of  soda),  and  is  much  more  fusible  than  either  of 
the  salts  separately. 

The  mode  of  ascertaining  the  purity  of  carbonate  of  soda  has  been  mentioned 
above;  carbonate  of  potassa  is  liable  to  the  same  impurities. 

It  is  highly  important  that  this  reagent  be  perfectly  pure,  since  it  is  constantly 
employed  in  the  analysis  of  insoluble  substances,  such  as  the  natural  silicates. 
This  mixture  may  be  advantageously  prepared  by  incinerating  the  double  tartrate 
of  potassa  and  soda  (Roclielle  salt)  in  a  platinum  dish,  till  all  the  carbon  has  burnt 
off,  which  may  be  hastened  by  stirring. 

Cyanide  of  potassium  has  already  been  mentioned  under  the  head  of  blowpipe- 
reagents  (p.  107);  it  should  be  perfectly  white,  and  must  be  kept  in  bottles  which 
are  well  closed  with  sound  corks,  since  glass  stoppers  are  very  liable  to  become 
fixed  in  the  bottles. 

We  have  already  mentioned  (p.  107)  the  use  of  cyanide  of  potassium  as  a  re- 
ducing agent ;  it  is  sometimes  employed,  also,  in  the  state  of  solution,  which  should 
be  prepared  as  it  is  wanted,  by  agitating  the  salt  with  cold  water,  since,  if  kept 
for  a  length  of  time,  or  if  heated,  this  solution  easily  undergoes  decomposition ; 
it  is  chiefly  used  in  the  separation  of  cobalt  and  nickel. 

For  carbonate  of  soda,  we  refer  to  the  article  on  blowpipe-reagents  (p.  106). 


SPECIAL   REAGENTS   EMPLOYED   IN    SOLUTION.  505 

Biborate  of  soda  has  also  been  mentioned  as  a  blowpipe-reagent  (p.  107),  and 
as  this  is  its  only  use,  we  have-  nothing  further  to  add  in  this  place. 

Hydrate  of  lime,  used  as  a  reagent,  should  be  introduced  into  well-closed  bottles 
•when  freshly  slaked ;  it  should  be  free  from  lumps  of  silicate,  and  must  not  effer- 
vesce very  strongly  with  hydrochloric  acid ;  hydrate  of  lime  is  used  to  liberate 
ammonia  from  its  compounds,  in  order  to  the  detection  of  this  substance. 

SPECIAL  REAGENTS  EMPLOYED  IN  SOLUTION. 

Sulphurous  Acid. — The  solution  of  sulphurous  acid  employed  in  analysis  is 
prepared  by  passing  the  gas  through  water  till  the  latter  is  saturated ;  it  is  used 
as  a  reducing  agent,  and  chiefly  to  convert  arsenic  into  arsenious  acid,  in  the 
course  of  detecting  the  bases. 

Oxalic  acid  is  occasionally  contaminated  with  nitric  acid,  which  may  be  de- 
tected by  its  property  of  bleaching  solution  of  indigo  upon  the  application  of  heat. 
Oxalic  acid  is  used  as  a  test  for  lime.  One  part  of  the  crystals  of  oxalic  acid  may 
be  dissolved  in  ten  parts  of  water. 

Hydrofluosilicic  Acid. — This  acid  is  employed  as  a  test  for  baryta,  and  is  liable 
to  be  contaminated  with  oxide  of  lead,  which  may  be  detected  by  hydrosulphuric 
acid.  The  introduction  of  this  impurity  may  be  avoided  by  keeping  the  acid  in 
bottles  of  German  glass.  Hydrofluosilicic  acid  should  produce  no  precipitate  in 
solutions  of  the  chlorides  of  strontium  and  calcium. 

Sulphate  of  Potassa. — Solution  of  sulphate  of  potassa  is  prepared  by  dissolv- 
ing, in  hot  water,  a  larger  quantity  of  the  salt  than  will  be  retained  in  solution 
at  the  ordinary  temperature;  the  cold  saturated  solution  is  preserved  for  use. 
This  reagent  is  used  in  the  separation  of  strontia  from  lime. 

The  bichromate  of  potassa  of  commerce  may  be  used  in  analysis;  one  part  of 
the  crystals  may  be  dissolved  in  twelve  parts  of  water. 

Acetate  of  potassa,  is  used  where  it  is  desired  to  replace  a  strong  acid  (e.  g. 
hydrochloric  or  nitric  acid)  by  acetic  acid ;  it  should  not  effervesce  with  acids, 
and  its  solution  must  not  be  tinged  by  sulphide  of  ammonium.  It  may  be  dis- 
solved in  three  parts  of  water. 

Ferricyanide  of  Potassium. — To  prepare  the  solution  of  this  salt,  the  crystals 
may  be  shaken  with  water  till  no  more  is  dissolved ;  the  solution  should  give  no 
precipitate,  but  merely  a  dark  color,  with  sesquichloride  of  iron. 

Sulphite  of  Ammonia. — A  solution  of  sulphite  of  ammonia,  prepared  by  satu- 
rating a  solution  of  ammonia  with  sulphurous  acid,  is  sometimes  substituted  for 
this  latter  in  reducing  arsenic  acid. 

Baryta-water  is  prepared  by  heating  the  crystals  of  baryta  with  water,  till  no 
more  is  dissolved ;  the  solution  should  be  kept  in  well-stoppered  bottles  nearly 
filled,  or  it  is  liable  to  absorb  carbonic  acid  from  the  air,  and  to  deposit  carbonate 
of  baryta. 

The  sulphate  of  magnesia  of  commerce  is  generally  sufficiently  pure  for  ana- 
lytical purposes ;  a  cold  saturated  solution  will  be  found  most  convenient. 

Nitrate  of  cobalt  has  been  already  alluded  to  as  a  blowpipe-reagent  (p.  107). 

Sulphate  of  Manganese. — A  moderately  dilute  solution  of  this  salt  is  employed 
as  a  test  for  hypochlorites. 

Acetate  of  Lead. — Solution  of  acetate  of  lead  is  prepared  by  dissolving  one  part 
of  the  crystallized  salt  in  6  parts  of  water;  it  is  chiefly  used  as  a  test  for  chromic 
and  hydrosulphuric  acids. 

Sulphate  of  Copper. — In  order  to  prepare  a  solution  of  sulphate  of  copper,  one 
part  of  the  crystals  is  dissolved  in  ten  parts  of  water;  the  use  of  this  reagent  is 
very  limited. 

Chloride  of  Mercury. — One  part  of  chloride  of  mercury  is  dissolved  in  twenty 
parts  of  water.  It  is  used  chiefly  as  a  test  for  tin. 


506        SPECIAL   REAGENTS   PRESEEVED   IN    THE    SOLID    STATE. 

Chloride  of  Tin. — A  solution  of  this  salt  is  useful  as  a  test  for  gold  ;  it  is  best 
prepared  by  boiling  granulated  tin  with  dilute  hydrochloric  acid  as  long  as  it  is 
rapidly  dissolved;  the  supernatant  liquid  may  then  be  decanted,  and  mixed  with 
about  half  its  volume  of  the  dilute  acid ;  if  this  last  precaution  be  neglected,  the 
solution  soon  becomes  opaque. 

Bichloride  of  platinum  in  the  form  of  a  strong  solution  (containing  about  5 
per  cent,  of  the  metal)  is  used  as  a  test  for  potassa;  it  should  not  contain  a  great 
excess  of  free  acid,  and  when  evaporated  to  a  thick  syrup,  should  form  a  perfectly 
clear  solution  in  alcohol. 

Nitrate  of  Silver. — Solution  of  nitrate  of  silver  is  prepared  by  dissolving  one 
parts  of  the  crystals  in  eight  parts  of  water,  and  is  particularly  useful  in  testing 
for  acids.  This  solution  should  be  perfectly  neutral  to  blue  litmus,  and  must  be 
free  from  copper,  which  would  be  indicated  by  a  blue  color  upon  addition  of  ex- 
cess of  ammonia. 

Alcohol. — The  spiritus  vini  rectificatissimus  of  the  druggist  is  sufficiently  strong 
for  the  limited  application  which  it  receives  in  qualitative  analysis.  It  should  not 
become  turbid  upon  addition  of  water,  nor  leave  any  residue  when  evaporated. 

Ether. — Rectified  ether  should  be  employed  when  required  in  analysis.  It  is 
almost  exclusively  used  in  testing  for  bromine. 

Solution  of  indigo  in  fuming  sulphuric  acid  (termed  sulphindigotic  acid)  is 
employed  for  the  "detection  of  nitric  acid  and  free  chlorine  or  its  oxides. 

SPECIAL  REAGENTS  PRESERVED  IN  THE  SOLID  STATE. 

Chlorate  of  potassa  is  a  very  useful  oxidizing  agent,  and  is  employed,  in  con- 
junction with  hydrochloric  acid,  to  dissolve  sulphur,  and  to  remove  organic  matters 
which  would  interfere  in  analysis. 

Phosphate  of  soda  and  ammonia  will  be  found  among  the  blowpipe  reagents 
(p.  107). 

Hydrate  of  Baryta. — Dry  (not  crystallized)  hydrate  of  baryta  is  used  in  the 
decomposition  of  insoluble  silicates  in  order  to  test  them  for  alkalies;  it  should 
therefore  be  free  from  these  latter,  which  may  be  ascertained  by  dissolving  in 
dilute  hydrochloric  acid,  precipitating  the  baryta  by  ammonia^and  sesquicarbonate 
of  ammonia,  with  the  aid  of  heat,  filtering  and  evaporating  to  dryness,  when  no 
residue  should  be  left. 

Dry  chloride  of  calcium^  obtained  by  drying  the  crystals  upon  a  sand-bath,  is 
employed  in  desiccating  gases.  It  should  not  possess  an  alkaline  reaction. 

Carrara  marble  is  necessary  for  evolving  carbonic  acid  in  testing  for  arsenic 
by  the  method  of  Fresenius. 

Sulphate  of  Iron. — Pure  green  crystals  of  sulphate  of  iron  are  employed  for 
analytical  purposes;  it  is  used  chiefly  in  testing  for  nitric  and  hydrocyanic  acids. 
This  salt  is  always  preserved  in  the  solid  state,  since  the  solution  rapidly  absorbs 
oxygen  from  the  air;  when  required  in  solution,  the  crystals  should  be  shaken 
with  cold  water. 

Binoxide  of  Manganese. — This  substance  is  useful  for  evolving  chlorine;  it 
need  not  be  chemically  pure,  but  should  be  free  from  any  considerable  quantity 
of  carbonate  of  lime,  which  may  be  detected  by  the  effervescence  with  dilute  nitric 
acid. 

Granulated  zinc  is  employed  in  analysis  chiefly  for  the  disengagement  of  hy- 
drogen; it  will  therefore,  in  general,  be  sufficiently  pure  if  the  gas  which  is  dis- 
engaged by  it  from  dilute  sulphuric  acid  be  free  from  antimony  and  arsenic,  which 
may  be  ascertained  by  Marsh's  test,  to  be  described  hereafter.  If  the  zinc  should 
be  required  for  other  purposes,  it  must  be  remembered  that  it  is  liable  to  contain 
lead  and  tin,  the  former  of  which  is  left  behind  in  the  form  of  black  scales  on 
boiling  the  zinc  with  dilute  hydrochloric  acid,  and  the  latter  may  be  detected  by 


I 

ANALYTICAL   CLASSIFICATION    OF   THE    METALS.  507 

mixing  the  hydrochloric  solution  with  chloride  of  mercury,  which  will  yield  a 
precipitate  of  the  subchloride  of  mercury. 

Copper. — This  metal  is  especially  useful  for  the  reduction  of  mercury  and 
arsenic  from  their  solutions;  it  should  be  employed  either  in  the  form  of  thin 
sheet  copper,  cut  into  strips  of  about  one  inch  by  |  inch,  or  in  rather  thin  wire, 
cut  into  lengths  of  an  inch.  It  should  be  cleaned  before  use,  by  allowing  it  to 
remain  for  a  few  seconds  in  concentrated  nitric  acid,  and  then  washing  with  water. 

Starch. — Ordinary  white  starch  is  used  in  the  detection  of  bromine  and  iodine. 

Sulphur. — Flowers  of  sulphur  are  employed  occasionally;  this  substance  should 
leave  no  residue  when  heated  in  a  porcelain  crucible. 

Sulphide  of  iron  is  largely  used  for  the  evolution  of  sulphuretted  hydrogen ; 
it  should  be  pretty  compact  and  homogeneous,  no  iron  filings  being  visible.  It 
is  employed  in  fragments  of  the  size  of  a  bean.  * 

DISTILLED  WATER. — Above  all  things,  it  is  of  course  necessary  that  the  dis- 
tilled water  employed  in  analysis  be  carefully  examined.  It  must  leave  no  trace 
of  residue  when  an  ounce  or  so  is  evaporated  in  a  clean  platinum  dish;  it  must 
not  produce  the  slightest  turbidity  with  nitrate  of  silver,  chloride  of  barium,  or 
oxalate  of  ammonia. 


ANALYTICAL    CLASSIFICATION    OF  THE    METALS. 

§  334.  In  order  to  acquire,  with  the  least  expenditure  of  time,  a  practical 
knowledge  of  qualitative  analysis,  this  study  may  be  divided  into  two  parts;  in 
the  first  part,  our  object  is  to  acquaint  ourselves  with  the  reactions  of  the  inor- 
ganic bases  and  acids,  and  afterwards,  with  those  of  the  organic  acids;  and  the 
knowledge  thus  obtained  will  be  applied  in  the  second  part  to  the  general  course 
of  qualitative  analysis,  i.  e.  to  effect  the  detection  of  these  bases  and  acids,  and 
their  separation  from  each  other. 

It  would  as  far  exceed  the  limits,  as  it  would  be  foreign  to  the  design  of  a 
work  of  this  nature,  to  give  a  complete  description  of  the  reactions  of  all  known 
acids  and  bases,  and  we  shall  therefore  confine  ourselves  to  those  which  are  gene- 
rally met  with  in  the  arts  and  manufactures,  and  in  pharmacy,  the  number  of 
which  is  comparatively  small;  the  reactions  of  the  rarer  metals  have  been  described 
in  former  pages. 

For  the  sake  of  convenience,  and  as  an  aid  to  the  memory,  the  metallic  oxides 
are  divided  intone  groups. 

In  the  first  group  are  included  the  three  alkalies,  potassa,  KO,  soda,  NaO,  and 
oxide  of  ammonium  (ammonia^),  NH40,  which  are  not  precipitated  by  any  of  the 
reagents  employed  in  separating  the  other  groups,  and  are  detected  by  special 
tests. 

The  second  group  consists  of  baryta,  BaO,  sfrontia,  SrO,  lime,  CaO,  and  mag- 
nesia, MgO,  which  are  not  precipitated  by  hydrochloric  acid,  by  hydrosulphuric 
acid,  by  ammonia  in  the  presence  of  chloride  of  ammonium,  nor  by  sulphide  of 
ammonium;  the  three  former,  baryta,  strontia,  and  lime,  are  thrown  down  as 
carbonates  when  sesquicarbonate  of  ammonia  is  added  to  their  solutions,  in  pre- 
sence of  chloride  of  ammonium  and  free  ammonia,  whilst  magnesia  is  not  pre- 
cipitated by  this  reagent,  but  separates  as  a  phosphate  upon  addition  of  phosphate 
of  soda. 

The  oxides  contained  in  the  third  group  are  such  as  are  not  precipitated  from 
their  solutions  by  hydrochloric  acid,  or  by  hydrosulphuric  acid  in  the  presence  of 
free  hydrochloric  acid,  but  which  are  separated,  either  as  hydrated  oxides  or  as 
sulphides,  on  the  addition  of  ammonia  in  excess,  and  of  sulphide  of  ammonium, 
even  if  chloride  of  ammonium  be  present  in  the  solution. 

This  group  comprehends  alumina,  A1203,  the  oxides  of  iron  FeO  and  FeaOB, 


508  ANALYTICAL   CLASSIFICATION   OF  THE   METALS. 

sesquioxide  of  chromium,  Cr203,  oxide  of  cobalt,  CoO,  oxide  of  nickel,  NiO, 
oxide  of  manganese,  MnO,  and  oxide  of  zinc,  ZnO. 

In  the  fourth  group,  we  find  those  oxides  the  solutions  of  which  are  not  pre- 
cipitated by  hydrochloric  acid,  but  yield,  on  addition  of  hydrosulphuric  acid,  the 
sulphides  corresponding  to  the  oxides;  the  metals  of  this  group,  therefore,  form 
sulphides  insoluble  in  water  and  in  dilute  hydrochloric  oxide. 

The  oxides  which  compose  this  group  are  oxide  of  mercury,  HgO,  oxide  of 
lead,  PbO,  teroxide  of  bismuth,  Bi03,  oxide  of  copper,  CuO,  oxide  of  cadmium, 
CdO,  teroxide  of  gold,  Au03,  binoxide  of  platinum,  Pt03,  teroxide  of  antimony, 
Sb03,  antimonic  acid,  SbO5,  oxide  of  tin,  SnO,  binoxide  of  tin,  SnOa,  arsenious 
acid,  As03,  arsenic  acid,  As05. 

The  fifth  group  includes  those  metallic  oxides,  the  chlorides  corresponding  to 
which  are  insoluble,'or  soluble  with  difficulty,  in  water;  the  solutions  of  these 
oxides,  therefore,  are  precipitated  by  hydrochloric  acid.  The  members  of  this 
group  are  oxide  of  silver,  AgO,  suboxide  of  mercury,  HgaO,  and  oxide  of  lead, 
PbO.1 

In  the  table  on  next  page  all  the  metals  are  arranged  on  the  principles  here 
developed. 

1  Oxide  of  lead  is  found  in  the  preceding  group  as  well  as  in  this,  since  the  chloride  of 
lead  is  not  quite  insoluble  in  water,  and  therefore  some  lead  will  escape  precipitation  by 
hydrochloric  acid,  but  may  be  thrown  down  as  sulphide  by  hydrosulphuric  acid. 


ANALYTICAL   CLASSIFICATION    OF   THE    METALS 


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510  REACTIONS   OF   THE   FIRST   GROUP. 


REACTIONS  OF  THE  METALLIC   OXIDES. 

It  will  be  observed,  in  the  following  account  of  the  behavior  of  metallic  oxides 
with  reagents : — 

1.  That,  unless  mention  to  the  contrary  is  made,  a  solution  of  a  neutral  salt  of 
the  oxide  under  examination  is  supposed  to  be  operated  upon. 

2.  That,  at  the  commencement  of  each  section,  we  shall  name  the  most  con- 
venient form  in  which  the  oxide  may  be  examined. 

3.  That  the  term  compound  of  an  oxide  is  applied  not  only  to  those  substances 
which  actually  contain  the  oxide  in  question,  but  also  to  such  haloid  compounds 
(chlorides,  e.g.'}  as  correspond  to  that  oxide;  thus,  the  chloride  of  mercury  is 
spoken  of  as  a  compound  of  the  oxide  of  mercury,  since  it  resembles  such  a  com- 
pound in  most  of  its  reactions. 

4.  That,  in  general,  only  those  reactions  are  set  down  which  admit  of  practical 
application  in  the  systematic  course  of  anaylsis,  those  which  possess  merely  a 
general  interest  being  omitted. 

The  student  is  cautioned  against  supposing  that  any  reaction  which  is  ascribed 
to  one  oxide  (and  not  to  others  of  the  same  group)  may  serve  as  a  characteristic 
test  for  that  oxide,  since  such  an  application  will  always  receive  especial  notice, 
and  the  reaction  is  omitted  in  the  case  of  the  other  oxides,  merely  because  it  is 
not  applied  in  the  systematic  course  of  analysis. 


§335.  FIRST   GROUP. 

Oxides  which  are  not  precipitated  by  the  reagents  employed  to  separate  the  other 

groups. 

POTASSA,  KO.    SODA,  NaO.     OXIDE  OF  AMMONIUM,  NH40. 
POTASSA,  KO. 

Solution  lest  fitted  for  the  reactions:  Chloride  of  Potassium,  KC1.1 

BICHLORIDE  OF  PLATINUM;  an  orange-yellow,  heavy,  crystallizing  precipitate 
of  the  double  Chloride  of  Platinum  and  Potassium  (KCl.PtCla);  somewhat 
soluble  in  water,  insoluble  in  alcohol;  not  more  soluble  in  dilute  acids  than  in 
water.  In  dilute  solutions,  this  precipitate  is  formed  only  after  some  time ;  the 
precipitation  is  promoted  by  agitation.  The  most  delicate  method  of  applying 
this  test  is  to  mix  the  solution  with  bichloride  of  platinum,  to  evaporate  to  dry- 
ness  upon  a  water-bath,  and  to  digest  the  residue  with  alcohol,  when  crystals  of 
the  double-salt  will  be  left  undissolved ;  the  addition  of  bichloride  of  platinum 
should  always  be  preceded  by  that  of  hydrochloric  acid,  to  convert  the  potassium 
into  chloride,  if  it  should  not  exist  already  in  that  form. 

TARTARIC  ACID,  in  rather  concentrated  solutions,  especially  on  agitating  vio- 
lently, a  white  crystalline  precipitate  of  Acid  Tartrate  (Bitartrate)  of  Potassa 
(KO.HO.T);  soluble  to  a  considerable  extent  in  water;  very  readily  soluble  in 
mineral  acids,  and  in  alkalies.  This  precipitate  is  generally  deposited  only  after 
some  time. 

BLOWPIPE. — Compounds  of  potassium,  heated  on  a  thin  platinum  wire,  in  the 
reducing  flame,  impart  a  violet  colour  to  the  outer  flame.  This  reaction  is  not 
visible  when  the  compound  contains  even  a  moderate  quantity  of  soda,  though, 
in  some  cases,  the  violet  flame  of  the  potassium  is  seen  for  an  instant  after  the 

1  In  the  first  group,  the  chlorides  may  always  be  used  to  exhibit  the  reactions. 


REACTIONS   OF   THE    SECOND   GROUP.  511 

yellow  colour  of  the  (more  easily  reducible)  sodium  has  disappeared.  Before 
applying  this  test,  the  operator  must  assure  himself  that  the  wire  itself  does  not 
impart  a  yellow  color  to  the  outer  flame.  (The  wire  must  be  repeatedly  washed 
with  distilled  water,  and  heated  in  the  inner  flame  until  it  no  longer  imparts  any 
color.) 

SODA,  NaO. 

If  a  solution  of  soda  be  mixed  with  excess  of  HYDROCHLORIC  ACID  and  BI-CHLO- 
RIDE  OF  PLATINUM,  and  gently  evaporated  in  a  watch-glass,  on  a  water-bath, 
radiated  needles  of  the  double  Chloride  of  Platinum  and  Sodium  (NaCl.PtCla) 
will  be  deposited. 

BLOWPIPE. — Compounds  containing  sodium,  when  exposed,  on  a  thin  (well- 
cleansed)  platinum  wire,  to  the  reducing-flame,  communicate  a  golden-yellow 
color  to  the  oxidizing  flame.  This  test  is  exceedingly  delicate,  permitting  the 
detection  of  the  least  trace  of  soda. 

There  exists  no  test  which  can  be  depended  upon  for  the  precipitation  of  small 
quantities  of  soda  in  solution. 

OXIDE  OP  AMMONIUM,  NH40. 

A  red  heat  always  volatilizes  oxide  of  ammonium,  in  whatever  form  of  combi- 
nation it  may  exist;  if  it  be  combined  with  a  fixed  acid  (as  phosphoric,  boracic, 
&c.),  the  latter  is  left  in  the  residue. 

HYDRATE  OF  LIME,  with  the  aid  of  a  gentle  heat,  evolves  ammonia  (NHS), 
which  may  be  recognized:  1,  by  its  pungent  odour,  2,  by  its  alkaline  reaction,  to 
moistened  test-papers,  and  3,  by  the  white  clouds  which  it  produces  on  the  ap- 
proach of  a  glass  rod,  moistened  with  moderately  dilute  hydrochloric  or  nitric  acid 
(diluted  to  the  point  at  which  they  cease  to  fume  in  the  air).  The  ammoniacal 
compound  (either  solid  or  dissolved)  should  be  stirred  in  a  small  dish,  with  dry 
hydrate  of  lime  and  a  little  water,  and  gently  heated  on  a  sand-bath. 

TARTARIC  ACID,  in  rather  concentrated  solutions,  a  white  crystalline  precipitate 
of  Acid  Tartrate  (Bitartrate)  of  Oxide  of  Ammonium  (NH4O.HO.T),  similar  in 
its  characters  to  the  bitartrate  of  potassa. 

BICHLORIDE  OF  PLATINUM;  a  light-yellow  crystalline  precipitate  of  the  double 
Chloride  of  Platinum  and  Ammonium  (NH4Cl.PtCla),  very  similar  in  its  re- 
actions to  the  corresponding  potassium-compound. 


§336.  SECOND  GROUP. 

Oxides  which  are  precipitated  from  their  solutions  as  carbonates  by  the  carbonates 

of  the  alkalies. 

BARYTA,  BaO.    STRONTIA,  SrO.    LIME,  CaO.    MAGNESIA,  MgO. 
BARYTA,  BaO. 

Solution  best  fitted  for  the  reactions :  Chloride  of  Barium,  BaCl. 

SESQUICARBONATE  OF  AMMONIA  ;  white  precipitate  of  Carbonate  of  Baryta 
(BaO.COs),  readily  soluble  in  hydrochloric  acid.  In  order  that  the  precipitation 
may  be  complete,  some  free  ammonia  should  be  added,  and  a  moderate  heat 
applied  to  the  solution,  to  decompose  any  (soluble)  bicarbonate  of  baryta  which 
might  be  formed. 

OXALATE  OF  AMMONIA  ;  white  precipitate  of  Oxalate  of  Baryta  (BaO.O), 
soluble  in  hydrochloric  acid. 

SULPHURIC  ACID  (dilute') ;  white  precipitate  of  Sulphate  of  Baryta  (BaO. 
S03)  (even  in  very  dilute  solutions)  insoluble  in  dilute  acids. 


REACTIONS   OP   THE   METALLIC   OXIDES. 

SULPHATE  OF  POTASS  A  gives  the  same  precipitate. 

SULPHATE  OF  LIME  also  gives  immediately  a  precipitate  of  Sulphate  of  Baryta. 

HYDROFLUOSILICIC  ACID;  a  white  precipitate  of  Silicofluoride  of  Barium 
(3BaF.2SiF3),  insoluble  in  dilute  acids;  this  precipitate  is  very  transparent, 
and  is  formed  only  after  some  time  in  dilute  solutions ;  in  order  to  separate 
baryta  completely  from  a  solution  by  this  reagent,  it  is  better  to  evaporate  to 
dryness,  and  to  treat  the  residue  with  strong  alcohol,  which  leaves  all  the  silicofluo- 
ride  of  barium  undissolved. 

PHOSPHATE  OF  SODA  ;  white  precipitate  of  Phosphate  of  Baryta  (2BaO.HO. 
P05),  soluble  in  hydrochloric  acid. 

BLOWPIPE. — Compounds  of  barium,  strongly  heated,  on  a  thin  platinum  wire, 
in  the  inner  flame,  impart  a  light  green  color  to  the  outer  flame ;  insoluble  com- 
pounds should  be  moistened  with  a  little  dilute  hydrochloric  acid  before  applying 
this  test. 

STRONTIA,  SrO. 
Solution  lest  fitted  for  the  reactions  :  Chloride  of  Strontium,  SrCl. 

SESQUICARBONATE  OF  AMMONIA  ;  the  same  reaction  as  in  the  case  of  baryta. 

OXALATE  OF  AMMONIA  }  same  as  with  baryta. 

SULPHURIC  ACID  (dilute) ;  white  precipitate  of  Sulphate  of  Strontia  (SrO. 
S03),  which,  being  somewhat  soluble  in  water,  is  not  formed  immediately  in  a 
dilute  solution ;  insoluble,  or  nearly  so,  in  dilute  acids. 

SULPHATE  OF  POTASSA  produces  the  same  precipitate  ;  if  a  solution  of  strontia 
be  mixed  with  an  excess  of  sulphate  of  potassa,  evaporated  to  dryness,  and  the 
residue  boiled  with  water,  the  latter  will  dissolve  so  little  sulphate  of  strontia, 
that  oxalic  acid  will  not  produce  a  precipitate  in  the  solution. 

SULPHATE  OF  LIME,  even  in  concentrated  solutions  of  strontia,  gives  a  precipi- 
tate only  after  standing  for  some  time  (varying  with  the  strength  of  the  solution 
of  strontia). 

PHOSPHATE  OF  SODA  ;  same  as  with  baryta. 

BLOWPIPE. — Compounds  of  strontium,  strongly  heated,  on  a  thin  platinum 
wire,  in  the  reducing  flame,  color  the  oxidizing -flame  most  intensely  carmine-red  ; 
insoluble  compounds  should  first  be  moistened  with  dilute  hydrochloric  acid. 

LIME,  CaO. 
Solution  best  fitted  for  the  reactions  :  Chloride  of  Calcium,  CaCl. 

SESQUICARBONATE  OF  AMMONIA;  a  white  precipitate  of  Carbonate  of  Lime 
(CaO.C03),  which  becomes  far  less  voluminous  on  heating  the  solution ;  some 
free  ammonia  should  be  added  in  this  reaction,  and  only  a  moderate  heat 
applied ;  for  if  the  solution  is  boiled,  the  ammoniacal  salt  may  decompose  the 
carbonate  of  lime,  reproducing  a  soluble  compound  of  that  base,  in  consequence 
of  the  great  volatility  of  the  carbonate  of  ammonia.  The  precipitate  dissolves 
very  readily  in  hydrochloric  acid. 

OXALATE  OF  AMMONIA;  white  precipitate  of  Oxalate  of  Lime  (CaO.O), 
soluble  in  hydrochloric  acid ;  this  precipitate  being  produced  even  in  very  dilute 
solutions,  especially  if  a  little  free  ammonia  be  added,  oxalate  of  ammonia  be- 
comes a  very  delicate  test  for  lime,  but  will  not  serve  to  distinguish  it  from 
baryta  and  strontia. 

SULPHURIC  ACID  (dilute),  only  in  concentrated  solutions,  a  white  precipitate 
of  Sulphate  of  Lime  (CaO.S03),  soluble  in  much  water. 

SULPHATE  OF  POTASSA,  a  precipitate  only  in  concentrated  solutions;  if  a 
solution  containing  lime  be  mixed  with  an  excess  of  sulphate  of  potassa,  evapo- 
rated to  dryness,  and  the  residue  boiled  with  water,  so  much  sulphate  of  lime  is 
dissolved  that  the  solution  gives  a  precipitate  with  oxalic  acid. 


THIRD   GROUP.  513 

PHOSPHATE  OP  SODA  ;  white  gelatinous  precipitate  of  Phosphate  of  Lime  (2 
CaO.HO.P05),  soluble  in  dilute  acids. 

BLOWPIPE. — Compounds  of  lime,  heated  on  a  thin  platinum  wire,  in  the 
inner  flame,  impart  an  orange-red  color  to  the  outer  flame, ;  insoluble  compounds 
of  lime  should  be  moistened  with  dilute,  hydrochloric  acid. 

MAGNESIA,  MgO. 
Solution  best  fitted  for  the  reactions:  Sulphate  of  Magnesia,  MgO.S08. 

SESQUICARBONATE  OF  AMMONIA;  no  precipitate  in  the  cold,  but,  on  boiling, 
a  white  precipitate  of  Basic  Carbonate  of  Magnesia,  which  contains  only  part  of 
the  magnesia,  the  remainder  existing  in  solution  as  a  double-salt  of  magnesia 
and  oxide  of  ammonium.  The  precipitate  dissolves  readily  in  chloride  of  ammo- 
nium, so  that  the  addition  of  this  salt  to  the  magnesia-solution  would  prevent 
the  production  of  a  precipitate. 

AMMONIA;  white  precipitate  of  Hydrate  of  Magnesia  (MgO.HO)  which  con- 
tains only  half  of  the  magnesia  present ;  for 

2(MgO.S03)-fNH3+2HO~MgO.HO+MgO.S03,NH4O.S03. 

Hydrate  of  magnesia  is  soluble  in  chloride  of  ammonium,  so  that  ammonia 
produces  no  precipitate  in  a  solution  of  magnesia  containing  chloride  of 
ammonium. 

POTASSA;  white  precipitate  of  Hydrate  of  Magnesia,  insoluble  in  excess. 

BARYTA  precipitates  the  whole  of  the  magnesia  in  the  same  form,  provided 
the  solution  be  free  from  ammoniacal  salts. 

CHLORIDE  OP* AMMONIUM,  AMMONIA,  AND  PHOSPHATE  OP  SODA,  produce, 
even  in  very  dilute  solutions,  a  white,  highly  crystalline  precipitate  of  Phosphate 
of  Magnesia  and  Oxide  of  Ammonium  (2MgO.NH4O.P05) ;  slightly  soluble  in 
water,  less  so  in  solution  of  ammonia,  and  readily  soluble  in  dilute  acids.  In 
dilute  solutions,  the  precipitate  is  only  deposited  after  some  time;  its  formation 
is  much  promoted  by  violent  agitation. 

BLOWPIPE. — Solid  compounds  of  magnesia,  strongly  heated  on  charcoal,  leave 
a  white,  infusible,  highly  incandescent  mass  ;  if  this  be  moistened  with  nitrate  of 
cobalt,  and  again  strongly  heated,  a  pale  rose-colored  compound  is  produced,  the 
color  of  which  is  more  visible  on  cooling. 


THIRD   GROUP. 

§  337.  Oxides,  the  solutions  of  which  are  not  precipitated  by  Hydrochloric  or 
Hydrosulphuric  Acid,  but  which  are  precipitated,  either  as  hydrates  or  as  sulphides, 
by  Sulphide  of  Ammonium  in  the  presence  of  Chloride  of  Ammonium  and  Am- 
monia. 

ALUMINA  (A1303)  OXIDE  OP  COBALT  (CoO) 

SESQUIOXIDE  OF  CHROMIUM  (Cra03)  OXIDE  OF  NICKEL  (NiO) 

SESQUIOXIDE  OF  IRON  (Fe203)  OXIDE  OF  MANGANESE  (MnO) 

OXIDE  OF  IRON  (FeO)  OXIDE  OF  ZINC  (ZnO) 

ALUMINA,  Ala03. 
Solution  best  fitted  for  the  reactions :  Alum,  A1203,3S03.KO,S03. 

AMMONIA,  even  in  presence  of  chloride  of  ammonium ;  a  very  gelatinous, 

semi-transparent  precipitate  of  Hydrate  of  Alumina;  more  visible  when  tke 

liquid  is  heated ;  slightly  soluble  in  excess  of  ammonia,  and  reprecipitated  on 

boiling  (this  solution  in  excess  does  not  take  place  if  a  sufficient  quantity  of 

83 


514  REACTIONS    OF   THE   METALLIC   OXIDES. 

chloride  of  ammonium  be  present) ;  soluble  in  hydrochloric  acid  (though  with 
some  difficulty,  unless  freshly  precipitated).  The  presence  of  fixed  organic  mat- 
ters (sugar,  tartaric  acid,  &c.)  interferes  with  the  precipitation. 

SULPHIDE  OF  AMMONIUM  ;  the  same  precipitate  of  Hydrate  of  Alumina, 
hydrosulphuric  acid  being  evolved. 

POTASSA  ',  a  similar  precipitate  of  Hydrate  of  Alumina;  readily  soluble  in  an 
excess;  completely  reprecipitated  by  adding  an  excess  of  acid,  and  subsequently 
excess  of  ammonia.  SILICATE  OF  POTASSA  also  precipitates  the  whole  of  the 
alumina  from  this  solution,  in  the  form  of  Silicate  of  Alumina,  which  is  insolu- 
ble in  potassa. 

PHOSPHATE  OF  SODA,  a  white  precipitate  of  Phosphate  of  Alumina  ;  soluble 
in  strong  mineral  acids,  and  reprecipitated  by  ammonia  ;  insoluble  (or  nearly  so) 
in  acetic  acid ;  readily  soluble  in  potassa,  and  reprecipitated  by  an  excess  of 
acetic  acid;  if  silicate  of  potassa  be  added  to  the  alkaline  solution  of  phosphate 
of  alumina,  the  alumina  is  precipitated,  the  phosphoric  acid  remaining  in  solution. 

BLOWPIPE. — Solid  compounds  of  alumina  strongly  heated  on  charcoal  leave 
a  white,  infusible,  and  highly  incandescent  residue ;  if  this  be  moistened  with 
solution  of  nitrate  of  cobalt,  and  again  strongly  heated,  it  furnishes  a  blue  mass; 
this  behavior,  however,  is  not  characteristic  of  alumina,  since  some  other  sub- 
stances (especially  phosphates)  exhibit  the  same  reaction. 

SESQUIOXIDE  OF  CHROMIUM,  Cr303. 
Solution  best  fitted  for  the  reactions:  Sesquichloride  of  Chromium,  CraCl3. 

AMMONIA,  even  in  presence  of  chloride  of  ammonium',  a  gfeenish-blue  preci- 
pitate of  Hydrated  Sesquioxide  of  Chromium;  slightly  soluble  in  an  excess, 
forming  a  pink  solution,  from  which  the  sesquioxide  is  reprecipitated  by  boiling ; 
readily  soluble  in  acids.  The  presence  of  fixed  organic  matters  interferes  with 
the  precipitation. 

SULPHIDE  OF  AMMONIUM  ;  the  same  precipitate  of  Hydrate,  sulphuretted 
hydrogen  being  evolved. 

POTASSA  ;  a  precipitate  of  Hydrated  Sesquioxide,  readily  soluble  in  excess  ; 
reprecipitated  entirely  by  boiling,  provided  no  fixed  organic  matters  be  present ; 
if  a  very  large  excess  of  potassa  be  employed,  prolonged  ebullition  is  necessary 
to  reprecipitate  the  sesquioxide.  When  mixed  with  a  considerable  quantity  of 
sesquioxide  of  iron,  the  sesquioxide  of  chromium  is  not  dissolved  by  an  excess  of 
potassa. 

Solid  compounds  containing  chromium,  when  fused  (on  platinum-foil)  with 
nitrate  of  potassa  and  a  little  carbonate  of  soda  (the  blowpipe-flame  being  directed 
upon  the  under  surface  of  the  foil),  yield  a  yellow  mass  of  Alkaline  Chromate 
(NaO.dOg)  which  may  be  dissolved  in  water,  and  tested  for  Chromic  Acid,  by 
adding  excess  of  acetic  acid  and  acetate >  of  lead,  which  gives  a  yellow  precipitate 
of  Chromate  of  Lead.  This  test  is  applicable  under  all  circumstances,  and  per- 
mits the  detection  of  very  small  quantities  of  chromium. 

BLOWPIPE. — Sesquioxide  of  chromium,  fused  with  a  bead  of  borax,  in  the 
inner  flame,  yields  a  yellowish-green  glass,  which  assumes  a  bright  emerald-green 
color  in  the  outer  flame. 

SESQUIOXIDE  OF  IRON,  Fe203. 
Solution  best  fitted  for  the  reactions:  Sesquichloride  of  Iron,  Fe3Cl3. 

AMMONIA,  even  in  the  presence  of  chloride  of  ammonium ;  a  reddish-brown, 
flocculent  precipitate  of  Hydrated  Sesquioxide  of  Iron,  insoluble  in  excess ;  readily 
soluble  in  hydrochloric  acid;  the  presence  of  fixed  organic  matters  (tartaric  acid, 
&G.)  prevents  the  precipitation. 

HYDROSULPHURIC  ACID,  in  solutions  of  compounds  of  sesquioxide  of  iron  with 


.9;  THIRD   GROUP.  515 

mineral  acids  (as  well  as  in  sesquichloride  of  iron),  a  white  precipitate  of  Sul- 
phur, the  hydrogen  of  the  hydrosulphuric  acid  serving  to  reduce  the  sesqui-eom- 
pound  of  iron  to  a  ^?roto-compound.  In  a  solution  of  a  compound  of  sesquioxide 
of  iron  with  a  weak  acid,  as  in  acetate  of  sesquioxide  of  iron  (or  sesquichloride 
of  iron  mixed  with  excess  of  acetate  of  potassa),  hydrosulphuric  acid  not  only 
reduces  the  sesquioxide  to  oxide,  with  separation  of  Sulphur,  but  precipitates  the 
whole  of  the  iron  as  black  sulphide  (FeS)  provided  there  be  not  too  great  an 
excess  of  free  organic  acid  present. 

SULPHIDE  OF  AMMONIUM  ;  a  black  precipitate  of  Sulphide  of  Iron  (FeS), 
mixed  with  Sulphur, 

FeaCl3-f  3NH4S=3NH4Cl+2FeS-f-S ; 

soluble  with  difficulty  in  acetic  acid;  readily  dissolved  by  mineral  acids.  When 
the  quantity  of  this  precipitate  is  very  small,  it  has  a  greenish  tinge.  In  solu- 
tions containing  much  fixed  organic  matter  (tartaric  acid,  &c.),  the  precipitate 
appears  to  be  partly  dissolved  by  an  excess  of  sulphide  of  ammonium,  imparting 
a  dark  green  color  to  the  liquid,  but  the  precipitation  is  complete  on  boiling. 

POTASSA;  the  red-brown  precipitate  of  Hydrate;  insoluble  in  excess;1  readily 
soluble  in  acids.  Fixed  organic  matters  prevent  the  precipitation. 

ACETATE  OF  POTASSA  ;  a  fine  red  liquid,  due  to  the  formation  of  Acetate  of 
Sesquioxide  of  Iron  (Fe203.3A). 

FERROCYANIDE  OF  POTASSIUM  ;  a  dark  blue  precipitate  (Prussian  Blue,  Fe4 
Cfy3)  of  Sesqui/errocyanide  of  Iron;  insoluble  in  acids  (except  oxalic);  de- 
composed by  alkalies.  This  is  an  exceedingly  delicate  test  for  sesquioxide  of 
iron ;  in  very  dilute  solutions,  merely  a  blue  tinge  is  produced,  and  after  long 
standing,  a  blue  precipitate  is  formed  at  the  bottom  of  the  vessel.  It  is  always 
advisable  to  acidify  solutions  with  acetic  acid  before  applying  this  test ;  should 
a  free  mineral  acid  be  present,  the  addition  of  ferrocyanide  of  potassium  should 
be  preceded  by  that  of  an  excess  of  acetate  of  potassa,  in  order  to  substitute  free 
acetic  acid  for  the  mineral  acid,  which  would  decompose  the  ferrocyanide  of  po- 
tassium, giving  rise  to  a  blue  color. 

FERRICYANIDE  OF  POTASSIUM  produces  merely  a  dark  brown  color. 

SULPHOCYANIDE  OF  POTASSIUM  gives  a  deep  blood-red  color  (due  to  Sesqui- 
sulphocyanide  of  Iron,  Fe2Csys)  which  disappears  on  the  addition  of  alkalies  or 
of  a  large  excess  of  a  strong  acid.  This  test  detects  very  small  quantities  of 
sesquioxide  of  iron,  and  may  be  applied  to  moderately  acid  solutions. 

BLOWPIPE. — Compounds  containing  iron,  when  fused  with  a  bead  of  borax, 
upon  platinum  wire,  yield,  in  the  oxidizing  /lame,  a  brownish-red  glass,  which 
assumes  a  dirty  (bottle-)  green  color  in  the  inner  flame,  from  the  reduction  of  the 
sesquioxide  of  iron  to  the  magnetic  (proto-sesqui)  oxide  (Fe304). 

OXIDE  OF  IRON,  FeO. 
Solution  best  fitted  for  reactions:  Sulphate  of  Oxide  of  Iron,  FeO.S03.a 

HYDROSULPHURIC  ACID  gives  no  precipitate  even  in  neutral  solutions  of  the 
salts  of  oxide  of  iron  with  the  strong  (mineral)  acids,  but  in  those  with  weak 
(organic)  acids,  it  produces  a  black  precipitate  of  Sulphide  of  Iron  (FeS) ;  the 
whole  of  the  iron  may  be  precipitated  in  this  way,  if  there  be  not  too  great  an 
excess  of  the  organic  acid.  The  characters  of  this  precipitate  have  been  already 
given  (see  above).  From  alkaline  solutions,  hydrosulphuric  acid  also  throws 
down  the  whole  of  the  iron. 

1  If  much  sesquioxide  of  chromium  be  present,  considerable  quantities  of  sesquioxide 
of  iron  may  be  dissolved  by  the  potassa. 

2  The  solution  should  be  freshly  prepared  for  each  experiment,  as  it  absorbs  oxygen  so 
rapidly  when  exposed  to  the  air. 


516  REACTIONS    OF   THE    METALLIC   OXIDES. 

SULPHIDE  OF  AMMONIUM  ;  a  black  precipitate  of  Sulphide  of  Iron  (FeS). 
The  remarks  made  at  p.  515  hold  good  also  in  this  case. 

AMMONIA;  a  light-colored  precipitate  of  Hydrated  Oxide  of  Iron  (FeO.HO) 
which  rapidly  absorbs  oxygen  from  the  air,  passing,  first,  into  the  dirty-green 
Magnetic  Oxide,  and  ultimately  into  red-brown  Sesquioxide  of  Iron  ;  the  pre- 
cipitate at  first  produced  contains  only  half  the  iron  present,  the  remainder  exist- 
ing in  solution  as  a  double-salt  of  Oxide  of  Iron  and  Oxide  of  Ammonium:  — 

2(FeO.SOs)+NH3+2HO=FeO.H04-FeO.S03,NH4O.S03; 

but  when  the  supernatant  liquid  (containing  excess  of  ammonia)  is  exposed  to 
air,  it  absorbs  oxygen,  and  deposits  the  whole  of  the  iron  in  the  form  of  Sesqui- 
oxide. 

If  chloride  of  ammonium  (or  other  ammoniacal  salt)  be  added  to  the  solution 
of  oxide  of  iron,1  ammonia  will  not  produce  any  precipitate  in  it,  but  the  solu- 
tion, when  exposed  to  the  air,  absorbs  oxygen,  and  deposits  the  sesquioxide. 

POTASSA  ;  the  same  precipitate  of  Hydrated  Protoxide,  which  rapidly  absorbs 
oxygen. 

NITRIC  ACID,  added  to  a  cold  solution  of  oxide  of  iron,  produces  a  transient 
brown  color,  due  to  a  compound  of  the  iron-salt  with  binoxide  of  nitrogen  (see  p. 
341);  the  brown  color  disappears  on  heating,  giving  place  to  a  yellow,  the  whole 
of  the  iron  being  converted  into  sesquioxide. 

FERROCYANIDE  OF  POTASSIUM  ;  a  light  blue  (said  to  be  white  when  abso- 
lutely pure)  precipitate  of  a  Double  Ferrocyanide  of  Potassium  and  Iron  [KFe, 


03)  +  K3Cfy=2KFe3Cfy3+3(KO.S03); 
this  precipitate  is  insoluble  in  dilute  acids,  and  eagerly  absorbs  oxygen  from  the 
air,  being  converted  into  a  mixture  of  Prussian  blue  and  oxide  of  iron  (which  is 
dissolved  by  the  free  acid  if  any  be  present)  :  — 

3KFe3Cfy3+  04=3KO+  FeO-f  2Fe4Cfy3  ; 

this  reaction  is  visible  even  in  very  dilute  solutions;  free  alkalies  prevent  the 
formation  of  a  precipitate. 

FERRICYANIDE  OF  POTASSIUM  ;  a  dark  blue  precipitate  of  Ferricyanide  of 
Iron  (Fe3Cfdy)  ;  insoluble  in  dilute  acids;  decomposed  by  alkalies;  the  same 
remarks  hold  good  with  regard  to  the  delicacy  of  this  test  and  to  the  precautions 
necessary  in  its  application,  as  were  made  respecting  the  ferrocyanide  of  potas- 
sium as  a  test  for  sesquioxide  of  iron  (see  p.  515).  This  test  serves  to  distin- 
guish the  two  oxides  of  iron. 

BLOWPIPE.  —  Compounds  of  oxide  of  iron  may  be  tested  before  the  blowpipe 
in  the  same  way  as  those  of  the  sesquioxide. 

OXIDE  OF  COBALT,  CoO. 
Solution  best  fitted  for  the  reactions:  Nitrate  of  Cobalt,  CoO.N05. 

SULPHIDE  OF  AMMONIUM  ;  a  black  precipitate  of  Sulphide  of  Cobalt  (CoS)  ; 
very  sparingly  soluble  in  hydrochloric  acid,  soluble  in  nitric  acid. 

AMMONIA;  a  bluish-precipitate  of  a  Basic  Salt  of  Cobalt  (this  precipitate 
contains  only  part  of  the  oxide,  the  rest  remaining  in  solution  as  a  double-salt, 
with  the  salt  of  oxide  of  ammonium  produced  in  the  reaction)  ;  readily  soluble 
in  excess  of  ammonia,  forming  a  reddish-brown  solution  which  becomes  deeper  in 
color  (from  absorption  of  oxygen)  when  exposed  to  air. 

If  the  solution  contain  a  sufficient  quantity  of  an  ammoniacal  salt  (or  a  free 
acid),  it  is  not  precipitated  by  ammonia. 

1  Or  if  the  solution  contain  any  free  acid,  which  will  produce  an  ammoniacal  salt,  upon 
addition  of  ammonia. 


THIRD    GROUP.  517 

SESQUICARBONATE  OF  AMMONIA  ;  a  pink  precipitate  of  Carbonate  of  Cobalt 
(CoO.C03)  readily  soluble  in  excess,  forming  a  red  solution.  The  presence  of 
ammoniacal  salts  prevents  the  precipitation. 

POTASSA  ;  a  blue  precipitate  of  a  Basic  Salt  of  Cobalt  which,  when  boiled  with 
the  liquid,  assumes  a  brownish-red  color,  being  converted  into  the  Hydrated  Oxide 
of  Cobalt  (CoO,HO),  insoluble  in  excess  of  potassa,  readily  soluble  in  acids.  If 
ammoniacal  salts  be  present  in  the  solution,  potassa  produces  no  precipitate, 
until  the  solution  is  boiled,  when,  the  ammonia  being  expelled,  the  whole  of  the 
oxide  of  cobalt  is  precipitated. 

CYANIDE  OF  POTASSIUM  ;  a  brownish  precipitate  of  Cyanide  of  Cobalt  (CoCy); 
readily  soluble  in  excess,  being  converted  (completely  if  the  solution  be  boiled) 
into  Cobalticyanide  of  Potassium  (K3Co3Cyfi=K3Cocy);  dilute  acids  produce  no 
precipitate  in  this  solution,  since  the  Hydrocobalticyanic  Acid  (H3Cocy)  which 
is  separated,  is  perfectly  soluble  in  water.  If  the  solution  of  cobalticyanide  of 
potassium  be  strongly  acidulated  with  nitric  acid  (which  decomposes  the  excess 
of  cyanide  of  potassium,  producing  a  certain  quantity  of  nitrate  of  potassa), 
evaporated  to  dryness,  and  the  residue  fused  for  some  minutes  over  a  lamp,  the 
cobalticyanide  is  oxidized  and  decomposed;  on  washing  the  fused  mass  with  hot 
water,  the  black  Oxide  of  Cobalt  is  left,  and  may  be  tested  before  the  blowpipe. 

BLOWPIPE. — Compounds  of  cobalt,  fused  with  a  borax-bead  in  either  flame, 
produce  a  beautiful  blue  glass;  the  cobalt  must  be  employed  in  very  small  pro- 
portion. 

OXIDE  OF  NICKEL,  NiO. 
Solutions  best  fitted  for  the  reactions:  Sulphate  of  Nickel,  NiO.S03. 

SULPHIDE  OF  AMMONIUM  ;  a  black  precipitate  of  Sulphide  of  Nickel  (NiS) ; 
insoluble  in  colorless  sulphide  of  ammonium,  but  soluble  to  some  extent  in  the 
ordinary  yellow  sulphide,  which  contains  an  excess  of  sulphur,  forming  a  dark 
dirty-brown  solution,  which  deposits  the  whole  of  the  sulphide  of  nickel  when 
evaporated.  Sulphide  of  nickel  is  very  sparingly  soluble  in  hydrochloric  acid, 
but  readily  in  nitric  acid. 

AMMONIA  ;  a  light  green  precipitate  of  Hydrated  Oxide  of  Nickel  (NiO. HO), 
readily  soluble  in  excess,  forming  a  purplish-blue  solution  ;  this  precipitate,  how- 
ever, as  in  the  case  of  cobalt,  contains  only  part  of  the  nickel.  In  solutions  of 
oxide  of  nickel,  which  contain  much  ammoniacal  salt  or  free  acid,  ammonia  pro- 
duces no  precipitate. 

SESQUICARBONATE  OF  AMMONIA;  a  light  green  precipitate  of  Carbonate  of 
Nickel  (NiO.C02)  soluble  in  excess,  to  a  blue  liquid.  The  presence  of  ammo- 
niacal salt  (or  free  acid)  prevents  the  precipitation. 

POTASSA  ;  an  apple-green  precipitate  of  Hydrated  Oxide  of  Nickel ;  insoluble 
in  excess ;  readily  soluble  in  acids.  The  presence  of  ammoniacal  salts  inter- 
feres to  some  extent  with  this  precipitation  ;  and  it  is  necessary  to  boil  with  excess 
of  potassa,  until  all  ammonia  is  expelled,  in  order  to  separate  the  oxide  of  nickel 
completely. 

CYANIDE  OF  POTASSIUM  ;  a  yellowish-green  precipitate  of  Cyanide  of  Nickel 
(NiCy) ;  soluble  in  excess,  forming  a  double  Cyanide  of  Nickel  and  Potassium 
(NiCy,KCy),  from  which  acids  reprecipitate  the  cyanide  of  nickel ;  this  latter 
is  decomposed  by  boiling  with  potassa,  cyanide  of  potassium  being  formed,  whilst 
Oxide  of  Nickel  is  left  undissolved. 

BLOWPIPE. — Compounds  of  nickel,  fused  with  a  borax-bead,  in  the  outer  flame, 
yield  a  sherry-red  glass,  which  readily  changes  in  the  inner  flame  into  a  glass 
which  has  &  purplish- gray  color  when  it  contains  very  little  nickel,  and  a  dusky, 
turbid,  gray,  brown,  or  black  hue  when  the  amount  of  nickel  is  more  consider- 
able; if  a  minute  fragment  of  nitre  be  added  to  the  bead  after  exposure  to  the 


518  REACTIONS    OP   THE    METALLIC    OXIDES. 

inner  flame,  and  the  glass  again  fused  in  the  outer  flame,  it  acquires  a  rich  purple 
color.  Owing  to  the  difficulty  which  they  find  in  producing  a  well-defined  flame, 
inexperienced  operators  generally  obtain  a  grayish  bead  with  nickel-compounds, 
even  in  the  outer  flame. 

OXIDE  OF  MANGANESE,  MnO. 
Solution  best  fitted  for  the  reactions:  Sulphate  of  Manganese,  MnO.S03. 

SULPHIDE  OF  AMMONIUM  ;  a  flesh-colored  (buff)  precipitate  of  Sulphide  of 
Manganese  (MnS)  ;  soluble  in  hydrochloric  or  nitric  acid. 

AMMONIA  ;  a  white  precipitate  of  Hydrated  Oxide  of  Manganese,  which  be- 
comes brown  almost  immediately  from  absorption  of  oxygen  from  the  air,  and 
formation  of  a  higher  oxide;  the  precipitate  only  contains  part  of  the  manganese, 
the  remainder  being  left  in  solution  as  an  ammoniacal  double-salt ;  the  precipi- 
tate is  insoluble  in  excess  of  ammonia. 

No  precipitate  is  produced  by  ammonia  in  solutions  of  manganese  which  con- 
tain much  free  acid  or  ammoniacal  salt;  but  when  the  ammoniacal  liquid  is 
exposed  to  the  air,  it  absorbs  oxygen,  and  deposits  brown  flocks  of  Hydrated 
Binoxide  of  Manganese.  f.v 

SESQUICARBONATE  OF  AMMONIA  ;  a  white  precipitate  of  Carbonate  of  Manga- 
nese (MnO.COJ,  almost  insoluble  in  excess  (especially  on  boiling). 

POTASSA  ;  a  white  precipitate  of  Hydrated  Oxide  of  Manganese,  rapidly  be- 
coming brown  when  exposed  to  the  air;  insoluble  in  excess  of  potassa;  readily 
soluble  in  acids. 

The  presence  of  ammoniacal  salts  in  great  measure  prevents  the  precipitation. 

Solid  compounds  of  manganese,  fused  with  carbonate  of  soda  and  a  little  nitre 
on  platinum-foil,  yield  a  fine  green  mass  (blue  on  cooling)  of  Manganate  of  Soda; 
by  this  test,  the  very  smallest  quantities  of  manganese  may  be  detected.  When 
very  small  quantities  of  material  are  to  be  tested,  the  experiment  is  conveniently 
made  upon  a  loop  of  platinum-wire,  which  is  moistened  and  dipped  in  powdered 
carbonate  of  soda  ;  the  latter  is  fused  into  a  bead,  a  little  of  the  substance  taken 
upon  it,  and  then  a  minute  fragment  of  nitre;  on  fusing  the  bead  in  the  outer 
blowpipe  flame,  the  green  color  will  be  produced;  if  it  be  exposed  to  the  inner 
flame,  however,  the  color  vanishes. 

BLOWPIPE. — Compounds  of  manganese,  when  fused  with  a  borax-bead  in  the 
outer  flame,  impart  a  beautiful  violet-red  color  to  the  glass,  which  gradually 
fades  in  the  inner  flame,  ultimately  disappearing  altogether. 

OXIDE  OF  ZINC,  ZnO. 
Solution  best  fitted  for  the  reactions:  Sulphate  of  Zinc,  ZnO.S03. 

SULPHIDE  OF  AMMONIUM;  a  white  precipitate  of  Sulphide  of  Zinc  (ZnS); 
soluble  in  hydrochloric  or  nitric  acid. 

AMMONIA;  a  white  precipitate  of  Hydrated  Oxide  of 'Zinc ,  readily  soluble  in 
excess.  The  precipitate,  in  this  case,  does  not  contain  the  whole  of  the  zinc. 
Ammoniacal  salts  prevent  the  precipitation. 

SESQUICARBONATE  OF  AMMONIA  ;  a  white  precipitate  of  Basic  Carbonate  of 
Zinc,  soluble  in  excess.  Ammoniacal  salts  prevent  the  precipitation. 

POTASSA  ;  a  white  precipitate  of  Hydrated  Oxide  of  Zinc,  readily  dissolved 
by  an  excess;  hydrosulpfiuric  acid,  added  to  the  alkaline  solution,  produces  a 
white  precipitate  of  Sulphide  of  Zinc. 

•  BLOWPIPE. — Solid  compounds  of  zinc,  exposed  on  charcoal  to  the  inner  blow- 
pipe flame,  yield  a  highly  incandescent  mass,  which  is  yellow  while  hot,  and 
becomes  white  on  cooling;  if  this  mass  be  moistened  with  solution  of  nitrate  of 
cobalt,  and  again  strongly  heated,  a  fine  green  compound  is  produced. 


FOURTH   GROUP.    ; />  519 

Solid  compounds  of  zinc,  fused  with  carbonate  of  soda  on  charcoal,  in  the 
reducing  flame,  give  an  incrustation  of  Oxide  of  ZinCj  which  is  yellow  while  hot, 
and  becomes  white  upon  cooling. 


§  338.  FOURTH  GROUP. 

Oxides ,  the  sulphides  corresponding  to  which  are  insoluble  in  cold  dilute  mineral 
acids.  « 

OXIDE  OF  LEAD  (PbO).1 

OXIDE  OF  MERCURY  (HgO)  TEROXIDE  OF  BISMUTH  (Bi03) 

OXIDE  OF  COPPER  (CuO)  OXIDE  OF  CADMIUM  (CdO) 

TEROXTDE  OF  GOLD  (Au03)  BINOXIDE  OF  PLATINUM  (PtOa) 

OXIDE  OF  TIN  (SnO)  BINOXIDE  OF  TIN  (Sn03) 

TEROXIDE  OF  ANTIMONY  (SbOJ  ANTIMONIC  ACID  (Sb05) 

ARSENIOUS  ACID  (AsOa)  ARSENIC  ACID  (As05). 

OXIDE  OF  MERCURY  (HgO). 
Solution  best  fitted  for  the  reactions :  Chloride  of  Mercury,  HgCl. 

HYDROSULPHURIC  ACID,  when  added  in  small  quantity,  a  white  or  yellow 
precipitate,  which  is  a  Compound  of  Sulphide  of  Mercury  with  the  undecomposed 
Salt  (see  p.  465) ;  an  excess  of  the  reagent  converts  this  precipitate  into  black 
Sulphide  of  Mercury  (HgS)  ;  insoluble  in  dilute  sulphuric,  hydrochloric,  or  nitric 
acid  alone,  but  readily  soluble  in  a  mixture  of  hydrochloric  and  nitric  acids  with 
the  aid  of  heat;  soluble  to  a  very  slight  extent  in  the  sulphides  of  potassium 
and  ammonium;  dissolved  in  some  measure  by  hot  concentrated  hydrochloric 
acid;  converted  into  a  white  compound,  but  not  dissolved  to  any  extent,  by 
boiling  with  concentrated  nitric  acid. 

POTASSA;  in  small  quantity,  a  brownish  precipitate,  which  is  a  basic  com- 
pound, and  is  converted  into  yellow  Hydrated  Oxide  of  Mercury  when  treated 
with  an  excess  ofpotassa. 

AMMONIA;  a  white  precipitate  (see  p.  462)  soluble  to  some  extent  in  an 
excess,  especially  in  the  presence  of  ammoniacal  salts. 

METALLIC  COPPER,  introduced  into  a  solution  of  mercury,  especially  after 
acidification  with  hydrochloric  acid,  becomes  covered  with  a  white,  lustrous 
coating ;  when  moderately  heated,  the  copper  regains  its  original  color,  vapors  of 
mercury  being  evolved ;  this  test  is  exceedingly  delicate ;  slips  of  copper  wire, 
about  an  inch  in  length,  may  be  used ;  they  should  be  cleaned  by  shaking  for  a 
few  moments  with  concentrated  nitric  acid,  and  thoroughly  washed  ;  half  a  dozen 
such  slips  should  be  boiled  for  three  or  four  minutes  in  the  solution,  previously 
acidulated  with  hydrochloric  acid;  they  are  then  well  rinsed,  dried  by  pressure 
between  blotting-paper,  and  heated  in  a  glass  tube  of  }  inch  diameter,  constructed 
so  as  to  allow  the  passage  of  a  feeble  current  of  air;  a  coating  of  minute  Globules 
of  Mercury  is  formed  upon  the  cool  part  of  the  tube ;  these  may  be  united  into 
larger  globules  by  rubbing  with  a  glass  rod. 

CHLORIDE  OF  TIN  (SnCl)  added  in  small  quantity  to  a  solution  of  oxide  of 
mercury,  produces  a  white  precipitate  of  Subchloride  (Hg3Cl)  which  becomes 
gray,  from  reduction  to  the  metallic  state,  on  adding  an  excess  of  the  reagent. 

Solid  compounds  of  mercury,  mixed  with  a  large  excess  (at  least  1*2  parts)  of 

1  The  reactions  of  this  oxide  are  given  in  the  fifth  group,  to  which  it  more  properly 
belongs. 


520  REACTIONS   OF   THE   METALLIC   OXIDES. 

dry  carbonate  of  soda,  and  heated  in  a  perfectly  dry  tube  of  hard  glass,  having 
a  diameter  of  about  \  inch,  and  expanded  into  a  bulb  at  one  end,  furnish  minute 
globules  of  Metallic  Mercury  which  are  deposited  on  the  cool  part  of  the  tube, 
and  may  be  united  into  larger  globules  by  rubbing  with  a  glass  rod.  This  test 
is  exceedingly  delicate;  in  order  that  it  may  be  perfectly  successful,  the  mercury- 
compound  should  be  thoroughly  dried  (in  a  water-bath),  and  the  carbonate  of 
soda  should  be  ignited  immediately  previous  to  use;  in  order  to  prevent  the  sub- 
limation of  undecomposed  mercury-compounds,  it  is  well  to  cover  the  mixture  in 
the  bulb-tube  with  a  layer  of  pure  carbonate  of  soda. 

TEROXIDE  OP  BISMUTH,  Bi03. 

Solution  best  fitted  for  the  reactions:  Nitrate  of  Teroxide  of  Bismuth, 

Bi03.3N05. 

HYDROSULPHURIC  ACID  ;  a  black  precipitate  of  Tersulphide  of  Bismuth  (BiS3)  ; 
insoluble  in  cold  dilute  acids  and  in  alkaline  sulphides;  soluble  in  hot  dilute  nitric 
acid. 

WATER,  added  in  large  quantity  to  the  salts  of  bismuth,  decomposes  them, 
with  precipitation  of  a  white  basic  salt;  the  terchloride  exhibits  this  behavior  in 
the  most  striking  manner,  provided  too  large  an  excess  of  free  acid  be  not  pre- 
sent; in  order  to  apply  this  test  to  any  compound  of  bismuth  (except  the  sul- 
phate), an  excess  of  hydrochloric  acid  is  added,  the  solution  evaporated  just  to 
dryness,  the  residue  allowed  to  cool,  redissolved  in  a  little  water  with  addition  of 
a  single  drop  of  hydrochloric  acid,  and  the  clear  liquid  largely  diluted  with  water, 
when  a  milkiness  is  produced,  caused  by  the  minute  particles  of  a  highly  crys- 
talline precipitate  (see  p.  391),  which  subsides  after  some  time.  In  order  to 
test  the  sulphate  of  teroxide  of  bismuth  (which  is  not  decomposed  by  hydro- 
chloric acid)  in  this  manner,  it  must  first  be  decomposed  with  ammonia  in 
excess,  and  the  precipitated  teroxide  having  been  dissolved  in  nitric  or  hydro- 
chloric acid,  the  solution  may  be  treated  as  above.  This  is  an  exceedingly 
delicate  and  characteristic  test  for  bismuth. 

AMMONIA;  a  white  precipitate  of  Hydrated  Teroxide  of  Bismuth;  insoluble 
in  excess ;  soluble  in  dilute  acids. 

CHROMATE  OR  BICHROMATE  OF  POTASSA;  a  yellow  precipitate  of  Chromate 
of  Teroxide  of  Bismuth,  readily  soluble  in  dilute  nitric  acid. 

BLOWPIPE. — Solid  compounds  of  bismuth,  fused  with  carbonate  of  soda,  on 
charcoal,  in  the  reducing  flame,  yield  a  Globule  of  Metal,  which  is  flattened  by 
the  first  stroke  of  the  hammer,  but  soon  breaks  in  pieces,  especially  if  slightly 
rubbed ;  a  yellow  incrustation  of  Teroxide  appears  on  the  charcoal. 

OXIDE  OF  COPPER,  CuO. 
*       Solution  best  fitted  for  the  reactions:  Sulphate  of  Copper,  CuO.SO3. 

HYDROSULPHURIC  ACID;  a  black  precipitate  of  Sulphide  of  Copper  (CuS); 
insoluble  in  dilute  sulphuric  and  hydrochloric  acids,  even  upon  heating ;  readily 
soluble  even  in  cold  moderately  dilute  nitric  acid,  so  that,  in  precipitating  copper 
from  a  nitric  solution  by  hydrosulphuric  acid,  it  is  requisite  to  dilute  the  solution 
very  largely ;  soluble  to  a  slight  extent  in  sulphide  of  ammonium,  but  not  in 
sulphide  of  potassium. 

POTASSA;  a  blue  precipitate  of  Hydrated  Oxide,  insoluble  in  excess;  becomes 
black  when  heated  in  the  liquid,  being  converted  into  Anhydrous  Oxide.  The 
presence  of  fixed  organic  matters  (sugar,  tartaric  acid,  &c.)  causes  this  precipi- 
tate to  redissolve  in  excess  of  potassa,  with  a  deep  blue  color. 

AMMONIA;  a  greenish-blue  precipitate  of  a  basic  salt;  readily  soluble  in  ex- 


FOURTH  GROUP.  521 

cess,  with  a  fine  blue  color,  visible  even  when  very  minute  quantities  of  copper 
are  present. 

FERROCYANIDE  OF  POTASSIUM;  a  brownish-red  precipitate  of  Ferrocyanide  of 
Copper  (Cu3Cfy) ;  insoluble  \ndilute  acids,  readily  soluble  in  ammonia;  de- 
composed by potassa.  This  is  the  most  delicate  test  for  copper;  before  applying 
it,  the  solution  should  be  acidified  with  acetic  acid  (strong  mineral  acids  decom- 
pose the  reagent;  if  these  be  present,  an  excess  of  acetate  of  potassa  should  be 
added  to  neutralize  them);  with  very  small  quantities  of  copper,  no  precipitate 
is  formed,  but  a  pink  color  is  imparted  to  the  liquid. 

IRON,  or  steel,  perfectly  clean,  immersed  in  a  solution  of  copper,  slightly 
acidified  with  sulphuric  or  hydrochloric  acid,  becomes  coated  with  a  film  of  Me- 
tallic Copper,  known  by  its  color ;  this  test ,  enables  us  to  detect  very  minute 
quantities  of  copper. 

BLOWPIPE. — Solid  compounds  of  copper,  fused  with  carbonate  of  soda  in  the 
reducing  flame,  yield  a  mass  of  Metallic  Copper,  which  may  be  fused  into  a  very 
tough,  red,  malleable  globule  by  long  blowing;  no  incrustation  is  obtained;  the 
operation  is  assisted  by  adding  a  little  cyanide  of  potassium.  When  the  quantity 
of  copper  present  is  so  small  that  no  globule  can  be  obtained,  it  can  often  be 
detected  by  triturating  the  slag,  with  the  surrounding  parts  of  charcoal,  in  a 
small  agate  mortar,  and  levigating  the  powder  till  the  lighter  particles  are  washed 
away,  when  red  spangles  of  copper  become  visible. 

Compounds  containing  sulphur  or  arsenic  should  be  well  roasted  in  the  outer 
flame  before  reduction,  in  order  to  volatilize  these  substances,  which  would  injure 
the  malleability  of  the  metallic  globule. 

A  small  quantity  of  a  compound  of  copper,  fused  with  a  borax-bead  in  the 
outer  flame  of  the  blowpipe,  yields  a  glass  which  has  a  greenish-blue  color  when 
hot,  and  becomes  blue  on  cooling;  exposed  to  the  inner  flame,  this  glass  either 
loses  its  color,  or  becomes  tinged  of  an  opaque  red,  according  to  the  quantity  of 
copper  which  is  present. 

OXIDE  OF  CADMIUM,  CbO. 
Solution  best  fitted  for  the  reactions:  Chloride  of  Cadmium,  CdCl. 

HYDROSULPHURIC  ACID  ;  a  bright  yellow  precipitate  of  Sulphide  of  Cadmium 
(CdS);  insoluble  in  alkaline  sulphides;  insoluble  only  in  cold,  very  dilute  sjil- 
phuric,  hydrochloric,  and  nitric  acids;  if  the  acid  be  only  moderately  dilute,  the 
precipitate  may  dissolve,  especially  on  heating;  hence.it  is  necessary  to  dilute 
acid  solutions  of  cadmium  very  largely  before  treating  with  hydrosulphuric  acid. 
In  the  presence  of  bisulphide  of  tin,  it  has  been  found  that  a  considerable  quan- 
tity of  sulphide  of  cadmium  may  be  left  undissolved  even  by  boiling  dilute  nitric 
acid. 

AMMONIA;  a  white  precipitate  of  Hydrated  Oxide  of  Cadmium,  very  easily 
soluble  in  excess. 

CARBONATE  OF  AMMONIA;  a  white  precipitate  of  Carbonate  of  Cadmium 


£CdO  C0a),  slightly  soluble  in  excess. 
BLOWPIPE. — Solid 


compounds  of  cadmium,  fused  with  carbonate  of  soda,  in 
the  reducing  flame,  give  a  characteristic  red-brown  incrustation  of  oxide  of  cad- 
mium upon  the  charcoal,  near  the  outer  limit  of  the  oxidizing  flame. 

TEROXIDE  OF  GOLD,  Au03. 
Solution  best  fitted  for  the  reactions :  Terchloride  of  Gold,  AuCl3. 

HYDROSULPHURIC  ACID;  a  black  precipitate  of  Tersulphide  of  Gold  (AuS3); 
insoluble  in  sulphuric,  hydrochloric,  or  nitric  acid,  alone  (the  latter,  however,  is 


522  REACTIONS   OF   THE   METALLIC   OXIDES. 

capable  of  oxidizing  the  sulphur,  leaving  metallic  gold),  but  soluble  in  a  mixture 
of  nitric  and  hydrochloric  acids;  soluble  to  a  considerable  extent  in  the  alkaline 
sulphides. 

OXALIC  ACID  ;  on  boiling,  a  precipitate  of  finely  divided  Metallic  Gold,  appear- 
ing as  a  purple  powder,  which  afterwards  coheres  in  yellow  flakes  capable  of 
assuming  the  (/olden  -lustre  when  rubbed ;  if  a  very  small  quantity  of  gold  be 
present,  the  liquid  only  assumes  a  purple  tinge.  The  presence  of  much  free 
hydrochloric  or  nitric  acid  prevents  the  reduction;  in  such  a  case,  ammonia  may 
be  added  to  the  boiling  solution,  drop  by  drop,  until  the  free  acid  is  nearly 
neutralized. 

SULPHATE  OF  OXIDE  OF  IRON  also  precipitates  the  gold  as  a  bluish-black  pow- 
der, becoming  yellow  and  lustrous  when  rubbed;  if  the  precipitate  be  very  small, 
it  may  be  collected  upon  a  smooth  filter,  the  latter  washed,  dried,  and  spread  out 
upon  a  hard  smooth  surface;  if  the  precipitate  be  then  rubbed  with  a  burnisher 
(of  agate),  the  lustrous  spangles  will  be  visible. 

CHLORIDE  (SnCl)  AND  BICHLORIDE  OF  TIN  (SnCl3)  (mixed) ;  even  in  very 
dilute  solutions  of  gold,  a  purple  precipitate  (Purple  of  Cassius,  see  p.  395),  the 
tint  of  which  varies  according  to  the  quantity  of  gold  present;  the  precipitate  is 
insoluble  in  dilute  acids;  the  gold-solution  should  be  first  mixed  with  the  bichlo- 
ride of  tin,  and  the  chloride  then  added  drop  by  drop.  When  the  quantity  of 
gold  is  extremely  minute,  a  pink  tinge  pervades  the  solution. 

A  very  delicate  method  of  applying  this  test  is  as  follows :  sesquichloride  of 
iron  is  added  to  chloride  of  tin  (SnCl)  until  a  permanent  yellow  color  is  pro- 
duced, the  solution  is  then  considerably  diluted ;  the  gold-solution  having  like- 
wise been  much  diluted,  is  poured  into  a  beaker,  which  is  placed  on  a  sheet  of 
white  paper ;  a  glass  rod  is  dipped  into  the  tin-iron-solution  and  afterwards  into 
the  gold-solution,  when,  if  even  a  trace  of  the  precious  metal  be  present,  a  blue 
or  purple  streak  will  be  observed  in  the  track  of  the  glass  rod. 

This  purple  of  Cassius  test  has  the  advantage  of  being  applicable  even  in  very 
acid  solutions. 

BINOXIDE  OF  PLATINUM,  PtOa. 
Solution  lest  fitted  for  the  reactions:  Bichloride  of  Platinum,  PtCla. 

HYDROSULPHURIC  ACID  ;  black  precipitate  of  Bisulphide  of  Platinum  (PtS2); 
the  precipitation  is  not  complete  in  the  cold ;  in  order  to  remove  platinum  en- 
tirely from  a  solution,  by  hydrosulphuric  acid,  the  liquid  must  be  boiled  after 
every  saturation  with  the  gas,  until  a  specimen,  filtered  off,  again  saturated  with 
hydrosulphuric  acid-,  and  boiled,  gives  no  further  precipitate.  The  bisulphide  is 
insoluble  in  dilute  acids,  but  dissolves  to  a  great  extent  in  concentrated  nitric 
acid;  it  also  dissolves,  though  with  difficulty,  in  the  alkaline  sulphides. 

CHLORIDE  OF  AMMONIUM  ;  yellow  crystalline  precipitate  of  the  Double  Chlo- 
ride of  Platinum  and  Ammonium  (NH4Cl,PtCla)  ;  soluble  to  some  extent  in 
water,  insoluble  in  alcohol.  In  applying  this  test,  the  solution  should  be  allowed 
to  stand  for  about  twelve  hours,  wfcen  very  minute  quantities  of  platinum  may 
be  detected  by  the  formation  of  yellow  crystals  on  the  bottom  and  sides  of  the* 
tube. 

CHLORIDE  OF  TIN  (SnCl)  in  presence  of  free  hydrochloric  acid}  produces  a 
dark  brown-red  color  (due  to  the  reduction  of  bichloride  of  platinum  to  the  chlo- 
ride); ia- exceedingly  dilute  solutions,  the  color  is  yellow  and  becomes  darker  on 
standing ;  the  slightest  traces  of  platinum  are  indicated  by  this  test. 


FOURTH   GROUP.  523 

OXIDE  or  TIN,  SnO. 
Solution  lest  Jilted  for  the  reactions:  Chloride  of  Tin,  SnCl. 

HYDROSULPHURIC  ACID  ;  dark  brown  precipitate  of  Sulphide  of  Tin  (SnS)  ; 
insoluble  in  cold  dilute  acids;  converted  by  boiling  nitric  acid  into  insoluble 
Binoxide  of  Tin;  insoluble  in  pure  alkaline  sulphides,  but  soluble,  with  the 
aid  of  heat,  in  alkaline  sulphides  containing  an  excess  of  sulphur,  which  converts 
the  sulphide  into  Bisulphide  of  Tin;  hence,  the  ordinary  yellow  sulphide  of  am- 
monium is  capable  of  dissolving  the  sulphide  of  tin ;  if  the  solution  be  mixed 
with  an  excess  of  hydrochloric  acid,  the  sulphide  of  ammonium  is  decomposed, 
and  yellow  bisulphide  of  tin  precipitated. 

CHLORIDE  OF  MERCURY  (HgCl) ;  at  first,  a  white  precipitate  of  Subchloride 
(often  highly  crystalline),  which  after  a  time,  if  a  sufficient  quantity  of  the  tin- 
compound  be  present,  is  converted  into  a  gray  precipitate  of  Metallic  Mercury. 
Since  this  reaction  takes  place  even  in  highly  dilute  solutions,  and  in  the  pre- 
sence of  much  free  hydrochloric  acid,  it  is  very  valuable  for  the  detection  of  oxide 
of  tin. 

BLOWPIPE. — Solid  compounds  of  tin,  fused  on  charcoal,  with  carbonate  of  soda 
(or,  very  much  more  easily,  with  cyanide  of  potassium},  in  the  inner  flame,  yield 
a  white  malleable  globule  of  Tin,  and  a  very  slight  white  incrustation.  Even  if 
no  globule  be  obtained,  the  spangles  of  tin  are  often  visible  after  triturating  and 
levigating  the  fused  mass  and  surrounding  particles  of  charcoal. 

BINOXIDE  OF  TIN,  Sn03. 
Solution  best  fitted  for  the  reactions:  Bichloride  of  Tin,  SnCl3. 

HYDROSULPHURIC  ACID;  a  bright  yellow  precipitate  of  Bisulphide  of  Tin 
(SnSa);  insoluble  in  dilute  sulphuric  and  hydrochloric  acids;  converted  in  to  inso- 
luble Binoxide  of  Tin  by  boiling  nitric  acid ;  soluble  in  a  mixture  of  hydro- 
chloric and  (a  little')  nitric  acids,  with  the  aid  of  heat ;  soluble  in  alkalies,  or 
in  alkaline  sulphides^  and  reprecipitated  from  the.  solution  by  acids.1  When 
bisulphide  of  tin  is  added,  by  small  portions,  to  nitrate  of  potassa  in  a  state  of 
fusion,  it  is  rapidly  oxidized ;  the  fused  mass,  when  treated  with  water,  yields  a 
solution- which  contains  no  tin,  the  whole  of  this  metal  being  left  in  the  residue ; 
but  if  pieces  of  paper  be  also  deflagrated  with  the  nitre  (as  must  always  be  the 
case  when  the  precipitate  is  too  small  to  be  removed  from  the  filter),  the  aqueous 
solution  of  the  fused  mass  will  contain  a  certain  quantity  of  tin,  which  is,  how- 
ever, entirely  precipitated  on  acidulating  with  nitric  acid  and  boiling. 

Bisulphide  of  tin,  alone,  is  insoluble  in  a  solution  of  sesqui carbonate  of  am- 
monia, even  on  gently  heating,  but  when  mixed  with  one  of  the  sulphides  of 
arsenic,  it  is  dissolved  to  a  considerable  extent  by  the  sesquicarbonate. 

The  color  of  bisulphide  of  tin  is  much  impaired  by  admixture  even  of  minute 
quantities  of  other  sulphides. 

SESQUICARBONATE  OF  AMMONIA  ;  a  white  precipitate  of  Hydrated  Binoxide 
of  Tin;z  redissolves  to  some  extent  in  the  cold,  in  an  excess,  but  is  completely 
reprecipitated  on  boiling.  The  presence  of  certain  fixed  organic  matters  (tartaric 
acid,  e.  </.)  prevents  the  precipitation. 

CYANIDE  OF  POTASSIUM,  fused  with  binoxide  of  tin  in  a  covered  porcelain 

1  Sulphide  of  ammonium  does  not  extract  quite  the  whole  of  the  bisulphide  of  tin  when 
mixed  with  the  sulphide  of  mercury  or  cadmium,  and  extracts  only  a  small  part  of  it  when 
mixed  with  sulphide  of  copper. 

2  This  precipitate  passes  through  the  filter  when  washed  with  pure  water,  and  should 
therefore  be  washed  with  solution  of  sesquicarbonate  of  ammonia.  •< 


524  REACTIONS    OF   THE    METALLIC   OXIDES. 

crucible,  reduces  it  to  the  metallic  state;  if  the  fused  mass  be  heated  with  water, 
the  cyanate  of  potassa  is  dissolved  out,  and  the  particles  of  metal  subside;  these, 
after  decanting  the  supernatant  liquid,  may  be  heated  to  boiling  with  concen- 
trated hydrochloric  acid,  and  the  presence  of  Chloride  of  tin,  in  the  solution, 
proved  by  diluting  with  water  and  testing  with  chloride  of  mercury.  By  this 
method  very  small  quantities  of  tin  may  be  detected. 

BLOWPIPE. — Compounds  of  the  binoxide  furnish  the  same  result  as  those  of 
the  oxide  (see  p.  523)  when  examined  before  the  blowpipe. 

TEROXIDE  OP  ANTIMONY,  Sb03. 
Solution  best  fitted  for  the  reactions:  Terchloride  of  Antimony,  SbCla. 

(The  solution  of  terchloride  of  antimony  should  not  be  diluted  with  pure  water, 
but  with  water  acidulated  with  hydrochloric  acid.) 

HYDROSULPHURIC  ACID  ;  an  orange-red  precipitate  of  Tersulphide  of  Antimony 
(SbS3) ;  insoluble  in  cold  dilute  acids;  soluble  in  moderatelv  concentrated  hy- 
drochloric acid,  with  evolution  of  hydrosulphuric  acid ;  when  boiled  with  nitric 
acid,  partly  dissolved,  a  white  residue  being  left ;  the  quantity  dissolved  in- 
creases with  the  dilution  of  the  acid ;  soluble  in  alkalies,  and  in  alkaline  sul- 
phides, and  reprecipitated  by  acids,  soluble  to  a  very  slight  extent  in  sesquicar- 
bonate  of  ammonia,  even  on  gentle  heating. 

WATER,  added  in  large  quantity  to  a  solution  of  terchloride  of  antimony,  not 
containing  much  free  hydrochloric  or  tartaric  acid,  produces  a  white  precipitate, 
which  is  an  Oxychloride ;  this  precipitate  is  distinguished  from  that  furnished 
by  bismuth  under  similar  circumstances,  by  its  solubility  in  tartaric  acid. 

POTASSA;  a  white  precipitate  of  Hydrated  Teroxide  of  Antimony,  soluble  in 
excess  ;  if  this  solution  be  mixed  with  nitrate  of  silver,  it  gives  a  black  precipi- 
tate of  Metallic  Silver  (insoluble  in  ammonia),  the  teroxide  of  antimony  being 
converted  into  antimonic  acid. 

The  presence  of  tartaric  acid  prevents  the  precipitation  by  potassa. 

SESQUICARBONATE  OP  AMMONIA  ;  a  white  precipitate  of  Hydrated  Teroxide 
of  Antimony,  soluble  to  a  considerable  extent  in  excess  of  the  precipitant,  espe- 
cially on  heating.  The  presence  of  tartaric  acid  prevents  the  precipitation. 

METALLIC  ZINC  precipitates  antimony  from  its  solutions  as  a  black  powder. 

If  a  solution  containing  antimony  be  introduced,  through  a  funnel-tube,  into 
an  apparatus  from  which  hydrogen  is  being  evolved  from  dilute  sulphuric  acid  by 
the  action  of  zinc,  the  reduced  antimony  will  combine  with  part  of  the  nascent 
hydrogen,  and  will  be  evolved  in  the  form  of  Antimoniuretted  Hydrogen  gas 
(SbH3).  If  the  gas  be  dried  by  passing  through  a  tube,  the  anterior  portion 
of  which  is  loosely  filled  with  cotton  wool,  and  the  remoter  part  with  chloride  of 
calcium,  and  be  then  allowed  to  escape  from  a  tube  of  hard  glass1  drawn  out  to 
a  fine  point,  the  presence  of  antimony  may  be  recognized  by  the  following  re- 
actions : — 

1.  The  gas  will  burn  with  a  bluish-green  flame,  emitting  white  fumes  of  Ter- 
oxide of  Antimony,  which  may  be  condensed  in  a  cold  beaker,  dissolved  in 
hydrochloric  acid,  and  tested  with  hydrosulphuric  acid. 

2.  If  the  inner  surface  of  a  porcelain  capsule  be  depressed  upon  the  flame,  a 
black  spot  of  metallic  antimony  will  be  deposited  upon  it,  which  is  lustrous  only 
when  in  thin  layers ;  this  coating  of  metal  may  be  dissolved  in  aqua  regia  and 
tested.     (The  operator  should  take  care  to  prove,  before  commencing  this  expe- 
riment, that  the  flame  of  the  hydrogen  itself  deposits  no  spot  upon  porcelain.) 

1  Hard  glass  should  be  used  for  all  experiments  of  this  description,  because  of  the  high 
temperature  necessary,  which  would  fuse  ordinary  English  glass,  and  because  the  reduc- 
tion of  the  lead  contained  in  the  latter  might  lead  to  error. 


FOURTH   GROUP.  525 

3.  The  glass  tube  from  which  the  gas  issues,  should  be  heated  with  a  spirit- 
lamp  in  the  centre;  a  lustrous  mirror  of  antimony  will  be  deposited  on  the  inside 
of  the  tube,  immediately  around  the  flame  of  the  lamp,  whilst  the  bluish-green 
tint  of  the  hydrogen-flame  in  great  measure  disappears. 

These  reactions  should  be  compared  with  those  of  arseniuretted  hydrogen 
under  similar  circumstances. 

If  granulated  zinc  be  boiled  with  a  solution  of  antimony  to  which  a  very  large 
excess  of  potassa  has  been  added,  the  hydrogen  which  is  evolved  is  free  from 
antimoniuretted  hydrogen. 

BLOWPIPE. — Solid  compounds  of  antimony,  when  fused  with  carbonate  of 
soda,  on  charcoal,  in  the  reduciny  flame,  yield  a  globule  of  metal,  which  vola- 
tilizes if  subjected  for  a  considerable  period  to  the  action  of  the  flame,  and  emits 
white  fumes  of  teroxide;  the  globule  is  exceedingly  brittle,  and  may  be  readily 
rubbed  to  a  black  powder.  The  charcoal  becomes  coated  with  a  widely  difl'used 
white  incrustation,  which  has  a  bluish  appearance  when  in  thin  layers. 

ANTIMONIC  ACID,  Sb05. 
Solution  best  fitted  for  the  reactions:  Antimoniate  of  Potassa,  KO.Sb05. 

STRONG  MINERAL  ACIDS,  especially  nitric,  produce  a  white  precipitate  of  Hy- 
drated  Antimonic  Acid,  which  redissolves  to  a  great  extent  in  excess  of  acid, 
particularly  in  hydrochloric  acid. 

HYDROSULPHURIC  ACID,  in  a  solution  of  an  antimoniate,  produces  no  precipi- 
tate, but  if  an  excess  of  hydrochloric  acid  be  previously  added,  an  orange-red 
precipitate  of  Pentasulphide  of  Antimony  (SbS5),  the  behavior  of  which  is 
similar  to  that  of  the  tersulphide  (see  p.  524).  It  is  necessary  to  state,  in  addi- 
tion, that  when  pentasulphide  of  antimony  is  deflagrated  with  nitre,  and  the 
fused  mass  digested  with  water,  almost  the  whole  of  the  antimony  remains  in 
the  residue. 

POTASSA  ;  no  precipitate.1  If  to  the  solution  containing  excess  of  potassa, 
nitrate  of  silver  be  added,  merely  a  brown  precipitate  of  Oxide  of  Silver  is 
obtained,  which  redissolves  completely  in  excess  of  ammonia  (see  p.  524). 

SESQUICARBONATE  OF  AMMONIA  f  no  precipitate. 

Compounds  of  antimonic  acid  exhibit  the  same  reactions  with  zinc,  and  before 
the  blowpipe,  as  those  of  the  teroxide  of  antimony. 

ARSENIOUS  ACID,  As03. 

Solution  best  fitted  for  the  reactions  :  Arsenious  Acid  in  saturated  aqueous 

solution. 

HYDROSULPHURIC  ACID,  in  a  pure  solution  of  arsenious  acid,  a  yellow  color  at 
first,  and  after  a  time,  especially  on  heating,  a  yellow  precipitate ;  if  a  little  hy- 
drochloric acid  be  added  before  the  hydrosulphuric  acid,  the  yellow  precipitate  of 
Tersulphide  of  Arsenic  (AsS3)  is  obtained  at  once;  insoluble  in  cold  dilute  acids, 
slightly  soluble  in  hydrochloric  acid,  with  the  aid  of  heat,  and  readily  so  in  hot 
nitric  acid;  soluble  in  sesquicarbonate  of  ammonia,  especially  on  gently  heating; 
very  readily  soluble  in  the  alkalies  and  alkaline  sulphides,  and  reprecipitated  by 
acids.  When  deflagrated  with  nitre,  the  fused  mass  is  entirely  soluble  in  water, 
and  Arsenic  Acid  may  be  detected  in  the  solution. 

When  tersulphide  of  arsenic  is  fused  with  a  large  excess  of  carbonate  of  soda 

1  This  is  strictly  true  in  the  case  of  antimoniate  of  potassa ;  but  if  this  reagent  be 
added  to  a  hydrochloric  solution  of  antimonic  acid,  a  white  precipitate  is  produced,  which 
dissolves  almost  entirely  in  an  excess  of  the  precipitant. 

2  The  same  remark  applies  here  as  in  the  case  of  potassa. 


526  REACTIONS   OF   THE    METALLIC   OXIDES. 

and  cyanide  of  potassium,  the  arsenic,  is  reduced  and  volatilized,  and  if  the 
operation  be  conducted  in  an  apparatus  so  constructed  that  the  vapors  of  arsenic 
may  be  preserved  from*  con  tact  with  the  air,  and  may  be  recondensed  on  a  parti- 
cular portion  of  the  tube,  the  smallest  quantities  of  arsenic  may  be  thus  detected. 
The  test  founded  hereupon  is  known  as  that  of  Fresenius  and  Babo,  and  requires 
a  special  description  in  this  place,  since  it  is  now  generally  esteemed  the  safest 
test  for  arsenic  in  judicial  investigations. 

The  apparatus  consists  of  a  small  two-necked  bottle  for  evolving  carbonic  acid, 
furnished  with  a  funnel-tube,  and  an  egress-tube  for  the  gas,  which  is  conducted 
into  a  small  wash-bottle  containing  concentrated  sulphuric  acid,  intended  to  dry  the 
gas;  from  this  wash-bottle,  a  second  tube  passes  which  is  bent  at  right  angles,  and 
connected,  by  means  of  a  cork,  with  the  reduction-tube ;  this  latter  is  made  out 
of  a  piece  of  hard  glass  tube  (combustion-tube)  somewhat  more  than  thr<ee-eighths 
of  an  inch  in  diameter,  and  drawn  out  at  one  extremity  to  a  long  open  point ;  the 
length  of  the  body  of  the  tube  should  be  about  four  inches,  that  of  the  point  at 
least  two  and  a  half  inches.  The  carbonic  acid  is  evolved  from  pretty  large  frag- 
ments of  marble  (no  powder),  which  are  covered  with  water  in  the  evolution- 
bottle  into  which  dilute  hydrochloric  acid  is  poured  through  the  funnel-tube. 

Fig.  76. 


A  mixture  of  (as  nearly  as  can  be  guessed)  three  parts  of  dry  carbonate  of  soda 
and  one  part  of  cyanide  of  potassium  is  thoroughly  dried  in  a  porcelain  capsule 
upon  the  sand-bath ;  one  part  of  the  arsenical  sulphide  (dried  in  the  water-bath) 
is  then  intimately  mixed,  in  a  small  (agate)  mortar,  with  at  least  twelve  parts  of 
the  above  reducing  mixture ;  the  powder  is  placed  in  a  strip  of  writing-paper 
folded  so  as  to  form  a  gutter,  which  is  introduced  into  the  body  of  the  reduction- 
tube,  so  that  the  mixture  may  lay  at  about  the  centre;  the  tube  is  then  turned 
half-round  upon  its  axis,  and  the  mixture  allowed  to  fall  upon  the  glass,  when 
the  gutter  may  be  carefully  withdrawn;  the  mixture  should  not  occupy  more 
than  an  inch  in  the  tube ;  the  latter  is  now  connected  with  the  carbonic  acid 
apparatus,  and  the  gas  allowed  to  flow  through  it  for  some  time;  when  it  is 
certain  that  all  air  has  been  expelled,  the  evolution  of  carbonic  acid  is  so 
moderated  (by  pouring  water  into  the  bottle)  that  only  one  bubble  shall  pass 
through  the  wash-bottle  in  a  second;  the  reduction-tube  is  now  heated  through- 
out its  whole  length,  by  waving  a  spirit-lamp  flame  beneath  it,  until  all  the 
moisture  is  expelled ;  the  spirit-lamp  is  then  placed  beneath  the  shoulder  of 
the  tube,  and  when  this  is  well  heated,  a  second  spirit-lamp  is  applied,  to  heat 
the  mixture,  commencing  at  the  posterior  part;  when  the  whole  of  the  mixture 
has  been  heated,  the  experiment  may  be  concluded  by  directing  a  blowpipe-flame 
upon  that  portion  of  the  tube;  until  the  mass  is  completely  fused;  the  vapors  of 


FOURTH   GROUP.  527 

metallic  arsenic  are  carried  forward  by  the  stream  of  carbonic  acid,  and,  since 
the  shoulder  of  the  tube  is  heated,  they  pass  on  and  condense  in  the  narrow 
point,  where  they  form  a  lustrous  mirror  of  about  an  inch  in  length;  a  distinct 
yarlic  odor  is  also  perceived  at  the  point  of  the  tube  throughout  the  experiment. 
When  the  quantity  of  arsenic  is  exceedingly  minute,  merely  a  thin  gray  film  is 
deposited,  which  is  only  visible  against  a  piece  of  white  paper. 

The  portion  of  the  point  which  contains  the  metallic  arsenic  may  be  cut  off 
with  a  sharp  file,  and  the  metal  dissolved  off  with  a  few  drops  of  concentrated 
nitric  acid,  the  solution  carefully  evaporated  till  the  excess  of  acid  is  expelled, 
water  added,  and  the  solution  tested  with  nitrate  of  silver,  and,  if  necessary, 
dilute  ammonia  added,  drop  by  drop,  when  the  brick-red  precipitate  of  Arseniate 
of  Silver  (see  p.  530)  will  be  obtained. 

This  test  of  Fresenius  and  Babo  possesses  advantages  which  entitle  it  to  a 
preference  over  all  other  tests  for  arsenic  hitherto  discovered;  for,  1.  It  can  be 
applied  to  the  very  smallest  quantities  of  material :  2.  Its  results  depend  very 
little  upon  the  skill  or  judgment  of  the  operator;  and,  3.  It  cannot  lead  us  to 
mistake  any  other  metal  for  arsenic;  antimony,  which  so  much  resembles  arsenic 
in  many  of  its  reactions,  does  not  respond  to  this  test.  It  is  true  that  mercury 
compounds,  when  treated  in  this  way,  would  yield  a  metallic  sublimate,  but  this 
differs  widely  from  that  of  arsenic,  and  other  reactions  would  invariably  prevent 
any  mistake  arising  from  this  cause. 

NITRATE  OF  SILVER  does  not  produce  a  precipitate  in  an  acjueous  solution  of 
arsenious  acid,  but  if  ammonia  be  gradually  added,  a  yellow  precipitate  of  Arse- 
nite  of  Silver  (2AgO.As03)  is  obtained ;  readily  soluble  in  ammonia  and  in 
nitric  acid  ;  great  care  is  necessary  in  neutralizing  with  ammonia,  which  should 
be  very  dilute,  and  added,  drop  by  drop,  with  frequent  agitation  ;  if  too  much 
ammonia  has  been  added,  the  precipitate  may  frequently  be  obtained  by  gently 
evaporating  the  solution  upon  a  water-bath  (all  sulphuretted  hydrogen  being  ex- 
cluded) ;  it  is  also  a  good  plan  to  neutralize  the  solution  before  adding  the 
nitrate  of  silver,  by  rendering  it  slightly  alkaline  with  ammonia,  and  then  eva- 
porating on  a  water-bath  till  the  excess  of  the  latter  is  expelled. 

The  application  of  nitrate  of  silver  as  a  test  for  arsenious  acid  is,  however, 
very  limited,  because  so  many  substances  (especially  chlorides)  interfere  with 
the  reaction. 

SULPHATE  OF  COPPER  produces  no  precipitate  in  a  solution  of  arsenious  acid, 
but  if  ammonia  be  carefully  added,  a  yellowish-green  precipitate  of  Arsenite  of 
Copper  (2CuO.As03,  Scheeles  Green)  is  obtained ;  soluble  in  nitric  acid  and  in 
ammonia :  the  same  remarks  apply  to  this  as  to  the  preceding  test. 

If  sulphate  of  copper,  in  small  proportion,  be  added  to  a  solution  of  arsenious 
acid,  afterwards  potassa  in  excess,  and  the  solution  boiled,  a  red  precipitate  of 
Suboxide  of  Copper  (Cu20)  is  obtained,  the  arsenious  acid  being  converted  into 
arsenic  acid;  this  test  is  only  useful  for  distinguishing  between  arsenious  and 
arsenic  acids,  and  would  be  valueless  as  a  test  for  arsenic,  since  many  other  sub- 
stances (e.  g.  sugar)  are  capable  of  producing  the  same  effect. 

REINSCH'S  TEST. — Clean  copper,  boiled  in  a  hydrochloric  solution,  containing 
arsenic,  becomes  coated  with  a  steel-gray  film  of  the  metal,  which,  if  the  quan- 
tity be  sufficient,  will  separate,  after  long  boiling,  in  large  black  scales.  This  is 
a  very  delicate  test  for  arsenic,  and  since  it  is  more  readily  applied  than  any 
other,  we  shall  consider  it  in  detail,  as  it  is  often  used  in  medico-legal  analyses. 

The  solution  to  be  tested,  which  may  contain  organic  matters,  but  should  be 
pretty  free  from  oxidizing  agents  (nitric  and  chloric  acids,  &c.)  and  not  very 
thick,  is  mixed  with  sufficient  hydrochloric  acid  to  render  it  very  distinctly  acid, 
and  boiled  with  several  pieces  of  copper  wire  (cleaned  with  concentrated  nitric 
acid,  and  washed)  about  an  inch  long,  for  two  or  three  minutes;  if  they  are  not 
then  coated,  the  boiling  may  be  continued  for  about  ten  minutes;  but  if  a  film 


528 


REACTIONS   OF   THE   METALLIC   OXIDES. 


is  deposited  upon  them  at  first,  they  should  be  withdrawn,  lest  it  may  scale  off; 
the  slips  are  then  well  washed  with  water,  and  carefully  dried,  either  by  pressure 
between  blotting-paper,  or  better,  in  a  water-bath;  they  are  afterwards  intro- 
duced into  a  tube  of  hard  glass,  about  £  inch  in  diameter,  and  so  constricted  as 
to  admit  of  the  passage  of  only  a  feeble  current  of  air;  this  tube  is  heated  gra- 
dually, in  an  oblique  position,  over  a  spirit-lamp,  when  a  sublimate  of  shining 
crystals  of  Arsenious  Acid  will  be  formed  in  the  cool  part  of  the  tube;  if  these 
be  examined  with  a  magnifier,  it  will  be  seen  that  they  are  octohedra,  like  crys- 
tals of  alum;  the  portion  of  glass  upon  which  these  crystals  are  deposited  may 
be  cut  off,  boiled  for  some  seconds  with  water,  and  the  solution  examined  for 
arsenious  acid,  especial  recourse  being  had  to  the  tests  with  hydrochloric  and 
hydrosulphuric  acids,  and  with  nitrate  of  silver. 

In  careful  hands,  this  test  leads  to  a  very  safe  conclusion  as  to  the  presence 
or  absence  of  arsenic,  since,  though  many  other  metals  may  be  deposited  upon 
the  copper,  none  but  arsenic  will  yield  a  crystalline  sublimate ;  this  test,  how- 
ever, is  generally  regarded  as  merely  a  trial  test,  so  that  if  it  should  give  no 
indication  whatever  of  the  presence  of  arsenic,  it  is  not  considered  necessary  to 
proceed  any  further. 

MARSH'S  TEST. — If  a  solution  of  arsenic  be  poured  into  an  apparatus  (b,  a,  c) 
from  which  hydrogen  is  evolved  by  the  action  of  zinc  upon  water  in  the  presence 
of  sulphuric  acid,  'Arseniuretted  Hydrogen  ( AsH3)  is  produced ;  the  gas  should 
be  dried  by  passing  through  a  tube  (d),  which  is  half  filled  (at  the  end  nearest 
to  the  evolution-bottle)  with  cotton-wool,  and  half  with  fragments  of  chloride  of 
calcium,  and  may  be  recognized  by  the  following  experiments. 

Fig.  77. 


1.  The  gas  is  allowed  to  escape  from  a  tube  of  hard  glass  (e)  about  six 
inches  long,  drawn  out  so  as  to  form  a  jet  at  its  extremity,  where  the  gas  may 
be  kindled;  it  burns  with  a  livid  blue  flame,  producing  Arsenious  Acid,  which 
may  be  condensed  in  a  cold  beaker,  dissolved  in  hot  water,  and  tested  (especially 
with  nitrate  of  silver,  and  with  hydrochloric  and  hydrosulphuric  acids). 

2.  By  depressing  the  inner  surface  of  a  porcelain  capsule  upon  the  flame,  a 
black  (generally)  lustrous  spot  of  metallic  arsenic  is  obtained  (this  experiment 
should  always  be  tried  with  the  hydrogen-flame  before  the  arsenical  solution  is 
poured  into  the  evolution- bottle)  ;*  this  spot  may  be  tested  by  dissolving  in  con- 
centrated nitric  acid,  evaporating  just  to  dryness  upon  a  sand-bath,  adding  water, 
and  afterwards  nitrate  of  silver,  with,  if  necessary,  a  little  dilute  ammonia,  when 
a  brick-red 'precipitate  of  Arseniate  of  Silver  will  be  obtained;  an  antimony 

1  The  porcelain  should  not  be  allowed  to  remain  in  the  flame  for  more  than  a  second 
or  two,  since  the  minute  spots  would  be  dispelled  if  the  porcelain  were  to  become  very 
hot. 


FOURTH   GROUP.  529 

spot,  when  treated  in  this  way,  generally  gives  a  slight  dirty-white  precipitate 
with  nitrate  of  silver. 

The  incrustation  of  arsenic  (whether  on  a  porcelain  surface  or  in  a  glass  tube) 
may  be  dissolved  by  solution  of  chloride  of  lime,  which  4oes  not  affect  the  anti- 
mony-incrustation :  this  test  may  serve,  to  some  extent,  to  distinguish  the  two 
metals,  but  is  not  adequate  to  the  detection  of  traces  of  antimony  in  a  mirror  of 
arsenic. 

3.  The  centre  of  the  tube  Q?)  through  which  the  gas  passes  may  be  heated 
with  a  spirit-lamp  (/),  when  the  arseniuretted  hydrogen  is  decomposed,  a  mirror 
of  metallic  arsenic  being  deposited,  while  the  hydrogen-flame  regains,  in  great 
measure,  its  natural  color ;  the  mirror  in  this  case,  in  consequence  of  its  greater 
volatility,  is  not  deposited  immediately  in  the  vicinity  of  the  spirit-lamp,  but  at 
a  considerable  distance  beyond  the  heated  part  of  the  tube;  if  this  portion  of  the 
tube  be  cut  off,  and  gently  heated,  the  peculiar  garlic  odor  will  be  perceptible ; 
the  crust  of  arsenic  may  also  be  tested  in  the  same  way  as  that  obtained  in  the 
porcelain  capsule  (see  2). 

Although  this  test  enables  us  to  detect  very  small  quantities  of  arsenic,  it  is 
not  now  generally  recommended,  in  consequence  of  the  danger  of  confounding 
antimony  with  arsenic ;  of  course,  in  a  mixture  of  the  two,  it  would  be  impossi- 
ble to  distinguish  either  with  certainty. 

Marsh's  test,  however,  may  afford  a  very  satisfactory  proof  of  the  absence  of 
both  these  metals.1 

FLEITMANN'S  TEST. — Tf  a  solution  containing  arsenic  be  mixed  with  a  large 
excess  of  a  concentrated  solution  of  potassa,  and  boiled  with  fragments  of  granu- 
lated zinc,  arseniuretted  hydrogen  is  evolved,  and  may  be  easily  recognized  by 
allowing  it  to  pass  on  to  a  piece  of  filter-paper  spotted  over  with  solution  of 
nitrate  of  silver;  these  spots  assume  a  purplish-black  color,  even  when  a  small 
quantity  of  arsenic  is  present.  This  experiment  may  be  performed  in  a  small 
flask,  furnished  with  a  perforated  cork  carrying  a  piece  of  glass  tube  of  about 
£-inch  diameter.  It  will  be  observed  that  this  test  serves  to  distinguish  arsenic 
from  antimony. 

Solid  compounds  containing  arsenic,  mixed  with  carbonate  of  soda  and  char- 
coal (Hack  /lux,  or  a  mixture  of  equal  parts  of  wood-charcoal  and  carbonate  of 
soda,  previously  ignited  in  a  covered  crucible),  and  heated  in  a  tube  of  hard 
glass,  expanded  into  a  bulb  at  one  extremity,  and  thoroughly  dried,  yield  a 
black  lustrous  ring  of  metallic  arsenic  upon  the  cool  part  of  the  tube. 

BLOWPIPE. — Solid  compounds  containing  arsenic,  when  heated  to  redness,  on 
charcoal,  in  the  reducing  flame,  emit  a  characteristic  garlic  odor,  probably  due 
to  an  oxide  of  arsenic  inferior  to  arsenious  acid. 

ARSENIC  ACID,  As05. 
Solution  best  fitted  for  the  reactions:  Arsenic  acid  in  aqueous  solution. 

HYDROSULPHURIC  ACID  does  not  produce  an  immediate  precipitate  in  solution 
of  arsenic  acid,  even  when  mixed  with  hydrochloric  acid,  but  if  the  solution  be 
heated  to  boiling,  or  allowed  to  stand  for  some  time,  a  yellow  precipitate  of  Pen- 
tasulphide  of  Arsenic  (AsS5)  is  obtained,  which  exhibits  the  same  characters  as 
the  tersulphide.  The  complete  removal  of  arsenic  acid  from  a  solution  by  means 
of  sulphuretted  hydrogen,  is  attended  with  some  difficulty ;  it  is  necessary  re- 
peatedly to  saturate  it  with  the  gas,  and  to  boil  after  each  saturation ;  it  is  bet- 
ter, however,  to  convert  the  arsenic  acid  into  arsenious  acid,  by  saturating  the 

1  A  great  obstacle  to  the  employment  of  Marsh's  test  is  the  difficulty  of  obtaining  zinc 
and  sulphuric  acid  perfectly  free  from  arsenic,  for  which  they  should  be  very  carefully 
tested  previous  to  use. 

34 


530  REACTIONS   OF  THE   METALLIC   OXIDES. 

liquid  with  sulphurous  acid,  and  subsequently  boiling  until  the  excess  of  the 
latter  is  expelled,  which  may  be  known  by  the  disappearance  of  the  odor.  The 
arsenic  may  then  readily  be  precipitated  by  hydrosulphuric  acid. 

NITRATE  OF  SILVER  ;  a  brick-red  precipitate  of  Arseniate  of  Silver  (3AgO. 
As05) ;  readily  soluble  in  nitric  acid  and  in  ammonia  ;  if  it  should  be  required 
to  apply  this  test  to  a  solution  containing  free  nitric  acid,  the  latter  may  be 
neutralized  with  ammonia,  and  the  excess  of  ammonia  expelled  by  evaporation ; 
if  chlorides  be  present,  the  solution  may  be  acidulated  with  nitric  acid,  the 
whole  of  the  chlorine  precipitated  by  nitrate  of  silver  ;  the  clear  fluid  containing 
excess  of  that  reagent  is  then  very  carefully  neutralized  with  dilute  ammonia, 
when  the  brick-red  precipitate  makes  its  appearance ;  it  is  a  good  plan  to  pour 
the  dilute  ammonia  very  gradually  upon  the  surface  of  the  acid  liquid,  so  as  to 
form  two  distinct  layers,  at  the  junction  of  which  a  brown  line  of  Arseniate  of 
Silver  may  be  seen. 

In  those  reactions  which  depend  upon  the  reduction  of  the  arsenic  to  the  me- 
tallic state,  arsenic  acid  resembles  the  arsenious. 


§339.  FIFTH   GROUP. 

Metallic  oxides,  the  chlorides  corresponding  to  which  are  insoluble  or  sparingly 
soluble  in  water  and  dilute  hydrochloric  acid. 

OXIDE  OF  SILVER  (AeO),  SUBOXIDE  OF  MERCURY  (Hg20),  OXIDE  OF 

LEAD  (PbO). 

OXIDE  OF  SILVER,  AgO. 
Solution  best  fitted  for  the  reactions:  Nitrate  of  Silver,  AgO.N05. 

HYDROCHLORIC  ACID  ;  a  white  precipitate  of  Chloride  of  Silver  (AgCl), 
which  becomes  violet  when  exposed  to  light  ;  insoluble  in  water  and  in  nitric 
acid,  readily  soluble  in  ammonia.  When  this  precipitate  is  mixed  with  a  cer- 
tain quantity  of  subchloride  of  mercury,  it  no  longer  darkens  when  exposed  to 
light. 

SOLUBLE  CHLORIDES  affect  silver  salts  like  hydrochloric  acid. 

BLOWPIPE.  —  Solid  compounds  of  silver,  fused  with  carbonate  of  soda,  on 
charcoal,  before  the  blowpipe,  yield  a  globule  of  white,  malleable  metal,  without 
incrustation  of  the  charcoal  support. 

SUBOXIDE  OF  MERCURY,  HgaO. 
Solution  best  fitted  for  the  reactions  :    Nitrate  of  Suboxide  of  Mercury, 


HYDROCHLORIC  ACID  ;  a  white  (slightly  yellowish  in  large  masses)  precipi- 
tate of  Subchloride  of  Mercury,  HgaCl  ',  insoluble  in  water  and  in  cold  hydro- 
chloric and  nitric  acids  ;  blackened  by  ammonia,  being  converted  into  the  Sub- 
oxide,  which  is  not  soluble  in  ammonia. 

The  reactions  which  depend  upon  the  reduction  of  mercury  to  the  metallic 
state,  are  exhibited  also  by  the  oxide  of  mercury,  and  have  been  described  in 
the  section  containing  the  reactions  of  that  oxide  (see  p.  519). 

OXIDE  OF  LEAD,  PbO. 
Solution  lest  fitted  for  the  reactions:    Nitrate  of  Lead,  PbO.N05. 

HYDROCHLORIC  ACID  ;  in  moderately  concentrated  solutions,  a  white  precipi- 
tate of  Chloride  of  Lead  (PbCl);  soluble  in  much  cold  water,  and  therefore  not 


EEACTIONS   OF   THE   ACIDS.  531 

produced  in  dilute  solutions  ;  dissolves  pretty  readily  in  boiling  water,  and  is 
deposited  in  fine  needles  as  the  solution  cools ;  is  not  dissolved  by  ammonia. 

DILUTE  SULPHURIC  ACID  ;  in  very  dilute  solutions,  only  after  standing  for 
some  time  a  white,  heavy  precipitate  of  Sulphate  of  Lead  (PbO.S03) ;  very 
slightly  soluble  in  water  and  in  dilute  nitric  acid;  soluble  in  hot  hydrochloric 
acidj  and  in  potassa.  This  reaction  with  sulphuric  acid  serves  to  distinguish  the 
oxide  of  lead  from  all  other  oxides,  except  baryta  and  strontia. 

HYDROSULPHURIC  ACID  ;  a  black  precipitate  of  Sulphide  of  Lead  (PbS)  ;* 
insoluble  in  water,  and  in  cold  dilute  acids;  almost  entirely  dissolved  by  hot 
dilute  nitric  acid,  as  nitrate  of  lead,  a  residue  of  sulphur  with  a  little  sulphate 
of  lead  being  left;  concentrated  nitric  acid  converts  it  into  sulphate,  which  is 
left  undissolved. 

POTASSA  ;  a  white  precipitate  of  Hydrated  Oxide  of  Lead,  readily  soluble  in 
an  excess. 

AMMONIA;  a  white  precipitate  of  Hydrated  Oxide  of  Lead,  insoluble  in  ex- 
cess;2 readily  soluble  in  dilute  nitric  acid.  Solution  of  acetate  of  lead  does  not 
give  any  precipitate  immediately,  with  ammonia,  but  the  solution,  after  some 
time,  deposits  a  basic  salt  of  oxide  of  lead. 

CHROMATE  or  BICHROMATE  OF  POTASSA;  a  yellow  precipitate  of  Chromateof 
Lead  (PbO.Cr03);  insoluble  in  water  and  in  acetic  acid  ;  sparingly  soluble  in 
dilute  nitric  acid;  readily  soluble  in  potassa. 

BLOWPIPE. — Solid  compounds  of  lead,  when  fused  with  carbonate  of  soda  on 
charcoal,  in  the  inner  blowpipe-flame,  furnish  a  very  soft  malleable  globule  of 
metal,  which  marks  paper  like  a  pencil ;  the  charcoal  around  the  oxidizing  flame 
becomes  covered  with  a  yellow  (or  brownish)  incrustation  of  oxide  of  lead. 


REACTIONS   OF   THE   ACIDS. 

§  340.  In  considering  the  reactions  of  the  acids,  we  shall  divide  them  into 
inorganic  and  organic  acids,  restricting  the  latter  designation  to  those  which, 
when  heated  (either  alone  or  in  combination),  are  either  blackened,  from  sepa- 
ration of  carbon,  or  evolve  inflammable  gases,  so  that  they  appear  to  burn  with 
flame  when  heated  upon  platinum.  Among  the  inorganic  acids  we  are  com- 
pelled to  place  oxalic  acid  (although  it  is,  strictly  speaking,  an  organic  acid), 
since  its  compounds  usually  exhibit  none  of  the  ordinary  appearances  which  are 
taken  as  indications  of  the  presence  of  organic  acids.  The  acids  of  cyanogen  are, 
for  a  similar  reason,  included  in  this  class. 

The  following  acids  are  of  sufficient  importance  to  be  studied  in  this  work  : — 

Inorganic  :3  Sulphuric,  phosphoric,  boracic,  silicic,  sulphurous,  chromic,  hydro- 
fluoric, carbonic,  oxalic,  hydrochloric,  hydrobromic,  hydriodic,  hydrosulphuric, 
hydrocyanic,  hydrosulphocyanic,  hydroferrocyanic,  hydroferricyanic,  nitric,  chlo- 
ric, and  hypochlorous. 

Organic  :*  Tartaric,  tannic,  gallic,  citric,  uric,  benzoic,  succinic,  acetic. 

1  If  much  free  hydrochloric  acid  be  present,  this  precipitate  is  at  first  of  a  red  color  (see 
p.  479),  becoming  black  only  after  some  time. 

2  In  presence  of  aminoniacal  salts,  however,  this  precipitate  is  redissolved  to  some  ex- 
tent by  an  excess  of  ammonia  ;  so  that  if  a  solution  of  nitrate  of  lead,  mixed  with  a  large 
excess  of  free  nitric  acid,  be  decomposed  with  a  large  excess  of  ammonia,  a  considerable 
quantity  of  lead  may  be  found  in  the  filtered  solution. 

3  Arsenious  and  arsenic  acids  have  been  already  considered. 

4  The  history  of  the  organic  acids  will  be  given  in  a  subsequent  part  of  this  work. 


532  REACTIONS   OF   THE   ACIDS. 


INORGANIC   ACIDS. 

The  inorganic  acids  are,  for  the  convenience  of  study,  divided  into  three 
groups,  according  to  their  behavior  with  reagents. 

The  first  group  includes  those  acids  which  are  precipitated  from  the  solutions 
of  their  neutral  salts  by  chloride  of  barium — viz  :  sulphuric,  phosphoric,  boracic, 
silicic,  sulphurous,  chromic,  hydrofluoric,  carbonic,  and  oxalic  acids. 

The  acids  contained  in  the  second  group  are  such  as  are  precipitated  by  nitrate 
of  silver  from  solutions  slightly  acidified  with  nitric  acid;  these  are  hydrochloric, 
hydrobromic,  hydriodic,  hydrosulphuric,  hydrocyanic,  hydrosulphocyanic,  hydro- 
ferrocyanic,  and  hydroferricyanic  acids. 

In  the  third  group  we  find  those  acids  which  we  are  not  able  to  precipitate 
from  their  solutions,  in  consequence  of  the  solubility  of  all  their  compounds; 
they  are  nitric,  chloric,  and  hypochlorous  acids. 


§341.  FIRST    GROUP. 

Acids  precipitated  from  solutions  of  their  neutral  salts  by  chloride  of  barium. 

FIRST  SECTION.  Acids  which  are  not  affected  when  heated  (either  alone  or  in 
combination)  with  concentrated  sulphuric  acid. 

SULPHURIC  ACID  (S03)        PHOSPHORIC  ACID  (P05) 
BORACIC  ACID  (B03)  SILICIC  ACID  (Si08) 

SULPHURIC  ACID. 
Solution  best  fitted  for  the  reactions:  Sulphate  of  Magnesia,  MgO.S03. 

CHLORIDE  OF  BARIUM  ;  in  neutral,  acid,  or  alkaline  solutions,  a  white  pre- 
cipitate of  Sulphate  of  Baryta  (BaO.S03),  soluble  to  a  very  slight  extent  in 
hot  hydrochloric  acid.  In  strongly  acid  solutions  the  precipitate  is  not  formed 
immediately.  When  this  test  is  to  be  applied  in  solutions  containing  much  free 
hydrochloric  or  nitric  acid,  they  should  first  be  largely  diluted,  lest  a  precipitate 
of  chloride  of  barium  or  nitrate  of  baryta  should  be  formed,  since  these  salts  are 
sparingly  soluble  in  strongly  acid  liquids. 

CHLORIDE  OF  CALCIUM;  in  concentrated  solutions,  a  white  precipitate  of  Sul- 
phate of  Lime  (CaO.S03);  insoluble  in  acetic  acid;  soluble  in  much  water; 
soluble  in  hot  hydrochloric  acid. 

BLOWPIPE. — Solid  sulphates,  fused  on  platinum  wire  with  a  mixture  of  car- 
bonate of  soda  and  charcoal — in  the  reducing  flame,  yield  a  bead  containing 
Sulphide  of  Sodium  (NaS) ;  if  this  bead  be  placed  upon  a  clean  piece  of  silver, 
and  moistened  with  dilute  hydrochloric  acid,  Hydrosulphuric  Acid  is  evolved, 
and  produces  a  black  stain  (AgS)  upon  the  metal.  In  this  test,  the  carbonate  of 
soda  must,  of  course,  be  free  from  sulphate. 

Any  compound  of  sulphur  will  exhibit  this  reaction. 

PHOSPHORIC  ACID. 

(We  shall  confine  our  attention  here  merely  to  common  phosphoric  acid 
(3HO.P05),  since  the  pyro  and  meta-phosphoric  acids  are  of  much  less  frequent 
occurrence,  and  their  reactions  have  been  described  in  the  former  part  of  this 
work). 


.*.  FIRST   GROUP.  533 

Solution  lest  fitted  for  the  reactions:  Phosphate  of  Soda,  2NaO.HO.P05. 

CHLORIDE  OP  BARIUM  ;  in  neutral  or  alkaline  solutions,  a  white  precipitate  of 
Phosphate  of  Baryta  (2BaO.HO.P05);  readily  soluble  in  hydrochloric  acidj  and 
reprecipitated  by  ammonia. 

CHLORIDE  OF  CALCIUM,  in  neutral  or  alkaline  solutions,  a  white  precipitate  of 
Phosphate  of  Lime  (2CaO.HO.P05) ;  soluble  in  acetic  or  hydrochloric  acid,  and 
reprecipitated  by  ammonia. 

NITRATE  OF  SILVER,  in  neutral  or  very  slightly  alkaline  solutions,  a  yellow 
precipitate  of  Tribasic  Phosphate  of  Silver  (3AgO.P05);  soluble  in  nitric  acid 
or  in  ammonia. 

SESQUICHLORIDE  OF  IRON,  in  neutral  or  slightly  alkaline  solutions,  or  in 
solutions  containing  free  acetic  acid,  a  yellowish-white  gelatinous  precipitate  of 
Phosphate  of  Sesquioxide  of  Iron  (Fe^jPO^),  insoluble  in  acetic  acid;  soluble 
to  some  extent  in  solution  of  acetate  of  sesquioxide  of  iron  ;  readily  soluble  in  the 
mineral  acids;  decomposed  by  alkalies;  completely  decomposed  by  boiling  with 
sulphide  of  ammonium,  sulphide  of  iron  being  left,  and  phosphate  of  ammonia 
remaining  in  solution. 

TARTARIC  ACID  and  other  fixed  organic  matters  prevent  the  precipitation  of 
phosphate  of  sesquioxide  of  iron. 

In  applying  this  test  to  the  solution  of  a  phosphate  (e.g.  phosphate  of  lime) 
in  hydrochloric  (or  any  other  mineral)  acid,  it  is  requisite  to  replace  the  latter 
by  acetic  acid,  which  may  be  effected  by  the  addition  of  an  excess  of  acetate  of 
potassa ;  sesquichloride  of  iron  should  then  be  cautiously  added ;  the  first  drop 
will  produce  a  precipitate  if  any  notable  amount  of  phosphoric  acid  be  present; 
in  order  to  separate  all  the  phosphoric  acid  from  the  solution,  sesquichloride  of 
iron  must  be  added  until,  after  the  subsidence  of  the  precipitate,  the  supernatant 
liquid  has  a  red  tint,  due  to  the  acetate  of  sesquioxide  of  iron,  which  may  hold 
in  solution  a  little  of  the  phosphate ;  in  order  to  precipitate  the  latter,  the  solu- 
tion (with  the  suspended  precipitate)  must  be  boiled  for  a  minute  or  two,  when 
the  acetate  of  sesquioxide  of  iron  is  decomposed,  with  separation  of  a  basic  ace- 
tate, which  is  precipitated  together  with  the  phosphate  ;*  for  the  detection  of  the 
phosphoric  acid  in  the  mixed  precipitate  of  phosphate  and  basic  acetate  of  ses- 
quioxide of  iron,  this  is  collected  on  a  filter,  washed  and  dissolved  off  the  filter 
with  warm  dilute  hydrochloric  acid  ;  the  solution  is  mixed  with  excess  of  am- 
monia  and  sulphide  of  ammonium,  boiled  and  filtered  off  from  the  sulphide  of 
iron;  the  Bltrate  is  concentrated  by  evaporation,  again  filtered,  if  necessary, 
from  a  little  separated  sulphur,  and  tested  for  phosphoric  acid  with  a  mixture 
of  chloride  of  ammonium,  ammonia  and  sulphate  of  magnesia,  as  described 
below. 

A  mixture  of  CHLORIDE  OF  AMMONIUM,  AMMONIA,  and  SULPHATE  OF  MAG- 
NESIA, gives  a  white,  highly  crystalline  precipitate  of  Phosphate  of  Magnesia  and 
Oxide  of  Ammonium  (2MgO.NH4O.P05) ;  somewhat  soluble  in  water,  less 
soluble  in  solution  of  ammonia,  readily  soluble  in  acids.  In  dilute  solutions  this 
precipitate  is  formed  only  after  some  time;  the  solution  should  be  violently  agi- 
tated. Care  must  be  taken  that  sufficient  chloride  of  ammonium  is  present  to 
prevent  the  precipitation  of  hydrate  of  magnesia.  This  test  should  not  be  ap- 
plied to  solutions  containing  tartaric  acid,  since  a  mixture  of  that  acid  with 
chloride  of  ammonium,  ammonia,  and  sulphate  of  magnesia,  deposits  a  crystal- 
line precipitate  after  a  time.  The  application  of  this  test  is  unfortunately 
restricted  to  those  phosphates  which  are  soluble  in  water,  since  the  free  ammonia 
(necessary  to  its  success)  would  precipitate  unchanged  any  phosphate  which  had 
been  dissolved  in  an  acid. 

1  The  solution  filtered  off  from  this  precipitate  will  be  colorless  (or  very  nearly  so)  if 
the  operation  is  successful. 


534  REACTIONS    OF   THE   ACIDS. 

MOLYBDATE  OF  AMMONIA;  even  in  solutions  containing  free  nitric  acid,  a 
yellow  precipitate  (see  p.  447),  which  is  most  evident  when  a  small  quantity  of 
phosphoric  acid  is  present.  This  test  is  especially  adapted  for  the  detection  of 
minute  quantities  of  phosphoric  acid  in  a  nitric  solution  of  phosphate  of  alumina, 
phosphate  of  lime,  &c. 

BORACIC  ACID. 

Solution  best  fitted  for  the  reactions:  Biborate  of  Soda,  Na0.2B03. 

CHLORIDE  OF  BARIUM,  in  neutral  and  alkaline  solutions,  a  white  precipitate 
of  Borate  of  Baryta  (BaO.B03),  soluble  in  hydrochloric  acid.  Since  borate  of 
baryta  is  soluble  to  some  extent  in  ammoniacal  salts,  no  precipitate  is  produced, 
if  these  be  present  in  sufficient  quantity ;  for  the  same  reason,  when  borate  of 
baryta  is  dissolved  in  a  large  excess  of  hydrochloric  acid,  ammonia  does  not  re- 
precipitate  it. 

CHLORIDE  OF  CALCIUM;  in  neutral  and  alkaline  solutions,  a  white  precipitate 
of  Borate  of  Lime  (CaO.BO3),  soluble  in  acetic  acid ;  this  precipitate  is  also 
dissolved  by  ammoniacal  salts. 

NITRATE  OF  SILVER  ;  a  white  precipitate  of  Borate  of  Silver  (AgO.B03), 
soluble  in  nitric  acid  and  in  ammonia. 

If  a  solution  containing  boracic  acid  be  mixed  with  about  half  its  volume  of 
concentrated  sulphuric  acid,  an  equal  volume  of  alcohol  (or  naphtha}  added,  and 
the  mixture  kindled,  it  will  burn  with  a  fine  green  flame;  the  mixture  should  be 
well  stirred  whilst  burning,  and  should  be  allowed  to  burn  out  before  the  absence 
of  boracic  acid  is  inferred  from  the  non-appearance  of  the  green  flame.  The  pre- 
sence of  copper  (which  might  also  color  the  flame)  is  to  be  avoided  in  this  expe- 
riment. 

SILICIC  ACID. 
Solution  best  fitted  for  the  reactions:  Silicate  of  Potassa,  KO.Si03. 

CHLORIDE  OF  BARIUM  ;  in  neutral  and  alkaline  solutions,  a  white  precipitate 
of  Silicate  of  Baryta  (BaO.Si03),  soluble  (entirely,  or  in  great  measure)  in 
hydrochloric  acid. 

CHLORIDE  OF  CALCIUM  ;  a  similar  reaction. 

HYDROCHLORIC  ACID  ;  in  pretty  concentrated  solutions,  a  gelatinous  white 
precipitate  of  Hydrated  Silicic  Acid;  soluble,  entirely,  or,  in  great  measure,  in 
excess,  and  reprecipitated  by  excess  of  ammonia.  If  the  hydrochloric  solution 
be  evaporated  to  dryness,  and  the  residue  heated  with  hydrochloric  acid,  the 
whole  of  the  silicic  acid  will  be  left  undissolved  in  the  form  of  white  flakes. 

NITRIC  ACID  acts  in  a  'similar  manner,  but  does  not  readily  redissolve  the 
gelatinous  silicic  acid  which  is  precipitated  at  first. 

Insoluble  silicic  acid  (quartz,  sand,  &c.),  when  fused,  on  platinum  foil,  with 
CARBONATE  OF  POTASSA  OR  SODA  (3  or  4  parts),  expels  the  carbonic  acid, 
forming  an  alkaline  silicate,  which  dissolves  entirely  (or  nearly  so)  in  water;  for 
the  complete  success  of  this  experiment,  the  silica  must  be  reduced  to  an  im- 
palpable powder. 

BLOWPIPE. — If  a  bead  of  carbonate  of  soda  be  made  upon  a  loop  of  platinum 
wire,  and,  having  been  dipped,  while  hot,  into  powdered  silicic  acid,  be  again 
fused  in  the  hottest  part  of  the  blowpipe  flame,  a  point  will  be  attained,  in  re- 
peating this  operation,  when  the  bead  remains  transparent  on  cooling  (whereas 
the  bead  of  pure  carbonate  of  soda  becomes  opaque) ;  this  is  a  very  characteristic 
reaction  of  silicic  acid;  the  bead  is  usually  of  a  yellowish  color,  from  the  pre- 
sence of  a  little  iron. 

§  342.  SECOND  SECTION  OF  THE  FIRST  GROUP.     Acids  which  are  decomposed 


FIRST   GROUP.  535 

or  expelled  when  Jieated  (either  alone  or  in  combination]  with  concentrated  sulphu- 
ric acid. 

SULPHUROUS  ACID  (S02)  CHROMIC  ACID  (Cr03) 

HYDROFLUORIC  ACID  (HF)        CARBONIC  ACID  (C0a) 

OXALIC  ACID  (C203). 

SULPHUROUS  ACID. 

Solution  best  fitted  for  the  reactions :    Sulphite  of  Oxide  of  Ammonium, 

NH4O.S02. 

Solid  sulphites  (sulphite  of  soda,  e.  #.),  heated  with  CONCENTRATED  SULPHU- 
RIC ACID,  are  decomposed  with  effervescence,  Sulphurous  Acid  being  evolved, 
which  may  be  recognized  by  its  characteristic  odor  of  burning  sulphur. 

HYDROCHLORIC  ACID  also  evolves  sulphurous  acid  from  its  salts  ;  the  decom- 
position is  attended  with  effervescence  (especially  on  heating)  if  the  solution  be 
not  too  dilute.  When  there  is  any  doubt  respecting  the  odor,  it  may  often  be 
set  at  rest  by  conducting  the  gas  (through  a  bent  tube)  into  a  saturated  solution 
of  sulphuretted  hydrogen,  in  which  sulphurous  acid  would  cause  a  separation  of 
Sulphur  (it  must  be  remembered  that  oxidizing  agents,  chlorine,  for  example, 
would  have  the  same  effect). 

CHLORIDE  OF  BARIUM  ;  in  neutral  and  alkaline  solutions,  a  white  precipitate 
of  Sulphite  of  Baryta  (BaO.S03)  soluble  in  hydrochloric  acid;  from  this  solu- 
tion (provided  it  be  first  boiled  to  expel  the  sulphurous  acid)  ammonia  does  not 
reprecipitate  the  sulphite.  If  the  hydrochloric  solution  of  sulphite  of  baryta  be 
boiled  with  a  few  drops  of  concentrated  nitric  acid,  a  precipitate  of  Sulphate  of 
Baryta  is  formed ;  this  precipitate  should  be  heated  with  a  considerable  quan- 
tity of  water,  lest  any  nitrate  of  baryta  should  have  been  thrown  down. 

CHLORIDE  OF  CALCIUM  ;  in  neutral  and  alkaline  solutions,  a  white  precipitate 
of  Sulphite  of  Lime  (CaO.SO3)  soluble  in  hydrochloric  acid. 

NITRATE  OF  SILVER,  a  white  precipitate  of  Sulphite  of  Silver  (AgO.S03) 
which  becomes  dark  gray  when  heated  in  the  liquid,  being  decomposed  into 
Sulphuric  Acid  and  Metallic  Silver. 

The  sulphites,  when  fused  with  carbonate  of  soda  and  charcoal,  exhibit  the 
same  behavior  as  the  sulphates  (see  p.  532). 

CHROMIC  ACID. 
Solution  best  fitted  for  the  reactions:  Chromate  of  Potassa,  KO.Cr03. 

Solid  chromates,  when  heated  with  CONCENTRATED  SULPHURIC  ACID  evolve 
Oxygen,  which  may  be  recognized  by  means  of  a  semi-extinguished  match;  Sul- 
phate of  Sesquioxide  of  Chromium  remains  in  the  solution  (see  p.  331). 

Chloride  of  barium,  in  neutral  and  alkaline  solutions ;  a  yellow  precipitate  of 
Chromate  of  Baryta  (BaO.Cr03),  soluble  in  hydrochloric  acid,  and  reprecipi- 
tated  by  ammonia. 

NITRATE  OF  SILVER,  a  purple-red  precipitate  of  Chromate  of  Silver  (AgO. 
Cr03)  soluble  in  nitric  acid  and  in  ammonia. 

ACETATE  OF  LEAD  ;  a  yellow  precipitate  of  Chromate  of  Lead  (PbO.Cr03) 
insoluble  in  acetic  acid. 

HYDROSULPHURIC  ACID  ;  in  neutral  and  alkaline  solutions,  a  greenish-gray 
precipitate  of  Sesquioxide  of  Chromium  mixed  with  Sulphur  (see  p.  332) ;  if 
hydrochloric  acid  be  added  before  hydrosulphuric  acid,  only  sulphur  will  be 
precipitated,  while  sesquichloride  of  chromium  will  be  found  in  the  (green) 
solution. 

SULPHUROUS  ACID,  added  to  an  acid  solution,  reduces  the  chromic  acid  to  the 
state  of  (Sulphate  of)  Sesquioxide  of  Chromium  (Cr803.3S03). 


536  REACTIONS   OF   THE   ACIDS. 

When  a  solution  containing  chromic  acid  is  heated  with  an  excess  of  hydro- 
chloric acid  and  a  little  alcohol)  the  chromic  acid  is  converted  into  sesquichloride 
of  chromium  (Cr2Cl3). 

HYDROFLUORIC  AciD.1 
Solution  best  fitted  for  the  reactions  :    Fluoride  of  Potassium,  KF. 

When  solid  fluorides  (fluoride  of  calcium)  are  heated  with  CONCENTRATED 
SULPHURIC  ACID,  Hydrofluoric  Acid  is  evolved,  and  may  be  recognized  by  its 
pungent  odor,  by  the  thick  fumes  which  it  produces  in  moist  air,  and  by  its  pro- 
perty of  corroding  glass. 

If  the  experiment  be  made  in  a  test-tube,  the  sides  of  the  latter  will  suffer 
considerable  corrosion,  which  will  not  be  perceived,  however,  until  the  tube  is 
washed  and  dried. 

It  is  much  better  to  perform  the  experiment  in  a  platinum  crucible ;  the 
powdered  fluoride  should  be  placed  in  the  latter,  a  quantity  of  concentrated  sul- 
phuric acid  poured  over  it,  and  the  mouth  of  the  crucible  covered  with  a  smooth 
glass  plate ;  if  the  crucible  be  now  gently  heated  on  a  sand-bath  for  half  an  hour, 
the  glass  plate  will  be  found  more  or  less  deeply  etched. 

If  a  very  small  quantity  of  a  fluoride  is  to  be  tested,  it  may  be  placed  in  a 
watch-glass,  an  excess  of  concentrated  sulphuric  acid  added,  and  the  mixture 
dried  upon  a  sand-bath  ;  if  the  mass  be  then  washed  off  the  glass,  and  the  latter 
dried,  the  corrosion  will  become  apparent. 

Neither  of  these  tests,  however,  can  be  applied  when  the  compound  contains 
silicic  acid,  since  the  nascent  hydrofluoric  acid  would  more  readily  act  upon  this 
than  upon  the  glass ;  the  following  test  must  then  be  employed. 

If  a  solid  fluoride  be  mixed  with  sand,  and  heated  with  concentrated  sulphuric 
acid,  Terfluoride  of  Silicon  is  evolved,  which  may  be  recognized  by  its  deposit- 
ing a  coating  of  Silicic  Acid  upon  moist  surfaces  (see  p.  220).  For  this  experi- 
ment, a  test-tube  or  small  flask  is  employed,  furnished  with  a  perforated  cork 
carrying  a  straight  piece  of  glass  tube,  about  £  inch  in  diameter,  and  6  inches 
long;  this  tube  is  wetted  internally  with  a  little  water,  without  wetting  the  cork ; 
if  the  mixture  of  the  fluoride  with  sand  and  sulphuric  acid  be  heated  in  the 
(well-dried)  flask,  the  terfluoride  of  silicon  is  evolved,  and  deposits  a  white  coat- 
ing of  silica  upon  the  walls  of  the  tube. 

If  this  experiment  be  carefully  performed,  it  enables  us  to  detect  very  small 
quantities  of  fluorine. 

CHLORIDE  OF  BARIUM  ;  in  neutral  and  alkaline  solutions,  a  white  precipitate 
of  Fluoride  of  Barium  (BaF)  soluble  in  hydrochloric  acid,  and  reprecipitated  by 
ammonia. 

CHLORIDE  OF  CALCIUM;  in  neutral  and  alkaline  solutions,  a  white  precipitate 
of  Fluoride  of  Calcium  (CaF),  insoluble,  or  nearly  so,  in  acetic  acid;  soluble 
to  some  extent  in  hydrochloric  acid,  and  reprecipitated  by  ammonia. 

Insoluble  fluorides  (fluoride  of  calcium)  when  finely  powdered  and  fused  with 
3  or  4  parts  of  carbonate  of  potassa  and  soda,  yield  a  mass  from  which  water 
extracts  the  Alkaline  Fluoride,  which  may  be  detected  by  adding  a  slight  excess 
of  acetic  acidy  and  chloride  of  calcium. 

CARBONIC  ACID. 

Solution  lest  fitted  for  the  reactions:  Carbonate  of  Soda,  NaO.COa. 
Solid  carbonates  (carbonate  of  lime)  are  decomposed,  even  in  the  cold,  by 

1  The  fluorides  are  considered  as  compounds  of  hydrofluoric  acid,  because,  although,  they 
really  do  not,  contain  this  acid,  they  are  produced  whenever  hydrofluoric  acid  comes  in 
contact  with  bases. 


SECOND   GROUP.  537 

CONCENTRATED  SULPHURIC  ACID,  Carbonic  Acid  being  evolved,  with  violent 
effervescence. 

HYDROCHLORIC  ACID  also  expels  the  carbonic  acid  with  effervescence;  this  is 
taken  advantage  of  in  testing  for  carbonic  acid ;  the  substance  is  treated  with 
hydrochloric  acid  in  a  test-tube,  and  the  evolved  gas  immediately  decanted  into 
another  test-tube  half  filled  with  baryta-water ;  the  Carbonate  of  Baryta  is 
formed  as  a  crust  upon  the  surface  of  the  liquid,  and  upon  agitating  the  latter, 
it  absorbs  the  rest  of  the  carbonic  acid  in  the  tube,  and  becomes  turbid. 

CHLORIDE  OF  BARIUM;  a  white  precipitate  of  Carbonate  of  Baryta  (BaO. 
C03),  readily  soluble  in  hydrochloric  acid,  and,  provided  the  solution  be  gently 
heated  to  expel  the  carbonic  acid,  not  reprecipitated  by  ammonia. 

CHLORIDE  OF  CALCIUM;  a  white  precipitate  of  Carbonate  of  Lime  (CaO.COJ 
soluble  in  acetic  acid. 

NITRATE  OF  SILVER;  a  white  precipitate  of  Carbonate  of  Silver  (AgO.C03), 
soluble  in  nitric  acid  and  in  ammonia. 

OXALIC  ACID. 
Solution  best  fitted  for  the  reactions:  Oxalate  of  oxide  of  ammonium,  NH40.0. 

Oxalic  acid,  or  an  oxalate,  in  the  solid  state,  heated  with  CONCENTRATED  SUL- 
PHURIC ACID,  yields  Carbonic  Oxide,  together  with  Carbonic  Acid  (see  p.  196), 
which  are  evolved  with  effervescence;  if  the  mouth  of  the  test-tube  be  approached 
to  a  flame,  the  carbonic  oxide  takes  fire,  and  burns  with  its  characteristic  blue 
flame. 

Solid  oxalic  acid,  heated  upon  platinum  foil,  evolves  white  irritating  vapors. 
When  heated  in  a  tube  open  at  both  ends,1  and  held  somewhat  obliquely  over 
a  flame  (to  produce  a  gentle  current  of  air),  part  of  the  hydrated  acid  is  vola- 
tilized without  decomposition,  and  recondenses  upon  the  cool  portion  of  the  tube 
in  long  needles. 

CHLORIDE  OF  BARIUM;  in  neutral  and  alkaline  solutions,  a  white  precipitate 
of  Oxalate  of  Baryta  (BaOXJ),  soluble  in  hydrochloric  acid,  and  reprecipitated 
by  ammonia. 

CHLORIDE  OF  CALCIUM;  a  white  precipitate  of  Oxalate  of  Lime  (CaO.O),  in- 
soluble in  acetic  acid;  readily  soluble  in  hydrochloric  acid. 

NITRATE  OF  SILVER;  a  white  precipitate  of  Oxalate  of  Silver  (AgO.O),  so- 
luble in  nitric  acid  and  in  ammonia. 

ACETATE  OF  LEAD;  a  white  precipitate  of  Oxalate  of  Lead  (PbO.O),  insolu- 
ble in  acetic  acid. 

§  343.  SECOND  GROUP. 

Acids  which  are  precipitated  by  nitrate  of  silver  from  solutions  slightly  acidified 

with  nitric  acid. 

HYDROCHLORIC  ACID  (HC1)  HYDROBROMIC  ACID  (HBr) 

HYDRIODIC  ACID  (HI)  HYDROSULPHURIC  ACID  (HS) 

HYDROCYANIC  ACID  (HCy)  HYDROSULPHOCYANIC  ACID  (HCsy) 

HYDROFERROCYANIC  ACID  (H2Cfy)  HYDROFERRICYANIC  ACID  (H3Cfdy). 

HYDROCHLORIC  ACID. 

Solution  best  fitted  for  the  reactions:  Chloride  of  Sodium,  NaCl. 
NITRATE  OF  SILVER;  in  neutral  and  acid  solutions,  a  white  curdy  precipitate 

1  Such  tubes  are  often  used  in  similar  experiments ;  they  should  be  thin,  and  have  a 
diameter  of  from  half  an  inch  to  one  inch. 


538  REACTIONS   OF   THE   ACIDS. 

of  Chloride  of  Silver  (AgCl),  which  becomes  violet  when  exposed  to  light ;  inso- 
luble in  nitric  acid;  soluble  in  ammonia,  and  reprecipitated  by  nitric  acid  in 
excess.  If  the  chloride  of  silver  be  washed  by  decantation,  dried  in  a  porcelain 
capsule,  and  heated  to  redness,  it  fuses  into  oily-looking  globules,  which  solidify 
into  horny  masses  on  cooling. 

SULPHURIC  ACID  and  BINOXIDE  OP  MANGANESE,  with  the  aid  of  heat,  de- 
compose the  chlorides,  evolving  Chlorine,  which  may  be  recognized  by  its  odor, 
and  by  its  property  of  bleaching  moist-colored  papers. 

Solid  chlorides  (chloride  of  sodium)  treated  with  CONCENTRATED  SULPHURIC 
ACID,  even  in  the  cold,  evolve  Hydrochloric  Acid  (with  effervescence),  which 
may  be  known  by  its  odor,  and  by  the  thick  white  fumes  which  it  produces  when 
escaping  into  the  air. 

Solid  chlorides  (in  a  perfectly  dry  state),  when  mixed  with  an  excess  of 
bichromate  of  potassa,  and  heated  with  concentrated  sulphuric  acid,  in  a  well- 
dried  test-tube,  evolve  brownish-red  vapors  of  Chlorochromic  Acid  (see  p.  334) ; 
these  should  be  conducted,  through  a  dry  bent  tube,  into  another  (dry)  test-tube 
surrounded  with  cold  water ;  the  vapors  then  condense  into  a  dark  red  liquid, 
which  is  decomposed  by  water;  if  this  liquid  be  treated  with  an  excess  of 
ammonia,  it  yields  a  yellow  solution  containing  Chloride  of  Ammonium  and 
Chromate  of  Ammonia,  and  if  this  be  mixed  with  excess  of  acetic  acid,  and 
acetate  of  lead,  a  yellow  precipitate  of  Chromate  of  Lead  is  obtained. 

HYDROBROMIC  ACID. 
Solution  lest  fitted  for  the  reactions:  Bromide  of  Potassium,  KBr. 

NITRATE  OP  SILVER  ;  in  neutral  and  acid  solutions,  a  yellowish-white  precipi- 
tate of  Bromide  of  Silver  ( AgBr),  which  becomes  violet  when  exposed  to  light ; 
insoluble  in  nitric  acid;  soluble,  though  less  easily  than  the  chloride,  in  ammo- 
nia, and  reprecipitated  by  nitric  acid;  if  the  bromide  of  silver  be  washed  by 
decantation,  dried,  and  heated  to  redness,  it  fuses  like  the  chloride. 

Solid  bromides  (bromide  of  potassium),  treated  with  CONCENTRATED  SUL- 
PHURIC ACID  in  the  cold,  evolve  fumes  Of  Hydrobromic  Acid  (similar  to  hydro- 
chloric  acid),  and  upon  heating  (especially  if  binoxide  of  manganese  be  added), 
vapors  of  Bromine : — 

KBr+2(HO.S03)=KO.S03+Br-f2HO  +  S03; 

the  bromine-vapors  may  be  recognized  by  their  red-brown  color,  their  peculiarly 
pungent  odor,  and  by  their  action  upon  a  little  starch-paste  (introduced  on  the 
end  of  a  glass  rod),  to  which  they  impart  a  fine  orange  color. 

Solid  bromides,  when  distilled  with  BICHROMATE  OP  POTASSA  and  CONCEN- 
TRATED SULPHURIC  ACID,  yield  pure  Bromine,  which  becomes  colorless,  or 
nearly  so,  when  treated  with  excess  of  ammonia.1 

CHLORINE-WATER,  added  to  a  solution  of  a  bromide,  liberates  the  bromine, 
which  imparts  an  orange  color  to  the  liquid;  an  excess  of  chlorine  should  be 
avoided,  since  it  converts  the  bromine  into  the  colorless  chloride  of  bromine. 
If  the  solution  containing  the  bromine  be  agitated  with  about  J  its  volume  of 
ether,  the  latter  dissolves  the  bromine,  and,  on  standing,  rises  with  it  to  the  sur- 
face, forming  a  red  layer  above  the  (now  nearly  colorless)  liquid.  The  ethereal 
solution  of  bromine  should  now  be  carefully  decanted  and  agitated  with  solution 
of  potassa,  when  it  becomes  nearly  colorless,  the  bromine  being  converted  into 
Bromide  of  Potassium  and  Bromate  of  Potassa  ;  the  solution  is  evaporated  in  a 
porcelain  dish  (the  glaze  of  which  will  suffer),  and  the  residue  heated  to  redness, 
when  the  bromate  of  potassa,  losing  its  oxygen,  is  converted  into  bromide  of 

1  This  affords  a  method  of  distinguishing  it  from  chlorochromic  acid,  which,  externally, 
it  much  resembles. 


SECOND   GROUP.  539 

potassium.  If  this  residue  be  now  heated  with  sulphuric  acid  and  linoxide  of 
manganese,  bromine  vapors  are  evolved,  and  may  be  recognized  by  the  starch- 
test. 

HYDRIODIC  ACID. 
Solution  best  fitted  for  the  reactions:  Iodide  of  Potassium,  KI. 

NITRATE  OF  SILVER;  yellow  precipitate  of  Iodide  of  Silver  (Agl),  which 
becomes  dark  when  exposed  to  light ;  insoluble  in  nitric  acid  and  in  ammonia. 

SULPHATE  OF  SUBOXIDE  OF  COPPER  (a  mixture  of  solutions  of  sulphate  ofcop- 
p&r  (1  part  of  the  crystals)  and  sulphate  of  iron  (2J  parts  of  the  crystals));  in 
neutral  and  slightly  alkaline  solutions;  a  brownish-white  precipitate  of  Sub- 
iodide  of  Copper  (Cu2I). 

BICHLORIDE  OF  PLATINUM  ;  a  dark  red  color.  This  reaction  is  mentioned, 
not  as  a  test  for  iodine,  but  because  it  interferes  with  the  detection  of  potassium, 
since  the  yellow  precipitate  of  the  double  chloride  of  platinum  and  potassium 
cannot  be  distinctly  seen  in  the  dark  red  liquid;  to  obviate  this  difficulty,  the 
iodine  should  be  expelled  by  evaporating  to  dryness  with  concentrated  nitric 
acid,  and  the  residue  may  then  be  dissolved  in  water,  and  tested  with  hydro- 
chloric acid  and  bichloride  of  platinum. 

STARCH  produces,  with  free  iodine,  a  fine  blue  compound ;  since  a  very  small 
quantity  of  iodine  suffices  for  this  purpose,  starch  is  employed  as  a  very  delicate 
test  for  that  substance.  The  solution  to  be  tested  should  be  mixed  with  a  small 
quantity  of  starch-paste  (prepared  by  heating  starch  with  water  till  the  granules 
have  burst),  and  concentrated  nitric  acid  (containing  one  of  the  red  oxides  of 
nitrogen  [N03  or  NOJ)  added  drop  by  drop.  An  excess  of  nitric  acid  destroys 
the  blue  compound;  alkalies  have  the  same  effect;  the  blue  color  disappears  if 
the  solution  be  heated.  When  the  starch  is  in  large  excess,  a  pink  or  violet 
compound  is  formed. 

Solid  iodides,  heated  with  CONCENTRATED  SULPHURIC  ACID,  evolve  violet  vapors 
of  Iodine  which  condense  upon  the  cool  part  of  the  tube  in  the  form  of  black 
scales;  if  a  little  starch-paste  be  exposed,  on  a  glass  rod,  to  these  vapors,  it 
assumes  a  dark  brownish-purple  color,  which  passes  inty  the  ordinary  indigo- 
blue  color  of  iodized  starch  when  stirred  up  with  water,  especially  if  a  little  more 
starch  be  added. 

CONCENTRATED  NITRIC  ACID  produces  a  black  precipitate  of  Iodine  in  solutions 
of  the  iodides. 

HYDROSULPHURIC  ACID. 
Solution  best  fitted  for  the  reactions:  Sulphide  of  Ammonium,  NH4S. 

NITRATE  OF  SILVER  ;  black  precipitate  of  Sulphide  of  Silver  (AgS) ;  insoluble 
in  cold  dilute  nitric  acid  /  soluble  in  hot  nitric  acid,  with  separation  of  sulphur ; 
insoluble  in  ammonia. 

ACETATE  OF  LEAD  ;  black  precipitate  of  Sulphide  of  Lead  (PbS). 

Sulphides,  treated  with  SULPHURIC  or  HYDROCHLORIC  ACID,  evolve  Hudrosul- 
phuric  Acid  (with  effervescence),  which  may  be  recognized  by  its  orfor}  and  by 
the  black  tinge  which  it  imparts  to  paper  impregnated  with  a  lead  salt.1 

Solid  sulphides  (sulphide  of  iron),  when  heated  with  NITRIC  ACID,  generally 
dissolve,  with  separation  of  sulphur,  unless  the  acid  is  very  concentrated. 

Solid  sulphides,  heated  in  a  tube  open  at  both  ends,  evolve  sulphurous  acid, 
which  may  be  recognized  by  its  odor. 

1  Some  sulphides,  as  those  of  copper  and  lead,  do  not  evolve  hydrosulphuric  acid; 
another  test  for  the  presence  of  sulphur  must  be  employed  in  such  cases. 


540  REACTIONS   OP   THE   ACIDS. 

Sulphides,  fused  on  platinum  wire  with  carbonate  of  soda,  in  the  reducing 
flame,  exhibit  the  same  deportment  as  the  sulphates  (see  p.  532). * 

HYDROCYANIC  ACID. 

Solution  best  fitted  for  the  reactions :  Cyanide  of  Potassium, 
KCy=KCaN. 

NITRATE  OF  SILVER;  a  white  precipitate  of  Cyanide  of  Silver  (AgCy),  which 
is  not  darkened  by  exposure  to  light ;  sparingly  soluble  in  cold  dilute  nitric  acid; 
soluble  in  the  concentrated  acid,  especially  on  heating;  readily  soluble  in  ammo- 
nia, and  partly  reprecipitated  by  the  careful  addition  of  excess  of  nitric  acid; 
readily  soluble  also  in  solution  of  cyanide  of  potassium. 

When  cyanide  of  silver  is  dried  and  heated  to  redness,  it  evolves  Cyanogen  ; 
if  the  experiment  be  performed  in  a  small  glass  tube  closed  at  one  end,  the  cyan- 
ogen may  be  recognized  by  its  odor,  and  by  its  burning  with  a  beautiful  peach- 
colored  flame,  a  residue  of  silver  and  paracyanide  of  silver  (isomeric  with  the 
cyanide)  is  left. 

If  the  cyanide  of  silver  be  heated  in  a  crucible,  only  Metallic  Silver  remains, 
which  is  entirely  dissolved  by  nitric  acid. 

A  MIXTURE  OP  PROTOSULPHATE  AND  SESQUiCHLORiDE  OP  IRON  ;  a  blue  pre- 
cipitate of  Sesquiferrocyanide  of  Iron  (Fe4Cfy3 — Prussian  blue)  ;a  insoluble  in 
dilute  acids,  decomposed  by  alkalies.  This  is  one  of  the  most  delicate  and  cha- 
racteristic tests  for  hydrocyanic  acid ;  since,  however,  the  reaction  does  not  take 
place  with  the  free  acid,  the  addition  of  an  excess  of  alkali  (potassa*)  should 
always  precede  that  of  the  iron-salts;  but  as  the  Prussian  blue  would  be  decom- 
posed by  the  alkali,  it  is  necessary  to  add  finally  an  excess  of  dilute  hydrochloric 
acid.  When  the  quantity  of  hydrocyanic  acid  is  very  minute,  a  bluish  color  is 
produced  at  first,  and  particles  of  Prussian  blue  are  deposited  after  a  time. 

When  free  hydrocyanic  acid  is  mixed  with  (yellow)  sulphide  of  ammonium 
containing  an  excess  of  sulphur,  Sulphocyanide  of  Ammonium  is  produced  : — 

HCy+NH4S+Sa=NH4CyS3(=NH4Csy)  +  HS; 

if  the  solution  be  evaporated  until  the  excess  of  sulphide  of  ammonium  is  expelled 
(which  is  known  by  tie  odor),  and  be  then  tested  with  sesquichloride  of  iron,  the 
blood-red  color  of  Sesquisulphocyanide  of  Iron  is  produced,  which  disappears  en- 
tirely on  adding  solution  of  chloride  of  mercury. 

Since  mere  traces  of  sulphocyanogen  give  the  blood-red  color,  this  becomes  an 
exceedingly  delicate  test  for  hydrocyanic  acid. 

Dilute  sulphuric  and  hydrochloric  acids  decompose  the  cyanides  with  evolution 
of  Hydrocyanic  Acid,  which  may  be  recognized  by  its  odor.  This  forms  the 
basis  of  an  excellent  process  for  examining  for  hydrocyanic  acid. 

The  substance  to  be  tested  is  placed  in  a  rather  tall  vessel  (a  narrow  beaker), 
and  an  excess  of  dilute  sulphuric  acid  mixed  with  it ;  the  mouth  of  the  vessel  is 
then  covered  with  a  watch-glass  (concave  surface  downwards)  moistened  inter- 
nally with  a  solution  of  nitrate  of  silver  ;  the  vessel  is  placed  in  a  warm  situa- 
tion, when  the  vapor  of  hydrocyanic  acid  which  is  evolved  produces  a  white 
film  of  Cyanide  of  Silver ;  this  watch-glass  may  now  be  replaced  by  another, 
moistened  with  yellow  sulphide  of  ammonium,  and,  after  a  short  time,  this  may 
be  removed,  the  excess  of  sulphide  of  ammonium  expelled  by  a  gentle  heat,  and 
the  residue  tested  with  sesquichloride  of  iron;  lastly,  the  vessel  may  be  covered 
with  a  third  watch-glass,  moistened  with  solution  of  potassa,  which,  after  a  few 
minutes,  may  fee  tested  with  the  mixed  iron  salts  and  hydrochloric  acid. 

1  Insoluble  sulphides,  fused  with  hydrated  alkalies,  yield  soluble  alkaline  sulphides. 

2  3KCy-f-FeO.SO,=K2Cy3Fe(=K2Cfy)-|-KO.S03,  and 

2FeaCl3-f3K2CtV=I'e4Cfy3-f6KCl 


THIRD   GROUP.  541 

Solid  cyanides,  heated  with  concentrated  sulphuric  acid)  evolve  Carbonic 
Oxide,  which  burns  with  a  blue  flame : — 

KC3N+2HO+2(HO.S03)=KO.S03+NH4O.S03+2CO. 

HYDROSULPHOCYANIC  ACID. 

Solution  best  fitted  for  the  reactions :  Sulphocyanide  of  Potassium, 

KCsy=KC>-S3. 

NITRATE  or  SILVER  ;  white  precipitate  of  Sulphocyanide  of  Silver  (AgCsy) ; 
insoluble  in  dilute  nitric  acid,  and  in  ammonia  ;  when  heated  to  redness,  sul- 
phocyanide  of  silver  is  decomposed,  leaving  only  metallic  silver. 

SESQUICHLORIDE  OF  IRON;  the  dark  blood-red  color,  already  noticed;  de- 
stroyed by  chloride  of  mercury. 

HYDROFERROCYANIC  ACID. 

Solution  best  fitted  for  the  reactions  :  Ferrocyanide  of  Potassium, 

KaCfy=K2Cy3Fe. 

NITRATE  OF  SILVER  ;  a  white  (or  nearly  white)  precipitate  of  Ferrocyanide 
of  Silver  (Ag2Cfy)  not  dissolved  by  dilute  nitric  acid  or  ammonia;  decomposed 
by  heat,  the  silver  being  reduced  to  the  metallic  state. 

The  reactions  of  this  acid  with  the  salts  of  iron  have  been  given  at  p.  516. 

HYDROFERRICYANIC  ACID. 

Solution  best  fitted  for  the  reactions  :  Ferricyanide  of  Potassium, 
K3Cfdy=K3Cy6Fea. 

NITRATE  OF  SILVER  ;  a  red-brown  precipitate  of  Ferricyanide  of  Silver  (Ag3 
Cfdy) ;  insoluble  in  dilute  nitric  acid;  soluble  in  ammonia  ;  decomposed  by 
heat,  with  reduction  of  silver. 

The  reactions  of  this  acid  with  iron-salts  have  been  given  at  p.  515. 

Sulphocyanides,  ferrocyanides,  and  ferricyanides  may  all  evolve  Carbonic 
Oxide  when  heated  with  concentrated  sulphuric  acid. 

The  two  latter,  when  heated  in  the  moist  state,  blacken,  and  evolve  Ammonia 
and  Hydrocyanic  Acid. 

All  three  salts  may  evolve  hydrocyanic  acid  when  heated  with  hydrochloric  acid. 


§344.    THIRD    GROUP. 
Acids  which  are  not  precipitable. 

NITRIC  ACID  (N05)  CHLORIC  ACID  (C105) 

HYPOCHLOROUS  ACID  (CIO). 

NITRIC  ACID. 

If  a  solution  of  a  nitrate  (nitrate  of  potassa)  be  mixed  with  about  half  its 
volume  of  concentrated  sulphuric  acid,  the  mixture  allowed  nearly  to  cool,  and 
a  crystal  of  sulphate  of  iron  then  dropped  into  it,  a  brown  ring  will  be  found 
around  the  crystal;  this  ring  will  only  appear  when  the  solution  has  been 
allowed  to  stand  for  some  time ;  agitation  and  elevation  of  temperature  should  be 
avoided,  since  they  tend  to  decompose  the  brown  Compound  of  Binoxide  of  Ni- 
trogen with  Sulphate  of  Iron  ;  the  formation  of  this  compound  is  explained  by 
the  following  equation  : — 

03)  +  KO.N05+4(HO.S03)=4(FeO.S03).N02-f 
3(Fe203.3S08)+KO.S03-f4HO. 


REACTIONS   OP  THE   ACIDS. 

If  the  above-mentioned  precautions  be  attended  to,  we  may  detect  very  small 
quantities  of  nitric  acid  by  this  test. 

If  a  solution  of  a  nitrate  (nitrate  of  potassa)  be  colored  distinctly  blue  with 
solution  of  indigo  (sulphindigotic  acid),  and  be  then  heated  with  a  little  concen- 
trated sulphuric  acid,  the  blue  color  will  give  place  to  a  yellow. 

Solid  nitrates  (nitrate  of  potassa)  when  heated  with  CONCENTRATED  SULPHU- 
RIC ACID,  evolve  fumes  of  Nitric  Acid,  often  accompanied  by  red-brown  vapors 
of  Peroxide  of  Nitrogen. 

If  a  solid  nitrate  be  heated  with  concentrated  sulphuric  acid  and  metallic  cop- 
per, red-brown  fames  of  Peroxide  of  Nitrogen  are  evolved. 

Solid  nitrates,  heated  with  hydrochloric  acid  (concentrated)  evolve  Peroxide 
of  Nitrogen  and  Chlorine. 

If  a  nitrate  be  heated  on  charcoal  before  the  blowpipe,  the  charcoal  burns  with 
deflagration,  at  the  expense  of  the  oxygen  furnished  by  the  salt. 

When  cyanide  of  potassium  in  small  quantity  is  fused  with  nitre  upon  pla- 
tinum foil,  pretty  violent  deflagration  ensues,  consequent  upon  the  sudden  evo- 
lution of  carbonic  acid  and  nitrogen,  caused  by  the  oxidation  of  the  cyanogen. 

CHLORIC  ACID. 

A  solution  of  a  chlorate  (chlorate  of  potassa)  behaves,  with  indigo  and  sul- 
phuric acid,  like  a"  nitrate. 

If  a  small  quantity  of  a  solid  chlorate  (chlorate  of  potassa)  be  dropped  into 
CONCENTRATED  SULPHURIC  ACID,  the  solution  immediately  assumes  a  deep  yellow 
color,  and  if  it  be  heated,  an  explosion  often  ensues,  from  the  sudden  evolution 
and  decomposition  of  the  Peroxide  of  Chlorine  (C104).  In  the  cold,  the  latter 
is  slowly  evolved,  and  may  be  recognized  by  its  deep  yellow  color  and  peculiar 
odor. 

Solid  chlorates,  when  heated  with  concentrated  hydrochloric  acid,  evolve  Eu- 
chlorine  (see  p.  138),  which  may  be  known  by  its  deep  yellow  color,  by  its  pecu- 
liar odor,  and  by  its  exploding  feebly  by  contact  with  flame. 

Chlorates,  like  nitrates,  deflagrate,  but  much  more  vividly,  on  charcoal,  and 
with  cyanide  of  potassium. 

HYPOCHLOROUS  ACID. 

Solution  best  fitted  for  the  reactions:    An  aqueous  solution  of  bleaching-powder 

(CaO.ClO+CaCl). 

Solutions  of  the  hypochlorites  bleach  organic  coloring  matters  (indigo,  litmus, 
&c.)  very  readily,  especially  when  mixed  with  a  little  free  acid. 

SULPHATE  OF  MANGANESE  gives,  with  solutions  of  hypochlorites,  a  black  pre- 
cipitate of  Binoxide  of  Manganese. 

Hypochlorites  evolve  chlorine  when  heated  with  sulphuric  and  hydrochloric 
acids. 


ORGANIC   ACIDS. 

§  345.  The  first  group  of  organic  acids  comprehends  those  which  are  imme- 
diately blackened  when  heated  with  concentrated  sulphuric  acid — viz.  tartaric, 
tannic,  and  gallic  acids. 

In  the  second  group  we  find  citric  and  uric  acids,  which  are  not  volatile  with- 
out decomposition,  but  are  not  immediately  blackened  when  heated  with  con- 
centrated sulphuric  acid. 

The  third  group  includes  those  acids  which  are  volatile  without  decomposi- 
tion j  benzoic,  succinic,  and  acetic  acids. 


REACTIONS   OF   THE   ACIDS.  .  543 


§346.  FIRST  GROUP. 

Acids  which  are  immediately  blackened  when  heated  with  concentrated 
sulphuric  acid. 

TARTARIC  ACID  (C8H4010=T) 
TANNIO  ACID  (C18H.09=Qt) 
GALLIC  ACID  (C7H03=G) 

TARTARIC  ACID. 
Solution  lest  fitted  for  the  reactions:    Tartrate  of  Soda,  2NaO/T. 

(A  perfectly  neutral  solution  of  this  salt  is  best  prepared,  extemporaneously, 
as  follows :  an  aqueous  solution  of  tartaric  acid  is  mixed  with  solution  of  car- 
bonate of  soda,  until,  after  heating  the  liquid  to  expel  the  free  carbonic  acid,  it 
has  only  a  slightly  acid  reaction  ;  a  small  excess  of  ammonia  is  then  added,  and 
the  solution  gently  evaporated  until  perfectly  neutral.) 

CONCENTRATED  SULPHURIC  ACID,  heated  with  (solid)  tartaric  acid,  or  a  tar- 
trate  decomposes  it  with  separation  of  Carbon,  which  renders  the  mixture  black; 
Carbonic  Oxide  (burning  with  a  blue  flame)  is  evolved  at  the  same  time. 

Solid  tartaric  acid  or  a  tartrate,  when  heated  on  platinum  foil,  chars,  often 
inflames,  burning  with  a  pale  flame,  and  evolves  a  peculiar  odor  of  burnt  sugar, 
which  is  perceived  more  readily  when  the  substance  is  heated  in  a  tube  open  at 
both  ends. 

CHLORIDE  OF  CALCIUM  ;  in  neutral  or  slightly  alkaline  solutions,  a  white  pre- 
cipitate of  Tartrate  of  Lime  (2CaO.T) ;  somewhat  soluble  in  water,  soluble  in 
solution  of  chloride  of  ammonium  ;*  soluble  also  in  potassa,  and  reprecipitated  on 
boiling ;  soluble  in  acetic  acid.  The  presence  of  ammoniacal  salts  always  retards 
or  prevents  this  precipitation,  which  is,  on  the  contrary,  promoted  by  the  addition 
of  free  ammonia. 

CHLORIDE  OF  BARIUM  ;  in  neutral  or  slightly  alkaline  solutions,  a  white  pre- 
cipitate of  Tartrate  of  Baryta (2BaO.T) ;  soluble  in  ammoniacal  salts;  soluble  in 
hydrochloric  acid. 

NITRATE  OF  SILVER  ;  a  white  precipitate  of  Tartrate  of  Silver  (2  AgO/T) ; 
readily  soluble  in  acids  and  in  ammonia. 

TANNIC  ACID. 
Solution  best  fitted  for  the  reactions :  Aqueous  solution  of  tannic  acid,  Qt. 

CONCENTRATED  SULPHURIC  ACID,  heated  with  (solid)  tannic  acid  produces, 
immediately,  a  dark,  purplish-black  liquid,  but  does  not  evolve  carbonic  oxide. 

When  heated  on  platinum,  tannic  acid  burns,  chars,  and  emits  a  peculiar 
odor. 

ALKALIES,  added  to  a  solution  of  tannic  acid,  cause  it  to  absorb  oxygen  from 
the  air,  and  to  assume  a  brown  color. 

SESQUICHLORIDE  OF  IRON  ;  a  bluish-black  precipitate  of  Tannate  of  Sesqui- 
oxide  of  Iron  (Fe203.Qt). 

DILUTE  SULPHURIC  (OR  HYDROCHLORIC)  ACID  produces,  in  a  pretty  concen- 
trated solution  of  tannic  acid,  a  white  precipitate,  which  is  an  insoluble  compound 
of  the  two  acids. 

1  When  this  precipitate  is  highly  crystalline,  it  is  most  difficult  to  redissolve  it  in 
chloride  of  ammonium. 


544  REACTIONS  OF  THE  ACIDS. 

GALLIC  ACID. 
Solution  lest  fitted  for  the  reactions  :  Aqueous  solution  of  gallic  acid,  G. 

CONCENTRATED  SULPHURIC  ACID  behaves,  with  gallic  acid,  much  in  the  same 
way  as  with  tannic  acid. 

Heat  also  affects  it  in  a  similar  manner,  though  the  odor  is  different. 
ALKALIES  cause  the  solution  of  gallic  acid  to  change  color  very  rapidly. 
SESQUICHLORIDE  OF  IRON  ;  a  bluish-black  precipitate. 

§347.  SECOND   GROUP. 

Acids  which  are  not  immediately  blackened  when  heated  with  concentrated 

sulphuric  acid. 

CITRIC  ACID  (C13H5011=Ci). 
URIC  ACID  (C10H3N405=U). 

CITRIC  ACID. 
Solution  lest  fitted  for  the  reactions  :  Citrate  of  Soda,  SNaO.Ci. 

(This  solution  may  be  prepared  exactly  as  recommended  in  the  case  of  tartaric 
acid.) 

CONCENTRATED  SULPHURIC  ACID,  when  heated  with  citric  acid,  decomposes  it 
with  evolution  of  Carbonic  Oxidej  which  burns  with  a  bluefla.me;  the  mixture 
blackens  only  after  long  boiling. 

Citric  acid,  when  heated  on  platinum  foil,  chars,  and  burns  with  a  pale  flame ; 
when  heated  in  a  tube  open  at  both  ends,  it  evolves  irritating  vapors. 

CHLORIDE  OF  CALCIUM,  added  to  a  neutral  solution  of  a  citrate,  does  not 
immediately  produce  a  precipitate  unless  the  solution  be  very  concentrated,  but, 
on  boiling,  Citrate  of  Lime  (SCaO.Ci)  being  less  soluble  in  hot  water  than  in 
cold,  is  immediately  precipitated;  it  is  soluble  in  much  water;  insoluble  in 
potassa ;  soluble  (though  with  some  difficulty)  in  chloride  of  ammonium;  the 
presence  of  free  ammonia  promotes  the  precipitation,  while  ammoniacal  salts 
prevent  it. 

CHLORIDE  OF  BARIUM;  a  white  precipitate  of  Citrate  of  Baryta  (SBaO.Ci); 
soluble  in  much  water,  in  free  acids  and  in  ammoniacal  salts. 

NITRATE  OF  SILVER;  a  white  precipitate  of  Citrate  of  Silver  (SAgO.Ci), 
readily  soluble  in  nitric  acid  and  in  ammonia. 

URIC  ACID. 

CONCENTRATED  SULPHURIC  ACID,  with  the  aid  of  heat,  dissolves  uric  acid 
without  change;  if  the  heat  be  long  continued,  the  liquid  becomes  dark. 

Uric  acid,  when  heated  alone,  evolves  an  odor  of  Ammonia  and  Hydrocyanic 
Acid,  followed  by  an  odor  similar  to  that  of  burnt  hair  ;  it  leaves  a  dark  carbon- 
aceous residue. 

Uric  acid  is  almost  insoluble  in  water  and  in  hydrochloric  acid. 

DILUTE  NITRIC  ACID,  with  the  aid  of  heat,  dissolves  uric  acid  with  efferves- 
cence and  evolution  of  red  fumes,  the  uric  acid  being  oxidized  at  the  expense  of 
the  nitric  acid.  If  the  nitric  solution  be  evaporated  just  to  dryness,  it  leaves  a 
yellow  residue,  which  becomes  reddish  on  further  heating,  and  assumes  a  fine 
purple-red  color  on  the  gradual  addition  of  ammonia  in  excess ;  this  reaction  is 
clue  to  the  production  of  a  peculiar  purple  body,  termed  Murexide,  resulting  from 
the  action  of  ammonia  upon  the  products  of  oxidation  of  uric  acid. 


REACTIONS   OP   THE   ACIDS.  545 

In  applying  this  test  to  very  small  quantities  of  material,  a  piece  of  platinum 
foil,  or  a  small  capsule  of  that  metal  may  be  employed. 

POTASSA  (diluted')  readily  dissolves  uric  acid,  which  is  reprecipitated  from  the 
solution  as  a  white  crystalline  powder  on  adding  hydrochloric  acid. 


§348.  THIRD   GROUP. 

Acids  which  are  volatile  without  decomposition. 

BENZOIC  ACID  (CMH503=Bz) 
SUCCINIC  ACID  (C8H3O5=S) 
ACETIC  ACID  (C4H303=A). 

BENZOIC  ACID. 

Solution  best  fitted  for  the  reactions  :  Benzoate  of  Oxide  of  Ammonium 

NH4O.Bz. 

(Prepared  by  dissolving  benzoic  acid  in  solution  of  ammonia,  and  evaporating 
at  a  gentle  heat,  until  the  solution  is  no  longer  alkaline.) 

Benzoic  acid,  heated  on  platinum  foil,  volatilizes,  in  great  part,  without  decom- 
position, yielding  highly  irritating  vapors,  having  the  odor  of  frankincense  ;  if 
the  flame  be  allowed  to  play  upon  it,  it  burns  with  a  bright,  smoky  flame. 
When  heated  in  a  tube  open  at  both  ends,  a  portion  of  the  acid  condenses  in 
feathery  crystals,  upon  the  cool  part  of  the  tube. 

When  heated  with  CONCENTRATED  SULPHURIC  ACID,  benzoic  acid  volatilizes, 
with  its  peculiar  odor,  but  is  not  blackened. 

NITRATE  OF  SILVER,  in  neutral  solutions,  a  white  precipitate  of  Benzoate  of 
Silver  (AgO.Bz)  readily  soluble  in  nitric  acid  (with  separation  of  benzoic  acid, 
if  the  solution  be  concentrated)  and  in  ammonia. 

SESQUICHLORIDE  OF  IRON  ;  in  neutral  solutions,  a  pale  buff  precipitate  of 
Benzoate  of  Sesquioxide  of  Iron  (Fe203.3Bz);  ammonia  in  excess  withdraws 
the  benzoic  acid  from  this  precipitate,  leaving  only  the  hydrated  sesquioxide  of 
iron. 

HYDROCHLORIC  ACID  precipitates  benzoic  acid  from  its  solutions,  if  they  be 
not  too  dilute,  in  white  crystalline  flakes. 

SUCCINIC  ACID. 
Solution  best  fitted  for  the  reactions:  Succinate  of  Oxide  of  Ammonium, 


(Prepared  in  the  same  way  as  the  benzoate.) 

Succinic  acid,  heated  on  platinum  foil,  evolves  vapors  which  excite  an  invo- 
luntary fit  of  coughing;  when  inflamed,  it  burns  with  a  much  paler  flame  than 
benzoic  acid  j  if  heated  in  a  tube  open  at  both  ends,  a  great  part  of  it  sublimes. 

It  behaves,  with  CONCENTRATED  SULPHURIC  ACID,  like  benzoic  acid. 

NITRATE  OF  SILVER;  same  result  with  succinic  acid  as  with  benzoic. 

SESQUICHLORIDE  OF  IRON,  in  neutral  solutions,  a  red-brown  precipitate  (Suc- 
cinate of  Sesquioxide  of  Iron)  which  is  decomposed  by  ammonia. 

CHLORIDE  OF  BARIUM  does  not  precipitate  a  solution  of  a  succinate,  even  after 
addition  of  free  ammonia,  but  if  alcohol  be  added  a  white  precipitate  is  pro- 
duced. 

35 


546  SYSTEMATIC   COURSE   OF   ANALYSIS. 


ACETIC  ACID. 

Heat  decomposes  the  solid  acetates  (acetate  of  potassa,  e.  #.),  with  evolution 
of  vapor  of  Acetone  (C3H30)  which  has  a  peculiar  aromatic  odor,  and  burns  with 
a  pale  flame. 

Acetates,  when  heated  with  CONCENTRATED  SULPHURIC  ACID,  evolve  Acetic 
Acid,  known  by  its  odor  of  vinegar. 

When  heated  with  concentrated  sulphuric  acid  and  alcohol,  the  acetates  fur- 
nish Acetic  Ether  (C4H5O.C4H303)  which  is  characterized  by  a  most  agreeable 
aromatic,  odor,  more  readily  perceived  when  the  solution  cools. 

SESQUICHLORIDE  OF  IRON  produces,  in  neutral  solutions  of  acetates  (acetate 
of  potassa),  the  fine  red  color  of  Acetate  of  Sesquioxide  of  Iron  (Fe203.3A) 
which  does  not  disappear  on  addition  of  chloride  of  mercury. 

NITRATE  OF  SILVER  ;  in  neutral,  pretty  concentrated  solutions,  a  white  crys- 
talline precipitate  of  Acetate  of  Silver  (AgO.A)  readily  soluble  in  nitric  acid, 
and  in  ammonia. 


SYSTEMATIC  COURSE  FOR  THE  ANALYSIS  OF 
SUBSTANCES  WHICH  MAY  CONTAIN  ALL  THE 
MORE  FREQUENTLY  OCCURRING  BASES  AND 
ACIDS. 

§  349.  In  the  following  systematic  course,  we  proceed  upon  the  supposition 
that  the  substance  under  examination  is  solid,  and  is  neither  a  metal  nor  an 
alloy,  since,  in  the  analysis  of  substances  of  this  description,  special  methods  are 
followed,  which  will  be  described  hereafter. 

The  process  of  analysis  is  divided  into  the  five  following  parts  : — 

1.  The  mechanical  division  of  the  substance  which  is  necessary  to  facilitate 
the  action  of  solvents. 

2.  The  preliminary  examination,  consisting  of  a  few  simple  experiments, 
from  which  we  may  obtain  very  valuable  information  as  to  the  nature  of  the 
substance,  before  proceeding  to  the  regular  analysis. 

3.  The  process  of  solution,  in  which  the  substance  is  treated  with  water  and 
acids;  or,  if  it  be  insoluble  in  these,  is  fused  with  alkaline  carbonates,  in  order 
to  reduce  it  to  a  fit  state  for  the  application  of  reagents. 

4.  The  treatment  with  general  reagents  which  serve  to  indicate  the  groups  to 
which  the  bases  and  acids  present  belong. 

5.  The  special  examination  for  the  individual  members  of  each  group. 

The  processes  for  the  detection  of  bases  and  of  acids,  though  separately  con- 
ducted, are  founded  upon  th.e  same  broad  principles.1 

MECHANICAL  DIVISION  OF  THE  SUBSTANCE. 

§  350.  The  substance  intended  for  analysis  should  first  be  coarsely  pounded 
in  an  iron  or  Wedgwood  mortar  (according  to  its  hardness),  and  afterwards 
ground  to  powder.  Few  substances  require  any  further  preparation,  but  in  some 
cases,  small  hard  fragments  remain  intermixed  with  the  powder ;  these  should 
be  separated  from  the  latter,  by  rubbing,  with  a  pestle,  or  with  the  fingers,  upon 
a  piece  of  muslin  stretched  across  the  mouth  of  a  beaker ;  any  fragments  remain- 

1  We  may  remind  the  student,  that  all  the  manipulations  involved  in  the  following 
analytical  operations  have  been  fully  described  in  a  former  portion  of  the  work. 


PRELIMINARY   EXAMINATION   FOR   BASES.  547 

ing  upon  the  muslin  must  be  powdered  and  sifted  until  entirely  reduced.  The 
whole  of  the  powder  should  be  well  mixed  before  separating  any  portion  for 
analysis. 


EXAMINATION    FOR    BASES. 

i 

§  351.  PRELIMINARY  EXAMINATION. 

Experiment  1. — A  small  portion  of  the  powder1  is  heated  in  a  glass  tube  open 
at  both  ends,  and  held  somewhat  obliquely,  to  allow  of  the  passage  of  a  slow 
current  of  air.3 

I.  The  substance  volatilizes,  either  entirely  or  partly : — presence  of  compounds 
of  ammonium,  mercury,  arsenic,  antimony,  or  cadmium,  or  of  sulphur,  oxalic 
acid,  or  some  organic  substance. 

Fumes  are  evolved,  having  the  odor  of  burning  sulphur : — presence  of  SUL- 
PHUR or  of  a  SULPHIDE. 

The  fumes  have  the  odor  of  garlic : — presence  of  ARSENIC. 

A  white  amorphous  sublimate  is  formed  upon  the  cool  part  of  the  tube : — 
presence  of  a  compound  of  AMMONIUM,  CADMIUM,  or  MERCURY.  (The  subli- 
mate of  arsenious  acid  sometimes  appears  amorphous  to  the  unassisted  eye.) 

A  white  sublimate  of  'minute  (octohedral)  crystals  is  formed  upon  the  side  of 
the  tube  : — probably  ARSENIOUS  ACID. 

A  sublimate  composed  of  very  distinct  crystals  is  formed  : — probable  presence 
of  certain  ORGANIC  ACIDS  (see  p.  545). 

A  gray  sublimate  is  formed: — probably  consists  of  globules  of  MERCURY, 
which  unite  into  larger  globules  when  rubbed  with  a  glass  rod. 

The  sublimate  is  yellow  : — probably  SULPHUR. 

II.  The  substance  changes  color,  without  evolution  of  odor : — probable  pre- 
sence of  a  heavy  metallic  oxide.3 

The  substance  blackens,  at  the  same  time  evolving  a  peculiar  odor : — presence 
of  organic  matter. 

III.  Deflagration  or  detonation  takes  place. 

Presence  of  a  nitrate  or  chlorate,  together  with  combustible  matter. 

Exp.  2.  The  substance  is  heated,  on  charcoal,  with  carbonate  of  soda,  in  the  re- 
ducing flame  of  the  blowpipe,  the  oxidizing  flame  being  allowed  to  spread  over 
the  charcoal4  (see  p.  109).  Should  no  reduced  metal  make  its  appearance  after 
exposure  for  two  or  three  minutes  to  the  flame,  a  little  cyanide  of  potassium 
may  be  added,  and  the  experiment  continued. 

If  no  metal  is  visible  at  the  end  of  the  operation,  the  test  specimen  and  sur- 
rounding particles  of  charcoal  should  be  levigated  as  directed  at  p.  109. 

I.  A  metallic  globule  is  obtained. 

The  globule  is  tested  as  to  its  malleability  (p.  109). 

Malleable  : — LEAD  (makes  a  black  streak  upon  paper) ;  a  yellow  incrustation 
is  formed  upon  the  charcoal.  TIN;  a  slight  white  incrustation.  COPPER  (known 
by  its  color).  SILVER. 

Semi-malleable : — BISMUTH  j  a  yellow  incrustation. 

1  Even  small  crystals  should  be  reduced  to  powder,  since  otherwise  they  are  liable  to 
decrepitate. 

2  This  experiment  is  sometimes  made  in  an  iron  spoon,  but  it  is  obvious  that  several 
valuable  indications  are  then  lost. 

3  All  oxides  fall  under  this  designation,  except  the  alkalies,  the  alkaline  earths,  and 
the  earths  proper  (alumina,  glucina,  &c.). 

4  Should  sulphur  be  present,  the  substance  should  be  roasted  for  some  time  in  the 
outer  flame,  as  directed  at  p.  109 ;  but  it  must  then  be  remembered  that  arsenic  and  cad- 
mium may  have  volatilized  during  the  roasting. 


548  THE   PROCESS   OF    SOLUTION. 


• 


Brittle: — ANTIMONY;  abundant  white  incrustation. 

II.  No  globule  is  obtained,  but  shining  metallic  spangles  are  observed  after 
levigation  :  probably  tin,  antimony,  or  copper. 

III.  No  metal  is  obtained,  but  merely  an  incrustation  on  the  charcoal. 

The  incrustation  is  white :  probably  due  to  ZINC  (the  incrustation  is  yellow 
while  hot).  ARSENIC  ;  a  garlic  odor  is  perceived  during  the  experiment.  Salts 
of  ammonium  and  mercury. 

The  incrustation  is  brown :  presence  of  CADMIUM. 

IV.  If  a  deflagration  be  observed  in  this  experiment,  it  indicates  the  presence 
of  a  nitrate  or  chlorate. 

V.  If  a  light-colored  infusible,  highly  incandescent  mass  be  left  upon  the 
charcoal,  it  is  probable  that  either  silica,  an  alkaline  earth,  or  an  earth,  or  oxide 
of  zinc,  is  present. 

Exp.  3. — The  substance  is  added,  by  small  portions  at  a  time,  to  a  bead  of 
borax,  and  heated,  first  in  the  outer,  then  in  the  inner  blowpipe-flame,  the  color 
produced  in  each  case  being  carefully  observed,  both  in  the  hot  and  cold  bead 
(see  p.  109). 

.1.  A  green  lead  is  obtained  in  the  outer  flame  :  presence  of  CHROMIUM  ;  the 
color  varies  from  greenish-yellow  to  yellowish-green  in  the  outer  flame,  and  be- 
comes a  pure  emerald  green  in  the  inner  flame.  COPPER  ;  bluish-green  (or 
greenish-blue),  either  disappearing  entirely,  or  requiring  a  partial  opaque-red 
color  in  the  inner  flame. 

II.  A  reddish-yellow  bead  is  obtained  in  the  outer  flame ;  presence  of  IRON  ; 
the  color  either  vanishes  or  fades,  on  cooling,  and  becomes  bottle-green  in  the 
inner  flame.     NICKEL  ;  the  color  vanishes  or  fades  on  cooling,  and  becomes 
dusky  purple  or  gray  in  the  inner  flame.     If  a  minute  particle  of  nitre  be  now 
added  to  the  bead,  and  the  latter  again  exposed  to  the  outer  flame,  it  acquires  a 
bluish-purple  tint. 

III.  A  violet  or  pink  (amethyst}  bead  is  obtained  in  the  outer  flame  :  pre- 
sence of  MANGANESE  :  the  color  vanishes  on  long  exposure  to  the  inner  flame. 

IV.  A  blue  bead  is  obtained  in  the  outer  flame :  presence  of  COBALT  ;   the 
color  is  pure  blue,  and  unchanged  by  exposure  to  the  inner  flame.    COPPER  ; 
greenish-blue  (or  bluish-green),  either  vanishing  or  becoming  tinged  opaque  red 
in  parts,  in  the  inner  flame. 

Exp.  4. — A  portion  of  the  substance  is  mixed,  in  a  dish,  with  hydrate  of 
lime  and  a  little  water,  and  a  gentle  heat  applied. 

Pungent  vapors  are  evolved,  which  yield  white  fumes  with  hydrochloric  acid, 
and  are  alkaline  to  moistened  test-papers.  Presence  of  AMMONIA. 

THE  PROCESS  OF  SOLUTION. 

§  352.  The  following  general  method  of  dissolving  a  substance  to  be  submitted 
to  analysis,  is  laid  down  upon  the  supposition  that  the  analyst  is  totally  ignorant 
of  the  nature  of  the  substance  (which  is  comparatively  seldom  the  case),  and,  in 
many  instances,  the  same  result  (viz.  the  complete  solution  of  the  matter)  may 
be  arrived  at  by  a  much  less  circuitous  path,  the  discovery  of  which,  however,  must 
obviously  be  left  to  the  judgment  (guided  by  experience)  of  the  analyst  himself. 

Before  describing  the  process  of  solution,  it  may  be  well  to  observe  that  when 
a  residue  is  left  after  treatment  with  any  solvent,  it  should  be  well  washed,  if 
possible,  by  decantation,  since  another  solvent  may  be  much  more  easily  applied 
to  a  residue  in  a  test-tube  than  to  one  which  has  been  thrown  upon  a  filter. 

I.  A  small  portion  (about  20grs.)  of  the  substance  is  boiled  with  a  moderate 
quantity  (2  or  3  drachms)  of  water,  in  a  test-tube ;  if  any  residue  remains,  it  is 
allowed  to  subside  in  the  tube,  if  possible,  the  supernatant  liquid  filtered,  and  a 
drop  or  two  of  the  filtrate  evaporated  upon  platinum  or  in  a  watch-glass  j  if  any 
considerable  residue  be  obtained,  the  aqueous  solution  is  set  aside  for  analysis. 


TREATMENT   WITH    GENERAL   REAGENTS.  549 

II.  The  residue  insoluble  in  water  is  washed  once  or  twice,  if  possible,  by 
decantation ;  this  residue  is  boiled  with  concentrated  hydrochloric  acid  (unless 
silver  or  lead  be  suspected,  when  concentrated  nitric  acid  should  be  employed), 
water  then  added,  the  whole  again  boiled,  the  residue,  if  any,  allowed  to  subside, 
and  the  supernatant  liquid  filtered. 

III.  The  portion  left  undissolved  by  hydrochloric  acid  is  washed  twice  or  thrice 
with  water,  and  boiled  with  concentrated  nitric  acid  (of  course,  if  nitric  acid  was 
employed  before,  hydrochloric  acid  must  be  used  here} ;  should  this  fail  to  dis- 
solve it,  a  few  drops  of  concentrated  hydrochloric  (or  nitric)  acid  are  added,  the 
whole  again  boiled,  diluted  with  water  and  the  boiling  repeated.    If  any  residue 
remain  after  this  treatment  with  nitro-hydrochloric  acid,  it  is  collected  upon  a 
filter,  washed,  dried,  and  set  aside  for  examination  by  Table  VIII. 

If  the  analyst  desire  to  ascertain  in  what  forms  of  combination  the  various 
constituents  of  the  substance  exist  (as  is  usually  the  case  in  the  analysis  of  arti- 
ficial products),  he  must  examine  the  aqueous  solution  separately  from  the  acid 
solutions.  The  examination  is  conducted  according  to  Table  I. 

If  a  solution  in  nitric  acid  has  been  prepared,  it  must  be  tested  with  a  little 
hydrochloric  acid,  and  should  this  produce  any  precipitate,  a  sufficient  quantity 
must  be  added  to  separate  the  silver  or  lead  as  completely  as  possible  from  the 
solution;  the  precipitate  is  set  aside  for  examination  by  Table  II.,  and  the  fil- 
trate is  mixed  with  the  other  acid  solution  of  the  substance  (the  subsequent 
process  being  conducted  as  in  the  following  case). 

Should  hydrochloric  acid  have  been  employed  first,  the  two  acid  solutions 
may  be  mixed  together,  and  if  any  precipitate  result  from  the  mixture,  it 
may  be  gently  warmed  with  a  slight  excess  of  hydrochloric  acid,  and  if  not  dis- 
solved, analyzed  as  an  insoluble  substance.  The  mixed  acid  solutions  should  be 
carefully  evaporated  to  a  very  small  bulk,  to  expel  the  greater  portion  of  the 
acid,  then  diluted  with  water  strongly  acidulated  with  hydrochloric  acid,  and 
analyzed  according  to  Table  I,  omitting,  of  course,  the  addition  of  hydrochloric 
acid. 

If,  however,  the  arrangement  of  the  constituents  be  a  matter  of  indifference, 
the  aqueous  solution  may  be  mixed  with  hydrochloric  acid,  in  order  to  separate 
any  silver,  lead,  or  suboxide  of  mercury  (Table  II.),  and  afterwards  added  to  the 
acid  solutions  of  the  substance;  any  precipitate  which  is  thus  produced  is 
warmed  with  hydrochloric  acid,  and,  if  undissolved,  analyzed  as  an  insoluble 
substance  (Table  VIII.). 

The  mixed  solutions  are  evaporated  to  expel  excess  of  acid,  diluted  with  water 
(strongly  acidulated  with  hydrochloric  acid),  and  examined  by  Table  I.,  omitting 
to  add  more  hydrochloric  acid. 

TREATMENT  WITH  GENERAL  REAGENTS. 

§  353.  In  using  the  following  general  table,  the  analyst  will  at  once  appreciate 
the  great  economy  of  time  which  will  result  from  his  proceeding  always  according 
to  some  regular  plan.  Thus,  it  is  advantageous  to  make  the  filtrate  the  chief 
object  of  attention,  setting  aside  each  precipitate,  as  it  is  obtained,  for  subsequent 
examination.  These  precipitates  may  be  well  washed  whilst  the  operator  is  pro- 
ceeding with  the  filtrate. 

Again,  the  time  occupied  in  the  evaporation  of  the  filtrate  from  the  sulphuret- 
ted hydrogen  precipitate  may  be  employed  in  the  examination  of  the  latter,  or 
of  the  precipitate  produced  by  hydrochloric  acid. 

Such  arrangements  as  these  will  readily  suggest  themselves  to  every  analyst, 
and  will  be  found  to  shorten  very  considerably  the  time  occupied  by  the  whole 
process,  especially  when  he  is  sufficiently  well  versed  in  it  to  examine  more  than 
one  substance  at  the  same  time. 


550 


TABLE   I. — EXAMINATION   TOR  BASES. 


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TABLE  II. — EXAMINATION  FOR  BASES. 


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TABLE  III.    (continued}  —  EXAMINATION   FOR  BASES. 


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556  NOTES   TO   PRECEDING    TABLES. 


NOTES  TO  TABLE  I. 

1.  It  must  be  borne  in  mind  that  certain  oxy chlorides,  e.  g.  those  of  antimony 
and  bismuth,  may  be  precipitated  upon  the  first  addition  of  hydrochloric  acid ; 
these  redissolve,  however,  in  an  excess  of  the  latter,  which  should  therefore  be 
added  as  long^as  it  appears  to  diminish  the  quantity  of  the  precipitate. 

2.  If  arsenic  have  been  detected  in  the  preliminary  examination,  this  filtrate 
must  now  be  completely  saturated  with  sulphurous  acid  (for  the  mode  of  prepa- 
ration^ see  p.  157),  and  evaporated  to  expel  excess  of  this  reagent,  which  reduces 
the  arsenic  acid  to  the  state  of  arsenious.     If  baryta,  strontia,  or  oxide  of  lead 
be  present,  the  sulphurous  acid  will  give  rise  to  a  precipitation  of  the  sulphates 
of  these  oxides;  the  precipitate  should  be  separated,  and  gently  heated  with 
concentrated  hydrochloric  acid ;  if  it  be  sulphate  of  lead,  it  will  dissolve,  and 
the  solution  may  be  mixed  with  that  from  which  the  precipitate  was  originally 
obtained,  but  if  it  be  insoluble  in  concentrated  hydrochloric  acid,  it  must  be 
examined  as  a  substance  insoluble  in  water  and  acids. 

3.  It  will  be  found  convenient,  in  many  cases,  to  test  a  small  portion  of  this 
filtrate  by  adding  a  saturated  solution  of  sulphuretted  hydrogen,  and  boiling ; 
for  if  no  change  be  thus  produced,  it  is  of  course  unnecessary  to  treat  the  whole 
of  the  solution  with  that  reagent. 

It  is  requisite,  especially  if  arsenic  or  platinum  be  present,  to  digest  the  liquid 
for  some  time  at  a  moderate  heat,  after  saturation  with  sulphuretted  hydrogen, 
and  to  repeat  the  operation  several  times  before  these  metals  are  completely 


Sulphuretted  hydrogen  often  produces  a  precipitate  of  sulphur,  arising  from 
the  presence  of  an  oxidizing  agent  (rdtric  acid,  sesquioxide  of  iron,  &c.);  this 
precipitate  may  be  distinguished  from  all  others  by  its  white  color,  and  by  its 
remaining  suspended  in  the  liquid,  and  may  be  neglected  altogether. 

If  the  application  of  sulphuretted  hydrogen  to  a  yellow  or  red  solution  should 
change  its  color  to  a  distinct  green,  from  the  reduction  of  chromic  acid,  it  will 
be  expedient  to  treat  the  whole  of  the  solution  with  sulphuretted  hydrogen,  in 
order  to  effect  the  complete  reduction. 

4.  The  necessity  of  these  operations  will  be  apparent  from  the  following 
remarks. 

If  the  excess  of  sulphuretted  hydrogen  were  not  expelled  from  the  filtrate 
before  adding  the  nitric  acid,  the  latter  might  give  rise,  by  oxidation  of  the  sul- 
phur, to  sulphuric  acid,  which  would  precipitate  baryta,  strontia,  and  perhaps 
even  lime,  as  sulphates. 

The  nitric  acid  is  added  in  order  to  oxidize  any  oxalic  acid  or  organic  matter, 
the  former  of  which  would  carry  down  the  baryta,  strontia,  and  lime  in  the  form 
of  oxalates,  upon  the  subsequent  addition  of  ammonia,  while  the  organic  matter 
may  interfere  materially  with  the  detection  of  the  various  bases.  It  is  advisable 
to  evaporate  with  nitric  acid,  even  though  the  preliminary  examination  may  not 
have  indicated  the  presence  of  oxalic  acid  or  of  organic  matter,  since  small  quan- 
tities of  these  might  easily  escape  detection. 

The  solution  must,  in  any  case,  be  evaporated  to  dryness,  in  order  to  convert 
any  silica  into  the  insoluble  form,  since  the  soluble  modification  might  be  easily 
mistaken  for  alumina. 

The  dry  residue  should  not  be  strongly  heated,  if  it  can  be  avoided,  since 
many  of  the  oxides  are  redissolved  with  considerable  difficulty  after  ignition. 

5.  An  experienced  eye  will   at   once  discern  whether  this  residue  consists 
solely  of  silica.     Its  color  will  show  whether  it  is  likely  to  contain  any  sesqui- 
oxides  of  iron  or  of  chromium  (which  redissolve  with  great  difficulty  after  strong 
ignition);  if  the  flakes  of  silica  be  mixed  with  a  white  powder,  this  will  proba- 


NOTES   TO   TABLES   II.    AND   III.  557 

bly  consist  of  sulphate  of  baryta  or  of  strontia,  arising  from  the  formation  of 
sulphuric  acid  by  the  oxidizing  action  of  the  nitric  acid.  When  the  analyst  is 
not  satisfied  that  this  residue  consists  of  silica  only,  he  should  examine  it  as  a 
substance  insoluble  in  water  and  acids.  (Table  VIII.) 

6.  Chloride  of  ammonium  is  added  to  prevent  the  precipitation  of  magnesia 
(in  any  other  form  but  that  of  phosphate)  by  ammonia. 

The  odor  will  show  when  an  excess  of  sulphide  of  ammonium  has  been  added. 
The  mixture  is  boiled  with  this  reagent  in  order  to  promote  the  decomposition 
of  any  phosphate  of  iron,  &c.,  which  might  be  precipitated  by  the  ammonia. 

7.  Small  quantities  of  the  oxalates  and  borates  of  the  alkaline  earths,  and  of 
the  fluorides  of  the  alkaline-earth-metals  may  also  be  obtained  in  this  precipitate, 
but  need  not  be  regarded,  since  their  bases  will  always  be  detected  in  the  filtrate, 
and  the  acids  cannot  be  overlooked  in  the  ordinary  method  of  examination  for 
acids. 

8.  Should  this  filtrate  have  a  brown  color,  indicative  of  dissolved  sulphide  of 
nickel,  it  is  evaporated  until  the  excess  of  sulphide  of  ammonium  is  expelled, 
acidified  with  dilute  hydrochloric  acid,  the  precipitate  thrown  upon  a  filter,  and 
examined  together  with  that  previously  obtained. 

9.  The  solution  should  not  be  boiled,  since  the  chloride  of  ammonium  might 
then  decompose  and  dissolve  the  carbonates  of  the  alkaline  earths. 

10.  The  presence  of  soda  may  be  confirmed,  and  some  idea  of  its  quantity 
obtained,  by  decanting  the  supernatant  liquid  (containing  excess  of  bichloride  of 
platinum)  from  this  crystalline  precipitate,  and  evaporating  it  slowly  down,  in  a 
watch-glass,  placed  upon  a  water-bath;  the  double  chloride  of  platinum  and  so- 
dium crystallizes  in  radiated  needles,  at  the  margin  of  the  evaporated  liquid. 

The  most  delicate  method  of  testing  for  potassa  consists  in  evaporating  the 
liquid,  mixed  with  bichloride  of  platinum,  to  dryness,  on  a  water-bath,,  and  treat- 
ing the  residue  with  alcohol  and  a  little  water,  when  the  crystalline  double  chlo- 
ride of  platinum  and  potassium  will  remain  undissolved. 

NOTES  TO  TABLE  II. 

1.  Boracic,  benzoic,  and  uric  acids  are  occasionally  precipitated  here,  if  the 
solution  be  pretty  concentrated;  the  two  former  are  dissolved  by  hot  water,  and 
the  uric  acid  by  heating  with  nitric  acid. 

2.  Should  this  precipitate  contain  very  much  chloride  of  lead,  it  should  be 
boiled  with  successive  quantities  of  water,  until  a  portion  of  the  solution,  decant- 
ed into  a  watch-glass,  no  longer  crystallizes  on  cooling. 

NOTES  TO  TABLE  III.1 

1.  When  a  large  quantity  of  precipitate  is  at  our  disposal,  it  is  convenient  to 

1  Ansell  has  recently  proposed  a  method  for  the  detection  of  antimony  and  arsenic  in 
the  presence  of  tin,  by  which  very  small  quantities  of  the  two  former  metals  may  be  de- 
tected. The  sulphides  precipitated  from  their  solution  in  sulphide  of  ammonium  are 
redissolved  in  nitro-hydrochloric  acid,  and  the  solution  poured  into  a  hydrogen-appa- 
ratus so  arranged  as  to  allow  the  gas  to  be  washed  with  a  dilute  solution  of  acetate  of 
lead,  which  absorbs  any  hydrochloric  acid  or  sulphuretted  hydrogen,  and  to  pass  the 
mixture  of  antimoniuretted,  arseniuretted,  and  free  hydrogen  into  a  test-tube  half- filled 
with  concentrated  nitric  acid,  which  converts  the  antimony  and  arsenic  into  antimonic 
and  arsenic  acids.  After  the  gas  has  passed  for  about  15  minutes,  the  nitric  solution  is 
evaporated,  the  residue  pretty  strongly  heated  on  a  sand-bath,  and  treated  with  warm 
water,  which  dissolves  the  arsenic  and  arsenious  acids ;  the  aqueous  solution  is  mixed 
with  nitrate  of  silver,  and  ammonia  very  cautiously  added,  which  causes  a  precipitate 
of  arseniate  or  arsenite  of  silver.  The  residue  of  antimonic  acid  is  dissolved  in  a  very 
little  nitro-hydrochloric  acid,  evaporated  as  far  as  possible,  and  tested  with  sulphuretted 
hydrogen  for  antimony.  In  order  to  detect  the  tin,  the  metallic  precipitate  is  washed 


558  NOTES   TO   TABLES   III.    AND   IV. 

treat  a  small  portion,  first,  with  sulphide  of  ammonium,  and  should  any  part  of 
it  be  dissolved,  to  digest  the  whole  of  the  precipitate  with  that  reagent.  In 
order  to  ascertain  whether  any  portion  of  the  precipitate  has  been  dissolved  by 
the  sulphide  of  ammonium,  the  solution  is  tested  with  a  slight  excess  of  hydro- 
chloric acid ;  if  the  precipitate  thus  obtained  be  white,  or  nearly  so,  it  will  con- 
sist of  sulphur  alone,  and  will  show  that  none  of  the  precipitate  has  been  dis- 
solved by  sulphide  of  ammonium ;  but  if  the  precipitate  have  a  decided  color,  it 
must  be  inferred  that  some  soluble  sulphide  is  present. 

The  readiest  method  of  detaching  the  precipitate  from  the  filter  is  to  open  the 
latter  very  carefully,  and  to  suspend  it,  with  one  hand,  against  the  side  of  the 
funnel,  whilst  the  sulphide  of  ammonium  is  dropped  from  the  bottle,  held  in  the 
other  hand,  in  such  a  manner  that  each  drop  may  carry  down  a  certain  quantity 
of  the  precipitate ;  in  some  cases  it  may  be  necessary  to  wash  the  precipitate  off 
the  filter  with  a  fine  stream  of  water  from  a  wash-bottle. 

2.  Except  where  copper  is  present,  very  small  quantities  of  bisulphide  of  tin 
can  be  left  behind  in  this  residue,  so  that  if  no  copper  be  present,  it  is  scarcely 
necessary  to  examine  it  for  tin,  unless  very  great  accuracy  be  desired. 

3.  It  is  necessary  that  this  precipitate  be  washed  till  all  adhering  chloride  of 
ammonium  is  removed,  since,  otherwise,  the  sulphide  of  mercury  might  be  partly 
dissolved  on  boiling  with  nitric  acid. 

4.  Sulphide  of  cadmium  is  only  found  in  this  residue  when  tin  is  present. 

5.  In  testing  very  small  quantities,  it  is  convenient  to  evaporate  to  dryness 
in  a  watch-glass,  to  add  a  single  drop  of  dilute  hydrochloric  acid,  then  a  few 
drops  of  water,  to  heat  until  the  residue  is  dissolved,  and  then  to  fill  the  watch- 
glass  to  the  brim  with  water;  sometimes  the  milkiness  does  not  appear  till  after 
two  or  three  minutes. 

6.  This  method  of  separating  the  sulphides  of  copper  and  cadmium  was  de- 
vised by  Dr.  Hoffmann  :  its  success  is  perfect,  if  due  care  be  taken  to  wash  the 
precipitate  thoroughly  and  rapidly,  so  that  it  may  not  be  oxidized  by  exposure, 
and  to  filter  quickly  after  boiling  with  sulphuric  acid. 

7.  Both  these  precipitates  are  dried,  ignited,  together  with  their  filters,  in  an 
open  porcelain  crucible ;  the  ash  fused  with  a  little  cyanide  of  potassium  in  a 
covered  crucible;  the  fused  mass  boiled  (in  the  crucible)  with  water,  the  reduced 
metal  (tin,  with  traces  of  antimony  and  copper)  allowed   to  subside,  and  the 
supernatant  liquid  poured  off;  the  metallic  particles  are  then  washed,  and  heated 
to  boiling  with  a  little  concentrated  hydrochloric  acid,  the  solution  diluted  with 
water,  filtered,  and  chloride  of  mercury  added ;  a  white  (or  gray)  precipitate  of 
subchloride  of  (or  metallic)  mercury,  appearing  immediately,  or  nearly  so,  indi- 
cates the  presence  of  tin. 

8.  No  bisulphide  of  tin  is  found  in  this  solution  unless  arsenic  is  present. 

9.  The  precipitate  should  be  removed,  as  far  as  possible,  from  the  filter,  and 
added,  by  small  portions  at  a  time,  to  fused  nitrate  of  potassa,  in  a  porcelain 
crucible ;  the  filter  (or  that  portion  of  it  which  is  covered  with  precipitate)  is 
cut  into  small  strips,  which  are  added  separately,  to  the  fused  mass ;  when  the 
whole  has  been  added,  the  mass  is  emptied  from  the  crucible  into  a  small  iron 
mortar  or  cup,  where  it  is  allowed  to  cool. 

NOTES  TO  TABLE  IV. 

1.  This  precipitate  is  also  liable  to  contain  small  quantities  of  the  higher  ox- 
ides of  manganese,  nickel,  and  cobalt,  arising  from  the  exposure  of  the  ammoni- 
acal  solution  to  the  air ;  hence  the  necessity  of  rapid  filtration.  Since  manga- 

off  the  zinc  in  the  generating  bottle,  and  boiled  with  hydrochloric  acid,  when  chloride 
of  tin  is  formed,  which  may  be  detected  by  the  well-known  reaction  with  chloride  of 
mercury. 


PRELIMINARY   EXAMINATION   FOR   ACIDS.  559 

nesc  has  been  sought  in  another  part  of  the  precipitate,  and  cobalt  and  nickel 
would  have  been  detected  in  the  commencement,  a  serious  error  need  scarcely 
be  feared  in  this  part  of  the  examination. 

2.  In  order  to  determine  the  state  of  oxidation  in  which  the  iron  existed 
originally,  it  is  necessary  to  test  a  portion  of  the  aqueous  or  hydrochloric  solu- 
tion of  the  substance. 

3.  Since  alumina  itself  is  not  very  easily  soluble  in  acetic  acid,  and  might 
therefore  be  mistaken  for  phosphate  of  alumina,  unless  a  sufficient  excess  of  acid 
was  added,  it  is  advisable,  if  a  precipitate  be  formed  in  this  part  of  the  table,  to 
dissolve  it  in  hydrochloric  acid,  to  add  an  excess  of  potassa,  and  to  separate  the 
alumina  by  silicate  of  potassa  (see  p.  514),  in  order  to  ascertain  the  presence  of 
phosphoric  acid. 

NOTES  TO  TABLE  V. 

1.  The  formation  of  an  immediate  precipitate,  though  conclusive  as  to  the 
presence  of  baryta,  does  not  negative  that  of  strontia. 

2.  Since  baryta  and  strontia  are  detected  elsewhere,  no  examination  of  this 
precipitate  is  necessary. 

3.  The  same  remark  may  be  applied  to  this  precipitate  of  silicofluoride  of 
barium. 

4.  Should  any  baryta  be  detected  by  this  test,  the  evaporation  with  hydro- 
fluosilicic  acid  and  extraction  with  alcohol  must  be  repeated. 


EXAMINATION   FOR  ACIDS. 

§  354.  PRELIMINARY  EXAMINATION. 

Experiment  1. — A  small  portion  of  the  powder  is  heated  in  a  glass  tube  open 
at  both  ends,  and  held  obliquely. 

I.  Evolution  of  sulphurous  acid  indicates  the  presence  of  SULPHUR  or  of  a 
SULPHIDE. 

II.  The  formation  of  a  distinctly  crystalline  sublimate  is  probably  due   to 
OXALIC  or  BENZOIC  acid. 

III.  The  various  ORGANIC  ACIDS  will  generally  evolve  peculiar  odors  or  in- 
flammable vapors  in  this  experiment  (see  the  Reactions  of  the  Organic  Acids). 

Experiment  2. — A  portion  of  the  powder  is  heated  nearly  to  boiling  with 
concentrated  sulphuric  acid.1 

I.  Fuming  acid  vapors  are  evolved :  probable  presence  of  HYDROCHLORIC, 
HYDROFLUORIC,  or  NITRIC  acid;  in  the  last  case,  the  fumes  will  generally  have 
SL  brown  color. 

The  fumes  should  be  distinguished,  as  far  as  possible,  by  the  odor. 
A  moistened  glass  rod  should  be  exposed  to  the  fumes }  if  it  be  covered  with 
a  ichite  film  (silicic  acid)  the  presence  of  a  FLUORIDE  may  be  inferred. 

II.  Effervescence  takes  place. 

This  may  proceed  from  the  evolution  of  carbonic  acid,  carbonic  oxide,  sul- 
phurous, or  hydrosulphuric  acid,  &c.  (Approach  the  mouth  of  the  tube  to  the 
flame.) 

Sulphurous  and  hydrosulphuric  acids  will  be  recognized  by  their  odor.  The 
evolution  of  the  former  does  not  indicate  with  certainty  its  presence  in  the  sub- 
stance, since  it  might  result  from  the  deoxidation  of  the  sulphuric  acid. 

1  The  application  of  heat  must  be  avoided  if  a  chlorate  be  present. 


560  EXAMINATION   FOR   ACIDS. 

If  the  gas  have  not  the  odor  of  hydrosulphuric  acid,  and  is  capable  of  burning 
with  a  blue  flame,  it  consists  of  carbonic  oxide,  which  may  result  from  the  pre- 
sence of:  1,  a  compound  of  CYANOGEN  (when  it  would  probably  be  accompanied 
by  hydrocyanic  acid)  ;  2,  TARTARIC  acid  (when  carbonization  would  take  place)  ; 
'6,  CITRIC  acid;  or,  4,  OXALIC  acid. 

III.  A  yellow  gas  having  the  odor  of  chlorine  is  evolved :  presence  of,  1 , 
HYPOCHLOROUS  acid ;  2,  CHLORIC  acid  (when  the  liquid  would  assume  a  deep 
yellow  color) ;  or,  3,  a  CHLORIDE,  together  with  an  oxidizing  agent  (such  as  a 
nitrate,  a  metallic  peroxide,  &c.). 

IV.  Brown,  brown-red,  or  purple  vapors,  are  evolved  :    These  may  consist  of 
one  of  the  lower  oxides  of  nitrogen  (indicative  of  the  presence  of  NITROUS  or 
NITRIC  acid),  or  of  BROMINE  or  IODINE;  the  vapors  should  be  tested  with  a 
little  starch- paste  on  a  glass  rod ;  if  the  starch  become  blue  or  purple  (whether 
at  once  or  after  diffusion  through  a  little  thin  starch-paste),  iodine  is  present;  if 
a  deep  orange  yellow  color  be  imparted  to  the  starch,  bromine  is  present. 

V.  Hydrocyanic  acid  (recognized  by  its  odor)  is  evolved :  presence  of  HYDRO- 
CYANIC, HYDROFERROCYANIC,  HYDROFERRICYANIC,  Or  HYDROSULPHOCYANIC  acid. 

In  the  last  case,  the  hydrocyanic  acid  would  be  accompanied  by  hydrosulphuric 
acid. 

VI.  ACETIC  acid  may  be  recognized  by  its  odor. 

VII.  If  the  sulphuric  acids  become  very  dark  in  this  experiment,  we  may 
infer  the  presence  of  non-volatile  organic  matters,  e.  g.  SUGAR,  STARCH,  TARTARIC, 
GALLIC,  or  TANNIC  acid;  if  it  blacken  but  slightly,  it  may  be  due  to  an  accidental 
impurity,  and  should  be  disregarded. 

VIII.  If  no  change  has  been  produced  by  heating  with  sulphuric  acid,  the 
acid  present  will  probably  be  found  to  be  either   SULPHURIC,   PHOSPHORIC, 
BORACIC,  or  SILICIC  ;  uric,  benzoic,  and  succinic  acids,  also  do  not  exhibit  any 
characteristic  behavior. 

Exp.  3.  Another  portion  of  the  original  solid  is  heated  with  dilute  hydrochlo- 
ric acid.1 

I.  Effervescence :  presence  of  HYDROSULPHURIC,  SULPHUROUS,  or  CARBONIC 
acid. 

The  evolved  gas  is  tested  :  1,  for  hydrosulphuric  acid  with  paper  moistened 
with  solution  of  acetate  of  lead ;  2,  for  sulphurous  acid  by  its  odor ;  and,  3, 
for  carbonic  acid  by  decanting  the  gas  into  lime-water  (see  p.  536). 

In  order  to  test  for  carbonic  acid  in  the  presence  of  sulphurous  acid,  a  little 
bichromate  of  potassa  may  be  added  before  treating  with  hydrochloric  acid. 

II.  A  gas  having  the  odor  of  chlorine  is  evolved  :  presence  of  CHROMIC, 
NITRIC,  CHLORIC,  or  HYPOCHLOROUS  acid,  or  of  some  indifferent  metallic  oxide. 

Hydrofluoric,  hydrocyanic  acid,  &c.,  may  also  be  evolved  in  this  experiment. 

PREPARATION  OF  THE  SOLUTION  ,TO  BE  EXAMINED  FOR  ACIDS. 

§  355.  The  solubility  of  the  substance  in  different  menstrua  will  have  been 
ascertained  in  the  examination  for  bases. 

The  aqueous  solution  is  always  examined  separately  for  acids. 

All  the  bases,  except  the  alkalies  and  alkaline  earths,  should  be  removed  from 
the  solution  to  be  tested  for  acids. 

In  general,  the  separation  of  the  bases  from  the  aqueous  solution  may  be 
effected  by  adding  a  slight  excess  of  carbonate  of  soda,  boiling,  and  filtering  off 
the  precipitate. 

In  some  cases,  however,  especially  where  organic  matter  is  present,  this 
method  is  not  applicable,  and  recourse  must  then  be  had  to  some  special  method ; 

1  This  experiment  may  be  omitted  when  the  preceding  one  has  not  furnished  any  result. 


EXAMINATION   FOR   ACIDS.  561 

thus,  for  example,  lead  and  copper  would  be  removed  by  sulphuretted  hydrogen, 
iron  by  sulphide  of  ammonium,  &c. 

After  the  removal  of  the  bases,  the  solution  must  be  neutralized;  if  acid, 
by  addition  of  ammonia  in  slight  excess;  if  alkaline,  by  adding  nitric  acid,  and 
gently  heating,  to  expel  any  free  carbonic  acid.  If  an  excess  of  nitric  acid  be 
added,  it  may  be  remedied  by  adding  a  slight  excess  of  ammonia. 

The  method  employed  for  dissolving  the  portion  insoluble  in  water  must  be 
framed  with  reference  to  the  results  of  the  preliminary  examination. 

If  the  preliminary  experiments  have  not  indicated  the  presence  of  any  organic 
acid,  of  oxalic,  hydrofluoric,  ht/drobromic,  or  hydriodic  acid,  or  of  a  cyanogen 
compound,  the  residue  left  by  water  may  be  dissolved  in  nitric  or  hydrochloric 
acid,  and  the  solution  tested  for  acids.  Of  course,  the  solution  must  always  be 
effected  with  nitric  acid,  in  order  to  test  with  nitrate  of  silver. 

Should  the  preliminary  examination  have  afforded  grounds  for  suspecting  the 
presence  of  any  of  the  above  acids,  the  residue  left  by  water  should  be  boiled  with 
a  strong  solution  of  carbonate  of  soda,  filtered,  the  filtrate  neutralized  with  nitric 
acid  (and  ammonia)  and  tested  for  acids. 

Any  portion  of  the  substance  which  is  insoluble  in  water  and  acids  must  be 
examined  by  Table  VIII. 

GENERAL  EXAMINATION  FOR  ACIDS. 

§  356.  The  analyst  may  often  economize  time  in  examining  for  acids,  by 
reflecting  upon  the  solubility  of  the  various  combinations  of  acids  and  bases; 
for  instance,  it  would  be  obviously  absurd  to  seek  for  sulphuric  acid  in  a  solution 
containing  baryta,  since  sulphate  of  baryta  is  insoluble  in  water  and  acids; 
again,  the  insolubility  of  phosphate  of  lime  would  preclude  the  possibility  of  the 
presence  of  phosphoric  acid  (to  any  notable  extent)  in  an  alkaline  solution  con- 
taining lime. 

In  detecting  the  acids,  the  analyst  proceeds,  as  in  examining  for  bases,  by  a 
method  of  exhaustion,  first  proving,  by  the  application  of  general  reagents,  that 
the  acids  present  are  members  of  certain  groups,  and  afterwards  having  recourse 
to  special  tests,  in  order  to  distinguish  the  individual  acids. 

Since  the  presence  of  organic  acids  necessitates  some  important  alterations  in 
the  method  of  examination,  we  have  subjoined  two  tables,  the  latter  of  which  is 
to  be  employed  whenever  the  operator  has  reason  (from  the  preliminary  examina- 
tion) to  suspect  the  presence' of  organic  acids. 

The  tables  are  followed  by  an  enumeration  of  such  special  tests  as  are  not 
included  in  them. 


36 


562 


TABLE   VI.  —  METHOD   OF   EXAMINATION   FOR  ACIDS. 


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TABLE   VII.  —  METHOD   OF   EXAMINATION   FOR   ACIDS. 


563 


5G4  SPECIAL   TESTS    FOR  INDIVIDUAL   ACIDS. 


NOTES  TO  TABLES  VI.  AND  VII. 

1.  The  following  acids  are  supposed  to  have  been  already  detected  and  sepa- 
rated as  they  would  be  in  following  the  systematic  Bourse. 

Silicic,  sulphurous,  carbonic,  hydrosulphuric,  arsenious,  and  arsenic  acids. 

2.  Since  the  borates  of  lime  and  baryta  are  soluble  in  aramoniacal  salts,  the 
non-formation  of  a  precipitate  is  not  to  be  regarded  as  establishing  the  absence 
of  boracic  acid. 

3.  Should  the  analyst  have  omitted  to  separate  arsenious  and  arsenic  acids 
from  the  solutions,  they  will  be  precipitated  also  by  this  reagent. 

4.  It  must  be  remembered  that  the  reactions  of  arsenic  acid  are  very  similar 
to  those  of  phosphoric  acid. 

5.  A  neutral  solution  is  most  easily  obtained  by  carefully  evaporating  the  am- 
moniacal solution  fill  it  is  no  longer  alkaline  to  test-papers. 

6.  When  freshly  precipitated,  cyanide  of  silver  is  pretty  soluble  in  nitric 
acid. 

7.  Tartrates  of  baryta  and  lime  being  soluble  in  ammoniacal   salts,  the  ab- 
sence of  tartaric  acid  is  not  certain  when  no  precipitate  is  produced. 

8.  The  same  remark  applies  to  the  citrates. 

In  order  to  test  for  tartaric  and  citric  acids  in  solutions  containing  ammoni- 
acal salts,  these  must  be  decomposed  by  evaporating  the  solution  with  repeated 
additions  of  carbonate  of  soda  as  long  as  any  ammoniacal  odor  is  perceptible ; 
the  excess  of  carbonate  of  soda  may  then  be  decomposed  by  a  very  slight  excess 
of  nitric  acid,  and  the  solution  rendered  alkaline  by  ammonia. 

It  is  exceedingly  difficult  to  distinguish  tartaric  and  citric  acids;  more  reli- 
ance must  be  placed  in  the  judgment  of  the  analyst  than  in  any  method  of  test- 
ing for  these  acids. 

9.  If  a  fixed  organic  substance  be  present  in  the  solution,  phosphate  of  iron 
will  not  be  precipitated. 

10.  If  &  fixed  organic  substance  be  present  in  the  solution,  the  deep  red  color 
will  sometimes  not  be  produced. 


SPECIAL  TESTS  FOR  INDIVIDUAL  ACIDS. 

PHOSPHORIC  ACID. — Test  with  a  mixture  of  chloride  of  ammonium,  ammo- 
nia, and  sulphate  of  magnesia  (p.  533). 

BORACIC  ACID. — The  green  alcohol  flame  (p.  534). 

HYDROFLUORIC  ACID. — The  production  of  terfluoride  of  silicon  (p.  536). 

HYDROCHLORIC  ACID  (in  presence  of  hydrobromic  acid). — The  production  of 
chlorochromic  acid  (p.  538). 

HYDROBROMIC  ACID  (in  presence  of  hydriodic  and  hydrochloric  acids). — To  a 
solution  containing  a  slight  excess  of  carbonate  of  soda,  add  a  mixture  of  solu- 
tions of  sulphate  of  copper  and  sulphate  of  iron  (see  p.  539),  until  the  whole  of 
the  iodine  is  precipitated ;  to  the  filtered  liquid,  add  a  slight  excess  of  carbonate 
of  soda,  again  filter,  and  treat  as  described  at  p.  538. 

HYDROCYANIC  ACID. — The  Prussian  blue  test ;  or  Liebig's  test  with  sulphide 
of  ammonium  (p.  540). 

TANNIC  ACID  (as  distinguished  from  gallic)  — The  production  of  a  white  pre- 
cipitate with  dilute  sulphuric  acid  (p.  543). 

BENZOIC  ACID. — The  separation  of  the  crystalline  acid  on  adding  Jiydrochloric 
acid  (p.  545). 


SPECIAL   TESTS   FOR   INDIVIDUAL   ACIDS.  565 

SUCCINIC  ACID  (as  distinguished  from  benzoic  acid). — The  production  of  a 
white  precipitate  on  adding  alcohol,  ammonia,  and  chloride  of  barium  (p.  545). 

ACETIC  ACID. — The  acetic  ether  test  (p.  545). 

URIC  ACID. — The  murexide  test  (p.  544). 

NITRIC  ACID. — The  test  with  sulphate  of  iron  (p.  542);  or  with  copper  (p. 
542). 

CHLORIC  ACID. — The  behavior  of  the  substance  with  concentrated  sulphuric  or 
hydrochloric  acid  (p.  542). 

HYPOCHLOROUS  ACID. — The  production  of  a  black  precipitate  with  sulphate 
of  manganese  (p.  542). 


566         TABLE   VII.  —  ANALYSIS   OF   INSOLUBLE   SUBSTANCES. 


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QUALITATIVE  ANALYSIS   OP   ALLOYS   AND  AMALGAMS.        567 


NOTES  TO  TABLE  VIII. 

1.  Substances  insoluble  in  water  and  acids  are  of  comparatively  rare  occur- 
rence, especially  among  artificial  products. 

The  following  are  most  frequently  met  with  :  silica,  and  the  silicates  of  various 
metallic  oxides;  the  sulphates  of  baryta  and  strontia;  the  fluorides  of  barium, 
strontium,  and  calcium;  chloride,  bromide,  and  iodide  of  silver;  the  insoluble 
modifications  of  sesquioxide  of  chromium,  alumina,  binoxide  of  tin,  and  anti- 
moniate  of  teroxide  of  antimony. 

2.  In  order  to  test  specially  for  alumina  and  silica,  the  finely-powdered  sub- 
stance may  be  fused,  in  a  silver  crucible,  with  pure  hydrate  of  potassa,  the  fused 
mass  dissolved  in  water,  the  solution  acidulated  with  hydrochloric  acid  and  eva- 
porated to  dryness;   the  residue  is  then  boiled  with  dilute  hydrochloric  acid, 
when  the  silica  is  left  undissolved;  the  solution  is  mixed  with  excess  of  ammo- 
nia, which  precipitates  the  alumina. 

We  may  also  test  for  silica  by  mixing  the  substance  with  fluoride  of  calcium, 
and  heating  with  concentrated  sulphuric  acid,  in  a  platinum  crucible,  when  ter- 
fluoride  of  silicon  will  be  evolved  (see  p.  536). 

3.  Should  there  be  any  portion  undissolved  by  the  acid,  it  will  probably  con- 
sist of  silica,  of  charcoal,  or  undecomposed  substance,  and  may  generally  be 
disregarded. 

4.  In  general,  the  only  bases  which  need  be  sought  for  in  this  solution  are  the 
oxides  of  tin  and  antimony,  but  alumina  and  even  small  quantities  of  lime  and 
oxide  of  iron  may  sometimes  be  found  in  it. 

5.  It  need  hardly  be  observed  that  the  organic  acids,  oxalic  acid,  &c.,  need  not 
be  sought  for  in  the  solution,  since  they  would  have  been  decomposed  by  the 
high  temperature  employed  in  the  fusion. 


QUALITATIVE  ANALYSIS  OF  ALLOYS  AND  AMALGAMS. 

§  358.  Since  compounds  belonging  to  this  class  always  contain  metals  in  an 
unoxidized  state,  they  exhibit  such  a  difference  in  their  general  behavior  as  to 
require  a  special  method  for  their  analysis. 

The  preliminary  experiment  on  charcoal  before  the  blowpipe-flame  is  the  only 
one  which  generally  yields  any  very  satisfactory  result;  though  it  is  sometimes 
useful  to  heat  the  alloy  gently  in  a  tube  closed  at  one  end,  when  arsenic  and 
mercury  will  sublime. 

The  method  employed  for  reducing  alloys  to  a  proper  state  of  division,  varies 
according  to  the  hardness  of  the  substance  operated  on. 

Some  alloys  may  be  cut  into  small  fragments  with  the  scissors  or  shears, 
others  may  be  broken  in  an  iron  or  steel  mortar ;  hard  alloys  which  are  not 
attracted  by  the  magnet  may  be  reduced  by  filing,  the  particles  of  steel  being 
afterwards  carefully  removed  with  a  magnet. 

It  is  unsafe  to  granulate  an  alloy  by  fusing  and  pouring  it  into  water,  since 
its  composition  may  be  materially  altered  by  such  an  operation. 

The  analysis  of  alloys  and  amalgams  is  conducted  according  to  the  following 
table.  * 


568 


TABLE   IX. — ANALYSIS    OF   ALLOYS. 

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NOTES   TO   TABLE   IX. 


NOTES  TO  TABLE  IX. 

1.  If  the  alloy  contain  a  large  proportion  of  tin  and  a  little  arsenic,  the  latter 
is  generally  left  in  the  residue,  and  must  be  sought  for  in  another  portion  of  the 
alloy  by  a  special  method. 

2.  The  more-easily  oxidizable  metals,  as  potassium,  sodium,  magnesium,  &c., 
are  not  generally  sought  in  alloys.     This  solution  may  also  sometimes  contain 
small  quantities  of  platinum  and  antimony,  which  must  not  be  disregarded  if  it 
be  the  object  of  the  analyst  to  detect  these  metals  in  particular.     Even  a  con- 
siderable amount  of  platinum  may  be  dissolved  by  nitric  acid  from  an  alloy  con- 
taining much  silver. 


570  QUANTITATIVE  ANALYSIS. 


QUANTITATIVE    ANALYSIS. 


APPARATUS  USED  IN  QUANTITATIVE  ANALYSIS. 

§  359.  The  following  is  a  list  of  such  apparatus,  not  mentioned  in  the  intro- 
duction to  qualitative  analysis,  as  will  be  required  by  the  student  in  commencing 
this  branch  of  chemistry. 

A  platinum  dish  capable  of  containing  about  four  ounces.1 

A  platinum  crucible  which  will  contain  from  four  to  six  drachms.  This  cru- 
cible should  be  provided  with  a  cover  made  in  the  form  of  a  capsule. 

Two  or  three  flasks  of  German  glass,  containing  about  one  pint.  They  should 
have  a  globular  form,  with  flat  bottoms,  and  lips  slightly  turned  out,  but  without 
rim  or  spout ;  their  necks  should  be  rather  narrow. 

A  washing-bottle  for  hot  water. 

One  or  two  German  beakers  of  about  one  quart  capacity. 

A  pair  of  watch-glasses,  to  fit  over  each  other. 

One  or  two  small  stoppered  weighing  bottles,  two  or  three  inches  long. 

A  wide  test-tube,  three  or  four  inches  long,  and  one  inch  in  diameter,  provided 
with  a  smooth,  sound  cork. 

Quantitative  filtering-paper. 

Several  glass  plates  of  various  diameters,  to  fit  over  funnels  and  beakers ;  some 
of  these  should  have  a  notch  in  the  side  to  admit  the  stem  of  a  funnel,  or  a 
glass  rod.  « 

A  water-oven  for  drying  filters,  &c. 

An  air-bath  ( Taylor's'). — A  water-bath. — A  pipette. — A  small  glass  siphon. — 
A  balance  and  weights. 

A  few  observations  on  the  above  articles  may  prove  of  service  to  beginners. 

The  quantitative  filtering-paper  should  not  only  possess  the  good  qualities 
requisite  in  that  used  in  qualitative  analysis,  but  should  leave  a  very  small 
amount  of  ash.  The  paper  should  be  cut  into  filters  of  different  sizes,  the  two 
most  useful  diameters  being  about  5J  and  7£  inches.  In  order  to  determine 
the  ashes  of  these  filters,  six  are  to  be  completely  incinerated  in  a  platinum  cru- 
cible (see  p.  575),  and  the  weight  of  the  resulting  ash  divided  by  the  number  of 
filters,  in  order  to  obtain  a  fair  average.  Good  filters  of  the  smaller  size  should 
not  leave  more  than  about  0.04  grain  of  ash.  The  Swedish  paper  leaves  even 
less  ash,  but  is  very  expensive  and  generally  filters  very  slowly. 

The  water-oven  should  be  made  of  copper,  and  provided  with  apertures  to 
allow  of  the  passage  of  a  current  of  air;  it  is  conveniently  supported  upon  a 
tripod,  over  a  gas-burner,  or  may  be  placed  upon  the  sand-bath.  A  somewhat 
imperfect  substitute  for  a  water-oven  may  be  made  by  immersing  a  beaker  in  an 
appropriate  vessel  of  water,  which  is  then  heated  to  the  boiling  point ;  filters, 
however,  are  dried  very  slowly  in  this  manner,  since  the  removal  of  the  moisture 
has  to  be  effected  by  the  irregular  current  of  air  in  the  beaker. 

1  This  costly  vessel  is  not  absolutely  indispensable ;  a  Berlin  dish  or  a  platinum  cruci- 
ble may,  with  some  sacrifice  of  time  and  convenience,  be  substituted  for  it  in  most  cases. 


OPERATIONS   IN   QUANTITATIVE   ANALYSIS.  571 

Two  air-laths  will  be  found  useful  in  the  laboratory;  one  of  these  should  be 
made  after  Taylor's  pattern,  with  double  bottom  and  sides,  a  tall  chimney  for 
promoting  a  current  of  air,  which  enters  through  apertures  at  the  bottom  of  the 
bath,  and  a  tube  for  introducing  a  thermometer.  An  apparatus  of  this  kind 
serves  for  drying  substances  at  regulated  temperatures  above  the  boiling  point 
of  water. 

The  other  air-bath  (to  be  used  for  evaporations,  &c.)  is  a  cylindrical  vessel  of 
tinned  iron,  7  inches  in  height,  and  9  in  diameter,  with  a  large  hole  close  to 
the  bottom,  for  the  entrance  of  air.  It  may  be  covered  with  a  sheet  of  porous 
paper,  supported  by  a  glass  rod. 

The  water-bath  is  a  pretty  capacious  vessel  of  copper  or  tin-plate,  furnished 
with  one  or  two  sets  of  movable  rings  for  various  dishes. 

The  balance  is,  of  course,  an  apparatus  of  the  first  importance  to  the  quanti- 
tative analyst,  and  much  care  should  be  therefore  bestowed  upon  its  selection. 
For  most  practical  purposes,  a  balance  capable  of  turning  with  0.01  grain,  when 
loaded  with  1,000  grains  in  each  pan,  will  be  found  sufficiently  accurate.  For 
very  accurate  analyses,  however,  especially  in  organic  chemistry,  a  balance  is 
required  which  turns  distinctly  with  0.001  grain.  A  balance  is  also  required 
which  will  carry  about  5,000  grains  in  each  pan,  and  yet  turn  with  0.1  grain. 
The  best  general  balance  will  be  found  in  one  which  is  capable  of  bearing  the 
above  weight,  and  yet  turns  with  0.01  grain. 

Our  space  will  not  permit  us  to  enter  into  all  the  details  necessary  to  be 
attended  to  in  a  good  balance,  but  we  think  it  advisable  to  lay  particular  stress 
upon  the  following  points.1 

The  balance  should  be  inclosed  in  a  tight  glass  case,  to  protect  it  from  the 
action  of  air  and  acid  fumes.  It  should  be  provided  with  a  handle  external  to 
the  case,  by  which  the  knife-edge  may  be  brought  down  on  to  the  agate  plane. 
The  beam  should  be  graduated,  so  that  the  smaller  weights  may  be  placed  upon 
it,  on  the  principle  of  the  steelyard,  a  little  rider  of  gold  wire  being  used  for  all 
the  smaller  weights,  and  shifted  along  the  beam  by  means  of  a  lever  worked 
from  the  outside  of  the  case.  The  pans  should  be  suspended  from  knife-edge 
supports. 

A  small  dish  containing  lumps  of  quicklime  should  be  kept  in  the  balance, 
to  absorb  moisture,  &c. 

OPERATIONS  IN  QUANTITATIVE  ANALYSIS. 

§  360.  Before  proceeding  to  consider  the  methods  actually  employed  for  the 
determination  of  various  substances,  it  may  be  well  to  describe  some  of  the  more 
important  manipulations,  upon  the  execution  of  which  the  success  of  the  quanti- 
tative analyst  will  entirely  depend. 

WEIGHING. — In  the  process  of  weighing,  the  following  cautions  should  be 
carefully  attended  $o. 

The  knife-edge  must  not  be  allowed  to  fall  suddenly  on  to  the  agate  plane, 
but  must  be  let  down  gradually  and  gently. 

The  fulcrum  must  not  rest  upon  the  planes  during  the  removal  or  addition  of 
a  weight.  The  pans  must  not  be  allowed  to  swing  to  and  fro.  Accurate  equi- 
librium is  best  indicated  by  a  gentle  oscillation  of  the  beam,  causing  the  index 
to  deviate  to  the  same  extent  on  either  side  of  the  scale ;  in  weighing  by  rest, 
an  error  may  be  caused  by  a  particle  of  dirt  upon  the  planes,  &c.  Of  course 
the  balance  must  be  so  placed  that  the  beam  is  truly  horizontal  (indicated  by  a 
pendulum,  or  by  spirit-levels),  and  should  stand  upon  a  firm  table.  The  weights 
are  always  lifted  with  pincers,  never  touched  with  the  fingers. 

1  These  remarks  refer  to  accurate  scientific  balances,  rather  than  to  such  as  may  be 
employed  for  the  practically  useful  analysis  of  ores,  &c. 


572  QUANTITATIVE   ANALYSIS. 

A  crucible  or  dish  must  never  be  weighed  while  hot,  for,  independently  of  the 
currents  of  air  produced  in  the  balance-case,  an  error  will  be  incurred  from  the 
circumstance  that  the  proper  amount  of  moisture  will  not  have  condensed  upon 
the  surface  of  the  vessel  until  it  has  cooled  to  the  temperature  of  the  air.  How- 
ever, it  is  sometimes  necessary,  in  the  case  of  very  hygroscopic  substances,  to 
weigh  the  crucible  and  its  contents,  when  just  on  the  point  of  cooling ;  in  such 
a  case,  the  weight  of  the  empty  crucible  should  be  taken  at  the  same  tempera- 
ture, when  the  second  of  the  above  causes  of  error  is  avoided. 

Solid  substances  are  usually  weighed,  when  they  are  not  very  hygroscopic,  in 
two  watch-glasses,  which  are  ground  at  the  edges  so  as  to  fit  closely  together,  or 
in  covered  crucibles.  Sometimes,  especially  when  the  substance  rapidly  absorbs 
moisture,  it  is  weighed  in  a  small  stoppered  bottle. 

Liquids  should  be  weighed  in  stoppered  bottles;  weighing  in  open  vessels  is 
to  be  avoided  in  most  cases,  the  loss  from  evaporation  at  the  surface  preventing 
accurate  determination  of  the  weight;  a  flask  may  sometimes  be  employed,  but 
never  a  beaker. 

In  order  to  avoid  the  trouble  of  detaching  each  particle  of  a  weighed  solid 
from  the  vessel,  it  is  usual  to  weigh  the  latter  again  afterwards,  together  with 
any  particle  of  the  substance  which  may  have  adhered  to  it. 

Filters  are  weighed  in  wide  tubes  closed  with  corks;  covered  crucibles  are 
sometimes  conveniently  substituted  for  these;  or,  in  the  case  of  large  precipitates, 
a  beaker  covered  with  a  glass  plate. 

MECHANICAL  DIVISION. — The  reduction  of  a  substance  to  a  proper  state  of 
division  is  far  more  important  in  quantitative  than  in  qualitative  analysis.  The 
methods  of  effecting  it  have  been  pointed  out  at  p.  84. 

SOLUTION. — For  quantitative  analysis,  substances  are  dissolved  either  in  flasks 
or  beakers;  the  latter  are  generally  employed  whenever  ebullition  is  not  neces- 
sary, since  the  residue  left  undissolved  is  so  much  more  easily  extracted  from 
them  than  from  flasks. 

When  the  solution  of  a  substance  is  attended  with  effervescence,  an  inverted 
funnel  must  be  placed  over  the  mouth  of  the  beaker,  with  its  rim  just  resting 
within  that  of  the  latter;  this  funnel  may  be  slipped  aside  vjhen  a  fresh  quantity 
of  the  solvent  is  to  be  added,  and  serves  to  prevent  any  loss  from  spirting. 
When  ebullition  is  absolutely  necessary,  the  solution  must  be  effected  in  a  flask, 
in  the  mouth  of  which  a  small  funnel  is  placed.  If  violent  and  prolonged  ebul- 
lition is  required  (as  in  the  complete  oxidation  of  sulphides  by  nitric  acid),  a  flask 
with  a  very  long  narrow  neck  is  used. 

When  a  Florence  flask  is  employed  for  solution,  it  should  be  placed  obliquely, 
to  guard  against  spirting. 

EVAPORATION. — Liquids  which  do  not  effervesce  when  heated  may  be  evapo- 
rated in  a  dish,  upon  a  sand  or  water-bath,  or  in  an  air-bath ;  the  liquid  must 
never  be  allowed  to  boil,  or  loss  will  surely  result  from  the  projection  of  drops 
of  the  liquid.  Evaporation  upon  a  water-bath,  although  often  much  slower  than 
upon  a  sand-bath,  is  far  safer,  because  the  temperature  never  rises  beyond  210°. 

If  evaporation  be  carried  to  dryness  upon  the  sand-bath,  it  must  be  well 
watched  towards  the  conclusion,  since  small  portions  of  the  solid  are  very  liable 
to  be  thrown  out  with  the  bubbles  of  vapor. 

In  these  cases  it  is  always  safer  to  employ  the  rough  air-bath  mentioned  above, 
within  which  the  dish  is  supported  upon  an  iron  ring,  at  about  2  or  3  inches 
from  the  bottom,  and  the  evaporation  may  proceed,  with  occasional  attention,  for 
many  hours,  without  danger  of  loss.  A  very  convenient  method  of  evaporating 
to  dryness,  consists  in  placing  the  dish  upon  an  empty  vessel  over  the  flame, 
when  heated  air  contained  in  the  vessel  communicates  a  perfectly  uniform  heat 
to  every  part  of  the  dish.  An  old  water-bath  or  common  tinned  iron  pot  may 


OPERATIONS   IN   QUANTITATIVE   ANALYSIS.  573 

be  used.     This  plan  is  particularly  applicable  when  a  liquid  is  to  be  evaporated 
to  dryness,  and  the  residue  strongly  heated. 

When  liquids  effervesce  upon  the  application  of  heat,  they  must  be  evaporated 
in  beakers  or  flasks  as  long  as  the  effervescence  continues,  when  they  may  be 
transferred  to  a  dish,  and  evaporated  as  above. 

Some  care  is  necessary  in  transferring  liquids  from  one  vessel  to  another;  the 
under  part  of  the  lip  of  the  vessel  to  be  poured  from  should  be  slightly  greased 
with  a  little  tallow,  to  prevent  any  drops  of  liquid  from  running  down  the  side. 
The  liquid  is  then  slowly  poured  down  a  glass  rod  held  obliquely  against  the  lip. 
The  vessel  should  be  afterwards  rinsed  twice  with  distilled  water. 

If  possible,  it  is  better  to  avoid  covering  a  dish  with  paper  during  an  evapora- 
tion, since  the  process  is  considerably  retarded  by  it,  and  the  cover  is  liable  to 
become  wetted  and  break,  when  it  may  fall  into  the  liquid  below;  however,  if 
there  be  dust  or  ashes  floating  in  the  surrounding  air,  the  dish  may  be  covered 
with  a  piece  of  filter-paper,  through  which  a  glass  rod  is  thrust  so  as  to  support 
it  upon  the  dish ;  the  paper  should  be  renewed  whenever  there  is  danger  of  its 
breaking. 

Some  salts  are  very  prone,  when  their  solutions  are  evaporated,  to  creep  up 
the  sides  of  the  dish,  and,  finally  even  over  the  edge. of  the  latter,  thus  causino- 
considerable  danger  of  loss;  this  may  generally  be  avoided  by  spreading  a  very 
thin  film  of  tallow  over  the  edge  and  inner  rim  of  the  dish. 

When  very  large  quantities  of  liquid  are  to  be  evaporated,  the  process  is 
usually  conducted  in  a  large  dish  until  the  liquid  has  attained  a  small  bulk, 
when  it  is  transferred  to  a  smaller  dish,  and  the  evaporation  continued.  Since, 
however,  some  loss  is  almost  always  incurred  in  transferring,  it  is  better,  when- 
ever it  is  possible,  to  evaporate  the  liquid  in  successive  portions  in  the  small 
dish. 

IGNITION. — The  greatest  care  is  requisite  in  the  ignition  of  substances  in  order 
to  prevent  loss  from  spirting  or  decrepitation. 

The  process  is  generally  conducted  in  dishes  of  porcelain  or  platinum,  and 
sometimes  in  crucibles  of  these  materials.  When  a  substance  is  ignited  in  a 
dish,  the  latter  should  at  first  be  heated  in  an  air-bath,  the  temperature  of  which 
is  gradually  increased,  until  it  is  perfectly  dry.  During  this  process  the  dish  is 
covered  with  a  piece  of  platinum  foil.  The  dish  is  then  (still  covered)  gradually 
heated  over  the  spirit-lamp  or  gas-flame  until  it  has  attained  the  proper  tem- 
perature. 

(Care  must  be  taken  before  weighing  a  dish  or  crucible,  that  every  particle  of 
carbon  which  may  have  been  deposited  from  the  flame,  is  removed  from  the  sur- 
face; this  may  be  effected  by  a  judicious  application  of  a  clear  flame,  or  by 
wiping  with  a  dry  or  damp  cloth  ;  in  the  latter  case,  the  dish  must  be  again 
heated  before  weighing.)  Should  any  matter  be  found  deposited  upon  the 
cover,  the  latter  should  be  removed  from  the  dish,  carefully  ignited,  and  re- 
placed. 

If  a  substance  is  ignited  in  a  crucible,  the  latter  is  at  first  supported  at  a  con- 
siderable distance  above  the  flame,  its  cover  loosely  placed  over  it,  and  a  mode- 
rate heat  (gradually  increasing)  applied,  until  but  little  vapor  is  given  off;  the 
crucible,  still  partially  closed,  is  then  strongly  heated,  and,  when  the  ignition 
appears  to  be  completed,  its  cover  is  removed,  the  crucible  placed  obliquely,  and 
the  lid  allowed  to  rest  against  its  mouth  so  as  to  produce  a  current  of  air,  which 
will  remove  the  last  traces  of  vapor,  &c.,  or  serve  to  oxidize  any  carbon  or  other 
substance  present  in  the  residue. 

During  ignition  in  porcelain  crucibles,  it  is  convenient  to  substitute  platinum 
covers  for  those  of  porcelain,  since  the  latter  are  apt  to  become  coated  with  a 
shiny  film  of  difficultly-combustible  carbon,  which  is  not  easily  removed. 

In  cases  where  there  is  much  difficulty  in  burning  off  the  last  traces  of  carbon, 


574  QUANTITATIVE   ANALYSIS. 

it  is  usual  to  direct  a  slow  current  of  oxygen  into  the  ignited  crucible.  This  is 
done  very  easily  from  a  gas-holder,  to  which  is  affixed  a  piece  of  flexible  tube 
terminating  in  a  glass  nozzle. 

PRECIPITATION. — Precipitation  is  always  effected,  if  possible,  in  a  beaker  or 
precipitating-glass,  since  the  precipitate  is  so  much  more  easily  removed  from 
these  vessels  than  from  flasks.  The  solution  is  always  well  mixed  with  the  pre- 
cipitant by  agitation,  or  by  stirring  with  a  glass  rod. 

When  the  precipitation  is  effected  by  a  gas  (e.  y.  by  sulphuretted  hydrogen), 
the  latter  is  conducted  in  a  slow  stream  into  the  solution  contained  in  a  precipi- 
tating glass  (Phillips) ;  it  is  advisable  to  place  in  the  mouth  of  the  glass  a  fun- 
nel, the  stem  of  which  has  been  cut  off  so  as  to  leave  a  short  wide  tube  through 
which  the  delivery-tube  of  the  sulphuretted  hydrogen  apparatus  may  pass. 

If  a  precipitate  subsides  very  readily,  it  may  conveniently  be  separated  from 
the  greater  part  of  the  supernatant  fluid  by  decantation,  the  clear  liquid  being 
removed  either  by  cautiously  inclining  the  vessel,  or  by  means  of  a  siphon  or 
pipette,  care  being  taken  to  avoid  removing  any  of  the  precipitate. 

It  is,  however,  more  usual  to  separate  precipitates  by  filtration,  in  which  pro- 
cess the  following  precautions  will  be  found  necessary. 

The  funnel  is  supported  either  in  the  mouth  of  a  precipitating-glass,  or  on  a 
retort  stand ;  in  the  latter  case  a  beaker  should  be  placed  beneath  to  receive  the 
filtrate ;  a  dish  must  not  be  used,  as  it  is  very  liable  to  be  overturned  and  to 
collect  dust  when  uncovered.  The  stem  of  the  funnel  should  be  made  to  touch 
the  side  of  the  beaker,  so  that  the  liquid  may  run  quietly  down,  and  not  splash. 
The  beaker  is  covered  with  paper  turned  down  over  the  edges,  or  with  a  notched 
glass  plate.  The  funnel  is  also  loosely  covered  with  a  glass  plate.  The  funnel 
must  be  somewhat  larger  than  the  filter,  which  should  be  closely  fitted  to  its  sides, 
and  then  moistened  with  water.  The  supernatant  liquid  should  first  be  poured 
upon  the  filter,  the  precipitate  being  left  "in  the  beaker,  and  afterwards  rinsed 
out  with  water.  The  filter  is  never  more  than  three-fourths  filled  with  the 
liquid. 

The  last  traces  of  precipitate  are  removed  from  the  containing  vessel  either  by 
mechanical  or  by  chemical  means ;  the  former  are  to  be  preferred  in  most  cases. 
A  very  convenient  instrument  for  this  purpose  is  a  glass  rod,  one  of  the  rounded 
extremities  of  which  is  covered  with  a  very  closely-fitting,  well-joined  cap  of 
caoutchouc,  with  which  the  sides  of  the  beaker  or  precipitating-glass  are  rubbed. 
To  detach  a  precipitate  from  the  sides  of  a  flask,  a  long  feather  is  used  from 
which  all  the  plumules  have  been  stripped,  except  a  little  tuft  at  the  end  ;  this 
feather  may  be  bent  so  as  to  reach  any  part  of  the  interior  of  the  flask.  To  re- 
move a  precipitate  by  chemical  means,  an  appropriate  solvent  is  employed,  and 
the  substance  is  then  repreci  pita  ted. 

Great  attention  must  be  paid  to  the  washing  of  precipitates,  without  which,  of 
course,  their  exact  weight  can  never  be  ascertained.  Precipitates  may  be  washed 
by  decantation,  by  filtration,  or  by  a  combination  of  the  two  methods. 

In  washing  the  precipitate  by  decantation,  it  is  repeatedly  stirred  up  with  the 
liquid  with  which  it  is  to  be  washed,  it  is  then  allowed  to  subside,  and  the  clear 
liquid  decanted,  either  with  or  without  a  siphon  (or  pipette) ;  the  operation  is 
repeated  until  the  precipitate  is  completely  washed. 

Precipitates  are  washed,  on  a  filter,  by  stirring  them  up  with  a  (not  too  forci- 
ble) stream  from  the  jet  of  the  washing-bottle. 

It  is  often  advantageous  to  combine  these  two  methods  of  washing,  the  preci- 
pitate being  stirred  up  with  the  liquid  to  be  used  for  washing,  allowed  to  sub- 
side, the  clear  liquid  decanted  through  the  filter,  and  the  precipitate  again 
washed  in  the  same  way ;  it  is  finally  thrown  upon  the  filter,  and  the  washing 
completed. 

The  commonest   method  of  ascertaining  whether  a  precipitate  is  perfectly 


OPERATIONS  IN   QUANTITATIVE  ANALYSIS.  575 

washed  consists  in  evaporating  a  few  drops  of  the  washings  upon  a  platinum- 
plate,  when  no  considerable  residue  should  be  left ;  or  sometimes  a  special  test 
is  applied  to  the  washings  when  one  can  be  found  which  is  sufficiently  delicate. 

DETERMINATION  OF  THE  WEIGHT  OF  PRECIPITATES. — Before  weighing  a 
precipitate,  it  must  be  freed  from  all  adhering  moisture,  which  may  be  effected 
either  by  mere  drying  or  by  ignition. 

The  precipitate  is  first  partially  dried  by  placing  the  funnel  which  contains  it 
either  in  an  air-bath,  or  at  some  distance  above  the  sand-bath,  where  it  may  be  sup- 
ported upon  an  iron  tripod.  The  subsequent  process  is  varied  according  as  the 
precipitate  is  to  be  weighed  after  drying  at  212°,  or  after  ignition.  In  the 
former  case,  the  filter,  with  its  contents,  may  be  carefully  folded  within  another 
filter,  and  placed  in  the  water-oven  ;  after  about  an  hour,  it  may  be  removed 
from  its  paper  case,  and  weighed  in  the  wide  tube  closed  with  a  cork ;  it  is  then, 
replaced  in  the  paper,  and  again  heated  in  the  water-oven  for  half-an-hour,  when, 
the  weight  is  again  determined,  and  so  on  until  no  further  alteration  in  weight 
is  perceptible.  The  filter  may  also  be  very  conveniently  dried  in  a  porcelain 
crucible,  or  in  a  small  beaker,  which  should  be  covered  during  the  weighing, 
since  dry  filter-paper  very  rapidly  absorbs  moisture  from  the  air. 

When  it  is  necessary  to  dry  filters,  in  order  to  ascertain  their  weight  before 
collecting  the  precipitate  upon  them,  the  operation  is  conducted  in  exactly  the 
same  manner. 

If  the  precipitate  is  to  be  ignited,  the  operation  proceeds  as  follows  :  A  cru- 
cible of  porcelain  or  platinum  (according  to  the  nature  of  the  precipitate)  is 
ignited,  allowed  to  cool,  and  weighed.  A  sheet  of  smooth  writing-paper  is  cut 
in  half;  one  half-sheet  is  placed  upon  the  clean  table,  the  other  half  is  then  cut 
again  in  half;  and  the  quarter-sheets  placed  side  by  side  upon  the  half-sheet; 
this  arrangement  will  be  found  the  most  convenient  for  collecting  any  stray  par- 
ticles of  precipitate.  The  crucible  is  placed  upon  one  of  the  quarter-sheets  of 
paper,  and  as  much  as  possible  of  the  precipitate  thrown  into  it,  having  been 
detached  by  gently  crumbling  the  filter  between  the  fingers.  The  filter  is  then 
doubled  up  several  times  in  the  direction  of  its  length,  and  held  at  the  top,  either 
in  a  pair  of  platinum-tongs  or  by  a  stout  wire  of  that  metal  coiled  loosely  round 
it.  The  flame  of  a  spirit-lamp  is  now  applied  to  the  apex  of  the  filter,  which  is 
held  over  the  mouth  of  the  crucible,  and  allowed  to  burn  away,  with  occasional 
contact  of  the  spirit-flame,  until  the  ashes  drop  into  the  crucible.  The  latter  is 
transferred  to  the  other  quarter-sheet  of  paper,  and  any  particles  which  may 
have  fallen  around  it  are  shaken  into  it.  The  crucible,  is  now  loosely  covered, 
and  heated  first  gently,  and  at  some  distance  from  the  flame,  and  afterwards  to 
redness ;  finally,  the  crucible  is  placed  obliquely,  with  the  lid  resting  against  its 
mouth,  until  every  trace  of  carbon  has  burnt  away,  which  may  be  assisted,  if 
necessary,  by  a  current  of  oxygen. 


§  361.  We  shall  now  enter  upon  the  consideration  of  the  various  methods 
employed  for  the  simple  determination  of  the  bases  and  acids. 

It  would  be  impossible,  within  the  limits  of  a  practical  manual,  to  describe  all 
the  methods  which  have  been  employed  for  the  determination  and  separation  of 
the  various  substances.  It  is  therefore  our  intention  merely  to  bring  forward  the 
best  processes  for  determining  the  chief  bases  and  acids,  so  that  the  student  may 
practise  them  in  the  laboratory,  and  thus  become  acquainted  with  the  general 
features  of  the  quantitative  estimation  of  each  substance. 

We  shall  also  subjoin  a  number  of  the  commonest  examples  involving  the 
quantitative  separation  of  those  bodies  which  are  most  frequently  associated,  but 
the  advanced  student  of  this  branch  of  analysis  will  soon  perceive  that  his  chief 


576  QUANTITATIVE   DETERMINATION   OP   THE   BASES. 

object  must  be  the  acquisition  of  such  a  knowledge  of  its  broad  principles  as  will 
enable  him  to  contrive  special  methods  for  individual  cases. 

In  describing  the  methods  employed  for  determining  the  bases,  we  shall  follow 
a  reverse  order  to  that  adopted  in  qualitative  analysis,  because  the  determination 
of  the  metals  of  the  fifth  group  is  effected  with  much  greater  facility  than  that 
of  the  first  group. 


QUANTITATIVE  DETERMINATION  OF  THE  BASES. 

OXIDE  OF  SILVER. 

(Either  crystallized  nitrate  of  silver,  or  pure  silver,  may  be  advantageously 
employed  in  determining  this  metal  for  practice ;  not  more  than  five  grains  of 
the  metal,  or  eight  grains  of  the  crystals,  dried  by  pressure  between  blotting- 
paper,  should  be  employed.  The  result  should,  in  any  case,  not  differ  by  more 
than  0.3  per  cent,  from  theory.) 

§  362.  Silver  is  generally  determined  in  the  form  of  chloride. 

The  solution  containing  silver  is  acidulated  with  nitric  acid,  and  hydrochloric 
acid  is  added  in  moderate  excess.  The  solution  is  gently  heated  for  some  time 
upon  the  sand-bath?  and  the  precipitate  allowed  to  subside.  If  the  quantity  of 
the  precipitate  be  considerable,  it  may  be  washed  by  decantation  (see  p.  574), 
until  the  washings  are  no  longer  rendered  turbid  by  nitrate  of  silver ;  it  is  then 
carefully  rinsed  out  into  a  porcelain  capsule  (which  has  been  previously  ignited, 
allowed  to  cool,  and  weighed),  perfectly  dried  upon  a  water-bath,  heated  gradu- 
ally over  a  flame  until  it  fuses,  and  its  weight  then  determined. 

If,  however,  only  a  small  quantity  of  chloride  of  silver  be  obtained,  it  must 
be  collected  upon  a  filter  of  known  ash,  washed,  till  the  washings  are  free  from 
silver,  first  with  water  acidulated  with  nitric  acid,  afterwards  with  pure  water, 
dried,  ignited,  after  having  detached  as  much  of  tire  precipitate  from  the  filter  as 
possible  (see  p.  575),  and  weighed.  Before  weighing,  it  is  more  correct  to 
moisten  the  ashes  with  nitric  acid,  to  dry,  in  the  partially  closed  crucible,  at  a 
considerable  distance  above  the  flame;  then  to  add  a  little  hydrochloric  acid, 
again  to  dry,  and  to  ignite  strongly. 

The  acidulation  with  nitric  acid,  before  the  precipitation  of  the  chloride  of 
silver,  is  necessary  to  promote  the  subsidence  of  the  precipitate.  The  ash  is 
treated  with  nitric  and  hydrochloric  acids,  in  order  to  reconvert  into  chloride  any 
silver  which  may  have  been  reduced  to  the  metallic  state  during  the  ignition. 

Calculation. 
AgCl        Ag 

As  143. 6  :  108.1  ::    Weight  of  precipitate  :  x 
x—  Quantify  of  silver  obtained. 

SUBOXIDE  or  MERCURY. 

(Pure  subchloride  of  mercury,  dried  in  a  water-bath,  until  its  weight  is  con- 
stant, may  be  employed  for  practice ;  about  ten  grains  will  be  sufficient.  The 
result  should  be  within,  at  most,  0.5  per  cent,  of  the  calculated  amount.) 

§  363.  The  determination  of  this  oxide  is  best  effected  by  converting  it  into 
the  oxide  of  mercury,  which  is  then  estimated  according  to  the  directions  given 
at  p.  577. 

The  oxidation  may  be  effected  by  heating  the  substance  with  nitric  acid,  and 
afterwards  adding  hydrochloric  acid,  by  degrees,  until  the  mercury-compound  is 
completely  dissolved. 


OXIDE   OF   MERCURY.  577 


OXIDE  OF  MERCURY. 

§  364.  Mercury  is  most  accurately  determined  either  as  metal,  in  the  dry  way, 
or  as  sulphide. 

Determination  as  Metal. — In  order  to  weigh  the  mercury  in  a  metallic  state, 
the  following  process  is  adopted : — 

(About  50  grains  of  pure  native  cinnabar  may  be  taken.  The  result  should 
be  within  0.5  per  cent,  of  that  obtained  by  calculation.) 

A  combustion-tube  of  hard  glass,  about  24  inches  long,  and  $  inch  in  diame- 
ter, is  drawn  out  over  the  lamp,  at  about  3  or  4  inches  from  one  extremity,  so 
as  to  leave  a  somewhat  narrow  open  passage,  which  is  then  loosely  plugged  with 
asbestos;  into  the  tube  thus  prepared,  a  layer  of  about  12  inches  of  a  mixture  of 
powdered  quicklime  with  about  £  of  dry  carbonate  of  soda  is  introduced. 

The  finely  powdered  substance  (previously  weighed)  is  placed  in  a  shallow 
mixing-mortar,  and  intimately  mixed,  by  degrees,  with  about  9  inches  of  the 
above  mixture,  transferred  from  the  tube  for  that  purpose.  The  mortar  is 
rinsed  out  with  a  little  more  of  the  mixture,  which  is  also  introduced  into  the 
tube,  and  the  latter  is  then  filled  up,  to  within  about  6  inches  of  the  top,  with 
the  mixture,  which  is  covered  with  a  loose  plug  of  asbestos.  This  extremity  of 
the  tube  is  then  drawn  out  in  such  a  manner  that  it  may  form  two  bulbs,  with  a 
prolongation  formed  by  the  extremity  of  the  original  tube,  which  should  be 
slightly  bent  up,  to  prevent  the  mercury  from  running  out.  The  tube  is  then 
rapped  horizontally  on  the  table,  so  as  to  form  a  passage  above  the  mixture,  and 
is  placed  in  a  Liebig's  combustion  furnace ;  the  hinder  end  of  the  tube  is  placed 
in  communication  with  an  apparatus  for  evolving  dry  carbonic  acid  gas,  having  a 
wash-bottle  containing  oil  of  vitriol,  so  that  the  operator  may  judge  of  the 
rapidity  with  which  the  gas  is  passing. 

A  slow  stream  (about  2  bubbles  per  second)  of  gas  should  be  passed  through 
the  tube  during  the  whole  operation. 

The  combustion-tube  is  now  surrounded  throughout  its  whole  length  with  red- 
hot  charcoal,  the  fire  being  raised,  at  the  end,  to  the  highest  temperature  which 
the  tube  will  sustain.  All  the  mercury  is  then  chased,  with  a  spirit-lamp,  into 
the  bulbs,  the  carbonic  acid  apparatus  disconnected,  and  that  part  of  the  tube 
which  contains  the  mercury  is  drawn  off  and  sealed  with  the  aid  of  the  blowpipe. 
The  mercury  is  rinsed  into  a  small  weighed  capsule  or  beaker,  washed  once  or 
twice  by  decantation,  dried  on  a  water-bath,  and  weighed. 

In  the  above  determination  it  is  recommended  to  employ  perfectly  dry  mate- 
rials, because  the  condensed  moisture  may  give  rise  to  considerable  inconve- 
nience. The  stream  of  carbonic  acid  is  employed  to  carry  forward  the  whole  of 
the  mercury. 

This  process  is  very  convenient  and  expeditious  for  the  determination  of  mer- 
cury in  its  ores,  but  is  far  inferior  in  accuracy  to  the  method  of  determining  that 
metal  as  sulphide. 

Determination  as  Sulphide. — (For  practice,  chloride  of  mercury  may  be  taken. 
About  15  grains  will  suffice.  The  amount  of  mercury  found  should  not  differ 
more  than  0.3  per  cent,  from  that  calculated.) 

The  actual  method  employed  for  the  determination  of  mercury  as  sulphide 
varies  according  to  the  nature  of  the  solution. 

1.  The  solution  is  free  from,  nitric  acid,  and  from  any  other  substance  which 
could  precipitate  sulphur  from  the  sulphuretted  hydrogen. 

The  solution  is  acidified  with  hydrochloric  acid,  diluted  with  a  considerable 
amount  of  water,  and  saturated  with  sulphuretted  hydrogen  (p.  574).  The  pre- 
cipitate is  collected  upon  a  filter  which  has  been  dried  and  weighed  (p.  575), 
37 


578  QUANTITATIVE  DETERMINATION   OF  THE   BASES. 

washed,  till  the  washings  have  no  longer  an  acid  reaction,  dried  at  212°,  and  its 
weight  determined  (p.  575). 

Calculation. 

HgS     Hg 

As  116  :  100  : :  Weight  of  precipitate  :  x 
x  =  Weight  of  mercury. 

2.  The  solution  contains  no  nitric  acid,  but  some  substance  capable  of  oxidizing 
the  hydrogen  of  the  sulphuretted  hydrogen. 

The  precipitate  obtained  as  above  is  washed  off  the  filter  into  a  flask,  heated 
with  hydrochloric  acid,  nitric  acid  being  gradually,  added  until  the  separated 
sulphur  is  yellow,  the  solution  diluted  with  water,  filtered,  and  treated  as  in 
case  3. 

3.  The  solution  contains  nitric  acid. 

In  this  case,  it  is  carefully  evaporated  with  hydrochloric  acid,  on  a  water- 
bath,  to  expel  the  nitric  acid,  the  solution  largely  diluted,  and  the  mercury  then 
precipitated  by  sulphuretted  hydrogen,  the  rest  of  the  determination  being  con- 
ducted in  the  usual  manner. 

When  the  suboxide  and  oxide  of  mercury  are  present  simultaneously,  and  it  is 
desired  to  determine  their  respective  amounts,  the  former  may  be  precipitated 
by  hydrochloric  acid,  collected  upon  a  weighed  filter,  washed,  and  dried  at  212°. 

OXIDE  OF  LEAD. 

(For  practice,  about  25  grains  of  nitrate  of  lead,  dried  in  a  water-oven,  may 
be  employed.  The  result  must  be  within  0.5  per  cent,  of  the  calculated  amount 
of  oxide  of  lead.) 

§  365.  This  oxide  is  usually  precipitated  either  as  sulphate  or  oxalate. 

1.  Precipitation  as  Sulphate. — The  solution,  which  should  not  be  very  dilute, 
is  mixed  with  a  slight  excess  of  dilute  sulphuric  acid,  and  with  about  twice  its 
volume  of  alcohol.     The  precipitate  of  sulphate  of  lead,  which  is  somewhat  solu- 
ble in  water,  is  allowed  some   hours  to  subside,  collected  upon  a  filter,  and 
washed  with  diluted  alcohol  till  the  washings  are  no  longer  acid.     It  is  then 
dried  and  ignited,  in  a  porcelain  crucible,  with  the  precautions  given  at  p.  575. 
After  ignition,  the  ash  is  moistened  with  concentrated  nitric  acid,  dried,  again 
moistened  with  dilute  sulphuric  acid,  dried,  and  gradually  ignited.     In  this  way, 
any  reduced  lead  is  reconverted  into  sulphate. 

Calculation. 

PbO.S03    PbO 

151.7  :  111.7  ::  Weight  of  precipitate  :  x 
x  =  Weight  of  oxide  of  lead. 

In  cases  where  the  addition  of  alcohol  is  inadmissible,  the  solution  must,  be 
precipitated  with  a  considerable  excess  of  dilute  sulphuric  acid  ;  the  precipitate, 
after  standing  for  some  time,  is  collected  upon  a  filter,  washed  with  water,  till 
the  washings  are  but  slightly  acid,  and  treated  as  before. 

The  presence  of  much  free  nitric  acid  prevents  the  complete  precipitation  of 
sulphate  of  lead;  when  this  acid  is  present,  therefore,  in  large  quantity,  the 
solution  must  be  evaporated  nearly  to  dryness  before  adding  the  diluted  sulphuric 
acid. 

2.  Precipitation  as  Oxalate. — The  solution  under  examination  is  mixed  with 
oxalate  of  ammonia,  and  ammonia  added  in  slight  excess.     The  precipitate  is 
collected  on  a  filter,  washed  with  water,  till  the  washings  leave  no  residue  on 
evaporation,  dried,  ignited  in  a  porcelain  crucible,  with  the  usual  precautions, 


OXIDE   OF   COPPER.  579 

and  weighed.  The  ash  is  afterwards  moistened  with  concentrated  nitric  acid, 
dried  at  a  gentle  heat,  and  again  ignited,  to  reoxidize  any  reduced  lead.  The 
whole  of  the  lead  is  thus  obtained  as  oxide,  into  which  form  the  oxalate  is  con- 
verted by  ignition. 

TEROXIDE  OF  BISMUTH. 

(For  practice,  two  determinations  should  be  made  in  an  aqueous  solution  of 
nitrate  of  bismuth ;  the  results  should  correspond  within,  at  most,  ^  of  the 
teroxide  of  bismuth  present.) 

§  366.  Teroxide  of  bismuth  is  precipitated  either  as  carbonate  or  as  ter- 
sulphide. 

1.  Precipitation  as  Carbonate. — The  teroxide  of  bismuth  can  only  be  precipi- 
tated in  this  form  from  solutions  which  contain  no  other  acid  but  nitric,  since  if 
any  sulphuric  or  hydrochloric  acid  be  present,  it  will  be  carried  down  in  the 
form  of  a  basic  salt,  and  cannot  be  removed  by  washing. 

The  solution  is  diluted  with  water  (any  precipitate  being  disregarded),  mixed 
with  excess  of  sesquicarbonate  of  ammonia,  and  gently  heated  for  some  time. 
The  precipitate  is  collected  on  a  filter,  washed  with  water,  dried,  and  afterwards 
treated  in  the  same  manner  as  the  oxalate  of  lead.  After  ignition,  it  is  pure 
teroxide  of  bismuth. 

2.  Precipitation  as  Tersulphide. — The  solution  is  largely  diluted  with  water 
acidulated  with  acetic  acid,  and  saturated  with  sulphuretted  hydrogen ;  the  pre- 
cipitate is  collected  upon  a  filter,  and  well  washed;  the  filter  is  then  perforated 
with  a  pointed  glass  rod,  and  the  precipitate  washed  completely  into  a  flask, 
where  it  is  to  be  heated  with  moderately  strong  nitric  acid  (which  may  be  pre- 
viously warmed  and  poured  over  the  filter,  to  dissolve  the  last  traces  of  the 
precipitate),  until  completely  decomposed.     The  solution  is  then  diluted  with 
water  acidulated  with  nitric  acid,  filtered,  the  filter  thoroughly  washed  with 
acidulated  water,  the  solution  evaporated,  if  necessary,  to  expel  the  greater 
excess  of  acid,  and  the  bismuth  precipitated  as  carbonate. 

OXIDE  OF  COPPER. 

(Crystallized  sulphate  of  copper  should  be  analyzed  for  practice,  all  adhering 
water  being  removed  by  pressure  between  blotting-paper.  20  grains  are  suffi- 
cient for  analysis.  The  amount  of  oxide  of  copper  obtained  should  not  differ 
more  than  0.3  per  cent,  from  the  calculated  result.) 

§  367.  Oxide  of  copper  is  precipitated  in  the  form  of  oxide  or  sulphide,  but 
is  always  determined  as  oxide. 

1.  Precipitation  as  Oxide. — The  moderately  diluted  solution  is  heated  nearly 
to  ebullition,  in  a  beaker,  and  mixed  with  an  excess  of  solution  of  potassa  (pre- 
viously diluted  with  water).     The  mixture  is  digested  for  some  time  at  a  tem- 
perature approaching  ebullition,  the  precipitate  allowed  to  subside,  collected  on 
a  filter  of  known  ash,  washed  with  boiling  water,  till  the  washings  leave  no  resi- 
due on  evaporation,  dried,  ignited  in  a  porcelain  crucible,  with  the  usual  precau- 
tions (p.  575),  and  weighed  when  just  on  the  point  of  cooling  (p.  572).     The 
weighing  should  be  executed  as  rapidly  as  possible,  since  oxide  of  copper  is 
exceedingly  hygroscopic. 

2.  Precipitation  as  Sulphide. — The  solution,  which  must  not  contain  a  large 
excess  of  free  -nitric  acid,  is  acidulated  with  hydrochloric  acid,  largely  diluted 
with  water,  and  saturated  with  sulphuretted  hydrogen ;  as  soon  as  this  reagent 
ceases  to  produce  any  further  precipitate,  the  latter  is  allowed  to  subside,  rapidly 
filtered  off,  and  washed  with  solution  of  sulphuretted  hydrogen  as  long  as  the 
washings  have  a  very  acid  reaction.     When  the  washing  is  completed,  the  apex 
of  the  filter  is  perforated  with  a  pointed  glass  rod,  and  the  sulphide  of  copper 


580  QUANTITATIVE   DETERMINATION   OP   THE   BASES. 

washed  off,  as  far  as  possible,  into  a  pretty  capacious  flask ;  the  filter  is  then 
dried,  incinerated  as  usual  in  a  porcelain  crucible,  and  the  ash  added  to  the  con- 
tents of  the  flask;  a  quantity  of  concentrated  nitric  acid  is  now  poured  into  the 
latter,  a  funnel  placed  in  the  mouth  to  prevent  loss  from  spirting,  and  the  mix- 
ture maintained  in  rapid  ebullition,  on  a  sand-bath,  until  the  sulphur  has  sepa- 
rated in  pure  yellow  fused  globules.  A  considerable  quantity  of  water  is  then 
added,  the  solution  filtered  off,  the  filter  being  washed  until  the  washings  are  no 
longer  tinged  by  sulphuretted  hydrogen,  and  the  copper  precipitated  as  oxide. 

DETERMINATION  OF  COPPER  IN  ORES. — This  is  effected  by  ascertaining  the 
quantity  of  a  standard  solution  of  sulphide  of  sodium  required  to  precipitate  the 
whole  of  the  copper  as  oxymJphide,  CuO,5CuS,  from  an  ammoniacal  solution. 

The  standard  solution  of  sulphide  of  sodium  is  prepared  by  saturating  a  solu- 
tion of  soda  with  sulphuretted  hydrogen,  and  afterwards  adding  an  equal  volume 
of  soda-solution  of  the  same  strength. 

In  order  to  graduate  the  solution,  about  10  grs.  of  pure  copper  (electrotype 
copper)  are  dissolved  in  nitric  acid,  the  solution  measured,  and  divided  into  two 
equal  parts;  one  part  is  somewhat  diluted  with  water,  and  mixed,  in  a  beaker, 
with  excess  of  ammonia;  the  solution  is  heated  just  to  the  boiling  point,  at 
which  it  is  maintained  whilst  the  sulphide  of  sodium  is  added,  cautiously,  from 
a  burette,  with  frequent  stirring,  until  the  liquid  has  lost  its  blue  color;  of 
course,  when  the  blue  color  begins  to  fade  away,  the  sulphide  must  be  very  care- 
fully added,  drop  by  drop,  till  the  exact  point  at  which  the  color  vanishes  has 
been  attained. 

The  result  of  this  experiment  is  confirmed  by  operating  upon  the  other  por- 
tion of  the  copper-solution ;  and  the  number  of  measures  of  the  sulphide  of 
sodium  required  for  100  grs.  of  copper  are  then  calculated  from  the  mean 
result. 

The  standard  solution  should  be  of  such  a  strength  that  1000  gr.  measures 
are  required  to  precipitate  10  grs.  of  copper. 

In  order  to  determine  the  amount  of  copper  in  an  ore,  it  is  reduced  to  a  fine 
powder,  and  about  10  grs.  of  it  dissolved  as  far  as  possible,  in  nitro-hydro- 
chloric  acid ;  the  solution  (not  previously  filtered)  is  diluted  with  water,  and 
mixed  with  a  considerable  excess  of  ammonia;  it  is  then  filtered,  and  treated  ex- 
actly as  directed  above,  the  amount  of  copper  being  calculated  from  the  number 
of  measures  of  standard  solution  employed. 

Since  the  sulphide  of  sodium  is  readily  oxidized  by  exposure  to  air,  it  should 
be  graduated  afresh  before  every  series  of  analyses. 

The  above  method  may  be  employed  for  the  determination  of  copper  in  its 
alloys  and  salts. 

It  has  been  proved  by  experiment  that  none  of  the  metals  associated  with  cop- 
per in  nature  can  interfere  with  this  determination,  except  silver,  mercury,  cobalt, 
and  nickel,  the  first  of  which  can  be  easily  removed  by  hydrochloric  acid  before 
applying  the  above  method. 

If  zinc  be  present  in  the  ore  analyzed,  it  will  be  indicated  by  the  formation  of 
a  white  precipitate  of  sulphide  on  adding  a  little  more  sulphide  of  sodium  after 
the  whole  of  the  copper  has  been  precipitated. 

OXIDE  OP  CADMIUM. 

(For  practice,  about  15  grains  of  pure  dry  sulphide  of  cadmium  may  be  ana- 
lyzed. The  result  should  be  within  0.5  per  cent,  of  the  calculated  amount  of 
metal.) 

§  368.  Cadmium  is  determined  as  oxide  or  suIpJiide. 

1.  Determination  as  Oxide. — The  moderately  diluted  solution  is  heated  nearly 
to  ebullition,  in  a  flask,  and  solution  of  carbonate  of  soda  gradually  added  in 
excess. 


BINOXIDE   OP  PLATINUM.  581 

The  mixture  is  then  boiled  for  a  few  minutes,  the  precipitate  allowed  to  sub- 
side, collected  on  a  filter,  washed  with  hot  water  till  the  washings  leave  no  resi- 
due on  evaporation,  dried,  detached  very  carefully  from  the  filter,  which  must 
be  completely  incinerated  before  being  introduced  into'  the  porcelain  crucible 
containing  the  precipitate,  ignited,  and  weighed. 

If  ammoniacal  salts  be  contained  in  the  solution,  the  ebullition  must  be  con- 
tinued until,  after  a  fresh  addition  of  carbonate  of  soda,  no  ammonia  can  be 
perceived. 

2.  Determination  as  Sulphide. — The  solution,  which  must  be  largely  diluted, 
and  not  very  strongly  acid,  is  saturated  with  sulphuretted  hydrogen,  and  allowed 
to  stand  for  some  time  for  the  precipitate  to  separate.  The  sulphide  of  cadmium 
is  collected  upon  a  weighed  filter,  washed  with  water  containing  sulphuretted 
hydrogen,  dried  at  212°,  and  weighed. 

If  there  exists  in  the  solution  any  substance  capable  of  precipitating  sulphur 
from  the  sulphuretted  hydrogen,  the  sulphide  obtained  as  above  must  be  dis- 
solved in  nitric  acid,  and  the  cadmium  precipitated  as  oxide. 

Calculation. 
CdS      Cd 

72  :  56  : :  Weight  of  Precipitate  :  x 
x  =  Weight  of  Cadmium. 

TEROXIDE  or  GOLD. 

(For  the  sake  of  practice,  a  solution  of  terchloride  of  gold  may  be  analyzed  by 
two  different  methods.  The  results  should  not  differ  by  more  than  -^  of  the 
metallic  gold  found.) 

§  369.  Gold  is  always  determined  in  the  metallic  state. 

1.  The  solution,  which  must  not  contain  any  free  nitric  acid,  is  acidified  with 
hydrochloric  acid,  and  mixed,  in  a  porcelain  dish,  with  a  clear  solution  of  sul- 
phate of  iron.     The  mixture  is  digested  at  a  gentle  heat  for  several  hours,  the 
precipitated  metal  collected  on  a  filter,  well  washed,  dried,  and  ignited. 

2.  The  solution,  which  must,  in  this  case  also,  be  free  from  nitric  acid,  is 
mixed,  in  a  beaker,  with  oxalate  of  ammonia,  and  a  slight  excess  of  hydrochloric 
acid;  the  mixture  is  heated  until  all  the  gold  is  precipitated  (which  may  be 
ascertained  by  testing  a  trace,  upon   a  watch-glass,  with  chloride  of  tin),  the 
metal  filtered  off,  washed,  dried,  and  ignited. 

Solutions  of  gold  which  contain  free  nitric  acid  must  be  evaporated  once  or 
twice,  to  a  small  bulk,  with  excess  of  hydrochloric  acid,  until  the  former  acid  is 
expelled  ;  of  course,  the  precipitation  of  metallic  gold  during  the  evaporation  will 
not  affect  the  determination. 

BINOXIDE  OP  PLATINUM. 

(Solution  of  the  bichloride  is  analyzed  for  practice ;  the  results  of  two  de- 
terminations should  not  differ  by  more  than  ^  of  the  metallic  platinum.) 

§  370.  Platinum,  like  gold,  is  determined  in  the  metallic  state. 

The  rather  concentrated  solution  (which,  if  acid,  should  be  nearly  neutralized 
with  ammonia)  is  mixed  with  an  excess  of  solution  of  chloride  of  ammonium, 
and  an  equal  volume  of  alcohol ;  the  mixture  is  set  aside  for  several  hours,  the 
precipitated  double- salt  collected  upon  a  filter  of  known  ash,  washed  with  spirit 
of  wine,  dried,  ignited,  in  a  platinum  crucible,  and  weighed.  The  precipitate 
should  not  be  detached,  but  wrapped  up  in  the  filter,  placed  in  the  crucible, 
which  is  then  loosely  covered,  and  gently  heated  as  long  as  any  fumes  are  dis- 
engaged ;  the  heat  is  then  gradually  raised,  and  the  incineration  completed  as 
usual. 

The  residue  is  pure  metallic  platinum  (together  with  the  ash  of  the  filter). 


582  QUANTITATIVE   DETERMINATION   OP   THE   BASES. 


OXIDE  AND  BlNOXIDE  OF  TlN. 

(Two  analyses  of  a  solution  of  bichloride  of  tin  may  be  made  for  practice.  The 
results  should  not  differ  by  more  than  j1^  of  the  metal  present.) 

§  371.  Tin  is  determined  either  in  the  form  of  linoxide  or  bisulphide. 

Determination  as  Binoxide. — When  the  tin  is  in  the  metallic  state,  it  is  boiled 
with  moderately  concentrated  nitric  acid  as  long  as  any  oxidizing  action  takes  place; 
a  considerable  quantity  of  water  is  then  added,  the  mixture  digested  for  some  time 
at  a  gentle  heat,  and  the  precipitate  allowed  to  subside;  the  latter  is  collected  upon 
a  filter  of  known  ash,  well  washed  with  hot  water,  dried,  ignited,  with  all  the  pre- 
cautions, in  a  porcelain  crucible,  and  weighed ;  before  weighing,  it  is  generally 
advisable  to  reoxidize  any  reduced  tin  by  moistening  the  ash  with  nitric  acid, 
drying  at  a  gentle  heat,  and  afterwards  strongly  igniting.1 

If  the  tin  be  contained  in  solution,  it  may  be  converted  into  binoxide,  if  not 
already  existing  in  that  form,  by  passing  a  few  bubbles  of  chlorine  gas ;  the  so- 
lution is  then  introduced  into  a  flask,  diluted  with  water,  mixed  with  a  consider- 
able excess  of  solution  of  sesquicarbonate  of  ammonia,  and  boiled  for  some  time; 
the  precipitated  binoxide  of  tin  is  collected  upon  a  filter  of  known  ash,  washed 
with  a  solution  of  sesquicarbonate  of  ammonia  (pure  water  washes  it  through  the 
paper)  till  the  washings  are  free  from  chloride  of  ammonium,  dried,  ignited,  with 
precautions,  and  weighed. 


Calculation. 


Sn03   Sn 


74  :  58  : :  Weight  of  precipitate  :  x 
x  =  Weight  of  tin. 

Determination  as  Sulphide.— In  order  to  precipitate  the  tin  as  a  sulphide,  the 
solution  may  be  diluted  with  water  acidulated  with  hydrochloric  acid,  and  satu- 
rated with  sulphuretted  hydrogen;  the  solution  is  digested  for  a  length  of  time 
at  a  gentle  heat,  the  precipitate  collected  upon  a  filter  of  known  ash,  well  washed 
and  dried;  it  is  then  detached,  as  far  as  possible,  from  the  filter  (which  is  incine- 
rated in  the  usual  way),  and  gradually  roasted  in  a  porcelain  crucible,  until  it  is 
entirely  converted  into  binoxide  of  tin ;  before  the  final  ignition,  a  fragment  of 
sesquicarbonate  of  ammonia  should  be  placed  in  the  crucible. 

In  some  cases,  when  there  is  no  substance  present  in  the  solution  to  precipitate 
sulphur  from  the  sulphuretted  hydrogen,  and  when  the  whole  of  the  tin  is  present 
in  the  form  of  binoxide,  the  bisulphide  of  tin,  precipitated  as  above,  may  be  col- 
lected upon  a  weighed  filter,  washed,  dried  at  212°,  and  weighed. 

Calculation. 
SnS2     Sn 

90  :  58  ::  Weight  of  precipitate  :  x 
x  =  Weight  of  tin. 

When  the  oxide  and  binoxide  of  tin  are  present  in  the  same  solution,  and  it 
is  desired  to  ascertain  their  respective  quantities,  two  weighed  portions  of  the 
solution  must  be  taken ;  in  one  of  these  the  total  amount  of  tin  may  be  determined 
as  above,  and  the  other  portion  may  be  gradually  added  to  an  excess  of  a  hot 
solution  of  chloride  of  mercury  which  has  been  mixed  with  hydrochloric  acid; 
the  precipitated  subchloride  of  mercury  is  collected  upon  a  weighed  filter,  well 
washed,  dried,  and  weighed.  From  the  weight  of  this  precipitate  the  amount  of 
oxide  of  tin  present  may  be  inferred. 

1  It  is  unsafe  to  attempt  the  determination  of  tin  by  evaporating  its  solution  with  nitric 
acid,  since  a  portion  is  volatilized  as  bichloride. 


DETERMINATION   OF   ANTIMONY  IN   ALLOYS. 

Calculation. 
Hg^Cl    SnO  * 

235.5  :  66  ::  Weight  of  precipitate  :  x 
x  :  Weight  of  oxide  of  tin. 

TEROXIDE  OF  ANTIMONY  AND  ANTIMONIC  ACID. 

(About  20  grains  of  tartar-emetic  may  be  analyzed  for  practice;  the  antimony 
sbould  not  differ  more  than  0.3  per  cent,  from  the  calculated  amount.) 

§  372.  Antimony  is  usually  determined  as  tersulphide  or  pentasulphide,  or  in 
the  form  of  antimoniate  of  teroxide  of  antimony  (antimonious  acid?). 

1.  Determination  as  a  Sulphide. — If  the  solution  contain  only  teroxide  of  an- 
timony, unaccompanied  by  antimonic  acid,  or  by  any  substance  capable  of  decom- 
posing sulphuretted  hydrogen,  so  as  to  give  rise  to  separation  of  sulphur,  it  is 
diluted  with  water  acidified  with  hydrochloric  acid,  and  thoroughly  saturated  with 
sulphuretted  hydrogen ;  after  standing  for  some  time,  the  precipitate  is  collected 
upon  a  weighed  filter,  well  washed,  dried  at  212°,  and  weighed. 

Calculation. 
SbS3      Sb 

177  :  129  : :  Weight  of  precipitate  :  x 
x  =  Weight  of  antimony. 

If,  however,  the  solution  contained  any  antimonic  acid,  or  some  substance 
capable  of  separating  sulphur  from  the  sulphuretted  hydrogen,  the  precipitate  is 
weighed,  together  with  the  filter,  a  portion  of  it  detached  and  projected  into  a 
flask,  the  filter  with  the  adhering  precipitate  being  again  weighed  to  ascertain 
how  much  has  been  removed.  The  portion  in  the  flask  is  now  treated,  gradually, 
with  the  most  concentrated  nitric  acid  (free  from  sulphuric  acid),  and  boiled  until 
the  oxidation  of  the  sulphur  is  complete.  The  greater  excess  of  the  nitric  acid 
is  boiled  off,  the  solution  largely  diluted  with  water  acidified  with  hydrochloric 
acid,  filtered,  and  the  sulphuric  acid  precipitated  as  sulphate  of  baryta,  from  the 
weight  of  which  we  may  calculate  the  amount  of  sulphur,  and  if  this  be  deducted 
from  the  weight  of  the  original  dry  precipitate,  we  obtain  that  of  the  antimony 
present. 

A  convenient  method  of  determining  the  antimony  directly  in  the  precipitate 
consists  in  dissolving  it  in  hydrochloric  acid,  and  subsequently  determining  the 
antimony  in  the  filtered  solution  as  antimonious  acid. 

2.  Determination  as  Antimonious  Acid. — The  solution  under  examination 
(which  must  not  contain  any  other  fixed  constituent)  is  mixed  with  a  considerable 
quantity  of  nitric  acid,  and  carefully  evaporated  to  dryness  in  a  weighed  porce- 
lain capsule  placed  upon  a  sand-bath,  or  in  an  air- bath;  the  residue  is  strongly 
ignited  until  its  weight  ceases  to  vary.     If  any  sulphuric  acid  be  present,  a  frag- 
ment of  carbonate  of  ammonia  should  be  placed  in  the  capsule  (which  must  then 
be  loosely  covered)  before  the  final  ignition. 

Calculation. 
SbOt       Sb 

161  :  129  : :  Weight  of  residue  :  x 
x  =  Weight  of  antimony. 

DETERMINATION  OF  ANTIMONY  IN  ALLOYS. 

Since  antimony  is  almost  always  associated  with  tin  in  alloys,  its  determination 
is  attended  with  considerable  difficulty,  from  the  remarkable  similarity  which 
exists  between  the  compounds  of  these  metals.  The  simplest  method  of  deter- 


584  QUANTITATIVE   DETERMINATION   OP   THE   BASES. 

mining  these  two  metals  is  that  recommended  by  Gay  Lussac.  Both  metals  are 
dissolved  in  aqua  regia,  the  solution  diluted,  and  digested  with  a  plate  of  pure 
zinc  until  the  whole  of  the  tin  and  antimony  is  precipitated;  the  weight  of  this 
precipitate  having  been  determined,  it  is  redissolved  in  hydrochloric  acid,  with 
addition  of  a  little  nitric  acid,  and  the  antimony  precipitated  from  the  diluted 
solution  by  a  plate  of  tin,  at  a  gentle  heat;  the  precipitated  antimony  is  collected 
and  weighed,  the  tin  being  determined  by  difference.  This  method,  however,  is 
liable  to  error  from  several  causes,  and  is  only  capable  of  yielding  an  approxima- 
tion to  the  amounts  of  tin  and  antimony  which  are  present. 

ARSENIOUS  ACID. 

(Two  determinations  of  arsenic  may  be  made  in  a  hydrochloric  solution  of 
arsenious  acid;  the  amount  of  arsenic  obtained  should  not  differ  by  more  than 
s\  of  its  weight  in  the  two  determinations. 

§  373.  Arsenious  acid  is  generally  determined  as  tersulpliide  of  arsenic. 

The  determination  is  conducted  on  the  same  principles  and  in  exactly  the  same 
manner  as  in  the  case  of  antimony. 

Calculation. 
AsS3    AsOi 

123  :  99  : :  Weight  of  precipitate  :  x 
x  =  'Weight  of  arsenious  acid. 

ARSENIC  ACID. 

(Two  determinations  may  be  made  in  a  solution  of  arsenic  acid.) 
§  374.  This  acid  is  weighed,  either  as  pentasulphide  of  arsenic,  or  as  arseniate 
of  sesquioxide  of  iron,  or  arseniate  of  magnesia  and  ammonia. 

1.  .Determination  as  Pentasulphide  of  Arsenic. — The  solution  is  mixed  with 
excess  of  ammonia,  and  colorless  sulphide  of  ammonium  added  till  the  precipi- 
tate first  produced  (if  any)  is  redissolved ;  acetic  acid  is  then  added  in  excess,  the 
solution  digested  in  a  warm  place  until  the  odor  of  sulphuretted  hydrogen  has 
disappeared,  the  precipitate  collected  upon  a  weighed  filter,  well  washed  with 
water,  dried,  and  weighed. 

A  portion  of  the  precipitate  is  then  shaken  out  of  the  filter  (which  is  then  again 
weighed  to  ascertain  how  much  has  been  detached)  into  a  large  flask,  and  care- 
fully treated  with  nitric  acid  of  moderate  strength;  as  soon  as  the  action  has 
Somewhat  moderated,  heat  is  applied,  and  continued  until  the  sulphur  (if  any) 
separates  in  pure  yellow  globules;  the  solution  is  then  diluted  with  water,  the 
separated  sulphur  collected  upon  a  weighed  filter,  well  washed,  dried  at  212°,  and 
weighed.  The  sulphuric  acid  contained  in  the  solution  is  determined  as  sulphate 
of  baryta  from  the  weight  of  which  the  amount  of  sulphur  is  calculated.  If  the 
sulphur  be  calculated  for,  and  deducted  from,  the  total  quantity  of  the  original 
precipitate,  we  obtain  the  amount  of  the  arsenic. 

2.  Determination  as  Arseniate  of  Sesquioxide  of  Iron. — This  method  consists 
in  dissolving  a  weighed  quantity  of  pure  iron  in  nitric  acid,  mixing  the  solution 
with  that  of  arsenic  acid,  and  precipitating  by  ammonia.     The  precipitate  of  basic 
arseniate  of  sesquioxide  of  iron  is  collected  on  a  filter,  well  washed  with  hot  water, 
dried,  carefully  ignited,  having  been  very  carefully  detached  from  the  filter,  and 
weighed.     The  ignition  should  not  be  sudden,  but  gradual,  so  that  the  trace  of 
ammonia  in  the  precipitate  may  be  volatilized  at  first. 

The  amount  of  sesquioxide  of  iron  which  the  pure  iron  ought  to  yield  is 
then  calculated,  and  deducted  from  the  weight  of  the  precipitate,  when  the  dif- 
ference gives  the  arsenic  acid. 

3.  Determination  as  Arseniate  of  Magnesia  and  Oxide  of  Ammonium. — The 


SESQUIOXIDE  OF  IRON.  585 

solution  is  mixed  with  free  ammonia,  and  a  mixture  of  sulphate  of  magnesia, 
chloride  of  ammonium  and  ammonia  added;  the  mixture  is  well  stirred  without 
touching  the  sides  of  the  vessel,  and  allowed  to  stand  for  24  hours ;  the  precipi- 
tate of  arseniate  of  magnesia  and  ammonia  is  collected  upon  a  weighed  filter, 
washed  with  water  containing  some  free  ammonia,  dried  at  212°,  and  weighed. 

Calculation. 
2  MgO.NH^O.AsOB+Aq.     AsO. 

190          :  115  ::  Weu/ht  of  precipitate  :  x 

x  =  Weiyht  of  arsenic  acid. 

In  order  to  determine  the  respective  amounts  of  arsenious  and  arsenic  acid 
when  both  are  present  in  the  same  solution,  the  total  quantity  of  arsenic  may  he 
ascertained  by  precipitation  as  a  sulphide  from  the  mixture  of  the  solution  with 
ammonia  and  sulphide  of  ammonium,  the  sulphur  being  afterwards  determined 
in  the  precipitate,  as  directed  above. 

Another  portion  of  the  solution  is  then  mixed  with  hydrochloric  acid,  and 
colored  blue  with  solution  of  indigo.  Solution  of  chloride  of  lime  of  known 
strength  (see  Chlorimetry)  is  added  from  a  burette  until  the  blue  color  just 
vanishes;  the  number  of  measures  of  solution  must  be  observed,  and  from  the 
quantity  of  chlorine  which  they  are  known  to  contain,  the  amount  of  arsenious 
acid  (now  converted  into  arsenic  acid)  is  calculated. 


99  : :  Amount  of  chlorine  employed:  x 

x  =  Weight  of  arsenious  acid. 

By  deducting  the  amount  of  arsenic  present  as  arsenious  acid  from  the  total 
quantity  known  to  be  contained  in  the  solution,  we  may  ascertain  the  weight  of 
arsenic  which  is  present  in  the  form  of  arsenic  acid. 

ALUMINA. 

(For  practice,  crystallized  alum  may  be  employed;  the  crystals  should  be 
coarsely  powdered,  and  dried  by  pressure  between  blotting-paper.  30  grains  will 
suffice  for  the  determination  of  alumina.  The  result  should  not  differ  more  than 
0.3  per  cent,  from  that  obtained  by  calculation.) 

§  375.  Alumina  is  always  weighed  as  such. 

The  solution  is  mixed  with  a  considerable  quantity  of  chloride  of  ammonium, 
and  a  slight  excess  of  ammonia ;  it  is  then  heated  for  some  time,  and  filtered ; 
the  precipitate  is  well  washed  with  boiling  water,  till  the  washings  are  free  from 
sulphuric  acid,  dried,  ignited  in  a  platinum  crucible,  and  weighed. 

The  presence  of  fixed  organic  matters,. it  will  be  remembered,  prevents  the 
precipitation  of  alumina. 

SESQUIOXIDE  OF  CHROMIUM. 

(For  .practice,  chrome-alum  may  be  employed.  30  grains  will  suffice.  The 
result  must  come  within  0*3  per  cent,  of  that  obtained  by  calculation.) 

§  376.  The  sesquioxide  of  chromium  is  weighed  in  the  pure  state. 

The  solution,  which  must  not  be  too  concentrated,  nor  contain  any  fixed  organic 
substance,  is  heated  nearly  to  ebullition,  and  mixed  with  a  very  slight  excess  of 
ammonia.  The  mixture  is  maintained  at  a  high  temperature  until  the  superna- 
tant liquid  appears  colorless,  when  the  sesquioxide  is  collected  upon  a  filter,  well 
washed  with  hot  water,  dried,  ignited  in  a  platinum  crucible,  and  weighed. 

SESQUIOXIDE  OF  IRON. 

(Two  determinations  may  be  made  in  a  solution  of  sesquichloride  of  iron ;  the 
results  should  agree  within  T^  Of  the  amount  of  sesquioxide  present.) 


586  QUANTITATIVE  DETERMINATION  OP  THE   BASES. 

§  377.  Sesquioxide  of  iron  is  weighed  in  the  pure  state. 
Different  processes  are  employed  for  the  determination  of  sesquioxide  of  iron, 
according  as  the  solution  contains  fixed  organic  matters  (as  tartaric  acid)  or  not. 

1.  In  Solutions  free  from  fixed  Organic  Matters. — The  solution  is  mixed  with 
an  excess  of  ammonia,  and  heated  nearly  to  ebullition ;  the  precipitate  is  col- 
lected upon  a  filter,  well  washed  with  hot  water  (till  the  washings  are  free  from 
chloride  of  ammonium,  which  would  cause  a  loss  of  iron  during  the  subsequent 
ignition),  dried,  incinerated,  in  a  platinum  crucible,  with  the  usual  precautions, 
and  weighed.    In  very  accurate  analysis,  it  is  well  to  moisten  the  ash  with  nitric 
acid,  to  dry,  and  ignite  again  before  weighing,  in  order  to  reoxidize  any  iron 
which  may  have  been  reduced. 

2.  In  Solutions  containing  fixed  Organic  Matters. — The  solution  is  rendered 
slightly  alkaline  with  ammonia,  and  mixed  with  an  excess  of  sulphide  of  ammo- 
nium ;  it  is  then  digested  for  some  time  at  a  moderate  heat,  until  the  solution 
has  a  pure  yellow  color,  when  the  precipitated  sulphide  of  iron  is  collected  upon 
a  filter,  and  well  washed  with  water  containing  sulphide  of  ammonium  ;  the  apex 
of  the  filter  is  then  perforated  with  a  glass  rod,  and  the  precipitate  washed  off 
into  a  flask  placed  below ;  the  remainder  of  the  precipitate  is  dissolved  off  the 
paper  with  warm  dilute  hydrochloric  acid,  in  which  the  whole  of  the  sulphide  is 
then  dissolved.     The  solution  is  heated  till  no  smell  of  sulphuretted  hydrogen 
is  perceptible,  boiled  with  nitric  acid  until  the  iron  is  peroxidized,  and  the  latter 
metal  is  then  determined  in  the  solution  as  directed  above. 

Sesquioxide  of  iron  is  sometimes  precipitated  as  succinate,  for  which  purpose 
the  solution  is  gradually  mixed  with  dilute  ammonia  until  a  slight  precipitate  is 
produced,  which  does  not  redissolve  entirely,  even  on  application  of  a  gentle 
heat.  A  perfectly  neutral  solution  of  succinate  of  ammonia  is  now  added  as  long 
as  any  precipitate  is  formed,  the  solution  gently  heated,  and  allowed  to  stand  for 
some  time;  the  precipitated  succinate  of  sesquioxide  of  iron  is  filtered  off,  washed, 
first  with  cold  water,  and  afterwards  with  warm  dilute  ammonia  (which  removes 
a  part  of  the  succinic  acid),  dried,  and  ignited  (with  all  the  precautions  given  at 
p.  575)  in  a  platinum  crucible ;  before  weighing,  the  ignited  precipitate  may  be 
moistened  with  nitric  acid,  dried,  and  again  ignited.  In  this  way,  pure  sesqui- 
oxide of  iron  is  obtained. 

For  the  method  of  determining  the  sesquioxide  of  iron  by  means  of  perman- 
ganate of  potassa,  see  analysis  of  iron  ores. 

OXIDE  OP  IRON. 

(Crystallized  sulphate  of  iron  may  be  dried  by  pressure  between  blotting-paper, 
and  analyzed  for  practice.  20  grains  should  be  taken.  The  amount  of  oxide  of 
iron  found  should  be  within  0.3  per  cent,  of  the  calculated  quantity.) 

§  378.  Oxide  of  iron  is  always  weighed  in  the  form  of  sesquioxide. 

The  solution  of  the  compound  under  examination  is  heated  with  concentrated 
nitric  acid  (in  a  flask,  or  beaker  covered  with  an  inverted  funnel)  until  no  more 
red  fumes  are  evolved ;  the  solution  then  contains  sesquioxide  of  iron,  which  may 
be  determined  as  above. 

Calculation. 

Fe203    IFeO 

As  80  :  72  : :    Weight  of  precipitate  :  x 
x  =  Weight  of  oxide  of  iron. 

For  the  determination  of  oxide  of  iron  by  means  of  permanganate  of  potassa, 
see  analysis  of  iron  ores. 

To  determine  the  respective  quantities  of  oxide  and  sesquioxide  of  iron  present 
in  the  same  solution,  the  total  quantity  of  iron  is  first  ascertained  according  to 


OXIDE   OF  NICKEL.  587 

the  methods  given  above,  and  the  amount  of  iron  present  in  the  form  of  oxide  is 
then  estimated  by  means  of  the  standard  solution  of  permanganate  of  potassa ; 
if  the  weight  of  sesquioxide  of  iron  corresponding  to  the  iron  present  in  the 
form  of  oxide,  be  calculated  and  subtracted  from  the  total  weight  of  sesquioxide 
previously  obtained,  the  difference  shows  the  quantity  of  sesquioxide  of  iron 
actually  existing  in  the  solution. 

OXIDE  OF  COBALT. 

(Two  determinations  may  be  made,  for  practice,  in  a  solution  of  nitrate  of 
cobalt,  free  from  nickel.  The  results  should  not  differ  by  more  than  (at  most) 
-^j  of  the  oxide  of  cobalt  obtained.) 

§  379.  Cobalt  is  always  weighed  in  the  metallic  state.  It  is  sometimes  pre- 
cipitated as  oxide,  sometimes  as  sulphide. 

1.  Precipitation  as  Oxide. — The  solution  is  mixed  with  an  excess  of  a  strong 
solution  of  potassa,  and  heated  till  the  precipitate  has  acquired  a  brownish  color; 
it  is  then  collected  upon  a  filter  of  known  ash,  well  washed  with  hot  water,  and 
dried.     The  precipitate  is  detached,  as  far  as  possible,  from  the  filter,  carefully 
ignited,  and  weighed ;  the  filter  is  incinerated  and  weighed  separately. 

A  portion  of  the  precipitate  is  introduced  into  a  weighed  bulb-tube  of  hard 
glass,  which  is  then  again  weighed,  and  connected  with  an  apparatus  for  evolv- 
ing dry  hydrogen;  as  soon  as  the  apparatus  is  filled  with  hydrogen,  a  gradually 
increasing  heat  is  applied  to  the  bulb,  which  is  ultimately  raised  to  bright  red- 
ness, and  maintained  at  that  temperature  as  long  as  any  water  is  formed.  The 
last  traces  of  moisture  are  chased  out  of  the  tube  with-  a  spirit-flame,  and  the 
tube  allowed  to  cool,  while  the  hydrogen  is  still  passing ;  the  tube  is  then  de- 
tached, held  obliquely  for  some  time  to  allow  the  displacement  of  the  hydrogen 
by  atmospheric  air,  and  the  weight  of  the  metallic  cobalt  determined. 

If  the  precipitate  be  not  pure,  or  if  the  heat  applied  in  its  reduction  be  not 
sufficiently  intense,  it  will  be  pyrophoric,  oxidizing  immediately  on  contact  with 
air. 

2.  Precipitation  as  Sulphide  of  Cobalt. — The  solution  is  mixed  with  some 
chloride  of  ammonium  and  an  excess  of  ammonia;   sulphide  of  ammonium  is 
then  added  as  long  as  any  precipitate  is  formed,  the  sulphide  of  cobalt  is  washed 
with  water  containing  sulphide  of  ammonium,  the  filter  then  perforated  (so  that 
the  precipitate  may  be  washed  into  a  flask),  and  afterwards  incinerated,  the  ash 
being  added  to  the  contents  of  the  flask;  these  are  then  heated  with  concentrated 
nitro-hydrochloric  acid,  until  the  separated  sulphur  has  a  pure  yellow  color.   The 
solution  is  diluted  with  water,  filtered  off,  and  the  cobalt  precipitated  as  oxide, 
which  is  afterwards  reduced  to  the  metallic  state. 

OXIDE  OF  NICKEL. 

(For  practice,  two  determinations  may  be  made  in  the  same  solution.  The 
results  should  be  as  accurate  as  in  the  case  of  cobalt.) 

§  380.  This  oxide  is  always  weighed  in  the  pure  state}  but  is  sometimes  pre- 
cipitated in  the  form  of  sulphide. 

In  order  to  precipitate  the  oxide  of  nickel,  the  solution  is  heated  with  an  excess 
of  potassa,  nearly  to  ebullition.  The  precipitate  is  collected  upon  a  filter,  well 
washed  with  boiling  water,  dried,  and  ignited. 

If  the  nickel  is  to  be  precipitated  as  sulphide,  the  solution  is  nearly  neutral- 
ized with  ammonia,  and  mixed  with  a  slight  excess  of  freshly-prepared  colorless 
sulphide  of  ammonium.  The  precipitate  is  collected  upon  a  filter,  washed  rapidly 
with  water  containing  a  little  colorless  sulphide  of  ammonium,  and  treated  as  in 
the  case  of  sulphide  of  cobalt. 


588  QUANTITATIVE   DETERMINATION   OF   THE  BASES. 


OXIDE  OF  MANGANESE. 

(Pure  crystals  of  sulphate  of  manganese  may  be  employed.  They  should  be 
powdered,  dried  between  blotting-paper,  and  about  15  grains  employed  for 
analysis;  the  oxide  of  manganese  should  be  determined  within  0.3  per  cent.) 

§  381.  Oxide  of  manganese  is  generally  determined  in  the  form  of  protases- 
quioxide  (Mn304).  It  is  precipitated  sometimes  as  hydrate,  sometimes  as  car- 
bonate of  oxide  of  manganese;  occasionally,  the  manganese  is  separated  in  the 
form  of  sulphide. 

1.  Precipitation  as  Hydrate. — The  solution  is  heated  nearly  to  boiling,  and 
mixed  with  excess  of  solution  of  potassa;  heat  is  then  applied  for  some  time,  the 
precipitate  filtered  off,  well  washed  with  hot  water,  dried,  and  strongly  ignited, 
with  the  usual  precautions. 

Calculation. 
Mn304      BMnO 

114.8  :  106.8  ::    Weight  of  precipitate  :  x 
x  =  Weight  of  oxide  of  manganese. 

2.  Precipitation  as  Carbonate. — The  process  is  conducted  in  quite  the  same 
way  as  in  the  preceding  case,  solution  of  carbonate  of  soda  being  substituted  for 
the  potassa. 

3.  Precipitation  as  Sulphide. — The  solution  is  mixed  with  chloride  of  ammo- 
nium, an  excess  of  ammonia  is  then  added,  and  afterwards  sulphide  of  ammo- 
nium ;   the  precipitate  is  allowed  to  subside,  the  supernatant  liquid  filtered  off, 
the  precipitate  subsequently  collected  upon  the  filter,  and  washed  with  water  con- 
taining sulphide  of  ammonium.     It  is  then  washed  off  the  filter  (which  is  per- 
forated for  that  purpose)  into  a  flask,  the  adhering  particles  dissolved  off  with 
hydrochloric  acid,  in  which  the  whole  of  the  precipitate  is  afterwards  dissolved ; 
the  solution  is  then  heated  until  no  more  sulphuretted  hydrogen  is  evolved,  and 
the  manganese  then  precipitated  as  carbonate. 

OXIDE  OF  ZINC. 

(For  practice,  sulphate  of  zinc  may  be  employed.  10  or  15  grains  may  be 
taken.  The  result  should  be  within  0.3  of  the  calculated  amount.) 

§  382.  Oxide  of  zinc  is  always  weighed  in  the  pure  state,  but  may  be  precipi- 
tated either  as  carbonate  or  sulphide. 

In  order  to  precipitate  the  oxide  of  zinc  as  carbonate,  the  solution  is  treated 
exactly  as  in  the  case  of  cadmium  (see  p.  580).  The  filtrate  must  always  be 
mixed  with  sulphide  of  ammonium,  to  ascertain  if  the  precipitation  be  complete; 
should  this  reagent  give  rise  to  any  considerable  precipitate,  it  must  be  collected 
and  treated  as  under. 

When  the  zinc  is  to  be  precipitated  as  sulphide,  it  is  mixed  with  excess  of 
ammonia,  and  the  subsequent  process  conducted  as  in  the  case  of  manganese, 
(see  above). 

BARYTA. 

(Pure  crystallized  chloride  of  barium,  dried  between  blotting-paper,  may  be 
employed  for  practice.  15  or  20  grains  will  be  found  sufficient.  The  result 
should  not  differ  by  more  than  0.2  from  the  theoretical  percentage,  when  the 
baryta  is  weighed  as  sulphate,  nor  more  than  0.5  when  it  is  obtained  as  car- 
bonate.) 

§  383.  Baryta  is  determined  either  as  sulphate  or  carbonate. 

1.  Determination  as  Sulphate. — The  solution  is  heated  nearly  to  ebullition, 
dilute  sulphuric  acid  added  to  complete  precipitation,  and  the  mixture  allowed 


STRONTIA.  589 

to  stand  for  some  hours,  until  the  precipitate  has  completely  subsided.  The 
supernatant  liquid  is  then  carefully  decanted  on  to  the  filter  (or  it  may  even,  in 
some  cases,  be  drawn  off  by  a  siphon),  and  the  precipitate  then  rinsed  out  on  to 
the  same  filter  with  a  moderately  diluted  hot  solution  of  chloride  of  ammonium. 
The  filter  should  never  be  filled  more  than  half  full,  and  each  portion  of  liquid 
should  be  allowed  to  drain  through  before  another  is  added.  The  addition  of 
chloride  of  ammonium  is  necessary,  to  prevent  the  precipitate  from  passing 
through  the  pores  of  the  filter. 

If,  notwithstanding,  the  filtrate  should  be  turbid,  it  must  be  set  aside,  the 
particles  allowed  to  subside,  and  again  thrown  upon  the  filter. 

The  sulphate  of  baryta  is  washed  with  hot  water  till  the  washings  are  free 
from  sulphuric  acid,  dried,  ignited,  and  weighed. 

Calculation. 
BaO.S03        BaO 

116.5    :    76.5    ::    Weight  of  precipitate  :  x 
x  :  Weight  of  baryta. 

2.  Determination  as  Carbonate. — The  solution,  which  should  not  be  too  con- 
centrated, is  mixed  with  excess  of  ammonia  and  sesquicarbonate  of  ammonia, 
and  gently  heated  for  a  considerable  time. 

The  precipitate  is  filtered  off,  washed  with  ammoniacal  water,  dried,  ignited, 
and  weighed.  The  ignition  should  not  be  too  intense. 

Calculation. 
BaO.C02      BaO 

98.5    :    76.5    ::    Weight  of  precipitate  \  x 
x  :  Weight  of  baryta. 

STRONTIA. 

(Pure  nitrate  of  strontia  may  be  taken.  20  grains  should  be  employed.  The 
result  ought  not  to  differ  more  than  0.5  per  cent,  from  the  theoretical  amount 
when  the  strontia  is  precipitated  as  carbonate,  nor  more  than  -g\  of  the  whole 
amount  of  strontia  when  determined  as  sulphate.) 

§  384.  1.  Determination  as  Sulphate  of  Strontia. — The  solution,  which  must 
not  be  too  dilute,  is  mixed  with  an  excess  of  dilute  sulphuric  acid,  and  allowed 
to  stand  for  several  hours.  The  precipitate  of  sulphate  of  strontia  is  collected 
upon  a  filter,  washed  with  water  till  the  washings  are  no  longer  acid,  dried,  and 
ignited,  the  precipitate  being  very  carefully  detached  from  the  filter. 

If  it  be  admissible  to  mix  the  solution,  after  adding  sulphuric  acid,  with  an 
equal  volume  of  alcohol,  and  to  "wash  the  precipitate  with  dilute  alcohol,  the 
result  will  be  much  more  accurate. 

Calculation. 
SrO.S03        SrO 

91.8    :    51.8    ::    Weight  of  precipitate  :  x 
x  =  Weight  of  strontia. 

2.  Determination  as  Carbonate. — The  process  is  conducted  exactly  as  in  the 
case  of  baryta. 

Calculation. 
SrO.C02        SrO 

73.8    :    51.8    ::    Weight  of  precipitate  :  x 
x=  Weight  of  strontia. 


590  QUANTITATIVE  DETERMINATION   OF   THE   BASES. 

LIME. 

(Pure  calcareous  spar,  or  even  white  marble,  may  be  analyzed  for  practice. 
10  to  15  grains  should  be  taken.  The  amount  of  lime  found  should,  if  the  spe- 
cimen be  pure,  differ  from  the  calculated  quantity  by  not  more  than  0.3  per 
cent.  ;  or  two  determinations  should  come  within  so  much  of  each  other.) 

§  385.  Lime  is  generally  precipitated  as  oxalate,  and  weighed  as  carbonate. 

The  solution  is  rendered  ammoniacal  and  completely  precipitated  with  oxalate 
of  ammonia  ;  it  is  gently  heated  until  the  precipitate  has  subsided,  the  latter 
collected  on  a  filter  (the  supernatant  liquid  being  poured  through  first),  washed 
with  hot  water,  dried,  and  very  gently  ignited,  the  filter  being  incinerated  as 
usual.  The  mass  is  then  drenched  with  a  strong  solution  of  sesquicarbonate  of 
ammonia,  dried  in  an  air-bath,  and  weighed.  This  treatment  is  repeated  until 
no  further  increase  of  weight  is  perceived  (that  is,  till  all  the  lime  which  had 
been  caustified  by  ignition  has  been  recarbonated). 

Calculation. 
CaO.C02     CaO 

50    :    28   ::  Weight  of  ^precipitate  :  x 
x  =  Weight  of  lime. 

MAGNESIA. 

(Crystallized  sulphate  of  magnesia  may  be  analyzed  for  practice,  15  to  20 
grains  being  employed.  The  result  should  not  differ  by  more  than  0.3  per  cent. 
from  the  theoretical  amount.) 

§  386.  Magnesia  is  usually  determined  as  pyropTiosphate,  being  precipitated, 
for  that  purpose,  in  the  form  of  phosphate  of  magnesia  and  ammonia. 

The  solution  is  mixed  with  enough  chloride  of  ammonium  to  prevent  precipi- 
tation by  ammonia.  An  excess  of  the  latter  is  then  added,  and  afterwards  a 
slight  excess  of  phosphate  of  soda.  The  mixture  is  well  stirred  with  a  glass  rod,  which 
should  not  touch  the  sides  of  the  beaker,  and  allowed  to  stand  for  at  least  twelve 
hours.  The  precipitate  is  then  collected  upon  a  filter,  washed  with  water  con- 
taining about  one-eighth  its  volume  of  strong  ammonia,  until  the  washings  leave 
no  considerable  residue  on  evaporation  ;  the  washed  precipitate  is  dried,  carefully 
ignited  (p.  573),  and  weighed  as  pyrophosphate  of  magnesia. 

Calculation. 


112      :      40     ::      Weight  of  precipitate  :  x 

x  =  Weight  of  magnesia. 

POTASSA. 

(Perfectly  pure  nitre,  powdered  and  dried  in  a  water-bath,  may  be  employed 
for  practice.  Fifteen  grains  may  be  taken  for  determination  by  the  first  two 
methods,  and  five  grains  for  the  last.  The  amount  of  potassa  found  should  be 
within  0/2  per  cent,  of  that  obtained  by  calculation.) 

§  387.  Potassa  is  determined  either  as  sulphate  of  potassa,  as  chloride  of 
potassium,  or  as  the  double  chloride  of  platinum  and  potassium. 

1.  Determination  as  Sufyhate  of  Potassa.  —  The  solution  is  mixed  with  some- 
what more  sulphuric  acid  than  is  thought  necessary  to  combine  with  the  whole 
of  the  potassa,  and  carefully  evaporated  to  dryness  in  a  platinum,1  or  porcelain 
capsule  or  crucible  (which  must  be  loosely  covered  towards  the  end  of  the  operation) 
placed  in  an  air-bath  ;  the  residue  of  sulphate  of  potassa  is  cautiously  dried  and 

1  Of  course,  the  use  of  the  platinum  vessel  must  be  avoided  when  nitric  and  hydro- 
chloric acids  are  present  together  in  the  solution. 


SODA.  591 

ignited.  The  ignition  is  afterwards  repeated,  when  a  fragment  of  sesquicarbonate 
of  ammonia  is  placed  in  the  crucible,  to  decompose  any  bisulphate  of  potassa 
which  may  have  been  produced.  Since  sulphate  of  potassa  is  very  liable  to 
decrepitate,  great  care  must  be  employed  in  igniting  it. 

Calculation. . 
KO.S03      KO 

87     :     47     ::      Weight  of  residue  :  x 
x  —  Weight  of  potassa. 

2.  Determination  as  Chloride  of  Potassium. — The  solution  is  mixed  with  ex- 
cess of  hydrochloric   acid,   evaporated  to  dryness,1  as  in   the  preceding   case, 
cautiously  heated  to  dull  redness,  and  weighed. 

Calculation. 
KCl      KO 

74.5  :  47    : :    Weight  of  residue  :  x 
x  —  Weight  of  potassa. 

It  need  hardly  be  remarked  that  these  methods  are  inapplicable  when  other 
fixed  substances  are  present. 

3.  Determination  as  the  Double  Chloride  of  Platinum  and  Potassium. 

If  the  acid  present  be  volatile,  the  solution  may  be  mixed  with  hydrochloric 
acid  and  excess  of  bichloride  of  platinum,  and  evaporated  to  dryness  on  a  water- 
bath.  The  residue  is  then  stirred  up  and  digested  with  alcohol  of  about  80  per 
cent.  (If  there  be  a  due  excess  of  bichloride  of  platinum,  the  solution  will 
have  a  distinct  yellow  color ;  if,  however,  this  is  not  the  case,  it  must  be  again 
evaporated  to  dryness,  treated  with  water,  some  more  bichloride  of  platinum 
added,  and  the  evaporation  repeated.)  The  residue  of  chloride  of  platinum  and 
potassium  is  collected  on  a  weighed  filter,  washed  with  spirit,  dried  at  212°,  and 
weighed. 

When  a  non-volatile  acid  is  present,  the  solution,  which  must  be  pretty  con- 
centrated, is  mixed  with  hydrochloric  acid  and  bichloride  of  platinum,  and  a 
considerable  quantity  of  strong  alcohol  added.  The  mixture  is  set  aside  for 
twenty-four  hours,  the  precipitate  collected  on  a  filter,  washed  with  spirit,  dried, 
and  weighed. 

Calculation. 
KCLPtCl2        KO 

244.2      :     47     ::     Weight  of  precipitate  :  x 
x=  Weight  of  potassa. 

SODA. 

(Fifteen  grains  of  perfectly  pure,  ignited  carbonate  of  soda,  may  be  employed 
for  practice.  The  amount  of  soda  obtained  should  be  within  0.2  per  cent,  of  the 
calculated  quantity.) 

§  388.  Soda  is  generally  determined  either  as  sulphate  of  soda,  or  as  chloride 
of  sodium. 

Both  determinations  are  effected  in  quite  the  same  way  as  in  the  case  of  potassa. 

Calculations. 
NaO.S03      NaO 

1.  71      :      31    ::     Weight  of  residue :  x 
NaCl  NaO 

2.  58.5    :      31    ::     Weight  of  residue  :  x 

x  =  Weight  of  soda. 

1  A  platinum  vessel  must  not  be  used  when  nitric  acid,  &c.  are  present. 


592  QUANTITATIVE   DETERMINATION   OF   THE   ACIDS. 


OXIDE  OF  AMMONIUM. 

(Pure  chloride  of  ammonium  may  be  analyzed  for  practice  ;  it  should  be  dried 
in  the  water-bath.  About  10  grains  may  be  taken  for  the  first  method,  the  re- 
sult of  which  should  not  differ  by  more  than  (at  most)  0.5  per  cent,  from  the 
calculated  amount  of  oxide  of  ammonium.  For  the  second  method,  5  grains 
may  be  employed.  The  oxide  of  ammonium  should  be  found  within  0.2  per 
cent.) 

§  389.  Oxide  of  ammonium  is  determined  either  as  chloride  of  ammonium 
or  as  the  double  chloride  of  platinum  and,  ammonium. 

1.  Determination  as  Chloride  of  Ammonium.  —  The  compound  under  examina- 
tion is  placed  in  a  capacious  (pint)  flask,  furnished  with  a  sound  cork,  bearing  a 
long  funnel-tube  and  a  rather  wide  tube  bent  twice  at  right  angles.     The  longer 
limb  of  this  tube  should  be  about  18  inches  in  length.     A  few  ounces  of  water 
are  poured  upon  the  ammoniacal  compound,  so  as  to  cover  the  extremity  of  the 
funnel-tube,  through  which  an  excess  of  solution  of  potassa  is  then  poured,  and 
the  extremity  of  the  delivery-tube  allowed  to  dip  about  three  inches  below  the 
purface  of  a  mixture  of  concentrated  hydrochloric  acid  with  2  volumes  of  water 
contained  in  a  small  flask.     The  evolution-flask  is  placed  upon  a  sand-bath,  and 
its  contents  heated  to  ebullition,  at  which  point  they  are  maintained  for  about 
half  an  hour.     When  the  ebullition  has  been  continued  for  this  period,  the  appa- 
ratus is  allowed  to  cool,  and  the  receiving-flask  then  withdrawn.    The  solution  of 
chloride  of  ammonium  is  carefully  evaporated  to  dryness  on  a  water-bath,  in  a 
platinum  dish,  and  dried  (on  a  water-bath)  till  the  weight  is  constant.     The 
dish  is  then  gradually  ignited  till  all  chloride  of  ammonium  is  volatilized,  and 
again  weighed.     The  difference  is  the  weight  of  the  chloride  of  ammonium. 

Calculation. 
NH^Cl  NH40 

53.5  :  26  :  :    Weight  of  Chloride  :  x 
x  =  Weight  of  Oxide  of  Ammonium. 

2.  Determination  as  the  Double  Chloride  of  Platinum  and  Ammonium.  —  This 
is  effected  in  exactly  the  same  way  as  the  analogous  determination  of  potassa. 

The  result  may  be  controlled  by  carefully  igniting  the  precipitate,  and  deter- 
mining the  weight  of  the  spongy  platinum. 

Calculation. 


NH4CLPtCl2         ^ 

1.  223.2     :     26  ::    Weight  of  precipitate  .  x 

Ft         NH40 

2.  98.7     :     26  ::    Weight  of  metal  :  x 

x  =  Weight  of  oxide  of  ammonium. 


QUANTITATIVE   DETERMINATION   OF   THE   ACIDS. 

SULPHURIC  ACID. 

(For  practice,  this  acid  may  be  determined  in  15  grains  of  alum ;  the  amount 
of  sulphuric  acid  should  agree,  within  0.3  per  cent.,  with  that  obtained  by  cal- 
culation.) 

§  390.  Sulphuric  acid  is  determined  as  sulphate  of  baryta. 

The  solution  is  acidified  with  hydrochloric  acid,  precipitated  with  chloride  of 
barium,  heated,  in  order  that  the  precipitate  may  subside,  and  carefully  filtered. 


BORACIC   ACID.  593 

The  sulphate  of  baryta  is  well  washed  with  boiling  water,  until  the  washings  are 
no  longer  rendered  turbid  by  sulphuric  acid,  dried,  ignited,  and  weighed. 

When  nitric  acid  is  present,  the  solution  containing  the  sulphuric  acid  must 
be  largely  diluted  before  precipitation,  and  the  sulphate  must  be  washed  for  a 
long  time  with  boiling  water. 

Calculation. 
BaO.SOs       S03 

116.5     :     40  ::    Weight  of  precipitate  :  x 
x  =»  Weight  of  sulphuric  acid. 

PHOSPHORIC  AciD.1 

(Pure  crystallized  phosphate  of  soda  may  be  analyzed,  after  drying  between 
blotting-paper.  80  grains  may  be  employed  for  the  first  method,  and  half  that 
quantity  for  the  second.) 

§  391.  Phosphoric  acid  may  be  determined  as  phosphate  of  lead,  or  as  basic 
phosphate  of  sesquioxide  of  iron. 

1.  Determination  as  Phosphate  of  Lead. — The  solution  is  acidified  with  acetic 
acid,  and  solution  of  acetate  of  lead  added  to  complete  precipitation ;  the  preci- 
pitate (3PbO.P05)  is  filtered  off,  washed,  dried,  ignited  with  the  usual  precau- 
tions (especially  removing  the  precipitate,  as  far  as  possible,  from  the  filter),  in 
a  porcelain  crucible,  and  weighed. 

Calculation. 
SPbO.POs      P05 

407.1     :     72  : :    Wei<jht  of  precipitate  :  x 
x  =  Weight  of  phosphoric  acid. 

To  control  this  determination,  the  precipitate  may  be  dissolved  in  nitric  acid, 
and  the  oxide  of  lead  determined  (see  p.  578). 

2.  Determination  as  Basic  Phosphate  of  Sesquioxide  of  Iron. — The   solution 
(which  must  not  contain  any  fixed  organic  matters)  is  mixed  with  a  large  excess 
of  a  solution  of  sesquioxide  of  iron  of  known  strength  ;  an  excess  of  ammonia  is 
then  added,  and  the  solution  digested  for  some  time  at  a  gentle  heat;  if  the  pre- 
cipitate originally  produced   by  ammonia  be   not  distinctly  brown-red,  enough 
sesquioxide  of  iron  has  not  been  added.     The  precipitate  is  collected  on  a  filter 
of  known  ash,  washed  with  hot  water,  dried,  and  very  strongly  ignited  in  a  por- 
celain crucible.     From  the  weight  of  the  precipitate,  the  amount  of  the  phos- 
phoric acid  is  obtained  by  deducting  that  of  the  sesquioxide  of  iron  which  has 
been  added. 

The  chief  objections  to  this  method  are  the  necessity  of  employing  a  very  large 
excess  of  sesquioxide  of  iron,  and  the  circumstances  that  all  the  loss  falls  upon 
the  phosphoric  acid. 

BORACIC  ACID. 

§  392.  Since  there  is  no  borate  sufficiently  insoluble  to  allow  the  boracic  acid 
to  be  advantageously  precipitated  in  that  form,  this  acid  is  usually  estimated  by 
loss. 

Free  boracic  acid  may  be  determined  in  a  solution  which  contains  no  .other 
acid  but  nitric,  by  carefully  evaporating  with  a  weighed  amount  of  pure  oxide  of 
lead,  igniting,  and  weighing.  The  quantity  of  boracic  acid  is  ascertained  by  de- 
ducting the  known  weight  of  the  oxide  of  lead. 

The  same  principle  is  applied  in  the  determination  of  other  free  acids. 

1  Only  the  tribasic  modification  is  here  alluded  to. 

38    ' 


594  QUANTITATIVE   DETERMINATION    OF   THE   ACIDS. 

The  compounds  of  boracic  acid  with  soda  may  be  analyzed  by  evaporating  with 
an  excess  of  pure  sulphuric  acid,  until  the  latter  begins  to  volatilize;  the  mass  is 
then  digested  for  24  hours  with  absolute  alcohol,  and  frequently  agitated;  the 
residual  sulphate  of  soda  is  collected  on  a  weighed  filter,  washed  with  alcohol  till 
the  washings  are  no  longer  acid,  dried,  ignited,  and  weighed. 

SILICIC  ACID. 

(Pure  quartz  or  sand  may  be  employed  for  practice;  they  should  be  previously 
ignited;  10  grains  will  be  amply  sufficient  for  determination.) 

§  393.  Silica  is  always  determined  in  the  insoluble  modification. 

If  the  substance  under  examination  is  decomposed  by  hydrochloric  acid,  it  is 
exposed,  in  fine  powder,  to  the  action  of  the  acid,  and  the  solution  afterwards 
evaporated  to  perfect  dryness.  The  dry  residue  is  heated  for  some  time  in  the 
air-bath,  moistened  with  concentrated  hydrochloric  acid,  digested  for  some  minutes 
at  a  gentle  heat,  a  considerable  quantity  of  dilute  hydrochloric  acid  added,  and 
the  whole  again  heated  until  apparently  nothing  but  silica  remains  undissolved. 
The  latter  is  collected  upon  a  filter  of  known  ash,  well  washed  with  hot  water, 
dried,  ignited,  and  weighed. 

The  ignition  of  silica  requires  some  special  precautions,  since,  at  a  red  heat, 
this  substance  is  so  very  light  that  particles  may  easily  be  carried  away  by  the 
slightest  current  of  air.  The  safest  method  is  to  empty  as  much  as  possible  of 
the  silica  into  a  crucible,  in  which  it  is  ignited  and  weighed,  the  crucible  being 
covered  throughout  the  operation;  the  filter  is  then  wrapped  up  and  placed  in  a 
platinum  crucible,  in  which  it  is  very  gradually  heated,  the  crucible  being  loosely 
covered,  until  all  the  paper  is  charred,  when  the  incineration  may  be  completed 
in  the  usual  manner. 

If  silver  or  lead  be  present,  nitric  acid  may  be  used,  in  the  above  process,  in- 
stead of  hydrochloric. 

If  the  compound  under  examination  be  not  capable  of  decomposition  by  acids, 
it  must  be  reduced  to  an  impalpable  powder,  and  intimately  mixed,  by  means  of 
a  rounded  glass  rod,  in  a  platinum  crucible1  placed  upon  a  sheet  of  paper,  with 
about  four  parts  of  pure  carbonate  of  potassa  and  soda.  A  layer  of  the  pure 
carbonates  is  placed  above  the  mixture ;  the  crucible  should  even  now  be  only 
half  filled.  It  is  then  loosely  covered,  and  gently  heated  for  some  time,  the 
heat  being  afterwards  very  gradually  increased  until  it  has  attained  to  bright 
redness,  and  the  mass  is  in  perfect  fusion,  in  which  state  it  is  retained  for  about 
an  hour. 

When  cool,  the  crucible,  and  its  cover  if  necessary,  are  placed  in  a  pretty  ca- 
pacious beaker,  and  a  few  ounces  of  water  poured  over  them,  so  that  they  may 
be  entirely  covered ;  they  are  allowed  to  digest  for  several  hours  in  the  cold,  with 
occasional  stirring,  until  the  mass  is  completely  dissolved  out  of  the  crucible;  the 
latter  is  then  removed  with  a  glass  rod  or  a  pair  of  platinum  tongs,  and  rinsed 
several  times  into  the  beaker,  the  contents  of  which  are  now  to  be  largely  diluted 
and  carefully  acidulated  with  hydrochloric  acid.  The  solution  is  heated  in  the 
beaker  (covered  with  a  funnel)  till  no  more  bubbles  of  carbonic  acid  are  evolved, 
when  it  may  be  transferred  to  a  large  dish,  and  the  further  process  conducted 
exactly  as  in  the  case  of  compounds  decomposed  by  hydrochloric  acid. 

In  the  above  process,  the  heat  is  gradually  applied  to  the  crucible,  in  order 
that  most  of  the  carbonic  acid  may  be  expelled  before  the  mass  enters  into  per- 
fect fusion;  without  this  precaution,  loss  from  spirting  is  inevitable. 

It  frequently  happens  that  the  fused  mass  is  not  entirely  dissolved  by  water ; 
it  may,  however,  easily  be  known  whether  the  decomposition  has  been  complete, 

1  If  easily  reducible  metals  be  present  (as  lead,  silver,  &c.),  of  course  a  platinum  cru- 
cible cannot  be  employed.  (See  Analysis  of  Lead-glass.) 


HYDROFLUORIC   ACID.  595 

for  otherwise,  after  addition  of  hydrochloric  acid,  fine  gritty  particles  of  unde- 
com  posed  substance  will  remain  at  the  bottom  of  the  beaker;  these  should,  if 
possible,  be  collected  and  weighed,  their  weight  being  deducted  from  that  of  the 
substance  originally  employed. 

For  the  analysis  of  silicates  by  means  of  hydrofluoric  acid,  sec  Analysis  of 
Glass. 

SULPHUROUS  ACID. 

§  394.  This  acid  may  be  weighed  in  the  form  of  sulphate  of  baryta. 

The  compound  under  examination  is  heated,  in  a  flask,  with  fuming  nitric  acid 
until  the  oxidation  is  complete;  the  solution  is  then  largely  diluted  with  water, 
and  the  sulphuric  acid  precipitated  as  sulphate  of  baryta  (see  p.  592.) 

Or  the  sulphurous  acid  may  be  oxidized  by  passing  a  slow  stream  of  chlorine 
through  the  solution. 

If  sulphuric  acid  be  present  at  the  same  time,  its  quantity  must  be  determined 
before  oxidation,  and  subsequently  deducted  from  the  total  amount. 

CHROMIC  ACID. 

(Bichromate  of  potassa,  dried  at  212°,  may  be  analyzed  for  practice.  15 
grains  will  be  found  sufficient.  The  percentage  of  chromic  acid  should  be  found 
within  0-3  per  cent.) 

§  395.  Chromic  acid  is  determined  either  as  sesquioxide  of  chromium,  or  as 
chroma  te  of  lead. 

1.  Determination  as  Sesquioxide  of  Chromium.  —  The  solution  is  mixed  with 
a  slight  excess  of  hydrochloric  acid,  a  moderate  quantity  of  alcohol  added,  and 
the  solution  heated  until  it  has  acquired  a  pure  green  color,  and  the  excess  of 
alcohol  has  evaporated. 

Or  the  acid  solution  may  be  mixed  with  a  strong  solution  of  sulphurous  acid, 
and  heated  until  the  color  is  changed  to  a  pure  green. 

The  sesquioxide  of  chromium  is  then  determined  in  the  usual  manner  (see  p. 
585). 

Calculation. 


Cr203  3 

77  A  :  101.4  ::  Weight  of  precipitate  :  x 
x  =  Weight  of  chromic  acid. 

2.  Determination  as  Chromate  of  Lead.  —  The  solution,  if  acid,  is  mixed  with 
an  excess  of  acetate  of  potassa,  if  neutral  or  alkaline,  with  an  excess  of  acetic 
acid,  and  acetate  of  lead  added  to  complete  precipitation.  The  precipitate  is 
allowed  to  subside,  collected  on  a  weighed  filter,  washed,  dried  at  212°,  and 
weighed. 

Calculation. 
PbO.Cr03        CrOz 

162.4     :     50,7  ::  Weight  of  precipitate  :  x 
x  =  Weight  of  chromic  acid. 

HYDROFLUORIC  ACID. 

§  396.  Fluorides  are  usually  analyzed  by  treating  a  weighed  portion  of  the  very 
finely  powdered  substance  with  concentrated  sulphuric  acid,  and  evaporating  to 
dryness  in  a  platinum  vessel  ;  the  mass,  when  ignited,  contains  the  bases  in  the 
form  of  sulphates,  and  if  their  respective  quantities  be  determined,  that  of  the 
fluorine  may  be  inferred. 

The  hydrofluoric  acid  contained  in  a  solution  may  be  estimated  as  fluoride  of 
calcium.  The  solution  is  mixed,  in  a  platinum  vessel,  with  excess  of  ammonia 


596  QUANTITATIVE   DETERMINATION   OF   THE  ACIDS. 

and  chloride  of  calcium ;  heat  is  then  applied,  and  the  mixture  allowed  to  digest 
for  some  time,  so  that  the  precipitate  may  subside.  The  latter  is  collected  upon 
a  filter,  washed,  first  with  hot  water,  then  with  very  dilute  acetic  acid,  to  remove 
any  carbonate  of  lime;  dried,  ignited,  and  weighed. 

Calculation. 
CaF     F 

39  :  19  : :  Weight  of  precipitate  :  x 
x  =  Weight  of  fluorine. 

CARBONIC  ACID. 

(For  practice,  the  acid  may  be  determined  in  20  grains  of  pure  ignited  car- 
bonate of  soda,  and  in  a  similar  quantity  of  calcareous  spar  or  white  marble.  The 
percentage  of  carbonic  acid  should  be  found  within  0.3  of  that  calculated.) 

§  897.  Carbonic  acid  is  either  directly  determined  as  carbonate  of  lime  or  in- 
directly as  carbonic  acid. 

The  direct  determination  as  carbonate  of  lime  is  rarely  executed  except  in  the 
analysis  of  waters,  to  which  we  therefore  refer  for  the  plan  of  operation. 

The  determination  of  carbonic  acid  by  loss  is  effected  by  decomposing  the  sub- 
stance with  sulphuric  or  dilute  nitric  or  hydrochloric  acid  (one  of  the  latter  being 
used  when  the  base  forms  a  sparingly  soluble  compound  with  sulphuric  acid),  in 
an  apparatus  arranged  in  such  a  manner  that  nothing  but  dry  carbonic  acid  can 
escape  from  it. 

The  apparatus  of  Fresenius  and  Will  (described  under  Alkalimetry)  is  best 
adapted  for  this  purpose.  The  operation  of  decomposing  a  carbonate  with  sul- 
phuric acid  is  described  in  the  same  section. 

When  the  carbonate  contains  a  base  which  forms  an  insoluble  or  sparingly 
soluble  compound  with  sulphuric  acid  (e.g.  lime),  the  operation  is  conducted  in 
a  somewhat  different  manner. 

A  quantity  of  dilute  nitric  or  hydrochloric  acid  (the  former  is  preferable  when 
no  deoxidation  is  likely  to  ensue)  is  introduced  into  the  generating-flask  of  the 
apparatus  above  alluded  to,  and  the  small  weighed  bottle  containing  the  substance 
is  suspended  by  a  horsehair  in  such  a  manner  that  its  orifice  shall  be  a  little  above 
the  level  of  the  acid.  The  drying-flask  is  half  filled  with  concentrated  sulphuric 
acid.  When  the  apparatus  has  been  weighed,  and  proved  to  be  perfectly  tight, 
a  quantity  of  acid  is  rinsed  into  the  substance,  and  the  agitation  is  repeated  at 
intervals  until  the  decomposition  is  completed;  the  generating-flask  is  then  heated 
to  about  100°,  the  wax  stopper  removed  from  the  tube,  and  suction  applied,  through 
a  vulcanized  connector,  to  the  tube  of  the  drying-flask,  so  as  to  draw  air  slowly 
through  the  apparatus  till  it  tastes  no  longer  of  carbonic  acid.  The  apparatus  is 
allowed  to  cool,  and  again  weighed,  when  the  loss  indicates  the  carbonic  acid. 

OXALIC  ACID. 

§  398.  This  acid  is  precipitated  as  oxalate  of  lime,  or  is  indirectly  estimated 
by  conversion  into  carbonic  acid  gas. 

In  order  to  determine  oxalic  acid  as  oxalate  of  lime,  the  solution  (which,  if 
containing  a  free  mineral  acid,  must  be  mixed  with  acetate  of  potassa)  is  slightly 
acidified  with  acetic  acid,  and  completely  precipitated  with  a  mixture  of  chloride 
of  calcium  and  acetate  of  potassa. 

The  precipitate  is  treated  exactly  as  directed  at  p.  590. 

Calculation. 
CaO.C02       C?03 

50       :      #6    : :     Weight  of  ignited  precipitate  :  x 
x  =  Weight  of  oxalic  acid. 


HYDRIODIC   ACID.  597 

The  indirect  estimation  is  effected  by  converting  the  oxalic  acid  into  carbonic 
acid,  by  treatment  with  binoxide  of  manganese  and  sulphuric  acid  in  a  Fresenius 
and  Will's  apparatus. 

The  details  of  the  operation  are  given  in  the  article  upon  the  valuation  of 
manganese-ores. 

Calculation. 


44    :    36  ::  Loss  of  the  apparatus  :  x 
x  =  Weight  of  oxalic  acid. 

HYDROCHLORIC  ACID. 

(About  10  grains  of  pure  ignited  chloride  of  sodium  may  be  employed  for 
practice;  the  percentage  of  chlorine  found  should  be  within  0.2  per  cent,  of  the 
theoretical  amount.) 

§  399.   Hydrochloric  acid  is  determined  as  chloride  of  silver. 

The  solution  is  acidulated  with  nitric  acid,  and  nitrate  of  silver  added,  with 
constant  stirring,  as  long  as  any  precipitate  is  formed.  The  chloride  of  silver  is 
then  treated  exactly  as  directed  for  the  determination  of  silver  (p.  576). 

Calculation. 
AgCl          Cl 

143.6  :  35.5  ::  Weight  of  precipitate  :  x. 
x  =  Weight  of  chlorine. 

Free  chlorine  may  be  converted  into  chloride  of  ammonium  by  treatment 
with  excess  of  ammonia. 

HYDROBROMIC  ACID. 

§  400.  This  acid  is  determined  as  bromide  of  silver. 

The  solution,  which,  if  alkaline,  should  be  nearly  neutralized  with  nitric  acid, 
is  precipitated  with  solution  of  nitrate  of  silver  mixed  with  free  nitric  acid,  gently 
heated,  the  precipitate  allowed  to  subside,  and  the  subsequent  operations  con- 
ducted as  in  the  case  of  chloride  of  silver  (p.  576). 

Of  course,  if  the  bromide  of  silver  be  collected  upon  a  filter  (which  should  be 
avoided  if  possible),  the  greatest  care  must  be  taken  to  detach  it  before  ignition. 
It  would  even  be  preferable  to  collect  it  upon  a  weighed  filter,  and  to  weigh  it 
after  drying  at  212°. 

Calculation. 
AgBr        Br 

188.1  :  80  ::  Weight  of  'precipitate  :  x. 
x  =  Weight  of  bromine. 

Free  bromine  may  be  converted  into  bromide  of  ammonium  by  treatment 
with  excess  of  ammonia. 

HYDRIODIC  ACID. 

§  401.  Hydriodic  acid  is  determined  as  iodide  of  silver.  To  describe  the 
process  would  be  merely  to  repeat  what  has  just  been  said  respecting  the  deter- 
mination of  hydrobromic  acid. 

Calculation. 
Agl  I 

235.2  :  127.1  ::  Weight  of  precipitate  :  x 
x  =  Weight  of  iodine. 

Free  iodine  is  to  be  converted  into  a  mixture  of  iodide  of  potassium  and  iodate 


598  QUANTITATIVE   DETERMINATION   OF   THE   ACIDS. 

of  potassa  by  treatment  with  solution  of  potassa  in  slight  excess.  The  solution 
is  then  nearly  neutralized  with  nitric  acid,  an  excess  of  nitrate  of  silver  added, 
and,  finally,  a  slight  excess  of  nitric  acid.  The  precipitate,  which  consists  of  a 
mixture  of  iodide  and  iodate  of  silver,  may  be  treated  exactly  as  if  it  consisted 
of  the  former  only,  since  iodate  of  silver,  when  ignited,  is  converted  into  the 
iodide. 

HYDROSULPHURIC  ACID. 

(For  practice,  pure  tersulphide  of  antimony  may  be  analyzed.) 
§  402.  Hydrosulphuric  acid  (sulphur)  is  determined  as  tersulphide  of  arsenic, 
or  as  sulphate  of  baryta. 

1.  Determination  as    Tersulphide  of  Arsenic. — If  the   hydrosulphuric  acid 
exists  in  solution,  the  latter  is  mixed  with  an  excess  of  a  rather  dilute  solution 
of  arsenious  acid  in  potassa.     The  mixture  is  then  slightly  acidified  with  hydro- 
chloric acid,  the  precipitated  tersulphide  of  arsenic  collected  on  a  weighed  filter, 
washed  with  water,  dried  at  212°,  and  weighed. 

But  if  the  hydrosulphuric  acid  is  to  be  determined  in  an  insoluble  substance, 
a  weighed  quantity  of  the  latter  is  placed  in  a  small  gas-evolution  flask,  provided 
with  a  funnel-tube,  and  with  a  delivery-tube  conveying  the  gas  into  a  dilute 
solution  of  arsenious  acid  in  potassa.  Enough  water  is  introduced  to  cover  the 
extremity  of  the  funnel-tube,  the  flask  is  placed  upon  a  sand-bath,  and  when 
the  apparatus  is  arranged,  dilute  sulphuric  or  hydrochloric  acid  is  gradually 
added,  and  a  gentle  heat  applied.  At  the  termination  of  the  process,  a  solution 
of  carbonate  of  soda  may  be  poured  through  the  funnel-tube,  when  the  evolved 
carbonic  acid  will  expel  the  last  traces  of  hydrosulphuric  acid.  The  delivery- 
tube  is  carefully  rinsed  into  the  potassa-solution,  the  tersulphide  of  arsenic  pre- 
cipitated from  the  latter,  by  adding  a  slight  excess  of  hydrochloric  acid,  collected 
on  a  filter,  washed,  dried  at  212°,  and  weighed. 

Calculation. 
AsSz       Sz 

123   :  48   : :    Weight  of  precipitate  :  x 
x=  Weight  of  sulphur  evolved  as  hydrosulphuric  acid. 

2.  Determination  as  Sulphate  of  Baryta. — For  this  purpose  the  sulphur  is 
oxidized  and  converted  into  sulphuric  acid,  which  may  be  effected  either  in  the 
wet  or  in  the  dry  way. 

Oxidation  in  ike  wet  way. — A  weighed  quantity  of  the  finely  powdered  sub- 
stance is  introduced  into  a  large  flask,1  and  gradually  drenched  with  the  most 
concentrated  nitric  acid ;  when  the  first  violence  of  the  action  has  abated,  heat 
is  applied,  and  continued  until  either  the  whole  of  the  sulphur  is  dissolved,  or 
until  that  portion  which  has  resisted  oxidation  has  separated  in  the  form  of  pure 
yellow  globules  (which  must  be  collected  upon  a  weighed  filter,  washed,  dried  in 
a  water- bath,  and  weighed).  The  solution  is  now  largely  diluted  with  water, 
the  sulphur  filtered  off,  and  the  sulphuric  acid  determined  in  the  filtrate  accord- 
ing to  the  method  given  at  p.  592. 

In  some  cases  it  is  advantageous  to  add,  from  time  to  time,  a  few  grains  of 
chlorate  of  potassa,  in  order  to  complete  the  oxidation. 

In  the  above  process,  hydrochloric  acid,  with  gradual  addition  of  chlorate  of 
potassa,  is  sometimes  employed  for  oxidation. . 

Oxidation  in  the  dry  way. — The  finely  powdered  substance  is  introduced  into 
a  porcelain  crucible,  placed  upon  a  sheet  of  paper,  and  intimately  mixed,  by 
means  of  a  glass  rod,  with  three  parts  of  pure  nitre  and  three  parts  of  dry  car- 

1  At  the  warehouses  for  chemical  apparatus,  there  are  large  green  globular  flasks  with 
very  long  necks,  which  are  peculiarly  adapted  for  sulphur  determinations. 


CHLORIC   ACID.  599 

bonate  of  soda,  in  fine  powder.  The  mixture  is  gradually  heated  in  the  covered 
crucible  until  the  oxidation  is  judged  to  be  complete.  When  cool,  the  fused 
mass  is  digested  with  water  (the  crucible  being  placed  in  a  beaker  or  dish,  and 
water  poured  over  it),  at  a  gentle  heat,  until  it  is  entirely  dissolved  out;  the 
crucible  is  then  removed  and  rinsed  into  the  solution,  which  is  to  be  passed 
through  a  filter,  the  residue  being  washed  with  hot  water  till  the  washings  are 
free  from  sulphuric  acid. 

The  solution  is  then  acidulated  (avoiding  loss  by  effervescence)  with  hydro- 
chloric acid,  and  the  sulphuric  acid  precipitated  as  sulphate  of  baryta. 

Calculation. 
BaO.S03    S 

116.5  :  16  ::  Weight  of  precipitate  :  x 
x  =  Weight  of  sulphur. 

Since  the  methods  of  determining  cyanogen  and  its  compounds  are  involved  in 
the  history  of  that  group  of  substances,  we  defer  their  consideration  to  a  subse- 
quent portion  of  this  work. 

NITRIC  ACID. 

§  403.  This  acid  is  almost  always  determined  indirectly. 

1.  The  substance   (in  a  perfectly  dry  state)  is  very  finely  powdered,   and 
mixed,  in  a  platinum  crucible,  with  two  or  three  parts  of  perfectly  anhydrous 
borax.     The  crucible  is  weighed,  and  gradually  heated  until  the  mass  is  in  a 
state  of  tranquil  fusion;  the  loss  of  weight  indicates  the  amount  of  nitric  acid. 

2.  A  weighed  quantity  of  the  substance  (which  must  be  free  from  chlorides) 
is  dissolved  in  a  little  water,  and  introduced  into  a  tubulated  retort,  connected, 
by  means  of  an  air-tight  cork,  with  a  quilled  receiver,  the  tube  of  which  dips 
into  a  strong  solution  of  hydrate  of  baryta  contained  in  a  flask.     A  slight  excess 
of  pure,  somewhat  dilute,  sulphuric  acid  is  then  added  to  the  solution  in  the 
retort,  which  is  then  distilled  to  dryness  at  a  moderate  heat. 

The  solution  in  the  flask  is  then  treated  with  a  few  bubbles  of  carbonic  acid, 
so  that  the  latter  may  be  in  slight  excess.  The  liquid  is  heated,  to  expel  all 
excess  of  carbonic  acid,  and  filtered,  the  precipitated  carbonate  of  baryta  being 
well  washed.  The  baryta  in  the  filtrate  (which  must  be  perfectly  neutral)  is 
then  determined  as  sulphate. 

Calculation. 
BaO.S03   NOS 

116.5  :  54  ::  Weight  of  precipitate  :  x 
x  =  Weight  of  nitric  acid. 

CHLORIC  ACID. 

§  404.  Chloric,  like  the  preceding  acid,  is  determined  indirectly. 

1.  The  dry  compound  may  be  ignited  until  the  chlorate  is  converted  into  a 
chloride,  and  the  amount  of  chloric  acid  calculated  from  the  loss  of  oxygen. 
This  determination  may,   of  course,   be  controlled   by  an  estimation  of  the 
chlorine. 

2.  The  chloric  acid  in  a  solution  may  be  liberated  by  sulphuric  acid,  and 
deoxidized  with  sulphurous  acid;   it  may  then  (after  expelling  the  excess  of 
sulphurous  acid  by  a  gentle  heat)  be  precipitated  and  weighed  as  chloride  of 
silver. 

For  the  determination  of  hypochlorous  acid,  see  the  article  on  Chlorimetry. 
The  quantitative  determination  of  the  organic  acids  falls  within  the  province 
of  organic  chemistry. 


600  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS, 


QUANTITATIVE  ANALYSIS;  SPECIAL  METHODS. 


IN  entering  upon  the  complete  analysis  of  substances,  the  student  will  find  it 
advantageous  to  attend  to  the  following  cautions. 

A  quantitative  analysis,  to  be  successful,  must  be  executed  as  rapidly  as  pos- 
sible, but  not  hurriedly. 

The  analyst  must  not  shrink  from  operations  because  they  are  tedious,  or  in- 
volve a  great  deal  of  weighing,  but  must  have  regard  chiefly  to  accuracy,  at  any 
sacrifice,  only  adopting  a  shorter  method  when  he  has  proved  by  experiment  that 
its  results  will  bear  comparison  with  those  obtained  by  the  process  which  it  is 
intended  to  supersede. 

It  is  much  better,  though  perhaps  less  strictly  scientific,  when  there  are  many 
constituents  to  be  determined  in  a  substance,  to  employ  separate  portions,  rather 
than  to  attempt  to  estimate  them  all  in  the  same  quantity  of  material. 

CHLORIDE  OF  SODIUM. 
NaCl. 

§  405.  The  chlorine  is  determined  in  one  portion  according  to  the  method 
given  at  p.  597. 

Ten  grains  of  ignited  chloride  of  sodium  may  be  employed  for  the  determina- 
tion of  the  sodium  as  sulphate  of  soda,  which  is  effected  according  to  §  388. 

It  is  customary,  in  quantitative  analysis,  to  calculate  the  weight  of  each  con- 
stituent upon  100  parts  of  the  substance  analyzed.  In  order  to  illustrate  the 
calculation  of  the  composition  of  a  substance  experimentally  and  theoretically, 
we  cite  an  analysis  of  chloride  of  sodium  : — 

Amount  employed  for  determination  of  chlorine  =  10  grs. 
Chloride  of  silver  obtained  =  24.51  grs. 

AgCl  Cl 

143.6  :  35.5  ::  24.51  :  x 

35.5x24.51 
x  =  — TJQ~~ =  6.059  =  amount  of  chlorine  found. 

JLrrO.D 

NaCl        Cl 
10  :  6.059  ::  100  :  x 

6.059  X  100 
x  =  -    — YQ =  60.59  =  percentage  of  chlorine  found. 

Amount  employed  for  determination  of  sodium  =  10  grs. 
Sulphate  of  soda  obtained  =  12.13  grs. 

NaO.SO.       Na 

71       :     23  ::  12.13  :  x 

12.13x23 
x  = ~j =  3.929  =  amount  of  sodium  found. 


HEAVY-SPAR.  601 

NaCl      Na 
10  :  3.929  ::  100  :  x 

3.929  X  100 
x  = r-Tj =  39.29  =  percentage  of  sodium  found. 

Found.  Calculated. 

Sodium 39.29  39.32 

Chlorine 60.59  60.68 

99.88  100.00 

CRYSTALLIZED  PHOSPHATE  OP  SODA. 
2NaO.HO.P05+24Aq. 

§  406.  The  crystals  should  be  coarsely  powdered,  and  pressed  between  blotting- 
paper. 

Determination  of  Water  of  Crystallization  (24  Aq). — About  20  grs.  of  the  salt 
are  placed  in  a  pretty  large  crucible  and  dried  in  an  air-bath,  at  a  gradually 
increasing  temperature,  which  must  not  exceed  580°  F.  (304°. 5  C.).  The  de- 
siccation is  continued  till  the  weight  ceases  to  vary. 

Determination  of  Water  of  Constitution  (HO). — The  dry  residue  is  carefully 
ignited  to  full  redness  till  its  weight  is  constant. 

Determination  of  Phosphoric  Acid. — About  30  grs.  of  the  crystals  are  dissolved 
in  water,  and  the  phosphoric  acid  precipitated  as  phosphate  of  lead  (see  p.  592). 

Determination  of  Soda. — The  filtrate  and  washings  from  the  precipitated  phos- 
phate of  lead  are  saturated  with  sulphuretted  hydrogen,  to  precipitate  the  excess 
of  lead  as  sulphide,  which  is  then  filtered  off ;  the  solution  is  evaporated  to  a 
small  bulk  in  a  beaker,  transferred  to  a  weighed  (platinum)  dish,  mixed  with 
excess  of  hydrochloric  acid,  and  the  soda  determined  as  chloride  (see  p.  591). 

HEAVY-SPAR. 
BaO.S03. 

§  407.  Any  traces  of  water  existing  in  the  mineral  may  be  expelled  by 
ignition. 

The  mineral  is  reduced  to  a  very  fine  powder,  and  about  15  grs.  are  intimately 
mixed  with  four  times  their  weight  of  dry  carbonate  of  potassa  and  soda  (per- 
fectly free  from  sulphuric  acid),  in  a  platinum  crucible.  The  mixture  should  be 
effected  with  a  warm  glass  rod ;  the  crucible,  which  must  not  be  more  than,  at 
most,  three-parts  filled,  is  heated,  either  over  a  good  gas-burner  or  in  a  coke-fire 
(being  then  imbedded  in  magnesia),  until  the  mass  is  perfectly  fused,  in  which 
state  it  is  retained  for  about  an  hour.  When  cool,  the  crucible  is  placed  in  a 
beaker,  and  digested  with  water  at  a  moderate  heat  till  the  mass  is  completely 
disintegrated ;  the  crucible  is  then  removed  with  a  glass  rod  or  platinum  tongs, 
and  well  rinsed  into  the  beaker ;  the  contents  of  the  latter  are  filtered  off,  and 
the  residue  washed  with  hot  water  till  the  washings  are  perfectly  free  from  sul- 
phuric acid. 

Determination  of  the  Baryta. — The  carbonate  of  baryta  is  placed,  together 
with  the  filter,  in  a  beaker,  a  considerable  quantity  of  water  poured  over  it,  and 
hydrochloric  acid  in  excess  gradually  added  (a  funnel  being  inverted  over  the 
beaker  to  prevent  loss).  The  whole  is  then  heated,  when  it  should  give  a  clear 
solution,  which  is  poured  off  through  a  filter,  in  order  to  separate  any  flocks  of 
paper,  and  the  baryta  determined  in  it  as  sulphate  (p.  588). 

Of  course,  both  filters  must  be  washed  with  hot  water,  till  the  washings  are 
quite  free  from  baryta. 

Should  the  hydrochloric  solution  be  milky,  it  is  a  proof  that  the  decomposition 


602  QUANTITATIVE   ANALYSIS;    SPECIAL    METHODS. 

of  the  sulphate  of  baryta  was  not  complete.  A  true  result  may  still  be  obtained 
by  collecting  the  undecomposed  sulphate  upon  another  filter,  incinerating  the 
two  filters  after  well  washing,  and  deducting  their  ashes,  when  the  weight  of  the 
undecomposed  sulphate  will  be  obtained,  and  may  be  subtracted  from  that  ori- 
ginally employed. 

Determination  of  Sulphuric  Acid. — The  filtrate  and  washings  from  the  car- 
bonate of  baryta  are  carefully  acidulated  with  hydrochloric  acid,  and  the  sulphuric 
acid  precipitated  as  sulphate  of  baryta  (p.  592). 

SEPARATION  OF  POTASSA  AND  SODA. 

KOCHELLE  SALT  (SEIGNETTE  SALT).    TARTRATE  OF  POTASSA  AND  SODA. 
KO.NaO.C8H4010+ 7  Aq. 

§  408.  The  crystals  should  be  dried,  as  usual,  by  pressure  between  blotting- 
paper. 

About  20  grs.  of  the  powdered  salt  are  very  gradually  heated,  and  incinerated 
till  perfectly  white  (p.  573).  The  residue  is  dissolved  in  water,  the  solution 
diluted  considerably  in  a  beaker,  and  acidulated  with  hydrochloric  acid ;  the  acid 
solution  is  heated  in  the  beaker  till  all  effervescence  has  ceased,  when  it  is  eva- 
porated to  a  small  bulk  in  a  porcelain  dish,  then  transferred  to  a  weighed  platinum 
capsule,  evaporated  to  dryness  (p.  573),  ignited,  and  weighed. 

The  mixture  of  chloride  of  potassium  and  chloride  of  sodium  which  is  thus 
obtained  is  dissolved  in  water,  and  the  potassium  determined  as  the  double  chlo- 
ride of  platinum  and  potassium,  according  to  the  directions  given  at  p.  591.  By 
calculating  the  amount  of  potassium  thus  obtained  as  chloride,  and  deducting  the 
weight  of  the  latter  from  that  of  the  mixed  chlorides,  the  weight  of  the  chloride 
of  sodium  is  ascertained.  By  a  simple  proportion,  the  weight  of  chloride  of  po- 
tassium or  of  sodium  may  be  converted  into  that  of  the  corresponding  oxide  (p. 

Oi7  J.  J  • 

MARBLE. 
CaO.COa. 

§  409.  The  best  white  marble  should  be  taken.     It  is  reduced  to  powder,  and 
gently  heated  to  expel  adhering  moisture. 
Determination  of  lime;  see  p.  590. 
Determination  of  carbonic  acid;  see  p.  596. 

SEPARATION  OF  LIME,  MAGNESIA,  AND  SESQUIOXIDE  OF  IRON. 
SEPARATION  OF  SILICIC  ACID  AND  ALUMINA. 

LIMESTONES. 

§  410.  A  specimen  of  limestone  should  be  employed  which  has  been  previously 
analyzed  qualitatively,  and  found  to  contain  the  following  constituents:  car- 
bonates of  lime  and  magnesia,  oxide  and  sesquwxide  of  iron,  oxide  of,  manganese, 
clay  (silicic  acid  and  alumina'),  sand,  water. 

Determination  of  Water. — About  100  grains  of  the  powdered  limestone  must 
be  feebly  ignited  in  a  porcelain  crucible  (uncovered)  for  ten  minutes;  should  the 
powder  blacken  during  this  ignition,  it  indicates  the  presence  of  organic  matter, 
and  the  ignition  must  be  continued  till  the  dark  color  has  disappeared.  The 
crucible  is  then  allowed  to  cool,  and  its  contents  wetted  with  a  strong  solution  of 
carbonate  of  ammonia  (to  reconvert  any  caustic  lime  into  carbonate) ;  the  crucible 
is  then  covered,  and  heated  at  a  considerable  distance  above  the  flame,  until  it 
suffers  no  further  alteration  in  weight;  should  the  residue,  when  moistened  with 
water,  exhibit  an  alkaline  reaction,  the  treatment  with  carbonate  of  ammonia  must 
be  repeated  till  no  further  alteration  in  weight  is  observed. 


ANALYSIS    OF   LIMESTONES.  603 

The  loss  of  weight  which  the  limestone  has  suffered  in  this  process  indicates 
the  amount  of  water  present;  the  determination,  however,  is  not  perfectly  accu- 
rate, since  the  loss  will  be  increased  by  the  expulsion  of  the  carbonic  acid  from 
the  carbonates  of  iron  and  manganese,  and  by  that  of  the  organic  matter;  another 
source  of  inaccuracy  is  the  conversion  of  the  oxides  of  iron  and  manganese  into 
higher  oxides.  However,  the  determination  will  be  found  sufficiently  accurate 
for  practical  purposes. 

Determination  of  Olay,  Sand,  Lime,  Magnesia,  and  Iron. — About  100  grains 
of  the  powdered  limestone  are  placed  in  a  tall  beaker  covered  with  an  inverted 
funnel  to  prevent  loss  from  spirting,  and  about  two  ounces  of  water  added;  dilute 
hydrochloric  acid  is  then  added  by  small  portions  at  a  time,  till  all  effervescence 
has  ceased;  the  beaker  is  gently  heated  on  a  sand-bath,  the  residue  allowed  to 
subside,  and  collected  on  a  filter  of  known  ash ;  this  residue  is  washed  with  hot 
water  till  the  washings  are  no  longer  acid  (these  being  mixed  with  the  filtrate), 
dried,  carefully  incinerated,  the  ash  moistened  with  nitric  acid  (to  reoxidize  any 
oxide  of  iron),  dried,  ignited,  and  weighed.  After  deducting  the  ash  of  the  filter, 
we  have  the  weight  of  the  clay  and  sand  contained  in  the  limestone. 

The  proportions  of  these  two  ingredients  may  be  judged  of  to  some  extent  from 
the  physical  properties  of  the  residue,  since  the  sand  would  be  gritty  to  the  touch ; 
or  they  may  be  roughly  separated  by  suspension  in  water,  when  the  particles  of 
clay  may  be  washed  away,  leaving  the  sand  at  the  bottom.  In  order,  however, 
to  determine  accurately  the  quantities  of  silica  and  alumina  contained  in  this 
residue,  from  10  to  20  grains  of  it,  in  a  state  of  impalpable  powder,  should  be 
mixed,  in  a  platinum  crucible,  by  means  of  a  glass  rod,  with  about  4  times  its 
weight  of  carbonate  of  potassa  and  soda,  and  fused,  by  a  gradually  increasing 
heat,  over  a  gauze  burner  or  Argand  spirit-lamp;  after  the  mass  has  been  retained 
in  fusion  for  about  half  an  hour,  the  crucible  is  allowed  to  cool,  placed  in  a  beaker 
(with  inverted  funnel),  covered  with  water,  and  heated,  with  constant  stirring,  till 
the  mass  is,  in  great  measure,  disintegrated;  hydrochloric  acid  is  then  added,  by 
degrees,  till  it  produces  no  more  effervescence ;  the  beaker  is  again  placed  on  the 
sand-bath  for  some  time,  till  no  more  bubbles  of  carbonic  acid  escape,  the  crucible 
removed  (and  well  washed),  and  the  contents  of  the  beaker  carefully  evaporated 
to  dryness  in  a  porcelain  dish ;  the  residue  is  well  dried,  and  mixed  into  a  paste 
with  concentrated  hydrochloric  acid — a  little  water  added,  the  mixture  heated 
for  some  minutes,  more  dilute  hydrochloric  acid  added,  the  digestion  continued 
for  half  an  hour,  and  the  solution  filtered  from  the  undissolved  silica,  which  is 
well  washed,  dried,  ignited,  and  weighed.  The  filtrate  from  the  silica  is  mixed 
with  excess  of  ammonia  which  throws  down  the  alumina,  to  be  washed,  dried, 
ignited,  and  weighed. 

The  solution  originally  filtered  from  the  clay  and  sand  should  be  carefully 
measured  or  weighed. 

About  i  of  this  solution  is  mixed  with  a  little  concentrated  nitric  acid,  and 
heated  nearly  to  boiling  (to  peroxidize  the  iron) ;  it  is  then  allowed  to  cool,  and 
mixed  with  excess  of  ammonia;  the  mixture  is  gently  heated  for  a  few  minutes, 
and  the  precipitate  collected,  washed,  dried,  ignited,  reoxidized  with  nitric  acid, 
and  weighed.  Its  weight  represents  that  of  the  sesquioxide  of  iron  (together 
with  small  quantities  of  silica,  alumina,  and  sesquioxide  of  manganese,  the  two 
former  of  which  render  the  precipitate  of  a  lighter,  and  the  latter,  of  a  darker 
color  than  pure  sesquioxide  of  iron)  contained  in  the  amount  of  limestone  cor- 
responding to  the  portion  of  solution  employed. 

The  filtrate  from  the  sesquioxide  of  iron  is  mixed  with  oxalate  of  ammonia  as 
long  as  any  precipitate  is  formed,  the  solution  heated,  the  precipitated  oxalate 
of  lime  treated  as  directed  at  p.  590 ;  the  filtrate  and  washings  being  set  aside 
for  the  following  determination.  Since  the  lime  is  weighed  in  the  form  of  car- 


604  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

bonate,  it  is  only  necessary  to  calculate  the  percentage  contained  in  the  lime- 
stone. 

In  order  to  ascertain  the  amount  of  magnesia  present,  the  solution  filtered 
from  the  oxalate  of  lime  is  mixed  with  a  considerable  quantity  of  phosphate  of 
soda,  and  the  determination  conducted  as  at  p.  590.  From  the  weight  of  the 
pyrophosphate  of  magnesia,  the  amount  of  carbonate  of  magnesia  contained  in 
the  limestone  may  be  readily  calculated  by  the  following  proportion  :  — 


112        :       84    ::    Weight  ofppt  :  x, 

where  x  represents  the  weight  of  carbonate  of  magnesia  to  which  the  pyrophos- 
phate corresponds. 

The  above  method  would,  of  course,  serve,  with  some  slight  modifications,  for 
the  analysis  of  many  calcareous  minerals,  and  of  specimens  of  clay,  marl,  &c. 

SEPARATION  OF  ALUMINA  AND  POTASSA. 

ALUM. 
KO.SO,.Ala08.3SO,+24Aq. 

§411.  The  coarsely  powdered  crystals  are  dried  between  blotting-paper. 

About  20  grs.  of  the  salt  are  dissolved  in  water,  and  the  alumina  precipitated 
as  directed  at  p.  585. 

The  filtrate  and  washings  from  the  alumina  are  evaporated  to  a  small  bulk  in 
a  porcelain  dish,  afterwards  transferred  to  a  weighed  platinum  capsule,  and  the 
evaporation  completed  very  cautiously  in  an  air-bath  (the  capsule  being  covered 
with  platinum-foil  towards  the  conclusion).  The  dry  residue  is  gradually  ignited 
in  the  covered  capsule,  until  no  more  fumes  are  perceived  ;  the  residual  sulphate 
of  potassa  is  allowed  to  cool,  and  weighed  (p.  643).  The  sublimate  of  ammo- 
niacal  salts  upon  the  cover  is  heated,  and  should  any  fixed  residue  remain,  its 
weight  must  be  determined  and  added  to  that  of  the  sulphate  of  potassa  in  the 
dish. 

The  sulphuric  acid  is  determined  in  15  grs.  of  alum,  as  directed  at  p.  592. 

SEPARATION  OF  THE  OXIDES  OF  IRON  AND  CHROMIUM. 

CHROME-IRON  ORE. 
FeO.Cr303. 

§  412.  The  mineral  is  powdered  as  finely  as  possible,  about  15  grains  of  it 
intimately  mixed  with  about  the  same  quantity  of  carbonate  of  potassa  and  nitre, 
and  fused  for  about  an  hour  at  a  bright  red  he£t,  in  a  platinum  crucible  (which 
is  not  much  attacked).  The  fused  mass,  together  with  the  crucible,  is  placed  in 
a  beaker,  and  heated  with  water  until  completely  disintegrated  ;  the  crucible  is 
then  removed  (being  well  rinsed  into  the  beaker),  the  solution  filtered,  and  the 
residue  well  washed  with  hot  water. 

This  residue,  which  contains  generally  some  undecomposed  mineral,  together 
with  sesquioxide  of  iron  and  some  impurities  of  the  ore,  is  treated  with  hot  con- 
centrated hydrochloric  acid  (for  which  purpose  it  is  best  to  incinerate  the  filter), 
the  undecomposed  mineral  filtered  off,  washed,  ignited,  and  weighed,1  and  the 
iron  precipitated  from  the  solution  by  ammonia,  being  subsequently  separated 
from  any  alumina  which  may  be  present,  according  to  the  method  given  in  the 
analysis  of  clay  (see  606). 

1  The  weight  of  undecomposed  mineral  must,  of  course,  be  deducted  from  that  originally 
employed. 


ANALYSIS    OF   CLAYS.  605 

The  solution  of  chromate  of  potassa  is  treated,  as  at  p.  595,  for  the  determina- 
•tion  of  the  chromium  as  sesquioxide. 

Calvert  has  recently  proposed  the  following  as  a  more,  satisfactory  method  of 
analyzing  chrome-iron  ore. 

About  15  grains  of  the  finely  powdered  ore  are  intimately  mixed  with  3  or  4 
parts  of  soda-lime  (prepared  by  slaking  quicklime  with  solution  of  caustic  soda, 
drying  and  calcining)  and  about  1  part  of  nitrate  of  soda.  The  mixture  is 
thoroughly  ignited,  in  a  platinum  crucible,  for  "2  hours,  being  stirred  frequently 
with  a  platinum  wire.  When  cool,  the  mass  is  treated  with  water,  to  which  a 
little  dilute  sulphuric  acid  is  afterwards  added ;  when  the  mass  has  been  thus 
detached  from  the  crucible,  the  latter  is  removed,  and  the  solution  mixed  with 
alcohol,  which  precipitates  the  sulphate  of  lime,  to  be  filtered  off,  and  washed 
with  dilute  alcohol  until  the  washings  are  colorless. 

The  residue  on  the  filter  may  contain  some  undecomposed  ore,  mixed  with  the 
sulphate  of  lime;  the  latter  may  be  removed  by  washing  with  boiling  water, 
and  the  undecomposed  ore  subjected  to  a  second  oxidation. 

The  red  solution  containing  the  chromic  acid  is  mixed  with  excess  of  ammo- 
nia and  oxalate  of  ammonia,  the  precipitate  (alumina,  sesquioxide  of  iron,  oxa- 
late  of  lime,  and  silica)  is  filtered  off,  and  well  washed.  The  chromic  acid  may 
then  be  determined  in  the  solution  by  reduction  with  alcohol  and  hydrochloric 
acid,  and  precipitation  as  sesquioxide  of  chromium  (p.  595). 

SEPARATION  OF  SILICA,  ALUMINA,  OXIDES  OF  IRON,  LIME  AND  MAGNESIA. 

CLAY. 

§  413.  Clay  is  composed  chiefly  of  silica ,  alumina,  and  water ;  but  generally 
contains,  as  impurities,  carbonates  oflime}  magnesia,  oxide  of  manganese,  oxide 
of  iron,  sand,  and  traces  of  alkalies. 

The  amount  of  water  in  the  original  clay,  which  should  first  be  dried  as  far 
as  possible  by  exposure  to  air,  may  be  determined  as  directed  for  limestones  (p. 
602). 

For  the  subsequent  analysis,  the  clay  must  be  reduced  to  a  very  finely  divided 
state. 

About  20  grains  of  the  finely  powdered  and  ignited  clay,  are  mixed  and  fused 
with  carbonate  of  potassa  and  soda,  as  directed  for  quartz  (p.  594) ;  the  fused 
mass  is  decomposed  with  dilute  hydrochloric  acid,  and  the  silica  determined  ex- 
actly as  in  the  case  above  referred  to ;  the  filtrate  from  the  silica,  which  con- 
tains the  bases,  is  concentrated  by  evaporation,  a  little  nitric  acid  being  added 
to  peroxidize  the  iron. 

The  solution  is  then  mixed  with  excess  of  ammonia  (and,  if  much  magnesia 
be  present,  some  chloride  of  ammonium),  gently  heated,  the  precipitated  alumina, 
sesquioxide  of  iron,  and  a  little  sesquioxide  of  manganese,  filtered  rapidly  off,  and 
well  washed  with  hot  water. 

The  lime  and  magnesia  in  the  filtrate  are  determined  as  in  the  analysis  of 
limestones. 

The  precipitate  is  dissolved  in  warm  dilute  hydrochloric  acid,  the  filter  being 
subsequently  well  washed.  Should  any  residue  of  alumina  remain  undissolved, 
the  filter  may  be  dried,  incinerated,  and  the  weight  of  the  alumina  ascertained  by 
deducting  that  of  the  ash. 

The  solution  containing  alumina  and  iron  is  introduced  into  a  weighed  dry 
flask,  and  its  weight  accurately  determined. 

About  half  of  it  is  then  poured  into  a  beaker,  and  the  weight  of  the  flask 
again  taken.  The  portion  thus  separated  is  precipitated  with  ammonia,  the  pre- 
cipitate filtered  off,  washed,  dried,  ignited,  and  weighed,  its  weight  being  after- 
wards calculated  for  the  whole  quantity  of  the  solution. 


606  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

The  other  half  is  mixed  with  excess  of  solution  of  potassa  (free  from  silica), 
heated  for  some  minutes  (in  a  silver  vessel,  or  one  of  hard  glass),  and  the  pre- 
cipitated seaquioxide  ojf  iron  (with  a  little  manganese)  well  washed  with  hot 
water,  redissolved  in  hydrochloric  acid,  precipitated  with  ammonia,  washed,  dried, 
ignited,  and  weighed.  If  its  weight  be  calculated  for  the  whole  quantity  of  solu- 
tion, and  deducted  from  that  of  the  mixed  alumina  and  iron,  we  obtain  the 
amount  of  alumina  present.1 

The  amount  of  carbonic  acid  contained  in  the  air-dried  clay  may  be  ascertained 
as  directed  at  p.  596. 

If  the  weight  of  the  sand  be  required,  it  may  be  ascertained  by  boiling  the 
clay  with  hydrochloric  acid  as  long  as  anything  is  dissolved,  washing  the  residue 
(silica  and  sand)  with  water,  and  boiling  it  repeatedly  with  a  strong  solution  of 
carbonate  of  soda,  which  leaves  only  sand,  to  be  washed,  dried,  ignited,  and 
weighed. 

SEPARATION  OF  ALUMINA  AND  PHOSPHORIC  ACID. 
WAVELLITE. 

§  414.  (If  this  mineral  be  not  procurable,  artificial  phosphate  of  alumina  may 
be  substituted  for  it.^ 

Wavellite  consists  essentially  of  phosphoric  acid  and  alumina,  but  generally 
contains,  in  addition,  oxide  of  iron,  lime,  and  silica. 

It  should  be  analyzed  qualitatively,  to  ascertain  its  true  composition. 

The  mineral  is  finely  powdered,  and  dried  by  ignition. 

About  20  grains  of  the  finely  powdered  mineral  are  intimately  mixed,  in  a  pla- 
tinum crucible,  with  about  30  grains  of  precipitated  silica,  and  120  grains  of 
carbonate  of  soda.  The  mixture  is  cautiously  fused  for  about  an  hour.  When 
cool,  the  mass  is  digested  with  water,  which  dissolves  the  whole  of  the  phos- 
phoric acid  and  part  of  the  silica,  leaving  the  remainder  of  the  latter,  together 
with  the  alumina,  iron,  and  lime,  undissolved.  Some  carbonate  of  ammonia  is 
added,  and  the  solution  digested  for  some  time,  at  a  gentle  heat  (in  order  to 
precipitate  a  little  silica  which  has  passed  into  solution). 

The  precipitate  is  filtered  off,  and  well  washed  with  hot  water.  The  phosphoric 
acid  is  then  determined  in  the  solution,  which  must  be  previously  acidified  with 
acetic  acid,  as  basic  perphosphate  of  iron  (see  p.  593). 

In  order  to  determine  the  alumina,  &c.,  the  precipitate  is  dissolved  off  the 
filter  with  warm  dilute  hydrochloric  acid,  the  solution  evaporated  to  dryness,  and 
the  residue  digested  with  hydrochloric  acid ;  the  solution  is  filtered  from  the  un- 
dissolved silica,  and  the  alumina,  sesquioxide  of  iron,  and  lime,  determined  as  in 
the  analysis  of  clays  (p.  605). 

The  silica  contained  in  the  mineral  is  determined  as  in  quartz  (p.  594). 

ANALYSIS  OP  IRON  ORES, 

and  determination  of  the  relative  quantities  of  oxides  of  iron. 
§  415.  The  iron  may  be  very  accurately  determined  in  the  wet  way  by  the 
process  of  Margueritte,  which  depends  upon  the  power  possessed  by  the  proto- 
salts  of  iron  to  reduce  permanganic  acid. 

The  process  may  be  divided  into  three  portions:  1.  The  preparation  of  a 
standard  solution  of  permanganate  of  potassa;  2.  The  solution  of  the  iron,  and 
its  reduction  to  the  state  of  protoxide;  and  3.  The  determination  of  the  iron. 

1  Rivot  introduces  the  ignited  mixture  of  alumina  and  sesquioxide  of  iron  into  a  small 
porcelain  boat,  and  heats  it  to  redness  in  a  porcelain  tube  through  which  dry  hydrogen  is 
passed  ;  when  no  more  water  is  formed,  showing  that  the  reduction  of  the  iron  is  com- 
plete, the  mixture  of  alumina  and  metallic  iron  is  digested  with  very  dilute  nitric  acid, 
which  dissolves  only  the  latter,  to  be  precipitated  by  ammonia,  and  determined. 


ANALYSIS   OP   IRON   ORES.  607 

In  order  to  prepare  the  standard  solution  of  permanganate  of  potassa,  2  parts 
of  binoxide  of  manganese,  1  part  of  chlorate  of  potassa,  and  3  parts  of  hydrate 
of  potassa  are  fused  in  a  Hessian  crucible  till  the  mass  has  a  fine  dark  green 
color  ;  it  is  then  broken  up,  and  digested  with  a  moderate  quantity  of  water;  the 
solution  is  decanted  from  the  residue,  heated  on  a  sand-bath,  and  nitric  acid 
added,  drop  by  drop,  till  the  green  solution  of  manganate  of  potassa  is  converted 
into  the  rose-violet  of  the  permanganate ;  the  solution  is  filtered  through  asbestos, 
and  carefully  preserved  out  of  contact  with  organic  matter. 

To  graduate  this  solution,  about  15  grs.  of  piano- wire  (accurately  weighed) 
are  dissolved  in  a  moderate  quantity  of  strong  hydrochloric  acid,  and  the  solu- 
tion divided  (by  measure)  into  two  equal  parts;  one  of  these  is  introduced  into 
a  large  flask,  and  diluted  with  about  twenty  ounces  of  water;  the  solution  of 
permanganate  is  now  added  from  a  burette,  very  gradually,  and  with  constant 
shaking,  until  a  pale  rose  color  pervades  the  liquid;  the  operation  is  repeated, 
even  more  carefully,  with  the  second  portion  of  the  iron-solution,  and  the  num- 
ber of  measures  of  permanganate  which  are  necessary  to  oxidize  100  grs.  of  iron 
calculated  from  the  mean  of  the  two  experiments. 

It  is  advisable  to  have  the  solution  of  permanganate  of  such  a  strength  that 
about  1000  grain  measures  correspond  to  10  grs.  of  iron. 

The  action  of  a  solution  of  permanganic  acid  upon  (proto-)  chloride  of  iron  in 
presence  of  hydrochloric  acid  is  represented  in  the  following  equation : — 

Mna07-flOFeCl  +  7HCl=2MnCl-f5FeaCl3  +  7HO. 

We  have  now  to  obtain  the  iron  in  a  state  of  solution,  which  is  effected  by 
boiling  about  15  grs.  of  the  finely  powdered  ore  with  hydrochloric  or  nitro- 
hydrochloric  acid,  according  to  its  nature ;  if  the  latter  be  employed,  the  solution 
must  be  evaporated  with  an  excess  of  hydrochloric  acid  to  expel  the  nitric  acid, 
the  residue  being  afterwards  redissolved  in  hydrochloric  acid.  The  solution  is 
then  boiled  with  a  little  concentrated  solution  of  sulphite  of  soda  until  it  has 
acquired  a  pale  green  color,  and  the  smell  of  sulphurous  acid  has  disappeared ; 
in  this  way  the  whole  of  the  sesquichloride  of  iron  is  reduced  to  (proto-) 
chloride. 

If  arsenic  or  copper  be  present  in  the  ore,  it  is  better  to  effect  this  reduc- 
tion by  boiling  with  a  little  zinc  (free  from  iron),  and  to  filter  off  the  reduced 
metals. 

The  solution  of  iron  is  largely  diluted  with  (about  30  ounces  of)  water  in  a 
capacious  flask,  and  the  permanganate-solution  gradually  added  from  the  burette 
in  the  manner  above  described.  Since  we  know  the  number  of  measures  of  the 
solution  required  to  peroxidize  100  grs.  of  iron,  we  have  only  to  calculate  by  a 
proportion  the  amount  of  metal  present  in  the  ore. 

This  method  is  very  convenient,  expeditious,  and  accurate,  but  unfortunately 
the  solution  of  permanganate  of  potassa  is  gradually  decomposed  when  kept,  so 
that  it  is  necessary  to  graduate  the  solution  afresh  before  every  series  of  deter- 
minations. 

If  it  be  desired  to  ascertain  the  degree  of  oxidation  in  which  the  iron  exists  in 
the  ore,  we  may  make  one  determination  according  to  the  above  directions,  and 
another  in  the  hydrochloric  solution  of  the  ore,  without  adding  any  reducing 
agent.  The  first  operation  gives  the  total  quantity  of  iron  present,  and  the 
second,  that  which  exists  as  (prot-)  oxide;  by  difference,  of  course,  we  obtain  the 
amount  of  sesquioxide.1 

1  Penny  has  proposed  a  method  for  the  determination  of  iron  in  ores,  which  consists  in 
reducing  the  sesquioxide,  as  above,  to  the  state  of  protoxide,  and  in  adding  to  the  diluted 
hydrochloric  solution,  a  solution  of  a  known  weight  of  bichromate  of  potassa,  from  a 
burette,  until  a  drop  of  the  liquid  no  longer  gives  a  blue  or  green  color  with  a  drop  of 


608  QUANTITATIVE   ANALYSIS;    SPECIAL    METHODS. 

The  determination  of  the  clay,  sand,  water,  lime,  and  magnesia,  may  be 
effected  in  the  same  way  as  in  the  analysis  of  limestones  (.see  p.  602). 

The  carbonic  acid  is  determined  according  to  the  directions  given  at  p.  596. 

SEPARATION  OP  THE  OXIDES  OF  IRON  AND  MANGANESE. 
MANGANIFEROUS  SPATHIC  IRON-ORE. 

§  416.  The  essential  constituents  of  this  ore  are  carbonates  of  iron  and  manga- 
nese, but  it  often  contains  carbonates  of  lime,  magnesia,  &c. 

About  15  grains  of  the  ore  are  dissolved  in  hydrochloric  acid,  the  iron  per- 
oxidized  with  a  little  nitric  acid,  and  the  sesquioxide  precipitated  as  succinate, 
according  to  the  directions  given  at  p.  586. 

The  manganese  is  precipitated  from  the  filtrate  as  sulphide  (.see  p.  588). 

The  iron  may  also  be  determined  by  means  of  a  standard  solution  of  perman- 
ganate of  potassa. 

The  carbonic  acid  in  spathic  iron  ores  may  be  estimated  as  at  p.  596. 

CRYSTALLIZED  SULPHATE  OF  COPPER. 
CuO.S03,HO-f4Aq. 

§  417.  The  powdered  crystals  are  pressed  between  blotting-paper. 

Determination  of  the  Water  of  •Crystallization. — About  20  grains  of  the  salt, 
in  fine  powder,  are  dried  in  the  water-oven  till  the  weight  ceases  to  vary. 

Determination  of  the  Water  of  Constitution. — The  residue  from  the  above 
experiment  is  dried  on  a  sand-bath,  at  about  400°  F.  (204°. 5  C.),  till  its  weight 
ceases  to  vary. 

Determination  of  the  oxide  of  copper,  see  p.  579. 

Determination  of  the  Sulphuric  Acid. — About  20  grains  of  the  salt  are  dis- 
solved in  water,  and  the  solution  precipitated  by  chloride  of  barium  (p.  592). 

SEPARATION  OF  CADMIUM  AND  ZINC. 
CALAMINE. 

§  418.  (A  specimen  should  be  selected  which  contains  both  zinc  and  cadmium.) 

The  mineral  may  be  freed  from  extraneous  moisture  by  drying  in  the  water- 
bath. 

A  quantity  of  the  mineral  depending  upon  the  amount  of  cadmium  present,  is 
dissolved  in  hydrochloric  acid,  and  the  cadmium  precipitated  from  the  highly 
dilute  solution  as  sulphide  (see  p.  581). 

The  zinc  is  subsequently  precipitated  from  the  filtrate  as  carbonate 
(see  p.  589). 

SEPARATION  OF  IRON  AND  COPPER. 

COPPER-PYRITES. 

Fe2S3.Cu2S. 

§  419.  15  grains  of  the  finely  powdered  mineral  are  treated  with  the  most 
concentrated  nitric  acid,  in  a  large,  long-necked  flask,  and,  when  the  oxidation 
is  less  violent,  heat  is  applied  until  the  sulphur  separates  in  pure  yellow  glo- 
bules, which  are  collected  on  a  weighed  filter,  well  washed,  dried,  and  weighed. 

solution  of  ferricyanide  of  potassium  upon  a  white  plate.     The  calculation  is  based  upon 
the  following  equation:  — 

K0.2Cr03-f6FeCl-f7HCl=3Fe2Cl3+Cr2Cl3+KCl-f7HO. 

Since  the  solution  of  bichromate  may  be  preserved  for  any  length  of  time,  this  process 
would,  in  some  cases,  be  preferable  to  that  in  which  permanganate  of  potassa  is  used. 


PEWTER.  609 

The  solution  is  evaporated  till  the  greater  excess  of  nitric  acid  is  expelled, 
largely  diluted  with  water,  and  the  sulphuric  acid  precipitated  with  chloride  of 
barium.  The  amount  of  sulphur,  calculated  from  the  sulphate  of  baryta,  is 
added  to  that  obtained  by  direct  weighing. 

From  the  filtrate,  the  excess  of  baryta  is  removed  by  sulphuric  acid  (added  in 
very  slight  excess)  and  the  copper  precipitated  as  sulphide  (p.  579). 

The  solution  filtered  from  the  sulphide  of  copper  is  evaporated  till  all  odor  of 
sulphuretted  hydrogen  has  disappeared,  heated  with  nitric  acid,  to  peroxidize 
the  iron,  which  is  then  precipitated  as  sesquioxide,  by  ammonia  (p.  586). 

TARTAR  EMETIC. 

TARTRATE  OF  ANTIMONY  AND  POTASSA. 
KO,Sb03.T+  Aq. 

§  420.  About  fifteen  grains  of  the  salt  are  dissolved  in  much  water,  the  solu- 
tion acidified  with  hydrochloric  acid,  and  the  antimony  precipitated  as  tersul- 
phide  (p.  583). 

The  solution  is  evaporated,  in  the  usual  manner,  to  dryness,  ignited  till  all 
organic  matter  is  burnt  oif,  and  the  potassium  determined  as  chloride  (p.  591). 

SEPARATION  OF  TIN,  ANTIMONY,  COPPER,  AND  BISMUTH. 
PEWTER. 

§  421.  (A  good  specimen  should  le  employed,  which  has  first  leen  analyzed 
qualitatively,  and  found  to  contain  the  above  metals.} 

Determination  of  Tin  and  Antimony  jointly. — About  10  grains  of  the  alloy, 
in  small  pieces,  are  oxidized  with  moderately  strong  nitric  acid,  in  a  beaker; 
most  of  the  acid  is  evaporated  oif,  the  solution  diluted  with  water,  and  the  resi- 
due collected  upon  a  filter,  washed  with  hot  water  till  the  washings  are  no  longer 
tinged  by  sulphuretted  hydrogen,  dried,  ignited,  with  precautions,  and  weighed. 

Determination  of  Antimony. — About  30  grains  of  the  alloy  are  dissolved  in 
hydrochloric  acid,  with  addition  of  chlorate  of  potassa,  and  the  antimony  precipi- 
tated in  the  metallic  state  by  means  of  a  plate  of  tin  (see  p.  584.)  The  solution 
should  first  be  heated  gently,  till  it  smells  no  longer  of  chlorous  acid.  If  the 
metallic  antimony  be  calculated  as  Sb04,  and  its  percentage  deducted  from  the 
percentage  of  residue  left  by  nitric  acid,  it  will  furnish  the  amount  of  binoxide 
of  tin,  from  which  that  of  the  tin  may  be  calculated. 

The  following  method  has  recently  been  proposed  by  Rose  for  the  separation 
of  antimony  and  tin. 

The  alloy  is  oxidized  with  nitric  acid  of  sp.  gr.  1.4.  The  excess  of  acid  is 
expelled  by  evaporation,  and  the  residual  oxide  heated  to  faint  redness;  It  is 
then  fused  for  some  time  in  a  silver  crucible,  with  a  considerable  excess  of  pure 
hydrate  of  soda.  The  mass  is  dissolved  in  water,  and  so  much  alcohol,  of  sp. 
gr.  0.83,  is  added,  that  its  volume  may  be  to  that  of  the  water  as  1  to  3.  The 
mixture  is  allowed  to  stand  for  some  time,  in  order  that  the  whole  of  the  anti- 
moniate  of  soda  may  be  deposited;  it  is  then  filtered  off  and  washed,  first  with 
a  mixture  of  equal  volumes  of  water  and  alcohol  of  sp.  gr.  0.83,  and  afterwards 
with  a  mixture  of  3  volumes  of  alcohol  of  0.83  and  1  volume  of  water,  until  a 
portion  of  the  filtrate,  after  acidulation  with  sulphuric  acid,  is  no  longer  precipi- 
tated, even  after  some  time,  by  sulphuretted  hydrogen.  It  is  recommended  to 
dissolve  a  little  carbonate  of  soda  in  the  weak  spirit  employed  for  washing. 

The  filtrate  (containing  the  stannate  of  soda)  is  gently  heated,  to  expel  the 
alcohol,  diluted  with  water,  acidulated  with  sulphuric  acid,  and  precipitated  by 
39 


610  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

sulphuretted  hydrogen.  The  bisulphide  of  tin  is  converted  into  binoxide  by 
roasting,  and  weighed. 

The  filter  containing  the  antimoniate  of  soda  is  placed,  while  yet  moist,  in  a 
beaker,  and  treated  with  a  mixture  of  hydrochloric  and  tartaric  acids,  the  filter 
being  afterwards  washed  with  the  mixture.  The  solution  is  saturated  with 
sulphuretted  hydrogen,  the  pentasulphide  of  antimony  collected  upon  a  weighed 
filter,  washed,  dried,  weighed,  and  the  antimony  in  it  determined  by  reducing  a 
weighed  portion  with  hydrogen  in  a  porcelain  crucible,  through  the  lid  of  which 
a  small  porcelain  tube  passes. 

Should  arsenic  be  present,  it  will  be  contained  in  the  alkaline  solution  as 
arseniate  of  soda.  This  solution  is  acidulated  with  hydrochloric  acid,  any  pre- 
cipitate being  disregarded  and  left  in  the  liquid,  and  saturated  with  sulphuretted 
hydrogen.  The  solution  is  allowed  to  stand  until  the  odor  of  sulphuretted 
hydrogen  is  scarcely  perceptible,  and  the  precipitate  collected  upon  a  weighed 
filter.  The  filtrate  is  heated  with  solution  of  sulphurous  acid,  and  again  satu- 
rated with  sulphuretted  hydrogen,  when,  if  any  sulphide  of  arsenic  be  precipi- 
tated, it  may  be  collected  upon  a  separate  filter,  since  it  contains  no  tin.  The 
original  precipitate,  containing  the  two  sulphides,  is  washed,  dried,  and  weighed. 
A  weighed  portion  of  it  is  afterwards  heated  in  a  current  of  sulphuretted  hydro- 
gen, when  the  sulphide  of  arsenic  is  volatilized.  The  residual  bisulphide  of  tin 
is  converted  into  binoxide  by  roasting,  and  weighed;  the  sublimed  sulphide  of 
arsenic,  together  with  the  small  portion  upon  the  other  filter,  is  converted  into 
arsenic  acid  and  determined  (p.  584). 

Determination  of  Copper  and  Bismuth. — About  30  or  40  grs.  of  pewter  are 
oxidized  with  nitric  acid,  as  for  the  determination  of  the  tin  and  antimony,  the 
solution  filtered  off,  and  the  teroxide  of  bismuth  precipitated  by  carbonate  of  am- 
monia, and  determined  as  at  p.  579. 

The  copper  is  precipitated  from  the  solution  by  sulphuretted  hydrogen,  and  the 
sulphide  treated  as  directed  at  p.  579. 

SEPARATION  OF  TIN,  LEAD,  AND  BISMUTH. 
ANALYSIS  OF  NEWTON'S  FUSIBLE  ALLOY. 

§  422.  About  10  grs.  of  the  alloy  are  oxidized  with  moderately  dilute  nitric 
acid,  with  the  aid  of  heat,  a  considerable  quantity  of  water  is  added,  and  heat 
again  applied,  in  order  that  the  nitrates  of  lead  and  bismuth  may  be  completely 
dissolved;  the  solution  is  allowed  to  subside,  the  residue  of  binoxide  of  tin  filtered 
off,  and  treated  as  directed  at  p.  582;  the  filtrate  is  evaporated  to  a  small  bulk, 
the  lead  precipitated  as  sulphate  (p.  578),  and  the  bismuth  determined  in  the 
filtrate,  as  directed  at  p.  579. 

SEPARATION  OF  ANTIMONY,  LEAD,  AND  BISMUTH. 
ANALYSIS  OF  TYPE-METAL. 

§  423.  About  10  grs.  of  the.  alloy  are  completely  oxidized  with  dilute  nitric 
acid,  the  greater  part  of  the  excess  of  acid  being  expelled  by  evaporation;  a  con- 
siderable quantity  of  water  is  then  added,  and  the  whole  boiled ;  the  residue  is 
collected  on  a  filter,  washed  till  the  washings  are  no  longer  blackened  by  sul- 
phuretted hydrogen,  dried,  incinerated  with  the  usual  precautions  for  easily 
reducible  oxides,  and  weighed ;  the  amount  of  antimony  is  then  calculated  from 
the  weight  of  antimonious  acid,  as  at  p.  583. 

The  lead  and  bismuth  may  be  determined  in  the  filtrate  in  the  same  manner 
as  in  the  analysis  of  Newton's  fusible  metal. 


ANALYSIS  OP  STANDARD  SILVER.          611 

SEPARATION  OF  TIN,  COPPER,  LEAD,  AND  ZINC. 
ANALYSIS  OF  BRASS,  BRONZE,  GUN-METAL,  &c. 

§  424.  These  alloys  are  liable  to  contain,  not  only  copper,  zinc,  and  tin,  but 
also  small  quantities  of  lead ;  the  following  method,  therefore,  will  be  applicable 
to  specimens  containing  any  of  these  metals. 

About  10  grains  of  the  alloy  are  boiled  with  moderately  dilute  nitric  acid  (1 
volume  of  concent,  acid  and  3  volumes  water)  in  a  beaker  covered  with  an  in- 
verted funnel,  and  the  solution  evaporated  (in  the  same  way)  to  a  small  bulk;  a 
considerable  quantity  of  water  is  then  added,  and  the  solution  set  aside  till  the 
residue  has  subsided;  this  residue  consists  of  binoxide  of  tin ,  the  amount  of  which 
is  determined  as  at  p.  582. 

The  filtrate  from  the  binoxide  of  tin  is  mixed  with  a  little  pure  dilute  sulphuric 
acid,  and  evaporated  to  a  small  bulk  to  expel  the  greater  part  of  the  nitric  acid ; 
a  little  water  is  then  added,  and  the  precipitated  sulphate  of  lead  determined  as 
at  p.  578. 

The  filtrate  from  the  sulphate  of  lead  is  diluted  with  a  considerable  quantity  of 
water,  and  saturated  with  sulphuretted  hydrogen ;  the  sulphide  of  copper  thus  pre- 
cipitated is  treated  as  directed  in  p.  579. 

The  solution  filtered  from  the  sulphide  of  copper  is  evaporated  considerably, 
to  expel  the  hydrosulphuric  acid,  and  to  concentrate  the  solution,  and  the  zinc 
afterwards  determined  as  basic  carbonate,  according  to  the  directions  given  at  p. 
588. 

SEPARATION  OF  COPPER.  ZINC,  AND  NICKEL. 
ANALYSIS  OF  GERMAN  SILVER. 

§  425.  This  alloy  may  be  analyzed  as  follows  : — 

About  10  grains  are  dissolved  in  nitric  acid,  the  solution  evaporated  till  the 
greater  excess  of  nitric  acid  is  expelled,  diluted  largely  with  water,  and  a  con- 
siderable quantity  of  hydrochloric  acid  added.  The  solution  is  then  completely 
saturated  with  sulphuretted  hydrogen,  the  precipitated  sulphide  of  copper  filtered 
off  and  treated  as  at  p.  579.  The  filtrate  and  washings  are  evaporated  to  a  small 
bulk,  mixed  with  an  excess  of  solution  of  acetate  of  potassa,  and  saturated  with 
sulphuretted  hydrogen;  the  precipitated  sulphide  of  zinc  is  filtered  off,  and  treated 
in  the  manner  directed  at  p.  588.  The  nickel  in  the  filtrate,  which  must  be 
evaporated  to  expel  excess  of  hydrosulphuric  acid,  is  determined  according  to  p. 
587. 

SEPARATION  OF  TIN,  ANTIMONY,  COPPER,  AND  LEAD. 
BRITANNIA-METAL. 

§  426.  The  tin  and  antimony  are  determined  as  in  the  analysis  of  pewter  (p. 
609).  The  lead  may  be  precipitated  with  carbonate  of  ammonia,  and  treated  ac- 
cording to  the  directions  given  for  oxalate  of  lead  (p.  578);  the  copper  is  sub- 
sequently removed  from  the  filtrate  by  sulphuretted  hydrogen  (p.  579). 

SEPARATION  OF  SILVER  AND  COPPER. 
ANALYSIS  OF  STANDARD  SILVER. 

§  427.  The  analysis  of  alloys  containing  only  silver  and  copper  is  very  easily 
effected  by  dissolving  them  in  nitric  acid,  precipitating  the  silver  as  chloride  (p. 
576),  and  subsequently  precipitating  the  copper  from  the  solution  by  potassa 
(p.  579). 


612  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

The  determination  of  silver  in  alloys  may  be  effected  with  great  rapidity  and 
accuracy  by  using  the  standard  solution  of  chloride  of  sodium,  that  is,  a  solu- 
tion, a  certain  number  of  measures  of  which  will  precipitate,  as  chloride,  a  known 
quantity  of  silver. 

The  solution  to  be  analyzed  is  mixed  with  some  diluted  nitric  acid,  gently 
heated,  and  the  standard  solution  of  chloride  of  sodium  gradually  added,  with 
frequent  agitation,  until  a  drop  fails  to  produce  a  fresh  precipitate  of  chloride  of 
silver ;  the  number  of  measures  of  solution  which  have  been  used  is  then  read 
off,  and  the  quantity  of  silver  calculated. 

SEPARATION  OF  GOLD,  SILVER,  AND  COPPER. 
ANALYSIS  OP  STANDARD  GOLD. 

§  428.  The  analysis  of  alloys  of  gold,  silver,  and  copper,  in  the  moist  way,  is 
attended  with  some  difficulty. 

The  general  method  consists  in  laminating  the  alloy,  and  boiling  with  nitro- 
hydrochloric  acid ;  if  the  metal  becomes  coated  with  chloride  of  silver,  it  must 
be  carefully  removed,  and  treated  with  ammonia,  so  as  to  expose  a  fresh  metallic 
surface,  the  ammoniacal  solution  being  afterwards  neutralized  with  hydrochloric 
acid,  and  added  to  the  solution  in  aqua  reyia;  the  residual  chloride  of  silver  is 
collected,  and  treated  as  at  p.  576. 

The  solution  containing  the  gold  and  copper  is  evaporated  to  dryness  on  a 
water-bath,  the  residue  dissolved  in  hydrochloric  acid,  and  again  evaporated,  to 
expel  all  nitric  acid ;  it  is  then  redissolved  in  dilute  hydrochloric  acid,  and  the 
solution  boiled  for  some  time  with  oxalic  acid ;  the  supernatant  liquid  is  decanted 
from  the  precipitated  gold,  the  latter  washed  with  a  little  ammonia,  to  remove 
any  oxalate  of  copper,  then,  with  water,  transferred  to  a  weighed  capsule,  dried 
in  an  air-bath,  ignited,  and  weighed. 

The  copper  may  be  determined  in  the  solution  by  precipitating  with  sulphuret- 
ted hydrogen,  and  subsequently  converting  the  sulphide  into  oxide  (p.  579). 

AMALGAMS. 
SEPARATION  OF  MERCURY  AND  ZINC. 

§  429.  The  amalgam  used  for  electrical  machines  may  be  analyzed  for  practice. 

Fifteen  grains  of  the  amalgam  are  dissolved  in  nitric  acid,  the  solution  evapo- 
rated with  hydrochloric  acid,  on  a  water-bath,  till  all  free  nitric  acid  is  expelled, 
and  the  mercury  precipitated  by  sulphuretted  hydrogen  (p.  577). 

The  filtrate  from  the  sulphide  of  mercury  is  evaporated  to  a  small  bulk,  to 
expel  excess  of  acid,  and  the  zinc  precipitated  as  basic  carbonate  (p.  588). 

SEPARATION  OF  MERCURY  AND  TIN. 

§  430.  Amalgam  of  tin  may  be  analyzed  by  a  process  similar  to  the  above, 
the  tin  being  determined  as  binoxide  (p.  582),  and  the  mercury  precipitated  as 
sulphide  (p,  577),  or  the  mercury  may  be  expelled  by  heat,  and  the  tin  con- 
verted into  binoxide  by  roasting. 

SEPARATION  OF  ARSENIC,  COBALT,  NICKEL,  AND  IRON. 
SPEISS-COBALT. 

§  431.  This  substance  contains  arsenic,  cobalt,  nickel,  iron,  sulphur,  and  silica. 
Since  the  arsenic  exists  in  very  large  proportion,  it  is  well  to  determine  it  in 
a  separate  quantity. 

Determination  of  Arsenic. — About  10  grs.  of  the  finely  powdered  substance 


ANALYSIS   OF   SPEISS-COB ALT.  613 

are  boiled  in  a  large  flask,  with  concentrated  nitric  acid,  till  no  further  action 
takes  place.  The  solution  is  diluted  with  water,  filtered,  mixed  with  excess  of 
ammonia  and  digested  with  colorless  sulphide' of  ammonium,  at  a  gentle  heat, 
for  a  considerable  time.  The  digestion  should  be  conducted  in  a  flask.  The 
solution  is  filtered  off,  and  the  residue  washed  with  water  containing  colorless 
sulphide  of  ammonium.  (If  yellow  sulphide  of  ammonium  were  employed,  some 
sulphide  of  nickel  might  be  dissolved.)  The  filtrate  is  decomposed  with  a  slight 
excess  of  acetic  acid,  and  the  precipitate  of  pentasulphide  of  arsenic  treated  as  at 
p.  584. 

If  this  precipitate  should  contain  any  sulphide  of  nickel  or  of  copper,  it  may 
be  dissolved  in  warm  ammonia,  and  reprecipitated  with  acetic  acid. 

Another  method  of  determining  the  arsenic  consists  in  expelling  the  excess  of 
acid  from  the  nitric  solution  by  evaporation;  diluting  largely  with  water,  reduc- 
ing the  arsenic  acid  by  sulphurous  acid,  evaporating  the  excess  of  the  latter,  and 
determining  the  arsenic  as  tersulphide  (p.  584). 

The  treatment  with  sulphurous  and  hydrosulphuric  acids  must,  however,  be 
repeated  several  times,  until  no  more  arsenic  is  separated. 

Determination  of  Sulphur. — About  20  grains  of  the  substance  are  boiled  with 
the  strongest  nitric  acid,  until  the  sulphur  is  either  completely  oxidized,  or  till 
the  excess  is  separated  in  clear  yellow  globules;  the  solution  is  then  diluted  with 
water  and  passed  through  a  weighed  filter. 

The  sulphuric  acid  in  the  solution  is  determined  as  sulphate  of  baryta,  from 
which  the  amount  of  sulphur  is  calculated. 

The  undissolved  residue  (sulphur  and  silica)  is  dried  at  212°  F.  and  weighed; 
it  is  then  ignited  in  the  usual  manner,  when  the  sulphur  is  volatilized  and  may 
be  estimated  from  the  loss. 

Determination  of  Iron,  Nickel,  and  Cobalt. — About  15  or  20  grs.  of  the  ore 
are  carefully  roasted  in  a  porcelain  crucible,  to  expel  as  much  as  possible  of  the 
sulphur  and  arsenic.  The  roasted  ore  is  then  treated  as  before,  with  nitric  acid, 
the  solution  evaporated  to  dryness,  the  residue  digested  with  concentrated  hydro- 
chloric acid,  water  added,  and  the  liquid  filtered.  The  filtrate  is  saturated  with 
sulphurous  acid,  digested  for  some  time  at  a  gentle  heat,  evaporated  to  expel 
excess  of  sulphurous  acid,  saturated  with  sulphuretted  hydrogen,  and  allowed 
to  stand  for  some  time  in  a  warm  place;  this  treatment  with  sulphuretted  hydro- 
gen is  repeated,  until  the  odor  no  longer  disappears  after  digestion  for  a  short 
time.  The  precipitate  is  filtered  off  and  washed.  The  filtrate  is  again  treated, 
in  the  same  way,  with  sulphurous  and  hydrosulphuric  acids,  as  long  as  any 
arsenic  is  separated.  The  filtrate  and  washings  are  then  concentrated  by  evapo- 
ration, and  the  iron  separated  as  succinate  (or  benzoate)  as  directed  p.  607. 

For  the  separation  of  the  cobalt  and  nickel,  the  solution  (free  from  iron, 
arsenic,  &c.),  slightly  acidified  with  hydrochloric  acid,  is  mixed  with  a  dilute 
solution  of  chloride  of  lime,  to  which  a  slight  excess  of  sulphuric  acid  has  been 
added,  by  which  the  chloride  of  cobalt  is  entirely  converted  into  sesquichloride. 
A  thin  cream  of  pure  carbonate  of  lime  is  then  added  in  excess,  and  the  mixture 
digested,  in  the  cold,  with  frequent  agitation,  for  at  least  24  hours.  The  nickel 
remains  in  solution  as  chloride,  while  the  cobalt  is  precipitated  in  the  form  of 
sesquioxide,  mixed  with  the  excess  of  carbonate  of  lime. 

The  precipitate  is  collected  upon  a  filter  and  thoroughly  washed;  the  filter  is 
then  placed  in  a  capacious  beaker,  and  covered  with  water,  to  which  hydrochloric 
acid  must  be  added  from  time  to  time,  until  the  precipitate  is  entirely  dissolved, 
which  may  be  promoted  by  gently  heating;  the  solution  is  separated  from  the 
filter-paper  (which  must  be  very  thoroughly  washed),  concentrated  by  evapora- 
tion, mixed  with  ammonia  in  slight  excess,  and  saturated  with  sulphuretted 
hydrogen ;  the  precipitated  sulphide  of  cobalt  is  filtered  off  and  treated  as  at 
p.  587. 


614  QUANTITATIVE   ANALYSIS;    SPECIAL    METHODS. 

The  solution  containing  the  chloride  of  nickel  is  concentrated  by  evaporation, 
mixed  with  a  slight  excess  of  ammonia  and  saturated  with  sulphuretted  hydro- 
gen j  the  precipitated  sulphide  of  nickel  being  dissolved  in  nitro-hydrochloric 
acid,  and  the  nickel  determined  as  at  p.  587. 

Another  process  for  separating  nickel  and  cobalt,  known  as  Liebiffs  method, 
is  executed  as  follows.  The  solution  is  mixed  with  a  considerable  quantity  of 
hydrocyanic  acid,  and  afterwards  nearly  neutralized  with  potassa;  heat  is  then 
applied  until  the  solution  becomes  clear  and  the  excess  of  hydrocyanic  acid  is 
expelled.  The  cobalt  is  thus  converted  into  cobalticyanide  of  potassium,  and 
the  nickel  into  the  double  cyanide  of  nickel  and  potassium.  An  excess  of 
freshly  precipitated  well-washed  oxide  of  mercury  is  now  added  to  the  hot  solu- 
tion, when  the  whole  of  the  nickel  is  precipitated,  partly  as  oxide,  partly  as 
cyanide.  The  solution  is  boiled  for  a  short  time,  to  convert  the  nickel  entirely 
into  oxide,  which  is  collected  upon  a  filter,  washed,  dried,  and  ignited,  when  the 
excess  of  oxide  of  mercury  is  expelled,  and  oxide  of  nickel  alone  remains. 

The  filtrate  containing  the  cobalt  is  mixed  with  excess  of  acetic  acid,  and  pre- 
cipitated, while  boiling,  with  sulphate  of  copper;1  the  mixture  is  boiled  until 
the  precipitated  cobalticyanide  of  copper  has  become  somewhat  granular,  and 
filtered.  The  precipitate  is  washed,  dried,  ignited,  dissolved  'in  hydrochloric 
acid  with  a  little  nitric,  the  solution  largely  diluted,  and  the  copper  precipitated 
by  sulphuretted  hydrogen;  the  solution  filtered  from  the  sulphide  of  copper  is 
concentrated  by  evaporation,  the  cobalt  precipitated  as  oxide,  by  boiling  with 
potassa,  and  determined  as  usual. 

DETERMINATION  OF  THE  VALUE  or  MANGANESE-ORES. 

§  432.  Since  the  natural  oxides  of  manganese  are  used  chiefly  for  the  prepa- 
ration of  chlorine  in  bleach- works,  it  is  important  that  we  should  possess  some 
ready  method  of  ascertaining  the  quantity  of  chlorine  which  a  given  amount  of 
the  ore  is  capable  of  eliminating,  as  well  as  the  quantity  of  hydrochloric  acid 
consumed,  which  will  depend  upon  the  nature  of  the  foreign  matters  contained 
in  the  ore. 

In  order  to  determine  bow  much  chlorine  may  be  liberated  by  a  certain 
amount  of  ore,  about  100  grains  of  the  latter,  in  a  state  of  very  fine  powder,  are 
heated  with  hydrochloric  acid,  in  a  flask  provided  with  a  bent  tube,  which  con- 
ducts the  chlorine  into  a  weak  solution  of  potassa  contained  in  another  flask ; 
care  is  taken  to  evolve  the  whole  of  the  chlorine,  and  the  solution  of  hypochlo- 
rite  of  potassa  and  chloride  of  potassium  is  then  tested  by  a  chlorimetric  pro- 
cess (p.  615). 

To  ascertain  how  much  hydrochloric  acid  is  consumed  in  the  evolution  of  the 
chlorine,  about  50  grains  of  the  finely  powdered  ore  are  dissolved  at  a  gentle 
heat  in  a  measured  quantity  of  dilute  acid  (of  known  strength),  and  the  excess  of 
acid  remaining  is  then  determined,  after  the  'complete  expulsion  of  the  chlorine, 
by  adding  a  standard  solution  of  carbonate  of  soda  until  a  permanent  precipitate 
begins  to  be  formed. 

A  very  neat  method  of  testing  the  ores  of  manganese  is  that  of  Fresenius  and 
Will,  which  consists  in  treating  the  ore  (previously  freed  from  earthy  carbonates 
by  washing  with  dilute  nitric  acid)  with  oxalate  of  potassa  and  sulphuric  acid, 
when  the  oxalic  acid  (C303)  is  converted  into  2  eqs.  of  carbonic  acid,  the  weight 
of  which  is  ascertained  from  the  loss  suffered  by  the  apparatus  (so  constructed 
that  no  aqueous  vapor  shall  be  carried  off). 

1  Wohler  recommends  the  precipitation  of  the  solution,  nearly  neutralized  with  nitric 
acid,  by  a  solution  of  nitrate  of  suboxide  of  mercury,  which  precipitates  the  mercury  as 
cobalticyanide ;  the  latter,  when  washed,  dried,  and  ignited,  leaves  the  black  interme- 
diate oxide  of  cobalt. 


CHLORIMETRY.  615 

Since  the  action  of  oxalic  acid  upon  binoxide  of  manganese,  in  the  presence 
of  sulphuric  acid,  is  represented  by  the  equation 


every  44  parts  (2  eqs.)  of  carbonic  acid  represent  8  parts  (1  eq.)  of  available 
oxygen,  and  consequently  35.5  parts  (1  eq.)  of  chlorine,  which  may  be  elimi- 
nated by  the  specimen. 

The  operation  is  conducted  exactly  as  the  determination  of  carbonic  acid  in 
an  alkaline  carbonate  (p.  616),  except  that,  instead  of  the  carbonate,  about  20 
grains  of  very  finely-powdered  binoxide  of  manganese,  and  twice  as  much  oxalate 
of  potassa,  are  placed  in  the  generating  flask.  The  operation  is  continued  until 
no  more  black  particles  of  binoxide  of  manganese  are  visible,  and  at  the  con- 
clusion, air  is  sucked  through  the  flasks  in  the  usual  manner. 

Calculation. 


2  2 

44  ::  43.6  ::   Carbonic  acid  evolved  '.  x 
x  =  Binoxide  of  manganese. 

If  the  ore  contain  any  carbonate  of  lime,  a  weighed  portion  must  be  washed 
with  very  dilute  nitric  acid,  and  subsequently  with  water,  dried,  and  the  avail- 
able oxygen  determined  as  above. 

CHLORIMETRY. 

§  433.  This  name  is  given  to  the  various  methods  of  determining  the  amount  of 
available  chlorine  contained  in  any  specimen  of  the  chloride  of  lime  of  commerce. 

The  oldest  of  these  methods  consists  in  ascertaining  what  weight  of  the  speci- 
men is  required  to  decolorize  a  given  quantity  of  a  standard  solution  of  indigo 
(in  sulphuric  acid),  previously  graduated  by  means  of  a  solution  of  potassa, 
which  has  absorbed  a  known  volume  of  chlorine.  This  method  has  been,  how- 
ever, for  the  most  part,  abandoned,  since  the  standard  solution  of  indigo  is 
changed  by  keeping. 

A  better  chlorimetric  process  consists  in  determining  the  amount  of  bleach 
necessary  to  convert  a  known  quantity  of  arsenious  acid  (As03)  into  arsenic  acid 
(AsOs). 

A  standard  solution  of  arsenious  acid  is  prepared  by  dissolving  about  140 
grains  of  the  pure  acid  in  a  little  dilute  hydrochloric  acid,  with  the  aid  of  heat, 
and  adding  as  much  distilled  water  as  will  bring  the  volume  to  10,000  grain 
measures;  if  the  operator  be  competent  to  determine  the  amount  of  arsenious 
acid  in  a  given  volume  of  this  solution,  it  will  be  found  the  best  course  ;  but 
otherwise,  the  weight  of  the  arsenious  acid  originally  employed,  and  the  volume 
of  the  solution  ultimately  prepared  from  it,  should  be  accurately  determined,  the. 
object  being  to  obtain  a  solution  of  arsenious  acid  of  known  strength. 

About  50  grains  of  a  fair  specimen  of  the  bleaching-powder  are  triturated  in 
a  mortar  with  a  small  quantity  of  water,  a  larger  quantity  being  afterwards  add- 
ed ;  the  solution  is  then  rapidly  filtered,  the  mortar  being  carefully  rinsed,  and 
the  filter  washed  with  cold  water  till  the  washings  do  not  bleach  solution  of  in- 
digo. The  volume  of  the  filtered  solution  is  then  accurately  determined. 

About  1000  grains  of  the  standard  solution  of  arsenious  acid  are  measured 
into  a  beaker,  mixed  with  a  moderate  quantity  of  dilute  hydrochloric  acid,  and 
colored  with  a  little  solution  of  indigo  ;  a  burette  is  then  filled  up  with  the  solu- 
tion of  bleach  prepared  as  above,  and  this  solution  added  to  that  of  arsenious 
acid,  with  constant  stirring,  until  the  color  of  the  indigo-solution  disappears, 
showing  that  an  excess  of  chlorine  has  been  added.  The  number  of  volumes  of 
solution  of  chloride  of  lime  necessary  to  effect  this  is  then  observed,  and  the 
amount  of  the  original  bleaching-powder  to  which  they  correspond  calculated  by 
a  proportion;  the  amount  of  arsenious  acid  employed  being  likewise  known, 


616  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

the  quantity  of  available  chlorine  present  in  the  bleaching-powder  is  calculated 
according  to  the  equation 

As03-f2HO  +  Cl2=As05+2HCl, 

by  which  it  will  be  seen  that  99  parts,  or  one  equivalent,  of  arsenious  acid  cor- 
respond to  71  parts,  or  two  equivalents,  of  available  chlorine.1 
99  :  71  :  :  Arsenious  acid  employed  :  x 
x  =  Available  chlorine. 

The  method  most  commonly  used,  however,  for  determining  the  value  of  spe- 
cimens of  bleaching-powder,  is  to  ascertain  the  quantity  of  the  latter  which  is 
required  to  peroxidize  a  known  weight  of  the  green  sulphate  of  iron. 

Pure  crystals  of  the  sulphate  are  powdered  and  dried,  by  pressure  between 
folds  of  blotting  paper  ;  about  50  grains  of  the  powder  are  accurately  weighed, 
and  dissolved  in  about  1000  grain-measures  of  cold  water;  the  solution  is  then 
acidified  with  sulphuric  acid. 

The  solution  of  bleaching-powder,  prepared  as  in  the  last  method,  is  then 
poured  from  a  burette  into  the  liquid,  until  the  latter  ceases  to  give  a  blue  pre- 
cipitate in  a  drop  of  solution  of  ferricyanide  of  potassium  (placed  on  a  white 
plate),  showing  that  all  the  oxide  of  iron  has  been  converted  into  sesquioxide. 
The  amount  of  bleaching-powder  employed  is  then  calculated,  and  the  available 
chlorine  deduced  according  to  the  equation 


by  which  we  see  that  278  parts,  or  2  eqs.,  of  crystallized  sulphate  of  iron  (FeO. 
S03.HO-f  6Aq)  correspond  to  35.5  parts,  or  1  eq.,  of  chlorine.3 
278  :  35.5  :  :  Sulphate  of  iron  employed  :  x 
x  =  Available  chlorine. 

ALKALIMETRY. 

Fie-  "8  §  434.  The  methods  of  determining  the  amount  of  available  alkali 
contained  in  various  specimens  of  commercial  potash  and  soda  are  known 
by  the  name  of  alkalimetry.  We  shall  first  consider  the  valuation  of 
potash,  and  subsequently  the  modifications  necessary  in  the  case  of 
soda. 

The  older  alkalimetrical  process  consists  in  ascertaining  how  many 
measures  of  dilute  sulphuric  acid  of  known  strength  are  required  to 
neutralize  a  given  quantity  of  carbonate  of  potassa.  For  this  purpose  a 
test-acid  is  first  prepared  by  mixing  about  1000  grs.  of  pure  oil  of  vitriol 
with  about  10,000  grs.  of  water  ;  this  acid  is  graduated  in  the  following 
manner  ;  about  20  grs.  of  perfectly  pure  and  dry  carbonate  of  soda  are 
accurately  weighed  and  dissolved  in  water  ;  the  solution  is  colored  blue 
with  a  few  drops  of  tincture  of  litmus,  and  the  test-acid  slowly  added 
from  a  graduated  burette,  the  liquid  being  constantly  stirred.  The 
first  addition  of  acid  merely  converts  the  carbonate  of  soda  into  bicar- 
bonate ;  carbonic  acid  is  afterwards  liberated,  and  colors  the  litmus 
wine-red,  but  when  an  excess  of  acid  is  added,  a  bright  red  tint  is  pro- 
duced, which  indicates  that  the  operation  is  completed.  Having  now 
observed  the  number  of  measures  of  dilute  acid  employed,  we  have  only 
to  calculate  the  amount  of  real  acid  which  they  contain. 

1  Penot  has  modified  this  process.     He  dissolves  4.44  parts  of  arsenious  acid,  and  13 
parts  of  crystallized  carbonate  of  soda  in  water,  and  adds  this  solution,  from  a  burette, 
to  the  solution  of  a  known  weight  of  chloride  of  lime,  until  the  liquid  no  longer  produces 
a  blue  color  upon  a  test-paper  impregnated  with  1  part  of  iodine,  7  parts  of  crystallized 
carbonate  of  soda,  and  3  parts  of  starch,  heated  with  water  until  the  blue  color  has  dis- 
appeared. 

2  Miiller  has  proposed  a  new  method  for  the  valuation  of  chloride  of  lime.     A  standard 


ALKALIMETRY.  617 


53     :     40  ::  20  grs.  :  x, 

where  x  represents  the  weight  of  SOS  contained  in  the  number  of  measures  of 
test-acid  employed.  In  making  use  of  this  acid  in  alkalimetrical  determinations, 
it  will  only  be  necessary  to  remember  that  1  eq.  or  40  parts  by  weight  of  S03, 
correspond  to  1  eq.  or  47  parts  by  weight  of  available  potassa,  or  31  parts  by 
weight  of  available  soda. 

In  order  to  test  the  carbonate,  a  fair  sample  (about  30  grs.)  is  dissolved  in 
water,  filtered,  if  necessary,  taking  care  to  wash  the  filter,  and  the  solution 
treated  in  exactly  the  s*ame  manner  as  above  described  for  the  solution  of  carbo- 
nate of  soda;  the  amount  of  available  potassa  present  may  then  be  calculated 
from  the  number  of  measures  of  acid  employed. 

This  process  is  very  simple,  but  liable  to  inaccuracy  from  various  sources ;  thus, 
the  sulphide  of  potassium  which  is  generally  contained  in  crude  potashes  neu- 
tralizes a  certain  quantity  of  acid,  thus  indicating  too  large  an  amount  of  alkali. 
Moreover,  the  presence  of  carbonate  of  soda  in  the  specimen  examined  would 
give  rise  to  error. 

The  alkalimetrical  method  of  Fresenius  and  Will  is  far  more  accurate  than  the 
above,  though  less  easy  of  execution.  It  consists  in  decomposing  the  alkaline 
carbonate  by  means  of  sulphuric  acid  in  an  apparatus  so  constructed  that  the 
carbonic  acid  evolved  passes  through  oil  of  vitriol,  and  therefore  carries  off  no 
moisture  with  it,  so  that  the  loss  of  weight  of  the  apparatus  after  the  operation 
represents  the  amount  of  carbonic  acid  which  was  present  in  the  carbonate  exa- 
mined. If  any  sulphide  of  potassium  be  present  in  the  specimen,  a  little  chro- 
mate  of  potassa  is  added,  to  oxidize  the  sulphuretted  hydrogen  which  is  liberated; 
of  course,  the  presence  of  carbonate  of  soda  would  also  give  rise  to  error  in  this 
process,  but,  in  such  a  case,  a  combination  of  the  two  alkalimetrical  methods 
would  be  advantageous. 

The  apparatus  employed  in  this  process  consists  of  two  flasks  (Fig.  78),  the 
generator  A,  which  should  be  capable  of  containing  about  three  fluidounces,  and 
the  drying  flask  B,  of  about  two  ounces  capacity; 
their  necks  should  not  be  very  wide.  The  generating- 
flask  is  fitted  with  a  very  sound  cork,  or,  furnished  with 
two  rather  narrow  tubes,  one  of  which,  b,  is  straight, 
and  passes  nearly  to  the  bottom  of  the  flask,  while 
the  other,  c,  is  bent  twice  at  right  angles,  so  as  to 
form  two  limbs  of  unequal  length,  the  shorter  of 
which  merely  passes  through  the  cork  of  the  gene- 
rator, while  the  longer  reaches  down  to  the  bottom  of 
the  dryfag-jlask  ;  through  the  cork  of  the  latter,  an- 
other straight  tube,  d,  is  inserted,  which  must  only 
project  a  little  into  the  flask.  The  horizontal  por- 
tion of  the  tube  between  the  two  limbs  should  be  of 
such  a  length  that  the  flasks  which  it  connects  may  almost  touch  each  other. 

In  order  to  determine  the  value  of  a  specimen  of  alkali  with  this  apparatus, 
an  accurately  weighed  quantity  (20  or  30  grs.)  is  shaken  out  of  the  weighing- 
bottle  into  the  gen erati rig-flask,  where  it  is  covered  with  about  half  an  inch  of 
water;  the  generator  is  then  connected  with  the  drying-flask,  which  is  about 

solution  of  protochloride  of  tin  is  graduated  by  ascertaining  how  many  measures  are  re- 
quired to  decolorize  a  solution  of  sesquichloride  of  iron,  of  known  strength,  to  which  a 
little  sulphocyanide  of  potassium  has  been  added.  A  measured  quantity  of  the  tin-solu- 
tion is  treated  with  the  solution  of  a  given  amount  of  chloride  of  lime,  and  the  amount  of 
tin  remaining  unconverted  into  bichloride  is  then  determined  by  means  of  the  above  iron- 
solution.  Since  the  tin  corresponds,  equivalent  for  equivalent,  to  the  available  chlorine, 
the  calculation  is  very  simple. 


618  QUANTITATIVE   ANALYSIS;    SPECIAL    METHODS. 

three  parts  filled  with  concentrated  sulphuric  acid.  In  order  to  ascertain  whether 
the  apparatus  is  perfectly  air-tight,  the  straight  tube  a  of  the  generating-flask  is 
closed  with  a  little  plug  of  wax,  and  a  few  bubbles  of  air  are  sucked  out  of  the 
apparatus  through  a  piece  of  caoutchouc  tube  fitted  on  to  the  straight  tube  d  of 
the  washing  flask.  If,  when  the  suction  is  discontinued,  the  sulphuric  acid  rises 
in  the  longer  limb  of  the  bent  tube,  and  retains  its  level  for  a  minute  or  two, 
the  apparatus  is  tight,  but  should  it  fall  gradually,  the  corks  must  be  carefully 
inserted  a  little  further  into  the  necks,  and,  if  this  fail,  they  must  be  replaced 
by  fresh  corks.  When  the  operator  is  assured  of  the  efficiency  of  the  apparatus, 
the  caoutchouc  tube  is  removed,  and  the  weight  of  the  whole  arrangement  carefully 
determined.  The  caoutchouc  tube  is  then  replaced,  and  suction  applied  as  before,  so 
as  to  rarefy  the  air  in  the  generator,  thus  allowing  the  pressure  of  the  external  air 
to  force  a  small  quantity  of  sulphuric  acid  over  when  the  suction  is  discontinued  ; 
care  must  be  taken  not  to  force  over  too  much  acid  at  first ;  the  contact  of  the 
sulphuric  acid  with  the  solution  of  the  carbonate  in  the  generator  gives  rise  to  a 
sudden  evolution  of  carbonic  acid,  the  greater  part  of  which  is  absorbed  by  the 
undecomposed  carbonate,  which  it  converts  into  bicarbonate;  when  the  action 
appears  to  have  ceased,  a  fresh  portion  of  the  acid  is  drawn  over,  and  this  is 
repeated  at  intervals  as  long  as  it  produces  effervescence,  the  quantity  of  acid 
being  regulated  according  to  the  passage  of  the  bubbles  through  the  sulphuric 
acid.  Ab  the  end  of  the  operation,  a  considerable  quantity  of  acid  is  forced  over, 
so  as  to  heat  the  contents  of  the  generating-flask  considerably,  in  order  that  the 
last  traces  of  carbonic  acid  may  be  expelled ;  the  wax-stopper  is  then  removed 
from  the  straight  tube  of  the  generator  (and  placed  upon  the  cork  of  the  latter, 
so  that  it  may  be  weighed,  as  before,  with  the  apparatus),  and  air  slowly  sucked 
through  the  drying-flask  (for  about  five  minutes)  as  long  as  it  tastes  of  carbonic 
acid.  It  will  be  obvious,  that,  at  the  commencement  of  the  operation,  so  much 
acid  should  be  placed  in  the  drying-flask  that  enough  may  be  now  left  to  effect 
the  exsiccation  of  the  gas  which  passes  through  it ;  this  requires  especial  atten- 
tion, on  account  of  the  higher  temperature  of  the  generating-flask,  which  pro- 
motes the  vaporization  of  the  water. 

The  apparatus  is  now  allowed  to  cool,  and  weighed.  The  difference  between 
the  two  weighings  gives  the  amount  of  carbonic  acid. 

Calculation. 

C02     KO.COt    NaO.C02 
22     :     69     or     53  : :  Loss  of  weight  :  x 
x  =  Weight  of  carbonate  ofpotassa  or  of  soda. 

The  amount  of  available  alkali  contained  in  any  specimen  of  the  carbonate  of 
soda  may  be  ascertained  by  the  methods  just  described ;  should  the  specimen  to 
be  examined  contain  any  hydrate  of  soda,  its  amount  may  be  ascertained  by 
making  two  determinations  of  carbonic  acid,  according  to  the  method  of  Frese- 
nius  and  Will,  one  determination  being  made  with  the  original  alkali,  the  other 
with  a  weighed  portion  which  has  been  moistened  with  carbonate  of  ammonia 
and  ignited,  in  order  to  convert  the  hydrate  of  soda  into  carbonate ;  of  course, 
the  increase  of  carbonic  acid  in  the  last  experiment  will  correspond  to  the  amount 
of  hydrate  of  soda  present. 

If  the  soda  to  be  examined  contain  much  carbonate  of  lime,  it  is  necessary  to 
separate  it  before  estimating  the  carbonic  acid ;  this  may  be  effected  by  exhaust- 
ing a  known  weight  of  the  specimen  with  water,  filtering  from  the  carbonate  of 
lime,  taking  care  to  wash  the  filter,  and  evaporating  the  filtrate  and  washings  to 
dryness ;  the  dry  residue  may  be  employed  for  the  determination  of  carbonic  acid. 

The  presence  of  sulphide  of  sodium  and  hyposulphide  of  soda  in  a  specimen  of 
the  carbonate  may  be  ascertained  by  dissolving  in  water,  rendering  the  solution 
slightly  yellow  with  a  few  drops  of  bichromate  of  potassa,  adding  excess  of  hy- 


ANALYSIS    OF   GUNPOWDER.  619 

drochloric  acid,  and  gently  heating;  if  either  of  these  salts  be  present,  the 
solution  will  assume  a  green  color;  in  the  process  of  Fresenius  and  Will,  it  is 
recommended,  if  the  alkali  contain  much  sulphide  of  sodium  or  hyposulphite  of 
soda,  to  introduce  a  little  chromate  of  potassa  into  the  flask  from  which  the  car- 
bonic acid  is  evolved,  in  order  to  oxidize  these  salts,  and  convert  them  into  sul- 
phate of  soda.  If  much  chloride  of  sodium  be  present,  the  excess  of  chromic 
acid  will  give  rise  to  a  disengagement  of  chlorine  from  this  salt ;  this  chlorine, 
being  evolved  as  gas,  will,  of  course,  add  to  the  loss  of  weight  of  the  apparatus, 
and  thus  increase  the  apparent  amount  of  carbonic  acid.  In  order  to  avoid  this, 
the  aqueous  solution  of  a  weighed  quantity  of  the  carbonate  may  be  mixed  with 
a  little  chlorate  of  potassa,  evaporated  to  dryuess  in  a  platinum  dish,  and  gently 
ignited  ;  in  this  way,  the  sulphide  of  sodium  and  hyposulphite  of  soda  will  be 
converted  into  sulphates,  and  the  carbonic  acid  may  now  be  determined  in  the 
residue  without  the  use  of  chromate  of  potassa. 

ACIDIMETRY. 

Determination  of  the  strength  of  a  specimen  of  Dilute  Nitric  Acid  (HON05). 

§  485.  A  weighed  or  measured  portion  of  the  acid  is  tinged  with  litmus,  and 
cautiously  neutralized  with  a  solution  of  carbonate  of  soda  of  known  strength 
(see  Alkalimetry,  §  434),  added  from  a  burette,  until  the  clear  red  color  gives 
place  to  the  wine-red  tint  caused  by  free  carbonic  acid.  The  amount  of  real  acid 
is  then  inferred  from  the  quantity  of  carbonate  of  soda  employed. 

2.  A  more  accurate  method  consists  in  placing  a  certain  quantity  of  the  acid 
in  the  generating-flask  of  a  Fresenius  and  Will's  apparatus,  and  suspending,  by 
means  of  a  horsehair,  a  small  bottle  containing  more  bicarbonate  of  soda1  than 
is  sufficient  to  neutralize  the  acid  employed.  When  the  apparatus  is  arranged 
and  weighed,  as  usual,  the  acid  is  gradually  rinsed  into  the  bicarbonate,  until  no 
more  carbonic  acid  is  evolved,  when  the  generating-flask  is  heated  to  about  130° 
F.,  air  drawn  through  in  the  usual  manner,  as  long  as  it  tastes  of  carbonic  acid, 
the  apparatus  allowed  to  cool,  and  weighed. 

Every  two  equivalents  of  carbonic  acid  evolved  correspond  to  one  equivalent 
of  real  acid  in  the  sample  analyzed. 

This  method  is  applicable  to  the  determination  of  the  strength  of  other  dilute 
acids. 

ANALYSIS  OF  GUNPOWDER. 

§  436.  I.  Determination  of  Moisture. — About  20  grains  of  the  powder,  very 
finely  pulverized,  are  exposed  over  sulphuric  acid,  in  vacuo,  until  a  constant 
weight  is  obtained. 

For  ordinary  purposes,  the  moisture  may  be  determined  by  exposing  the  pow- 
der to  the  temperature  of  the  water-oven,  until  it  ceases  to  lose  weight.  A  slight 
excess  is  generally  obtained  by  this  method,  since  a  small  portion  of  the  sulphur 
in  the  powder  is  expelled,  together  with  the  moisture. 

II.  Determination  of  Nitre. — The  dried  powder  is  transferred  to  a  small 
beaker,  in  which  it  is  drenched  with  about  three  ounces  of  hot  water,  and  allowed 
to  digest  for  some  time  upon  a  sand-bath  at  a  moderate  heat.  It  is  then  thrown 
upon  a  filter  of  known  weight,  previously  moistened,  and  is  washed  with  hot 
water,  until  a  drop  of  the  filtrate,  which  must  be  carefully  collected,  leaves  no 
residue  when  evaporated  upon  platinum  foil.  The  filter  and  residue  are  then 
dried  in  the  water-oven  (or,  still  better,  in  vacua},  until  their  weight  is  constant. 
The  difference  in  weight  between  the  residue  (minus  the  weight  of  the  filter) 
and  the  powder  employed,  will  represent  the  amount  of  nitre. 

1  This  must  be  perfectly  free  from  carbonate. 


620  QUANTITATIVE  ANALYSIS;    SPECIAL   METHODS. 

To  control  this  result,  the  filtrate  and  washings,  obtained  as  above  directed, 
are  carefully  concentrated  in  a  porcelain-dish,  at  a  moderate  heat,  upon  a  sand 
or  air-bath,  and  afterwards  transferred  to  a  weighed  platinum  (or  porcelain)  cap- 
sule,  and  evaporated  to  dryness  on  a  water-bath  ;  the  residue  is  then  exposed  to 
a  temperature  of  300°  F.  (149°  C.),  in  an  air-bath,  until  it  ceases  to  lose  weight. 
The  quantity  of  nitre  is  thus  determined  directly. 

III.  Determination  of  Sulphur. — This  ingredient  may  either  be  determined 
directly,  or  by  the  loss  of  weight  sustained  by  dry  powder,  upon  its  removal. 

Direct  Determination. — 1.  About  20  grains  of  the  dried  powder  are  mixed 
with  an  equal  weight  of  pure  carbonate  of  soda  (or  of  potassa),  about  20  grains 
of  nitre,  and  80  grains  of  pure  chloride  of  sodium  are  then  added,  the  whole 
intimately  mixed,  and  then  submitted  to  fusion  in  a  platinum  crucible,  the  ope- 
ration being  conducted,  and  the  sulphuric  acid  determined  in  the  fused  mass,  in 
the  manner  directed  at  p.  599. 

2.  A  tube  of  hard  glass,  provided  with  two  bulbs,  is  accurately  weighed  ; 
about  20  grains  of  dried  powder  are  introduced  into  one  of  the  bulbs,  and  the 
weight  of  the  tube  and  powder  noted  (the  difference  between  the  two  weights 
will  represent  the  amount  of  powder  employed).  The  extremity  of  the  tube 
nearest  to  the  bulb  containing  the  powder  is  then  attached  to  an  apparatus  in 
which  dry  hydrogen  is  disengaged.  A  slow  current  of  gas  is  allowed  to  pass 
through  the  tube ;  as  soon  as  the  atmospheric  air  is  completely  expelled,  the 
bulb  containing  the  powder  is  moderately  heated  by  means  of  a  spirit-lamp,  when 
the  sulphur  will  vaporize,  and  pass  over  into  the  second  bulb,  where  it  will  again 
condense;  the  space  of  tube  between  the  two  bulbs  must  be  warmed  with  the 
spirit-lamp  from  to  time,  to  prevent  any  sulphur  from  condensing  there.  When 
no  more  sulphur  is  expelled  from  the  powder,  which  is  finally  exposed  to  a  te.m- 
perature  approaching  dull  redness,  the  tube  is  allowed  to  become  nearly  cool ;  it 
is  then  carefully  cut  with  a  very  sharp  file  between  the  two  bulbs,  and  each 
part  is  afterwards  weighed,  cleaned  out,  and  reweighed.  The  amount  of  sulphur 
found  in  the  second  bulb  should  correspond,  within  the  limits  of  error  (0.5  per 
cent,  loss),  to  the  difference  between  the  first  and  the  final  weight  of  the  powder. 

A  slight  loss  of  sulphur  by  this  method  is  unavoidable,  small  portions  being 
carried  off  mechanically  by  the  current  of  hydrogen,  if  ever  so  slow,  while  a 
small  quantity  is  also  converted  into  hydrosulphuric  acid. 

By  adopting  the  following  modification  of  this  method,  very  accurate  results 
may,  however,  be  arrived  at : — 

Instead  of  a  tube  with  two  bulbs,  one  of  rather  wider  bore,  about  8  inches  in 
length,  is  employed,  provided  with  only  one  bulb,  at  about  2  inches  from  one 
extremity  of  the  tube.  A  small  plug  of  dry  asbestos  having  been  introduced 
into  the  long  arm  of  the  tube,  about  \  inch  distant  from  the  bulb,  the  former  is 
filled  with  thin  filaments  of  dry  bright  copper,  or  of  the  finely  divided  metal, 
reduced  from  the  oxide  by  hydrogen.  The  tube  is  then  accurately  weighed,  the 
dried  powder  (from  which  the  nitre  has  been  removed)  introduced  into  the  bulb, 
and  the  weight  again  ascertained  (the  difference  will  give  the  amount  of  powder 
employed).  The  operation  is  then  conducted  as  before,  with  this  difference,  that 
the  copper  is  first  raised  to  a  red  heat,  and  maintained  at  that  temperature, 
before  the  sulphur  is  expelled  from  the  powder.  The  sulphur-vapor,  coming  in 
contact  with  the  heated  metal,  will  at  once  combine  with  it,  and  no  loss  what- 
ever is  sustained.  When  the  operation  is  completed,  and  the  tube  is  cooled 
down  sufficiently  to  be  handled  without  inconvenience,  it  is  carefully  cut  between 
the  asbestos-plug  and  the  bulb;  the  latter,  containing  the  charcoal,  is  then 
placed  on  the  balance  while  warm,  and  rapidly  weighed ;  the  loss  of  weight 
expresses  the  amount  of  sulphur,  which  may  also  be  directly  inferred  from  the 
increase  of  weight  of  the  tube  containing  the  copper. 

Indirect  Determination. — A  weighed  portion  of  the  dry  residue  of  carbon  and 
sulphur  left  on  extracting  the  powder  with  water,  is  introduced  into  a  small 


ANALYSIS   OF   INSOLUBLE    SILICATES.  621 

flask,  and  boiled  for  some  time  with  a  solution  of  sulphide  of  potassium  or  of 
sodium,  or  of  sulphite  of  potassa  or  soda,  until  the  whole  of  the  sulphur  is  re- 
moved. The  carbon  is  then  collected  upon  a  weighed  filter,  well  washed,  dried 
in  a  water-oven,  and  weighed;  the  difference  between  this  weight  and  that  of 
the  original  residue  of  carbon  and  sulphur  indicates  the  amount  of  the  latter, 
which  must  now  be  calculated  for  so  much  of  this  residue  as  would  be  furnished 
by  100  parts  of  gunpowder;  the  result  is  the  percentage  of  sulphur. 

The  alkaline  sulphides  or  sulphites  employed  to  dissolve  the  sulphur  must  be 
perfect^  free  from  caustic  alkali,  since  the  latter  is  capable  of  attacking  char- 
coal which  has  not  been  very  thoroughly  charred.  A  mixture  of  bisulphide  of 
carbon  and  alcohol  may  also  be  employed  to  extract  the  sulphur. 

The  results  obtained  by  the  indirect  method  are  invariably  too  low,  since  the 
extraction  of  the  sulphur  is  never  complete. 

IV.  Determination  of  Carbon. — The  amount  of  this  constituent  will  have 
been  ascertained  by  difference,  and  controlled  by  direct  weighing  in  the  pre- 
ceding determinations.  It  is  sometimes  necessary,  especially  when  charbon 
roux  has  been  employed,  to  determine  the  amount  of  hydrogen  contained  in  the 
charcoal;  this  is  effected  by  burning  a  weighed  quantity  with  oxide  of  copper 
in  the  manner  to  be  described  in  a  future  part  of  the  work,  under  the  head  of 
Organic  Analysis. 

ANALYSIS  OF  INSOLUBLE  SILICATES. 
ANALYSIS  OF  GLASS. 

§  437.  It  is  of  the  highest  importance  that  the  glass  to  be  examined  should 
be  first  reduced  to  the  most  minute  state  of  division;  this  is  effected  by  leviga- 
tion,  in  the  manner  described  at  p.  86. 

The  general  method  to  be  pursued  in  the  analysis  of  glass  containing  lead 
differs  necessarily  somewhat  from  that  employed  in  the  analysis  of  all  other 
kinds  of  glass.  By  the  following  methods,  all  ordinary  constituents  of  glass 
may  be  determined;  if  the  specimen  to  be  examined  contain  any  of  the  more 
rarely  occurring  bases,  these  may  be  readily  determined,  according  to  the  appro- 
priate methods. 

Analysis  of  Glass  containing  no  Lead. — From  20  to  30  grains  of  the  finely- 
powdered  glass,  which  has  been  first  thoroughly  dried,  are  mixed  in  a  platinum 
crucible  of  sufficient  capacity,  with  from  3.5  to  4  times  that  weight  of  pure, 
dried,  and  finely-powdered  carbonate  of  soda.  The  mixture  may  be  effected  by 
stirring  with  a  small  glass  rod,  rounded  at  the  extremity;  this  stirring  must  be 
continued  until  the  mixture  appears  perfectly  uniform ;  any  particles  adhering 
to  the  rod  may  afterwards  be  carefully  removed  into  the  crucible  by  means  of  a 
pigeon's  feather.  The  crucible,  having  been  carefully  closed,  is  placed  in  a 
moderate  sized  Hessian  crucible,  into  which  has  been  tightly  pressed  a  quantity 
of  calcined  magnesia  sufficient  to  fill  it  to  about  one-half;  the  platinum  crucible 
is  carefully  pressed  into  this  bed  of  magnesia  to  such  an  extent  as  to  be  firmly 
supported  thereby  on  all  sides ;  it  is  thus  maintained  in  a  secure  position  during 
its  l?ubsequent  exposure  to  a  furnace-heat,  and  is  prevented  from  coming  in  con- 
tact with  the  Hessian  crucible,  to  the  bottom  or  sides  of  which  it  might  other- 
wise become  attached  during  the  operation.  The  Hessian  crucible  is  now  closed 
with  a  good  cover,  and  placed  upon  a  brick  support  in  an  ordinary  furnace,1 

1  This  fusion  may  be  more  conveniently  effected  over  a  good  gas-burner,  especially  if 
a  mixture  of  pure  carbonate  of  potassa  and  soda  be  employed,  and  the  crucible  placed  in 
a  jacket.  In  order  to  avoid  violent  effervescence,  the  mixture  should  be  fritted  by  a 
gentle  heat  for  half  an  hour,  so  that  most  of  the  carbonic  acid  shall  be  expelled  before 
the  heat  is  so  far  increased  as  to  fuse  the  mass. 


622  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

containing  only  a  small  fire ;  the  crucible  is  carefully  surrounded  with  coke,  and 
the  temperature  then  gradually  raised,  until  the  crucible  has  attained  a  bright 
red  heat,  in  which  state  it  is  maintained  for  nearly  an  hour ;  it  is  then  allowed 
to  cool  gradually.  When  the  temperature  is  sufficiently  low,  the  platinum  cru- 
cible is  removed  and  opened1  (any  adhering  particles  of  magnesia  having  been 
first  carefully  removed  from  the  exterior).  It  is  generally  found  that  portions 
of  the  mass  have  been  thrown  upon  the  inner  surface  of  the  cover,  by  the  effer- 
vescence occasioned  by  the  escape  of  carbonic  acid  during  the  fusion ;  both  -the 
crucible  with  its  contents  and  the  cover,  are  therefore  introduced  into  a  mode- 
rate-sized beaker,  which  is  then  filled  about  one-third  with  water,  strongly  acidu- 
lated with  pure  hydrochloric  acid;  the  mouth  of  the  beaker  is  closed  with  a 
light  inverted  funnel,  immediately  upon  the  introduction  of  the  liquid,  to  pre- 
vent any  loss  from  the  effervescence  that  ensues  as  the  fused  mass  comes  in 
contact  with  the  acid ;  the  beaker  is  then  maintained  at  a  gentle  heat,  until  the 
contents  of  the  crucible  are  completely  detached.  When  the  glass  under  exami- 
nation contains  much  manganese,  water  alone  must  be  used  for  extracting  the 
fused  mass  from  the  crucible,  since  hydrochloric  acid  would  be  decomposed  by 
the  manganic  acid  formed  in  the  fusion,  chlorine  being  evolved,  which  would  act 
injuriously  on  the  platinum  crucible.  In  such  cases,  after  the  fused  mass  has 
been  perfectly  removed  from  the  crucible,  an  excess  of  hydrochloric  acid  is  very 
gradually  added  ta  the  aqueous  solution.  An  acid  solution  of  the  mass  having 
been  obtained3  (the  crucible  and  lid  being  carefully  removed  from  the  beaker 
and  washed,  over  the  latter,  with  a  little  distilled  water),  it  is  carefully  trans- 
ferred to  a  porcelain  dish,  and  evaporated  to  dryness,  in  an  air-bath,  at  a  mode- 
rate temperature. 

The  residue  obtained  by  this  evaporation  is  moistened,  when  cool,  with  con- 
centrated hydrochloric  acid,  and  allowed  to  digest  for  some  time.  Water  is  then 
added,  and  the  insoluble  residue,  which  consists  of  the  whole  of  the  silicic  acid, 
collected  upon  a  filter,  thoroughly  washed  (the  filtrate  and  washings  being  pre- 
served), dried,  ignited  according  to  the  usual  method,  and  weighed.  Since 
ignited  silica  is  very  apt  to  be  carried  away  by  the  stream  of  gas  evolved  during 
the  incineration  of  the  filter,  it  is  advisable  to  transfer  as  much  of  the  silica  as 
possible  to  a  weighed  porcelain  crucible,  in  which  it  is  ignited,  apart  from  the 
filter,  which  is  subsequently  incinerated  in  a  platinum  crucible,  the  ash  being 
afterwards  added  to  the  silica. 

In  the  hydrochloric  acid  solution,  together  with  the  washings,  obtained  as 
above,  the  various  bases  existing  in  combination  with  the  silicic  acid  in  the  glass, 
with  the  exception  of  the  alkalies,  are  determined. 

This  solution  is  heated  with  a  little  nitric  acid,  to  peroxidize  any  iron ;  it  is 
then  mixed  with  a  considerable  quantity  of  solution  of  chloride  of  ammonium,  to 
retain  the  magnesia  in  solution  (and  also  the  protoxide  of  manganese,  if  there  be 
any),  and  afterwards  with  ammonia  in  excess,  which  precipitates  the  sesquioxide 
of  iron  and  alumina  together ;  this  precipitate  is  washed,  dried,  ignited,  and 
weighed ;  it  is  afterwards  dissolved  in  hydrochloric  acid  ;  this  solution  is  then 
digested  at  a  gentle  heat  with  a  considerable  excess  of  pure  potassa,  which  retains 
the  alumina  in  solution,  while  the  sesquioxide  of  iron  is  precipitated.  This.pre- 
cipitate  frequently  retains  a  small  portion  of  the  alumina,  and  also  of  the  potassa 

1  If  the  glass  contained  manganese,  the  fused  mass  obtained  as  above  will  possess  a 
bluish  green  or  greenish  color,  according  to  the  quantity  present. 

2  A  quantity  of  the  silicic  acid,  in  the  gelatinous  state,  is  generally  suspended  in  the 
solution,  a  portion  only  being  dissolved  in  the  acid,  unless  a  very  large  excess  of  alkaline 
carbonate  was  employed  in  the  fusion.      To  ascertain  whether  the  glass  has  been  per- 
fectly decomposed  by  the  fusion,  the  liquid  is  stirred  with  a  glass  rod,  which  is  allowed 
to  rub  against  the  sides  and  bottom  of  the  beaker ;  any  undecomposed  glass  would  be 
immediately  indicated  by  a  grating  noise. 


ANALYSIS   OP  GLASS.  623 

that  has  been  used  as  precipitant;  it  is  therefore  collected,  and  again  dissolved  in 
hydrochloric  acid,  and  reprecipitated  by  excess  of  potassa,1  filtered  off  (the  fil- 
trate, &c.  being  added  to  the  other  potassa-solution),  and,  after  being  thoroughly 
washed,  dried,  and  weighed  as  sesquioxide  of  iron  (p.  586).  The  difference 
between  the  .weight  of  this  sesquioxide  and  that  of  the  first  precipitate,  would 
give  the  amount  of  alumina  present  in  the  glass,  which  may  also  be  directly 
determined  in  the  potassa-solution  from  which  the  iron  was  separated  (provided 
the  potassa  employed  was  free  from  alumina)  by  acidifying  with  hydrochloric 
acid,  and  precipitating  the  hydrate  of  alumina  by  excess  of  ammonia  (p.  587). 

In  the  solution  from  which  the  alumina  and  sesquioxide  of  iron  have  been 
separated,  the  lime  and  magnesia  are  determined  in  the  manner  described  in  the 
analysis  of  limestones  (p.  603). 

The  alkalies  present  in  the  glass  must,  of  course,  be  determined  in  a  fresh 
portion  j  the  following  is  the  most  approved  method  : — 

A  flat-bottomed,  cylindrical  box,  about  six  inches  in  diameter,  and  four  inches 
high,  is  provided  with  a  tightly-fitting  leaden  cover.  The  bottom  of  the  box  is 
then  covered  with  a  layer  of  about  half  an  inch  of  powdered  fluor-spar,  which 
should  be  free  from  silica  and  galena,  and  to  this  is  added  sufficient  concentrated 
sulphuric  acid  to  form  a  thick  paste.  A  weighed  portion,  about  80  grains,  of  the 
finely-powdered  glass,  is  placed  in  a  platinum  dish,  and  covered  with  strong  solu- 
tion of  ammonia.  This  dish  having  been  placed  in  the  centre  of  the  box,  sup- 
ported upon  a  leaden  ring  of  about  1£  inch  in  height,  so  as  not  to  come  in  contact 
with  the  fluor-spar,  the  cover  is  adjusted,  and  the  box  placed  on  a  sand-bath, 
where  it  is  maintained  for  some  time  at  a  gentle  heat. 

The  sulphuric  acid  soon  acts  upon  the  fluoride  of  calcium  (fluor-spar),  giving 
rise  to  the  evolution  of  hydrofluoric  acid,  which  is  immediately  absorbed  by  the 
ammonia  with  which  the  powdered  glass  is  covered.  The  resulting  fluoride  of 
ammonium  acts  rapidly  on  the  silicic  acid  of  the  glass,  terfluoride  of  silicon  and 
water  being  produced,  and  the  bases  thus  gradually  liberated  from  their  combi- 
nations with  silicic  acid. 

After  having  been  subjected  to  the  action  of  the  hydrofluoric  acid  for  about 
10  or  12  hours,  the  dish  should  be  placed  in  an  air-bath,  its  contents  completely 
dried,  gently  ignited,  until  no  more  fumes  are  evolved,  and  weighed.  The  con- 
tents of  the  dish  are  then  again  moistened  with  ammonia,  and  the  whole  opera- 
tion repeated,  until  an  hour's  exposure  to  the  action  of  the  hydrofluoric  acid 
produces  no  alteration  in  the  weight  of  the  dry  mass. 

After  the  complete  decomposition,  the  dry  residue,  containing  the  metals  in 
the  form  of  fluorides,  is  digested  at  a  gentle  heat  with  concentrated  hydrochloric 
acid,  a  little  water  being  subsequently  added,  until  the  whole  is  dissolved.  The 
solution  is  then  evaporated  to  dryness,  the  residue  redissolved  in  a  little  water, 
and  heated  with  hydrate  of  baryta,  which  must  be  perfectly  free  from  alkalies, 
until  it  has  a  distinct  alkaline  reaction.  The  liquid  is  then  filtered  from  the  pre- 
cipitate (sesquioxide  of  iron,  alumina,  magnesia),  the  latter  washed  with  about 
half  a  pint  of  hot  water,  which  is  afterwards  mixed  with  the  filtrate.  The  whole 
solution  is  mixed  with  a  little  free  ammonia,  and  carbonate  of  ammonia  added 
sufficient  to  precipitate  the  whole  of  the  alkaline  earths  (baryta  and  lime),  which 
may  be  aided  by  a  gentle  heat.  The  precipitated  carbonates  having  been  fil- 
tered off  and  washed,  the  solution  is  evaporated  on  a  sand-bath  to  a  small  bulk, 
when  it  is  transferred  to  a  weighed  platinum  or  porcelain  dish,  evaporated  to 
dryness  in  an  air-bath,  and  afterwards  very  gradually  ignited,  until  no  more 
fumes  are  evolved.  It  is  advisable  to  cover  the  dish  with  a  piece  of  platinum 

1  When  the  quantity  of  sesquioxide  of  iron  present  is  considerable,  and  that  of  alumina 
comparatively  small,  it  is  necessary  to  repeat  this  operation  three  or  four  times,  in  order 
to  insure  the  perfect  separation  of  these  two  substances. 


624  QUANTITATIVE   ANALYSIS]    SPECIAL   METHODS. 

foil,  in  order  to  avoid  loss  by  spirting.  The  alkaline  chlorides  should  be  rapidly 
weighed,  whilst  still  rather  warm,  to  prevent  absorption  of  moisture. 

The  amounts  of  potassa  and  soda  in  these  chlorides  are  determined  as  in  Ro- 
chelle  salt  (p.  602). 

The  older  method  for  the  determination  of  alkalies,  which  is  still«employed  by 
some  chemists,  is  as  follows: — 

About  20  grains  of  the  finely  powdered  glass  are  intimately  mixed  with  from 
8  to  4  parts  of  dry  hydrate  of  baryta  (which  has  been  carefully  tested  for  alka- 
lies), and  pretty  strongly  ignited  in  a  platinum 'crucible,1  for  about  an  hour,  over 
a  good  gas-burner.  The  agglutinated  mass  is  then  detached  from  the  crucible, 
by  gently  squeezing  the  latter,  and  treated  in  a  beaker,  with  dilute  hydrochloric 
acid,  in  the  manner  described  at  p.  622.  If  necessary,  the  crucible  arid  its  cover 
may  also  be  immersed  in  the  acid.  The  solution  is  carefully  evaporated  to  dry- 
ness  in  an  air-bath,  the  residue  digested  with  a  little  water,  and  hydrate  of  baryta 
added,  till  the  reaction  is  distinctly  alkaline.  The  precipitate  is  removed  by 
filtration,  and  repeatedly  washed  with  hot  water,  which  is  allowed  to  mix  with 
the  filtrate.  The  latter  is  then  treated  with  ammonia  and  carbonate  of  ammonia, 
and  the  subsequent  processes  conducted  as  described  above. 

Analysis  of  Glass  containing  Lead. — The  silicic  acid  cannot  be  determined  in 
glasses  of  this  class  by  fusion  with  alkaline  carbonates,  as  just  now  described, 
since  the  presence  of  lead  forbids  the  use  of  platinum  crucibles,  whilst  porcelain 
crucibles  cannot  be  employed,  as  the  alkaline  carbonate  would  attack  them, 
taking  up  from  their  surface  a  portion  of  silica. 

The  following  method,  in  which  the  silicic  acid  is  determined  indirectly,  ap- 
pears to  yield  correct  results. 

About  30  grains  of  the  finely  powdered  glass  are  decomposed  by  fluoride  of 
ammonium  in  the  manner  described  above ;  the  resulting  mass  is  evaporated  to 
dryness,  and  the  residue  digested  with  pure  concentrated  nitric  acid  at  a  gentle 
heat,  whereby  the  various  bases  are  converted  into  nitrates.  Water  is  after- 
wards added,  and  the  liquid  evaporated  to  dryness  in  an  air-bath.  The  residue 
is  dissolved  in  much  water,  with  two  or  three  drops  of  dilute  nitric  acid,  and  the 
solution  completely  saturated  with  sulphuretted  hydrogen.  The  precipitated 
sulphide  of  lead  is  collected  upon  a  filter  of  known  ash,  washed  and  set  aside  to 
dry,  the  solution  is  evaporated  to  expel  excess  of  sulphuretted  hydrogen,  and 
subsequently  treated  in  the  manner  already  described,  p.  622,  for  the  determi- 
nation of  iron,  alumina,  lime,  and  magnesia.  The  dried  sulphide  of  lead  is 
transferred  from  the  filter  to  a  weighed  porcelain  crucible,  the  filter  is  then  held 
over  the  crucible  with  a  pair  of  forceps,  kindled  and  allowed  to  smoulder  until 
entirely  consumed,  the  ash  being  allowed  to  fall  into  the  crucible.  The  contents 
of  the  latter  are  then  moistened  with  concentrated  nitric  acid,  very  carefully 
dried  in  an  air-bath,  afterwards  ignited,  and  weighed. 

The  alkalies  are  determined  in  a  separate  portion  of  glass,  as  directed  p.  623. 

The  difference  between  the  original  weight  of  the  glass  and  joint  weight  of 
the  various  oxides  obtained  by  analysis,  would  give  the  amount  of  silicic  acid 
present,  though  somewhat  augmented  by  the  loss  which  is  inevitable  in  the  de- 
termination of  the  other  constituents. 

CAST-IRON. 

§  438.  A  piece  of  gray  cast-iron  should  be  taken;  it  may  be  reduced  to  a  fine 
state  of  division  with  the  aid  of  a  very  sharp  file. 

The  only  constituents  which  it  is  generally  necessary  to  determine  in  cast-iron, 

1  As  long  as  the  temperature  is  kept  within  moderate  limits,  the  platinum  crucible  is 
not  attacked  by  the  baryta ;  the  use  of  a  silver  crucible  is  attended  with  danger,  on  ac- 
count of  the  comparatively  easy  fusibility  of  the  metal. 


ANALYSIS    OF   CAST-IRON.  625 

are  iron,  carbon  (combined  and  unco mbined},  sulphur,  phosphorus,  silicon,  man- 
ganese, calcium,  and  sodium.1 

Determination  of  the  total  amount  of  Carbon. — About  50  grains  of  the  fine 
iron  filings  are  mixed  with  about  20  times  as  much  chromate  of  lead,  in  a  shal- 
low porcelain  mortar ;  |  of  the  mixture  is  set  aside,  and  the  remaining  |  are 
intimately  mixed  with  about  50  or  60  grains  of  chlorate  of  potassa. 

This  mixture  is  then  introduced  into  a  combustion-tube  of  hard  glass,  similar 
to  those  employed  in  organic  analysis.  It  is  well  to  introduce  first  an  inch  or 
two  of  a  pure  mixture  of  chlorate  of  potassa  and  chromate  of  lead.  The  re- 
mainder of  the  mixture  is  then  also  introduced  into  the  tube,  and  the  whole 
shaken  down  so  as  to  allow  a  free  passage  for  the  gas  evolved.  The  tube  is 
placed  in  a  Liebig's  combustion-furnace,  and  connected,  by  a  very  sound  cork, 
with  a  chloride  of  calcium  tube,  to  absorb  any  water  which  may  be  evolved.  To 
the  chloride  of  calcium  tube  is  attached,  by  means  of  a  caoutchouc  connector,  a 
Liebig's  potassa-apparatus,  containing  a  solution  of  potassa  of  sp.  gr.  1.27.  The 
weight  of  this  apparatus  must  be  most  accurately  determined  at  the  commence- 
ment of  the  experiment. 

In  order  to  ascertain  whether  the  apparatus  is  tight,  a  few  bubbles  of  air  are 
cautiously  sucked  out  through  the  potassa-apparatus,  which  is  inclined  for  that 
purpose,  so  that  the  orifice  of  the  egress- tube  may  be  from  potassa  (as  it  should 
be  throughout  the  experiment).  If,  after  a  few  bubbles  of  air  have  been  with- 
drawn, the  potassa  rises  in  the  other  limb  of  the  tube  to  a  higher  level  than  in 
the  rest  of  the  apparatus,  and  maintains  its  level  for  some  time,  it  is  a  proof  that 
the  apparatus  is  air-tight. 

The  tube  is  now  gradually  and  carefully  heated  throughout  its  whole  length, 
commencing  in  front,  with  redhot  charcoal,  the  fire  being  regulated  with  a  re- 
gard to  the  rapidity  of  the  passage  of  bubbles  through  the  potassa-apparatus. 

When  the  fire  is  carried  to  the  hinder  extremity  of  the  tube,  pure  oxygen  will 
be  disengaged  from  the  mixture  of  the  chlorate  of  potassa  and  chromate  of  lead, 
and  will  sweep  the  whole  of  the  carbonic  acid  out  of  the  tube.  At  the  conclu- 
sion, the  fire  is  raised  by  fanning  with  a  millboard-fan,  and  the  heat  continued 
as  long  as  any  bubbles  of  gas  are  evolved ;  the  operation  is  terminated  by  nip- 
ping off  the  extreme  point  of  the  tube,  and  the  potassa-bulbs  are  then  detached 
and  weighed. 

The  increase  of  weight  of  the  potassa-apparatus  after  the  experiment,  indicates 
the  amount  of  carbonic  acid  produced,  since  the  phosphorus  and  sulphur  have 
remained  in  the  tube  in  their  highest  states  of  oxidation. 

Calculation. 

rn         f1 
o  (./«         \j 

2z     :    6  : :    Weight  of  carbonic  acid  :  x 
x  =  Weight  of  carbon. 

Determination  ofuncombined  Carbon  and  Silicon. — About  100  grains  of  the 
iron  filings  are  gently  heated  with  dilute  hydrochloric  acid,  until  all  action  has 
ceased,  the  residue,  consisting  of  particles  of  graphite  and  silica,  is  collected  upon 
a  small  weighed  filter,  well  washed,  and  dried.  A  little  ether  is  then  poured  over 
it,  to  remove  any  oily  hydrocarbons  which  might  have  adhered,  the  filter  again 
dried  at  212°  F.,  and  weighed.  It  is  then  incinerated  in  the  usual  manner,  the 
combustion  of  the  graphite  being  effected  in  a  current  of  oxygen.  When  the 
weight  of  the  filter-ash  is  deducted,  the  amount  of  the  silica  is  known,  and  must 
be  subtracted  from  that  of  the  original  residue,  to  obtain  the  weight  of  the  un- 
combined  carbon. 

1  A  method  which  should  include  the  rare  metals  contained  in  cast-iron  'would  be  far 
too  laborious  to  be  generally  adopted  for  practice. 
40 


626  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

If  any  silica  is  contained  in  the  solution,  it  may  be  determined  in  the  usual 
manner  (p.  594). 

Determination  of  Iron,  Manganese,  Calcium,  and  Sodium. — The  filtrate  from 
the  silica  is  heated  with  nitric  acid,  in  order  toperoxidize  the  iron,  the  excess  of 
acid  evaporated,  and,  at  the  same  time,  the  solution  concentrated  to  a  small  bulk, 
and  the  iron  separated  as  succinate  or  benzoate  (p.  586). 

The  solution  filtered  from  the  iron-precipitate  is  evaporated  to  dryness,  and 
the  residue  heated,  to  expel  ammoniacal  salts.  It  is  then  dissolved  in  hydro- 
chloric acid,  a  slight  excess  of  ammonia  added,  then  some  sulphide  of  ammonium, 
the  solution  allowed  to  stand  for  some  hours,  and  gently  heated.  The  precipi- 
tated sulphide  of  manganese  is  filtered  off,  and  treated  as  at  p.  588. 

The  lime  in  the  filtrate  is  precipitated  as  oxalate  (p.  590). 

The  filtrate  from  the  oxalate  of  lime  is  carefully  evaporated  to  dryness,  the 
residue  ignited,  and  the  sodium  determined  as  chloride  (p.  591). 

Determination  of  Sulphur. — A  considerable  quantity  of  the  iron  (varying 
with  the  amount  of  sulphur  present)  is  dissolved,  in  a  large  flask,  in  fuming 
nitric  acid,  the  solution  evaporated  to  expel  the  greater  excess  of  acid,  largely 
diluted  with  water,  and  the  sulphuric  acid  precipitated  as  sulphate  of  baryta, 
which  must  be  very  well  washed  with  boiling  water  (p.  592),  dried,  ignited,  and 
weighed. 

Determination  of  the  Phosphorus. — The  iron  is  dissolved  in  aqua,  regia,  the 
solution  carefully  evaporated  to  dryness  to  expel  excess  of  acid,  the  residue 
treated  with  water,  and  mixed  with  a  considerable  excess  of  hydrosulphate  of 
sulphide  of  potassium,  with  which  it  is  digested,  at  a  temperature  approaching 
the  boiling-point,  for  several  hours,  when  the  iron  and  manganese  are  entirely 
converted  into  sulphides,  and  the  phosphoric  acid  passes  into  solution.  The  lat- 
ter is  mixed  with  a  slight  excess  of  hydrochloric  acid,  to  decompose  the  excess 
of  sulphide  of  potassium,  the  solution  boiled  until  no  more  sulphuretted  hydrogen 
is  evolved,  filtered,  if  necessary,  from  the  separated  sulphur,  and  the  phosphoric 
acid  determined  as  phosphate  of  iron  (p.  598). 

ULTRAMARINE. 
(The  artificial  pigment  is  to  be  employed.) 

§  439.  The  chief  constituents  of  ultramarine  are :  silica,  sulphuric  acid,  sul- 
phur, alumina,  soda,  lime,  oxide  of  iron. 

The  pigment  is  dried  in  the  water-bath  till  its  weight  ceases  to  vary. 

Determination  of  Sulphur. — About  20  grains  of  the  compound  are  oxidized, 
as  usual,  with  the  strongest  nitric  acid,  and  the  sulphur  determined  as  sulphate 
of  baryta,  from  the  weight  of  which  must  be  deducted  that  of  the  sulphate  of 
baryta  furnished  by  the  sulphuric  acid  already  existing  in  the  compound. 

Determination  of  the  Remaining  Constituents. — About  50  grains  are  boiled 
with  concentrated  hydrochloric  acid,  in  a  flask  ;  the  solution  together  with  the 
residue  of  silica,  transferred  to  a  dish  and  carefully  evaporated  to  dryness  in  the 
air-bath ;  the  dry  mass  is  digested  with  dilute  hydrochloric  acid,  the  silica  filtered 
off  and  determined  as  usual. 

The  filtrate  and  washings  are  evaporated  to  a  small  bulk,  introduced  into  a  dry 
weighed  flask,  and  the  weight  of  the  solution  determined.  About  one-fourth  of 
the  solution  is  then  poured  into  a  beaker,  and  the  sulphuric  acid  determined  as 
sulphate  of  baryta.  The  flask,  with  the  remainder  of  the  solution  is  again 
weighed,  and  then  the  amount  which  has  been  employed  is  determined. 

The  remainder  of  the  solution  is  boiled  with  nitric  acid,  to  peroxidize  the  iron, 
mixed  with  ammonia  in  excess,  and  the  precipitated  alumina  and  sesquioxide  of 
iron  determined  (if  the  amount  of  the  latter  be  sufficient)  as  in  the  analysis  of 
clay  (p.  605). 


SEPARATION    OF   CHLORINE,    BROMINE,    AND   IODINE.          627 

The  lime  is  precipitated  from  the  filtrate  as  oxalate,  and  the  soda  subsequently 
determined  as  chloride  of  sodium. 

SEPARATION  OF  CHLORINE,  BROMINE,  AND  IODINE. 

§  440.  It  occasionally  happens,  in  the  analysis  of  mineral  waters,  &c.,  that  a 
mixed  precipitate  is  obtained,  containing  chloride,  bromide,  and  iodide  of  silver, 
in  which  it  is  required  to  determine  the  amount  of  each  salt-radical. 

For  this  purpose,  a  convenient  quantity  of  the  precipitate  is  dried,  well  mixed, 
so  that  it  may  be  perfectly  homogeneous,  and  introduced  into  a  weighed  bulb-tube 
of  hard  glass,  in  which  it  is  fused,  and  its  weight  determined. 

The  bulb-tube  is  then  connected  with  a  small  retort  from  which  a  current  of 
bromine-vapor  can  be  passed  through  the  tube ;  a  delivery-tube  is  attached  to 
the  bulb-tube,  so  that  the  excess  of  bromine  may  be  passed  into  solution  of 
potassa.  The  precipitate  is  fused  in  an  atmosphere  of  bromine,  the  tube  being 
repeatedly  turned  to  expose  a  fresh  portion  of  the  precipitate  to  the  action  of 
the  vapor,  until  its  weight  no  longer  varies.  The  bromine  has  then  entirely  re- 
placed the  iodine,  the  amount  of  which  may  be  calculated  from  the  difference  of 
weight.  Of  course,  all  the  bromine  must  be  carefully  expelled  from  the  tube, 
and  replaced  by  air  previously  to  weighing. 

By  a  similar  operation  in  a  current  of  dry  chlorine,  the  bromine  may  be  dis- 
placed. 

Calculation. 
Difference  between 
eqs.  of  I  and  Br.  I 

1).  47.1       :       127.1  ::  1st  difference  of  weight  :  x 

x  =  Weight  of  iodine. 

Difference  between 
eqs.  of  Br.  and  Cl.          Br 
2).  44.5       :       80.0  ::  2d  difference  of  weight  :  y 

y  =  Weight  of  Bromine  originally  present,  together  ivith  that  which  has  replaced 

the  iodine. 

The  amount  of  bromine  equivalent  to  the  iodine  present  must  be  calculated, 
and  subtracted  from  y. 

The  joint  weight  of  the  bromide  and  iodide  of  silver  is  calculated,  and  sub- 
tracted Vrom  that  of  the  original  precipitate,  in  order  to  ascertain  the  weight  of 
the  chloride  of  silver. 

A  very  accurate  method  of  <  separating  chlorine,  bromine,  and  iodine,  when 
existing  in  solution,  is  executed  as  follows : — 

The  solution  is  mixed  with  nitrate  of  palladium  as  long  as  any  precipitate  is 
formed;  the  mixture  is  set  aside  for  12  hours,  the  brownish-black  iodide  of  pal- 
ladium collected  upon  a  weighed  filter,  washed  with  warm  water,  and  dried,  at 
a  temperature  which  must  not  exceed  176°  F.  (80°  C.);  until  its  weight  is  con- 
stant. 

Calculation. 
Pdl          I 

180.4  :  127.1  ::  Weight  of  precipitate  :  x 
x  =  Weight  of  iodine. 

The  chlorine  and  bromine  are  precipitated  from  the  filtrate  with^  nitrate  of 
silver,  and  their  relative  amounts  determined  by  heating  a  portion  of  the  pre- 
cipitate in  a  current  of  chlorine. 


628  QUANTITATIVE   ANALYSIS;    SPECIAL    METHODS 


ANALYSIS   OF   WATERS. 

§  441.  Since  the  number  of  substances  generally  contained  in  waters  is 
limited,  their  analysis  is  usually  effected  by  a  special  method. 

The  following  list  includes  those  substances  which  most  frequently  occur  in 
waters : — 

Bases.  Acids. 

Potassa  Sulphuric 

Soda  Phosphoric 

Lime  Silica 

Magnesia  Carbonic 

Alumina  Nitric 

Oxide  of  iron  Hydrochloric 

Hydrosulphuric 
Organic  matters. 

Lithia,  ammonia,  strontia,  oxide  of  manganese,  oxide  of  lead,  hydriodic  acid, 
hydrobromic  acid,  and  hydrofluoric  acid,  so  rarely  occur,  that  they  are  not  con- 
sidered in  the  general  plan  for  the  analysis. 

QUALITATIVE  ANALYSIS. 

This  portion  of  the  examination  may  be  divided  into 

1.  That  of  the  original  wafer,  which  should  embrace  the  detection  of  hydro- 
sulphuric  acid,  of  free  carbonic  acid,  and  of  organic  matter,  together  with  the 
determination  of  the  reaction  to  test-papers,  and  the  rough  test  of  the  hardness 
of  the  water. 

2.  That  of  the  precipitate  produced  ly  evaporation,  which  should  be  examined 
for  the  carbonates  of  lime  and  magnesia,  sulphate  of  lime,  sesquioxide  of  iron, 
silicic  acid. 

3.  The  analysis  of  the  filtrate,  in  which  there  should  be  sought  all  bases,1- 
silicic  acid,  sulphuric  acid,  hydrochloric  acid,  nitric  acid,  phosphoric  acid,  car- 
bonic acid. 

Waters  should  be  analyzed  as  soon  as  possible  after  they  are  taken  from  the 
source,  whence  they  should  be  collected  in  stoppered  bottles,  which  must  be 
quite  filled  with  the  water.  Corks  very  soon  reduce  the  sulphates  in  the  water 
to  the  state  of  sulphides. 

Forty  ounces  of  the  water  are  usually  sufficient  for  a  qualitative  analysis  for 
practical  purposes. 

Examination  of  the  original  Water. — 1.  A  little  of  the  water  is  placed  in  a 
test-tube,  and  a  slip  of  violet  litmus-paper  (to  show  both  acids  and  alkalies)  in- 
troduced; after  standing  for  some  time,  the  paper  is  compared  with  another 
piece  of  the  same  kind,  which  has  been  soaked  for  a  like  period  in  distilled  water. 

2.  About  two  fluidounces  of  the  original  water  are  evaporated  to  dryness  in  a 
porcelain  dish,  and  the  residue  heated ;  it  is  to  be  observed  whether  considerable 
charring  takes  place,  and  whether  any  odor  of  nitrogenized  organic  matter  is 
evolved. 

3.  The  presence  of  sulphuretted  hydrogen  in  the  water  is  ascertained  by  the 
odor,  and  by  the  production  of  a  black  or  gray  precipitate  with  acetate  of  lead. 

4.  In  order  to  detect  the  free  carbonic  acid,  about  half  an  ounce  of  the  water 

1  This  is  recommended,  because  the  trouble  involved  is  very  slight,  and  may  sometimes 
lead  to  the  discovery  of  a  base  (lead,  e.  g.)  which  would  otherwise  be  passed  over. 


QUALITATIVE   ANALYSIS*OF   WATERS.  629 

is  gradually  heated  in  a  large  test-tube,  when  bubbles  of  carbonic  acid  will  be 
evolved. 

Or  the  water  is  poured  into  a  little  lime-water,  when  the  free  carbonic  acid 
produces  a  white  precipitate,  which  redissolves  on  adding  a  large  quantity  of  the 
water. 

5.  In  order  roughly  to  test  the  hardness  of  waters,  they  are  mixed  with  a  few 
drops  of  an  alcoholic  solution  of  white  soap,  when  a  white  precipitate  of  greater 
or  less  quantity  will  make  its  appearance. 

As  much  of  the  water  as  can  be  conveniently  spared  is  evaporated  to  about  -3$ 
its  original  volume,  and  the  solution  filtered  off  from  the  precipitate. 

Examination  of  the  Filtrate. — The  examination  for  bases  is  conducted  as 
usual. 

Examination  for  Acids. — Silicic  acid  will  be  detected  in  the  examination  for 
bases. 

(The  reaction  of  this  filtrate  to  test-papers  should  be  tried ;  if  it  be  alkaline, 
fixed  alkaline  carbonates  are  contained  in  the  water). 

To  one  portion  of  the  solution  chloride  of  barium  is  added ;  a  white  precipi- 
tate may  consist  of  sulphate,  carbonate,  or  phosphate  of  baryta.  Dilute  hydro- 
chloric acid  is  added. 

Sulphate  of  baryta  would  be  left  undissolved,  indicating  the  presence  of  sul- 
phuric acid.  Phosphate  and  carbonate  of  baryta  would  be  dissolved,  the  latter 
with  effervescence. 

Another  portion  of  the  solution  is  mixed  with  nitrate  of  silver ;  the  precipitate 
may  consist  of  chloride  of  silver  (white),  carbonate  of  silver  (white),  or  phosphate 
of  silver  (yellow).  Dilute  nitric  acid  is  added. 

Chloride  of  silver  would  be  left  undissolved,  indicating  the  presence  of  hydro- 
chloric acid. 

Another  portion  of  the  solution  is  tested  for  phosphoric  acid  by  acidifying 
slightly  with  acetic  acid,  and  adding  a  single  drop  of  sesquichloride  of  iron;  a 
white  precipitate  of  phosphate  of  sesquioxide  of  iron  indicates  the  presence  of 
phosphoric  acid. 

Another  portion  of  the  solution  is  mixed  with  half  its  bulk  of  concentrated 
sulphuric  acid  (perfectly  free  from  nitric  acid),  allowed  to  become  nearly  cool, 
and  a  crystal  of  sulphate  of  iron  dropped  into  it.  After  standing  for  some  time, 
at  perfect  rest,  the  presence  of  nitric  acid  will  be  indicated  by  a  brown  halo 
around  the  crystal. 

Examination  of  the  Precipitate  produced  by  Evaporation. — This  precipitate  is 
dissolved  in  warm  dilute  hydrochloric  acid  (which  should  be  rinsed  round  the 
dish,  and  then  poured  over  the  filter).  The  presence  of  carbonic  acid  will  be 
indicated  by  the  effervescence. 

The  greater  part  of  the  solution  is  evaporated  to  dryness,  and  the  residue 
treated  with  dilute  hydrochloric  acid.  Insoluble  white  flakes  consist  of  silica. 

The  solution  filtered  from  the  silica  is  mixed  with  ammonia  in  excess.  A  red- 
brown  precipitate  consists  of  sesquioxide  of  iron. 

The  filtrate  is  gently  heated  with  carbonate  of  ammonia.  A  precipitate  of 
carbonate  of  lime  will  be  formed  if  lime  be  present. 

The  filtered  liquid  is  mixed  with  phosphate  of  soda,  violently  agitated,  and 
allowed  to  stand  for  24  hours.  A  white  crystalline  precipitate  of  phosphate  of 
magnesia  and  ammonia  indicates  the  presence  of  magnesia. 

The  remainder  of  the  hydrochloric  solution  is  tested  for  sulphuric  acid  with 
chloride  of  barium. 

The  points  which  it  is  generally  important  to  determine  in  the  quantitative 
analysis  of  mineral  waters  are : — 

The  total  weight  of  solid  matter  contained  in  the  water; 


630  QUANTITATIVE  ANALYSIS;    SPECIAL   METHODS." 

The  total  amounts  of  potassa,  soda,  lime,  magnesia,  oxide  of  iron,  sulphuric 
acid,  silicic  acid,  carbonic  acid,  chlorine,  organic  matter; 

The  amounts  of  lime,  magnesia,  and  sesquioxide  of  iron  contained  in  the 
precipitate  ; 

The,  degree  of  hardness  of  the  water; 

The  specijic  gravity  of  the  water 

The  constituents  are  generally  calculated  for  an  imperial  gallon  (70,000  grs.) 
of  distilled  water. 

Moreover,  when  the  water  contains  alkaline  carbonates,  we  generally  desire  to 
ascertain  their  amount. 

Also,  when  sulphuretted  hydrogen  is  present,  its  quantity  must  be  determined. 

About  eight  pints  of  water  will  usually  suffice  for  a  quantitative  analysis ;  but 
since  it  is  generally  necessary  to  conduct  two  analyses  at  once,  for  the  sake  of  a 
control,  twice  this  quantity  ought  to  be  provided. 

In  the  subsequent  analysis  the  water  may  either  be  measured  or  weighed ;  the 
latter  should  be  preferred  as  more  accurate,  when  it  is  practicable. 

For  measuring  the  water,  a  flask  should  be  employed  with  a  mark  on  the 
neck  showing  the  height  to  which  it  is  filled  by  a  weighed  amount  of  water. 

Determination  of  the  Specijic  Gravity  of  the  Water. — A  stoppered  bottle, 
capable  of  containing  about  four  ounces,  is  dried1  and  weighed.  It  is  then 
exactly  filled  with  the  water,  the  temperature  of  which  is  carefully  noted,  and 
again  weighed. 

Lastly,  after  rinsing,  it  is  filled  with  distilled  water  of  the  same  temperature, 
and  its  weight  again  determined. 

The  specific  gravity  is  then  obtained  by  dividing  the  weight  of  the  water  exa- 
mined by  that  of  the  distilled  water. 

This  determination  of  the  specific  gravity  serves  as  a  basis  for  the  calculation 
of  the  actual  weight  of  an  imperial  gallon  of  the  water ;  for  as 

Imperial  gaU. 
of  distilled  water. 

1  :  Sp.  gr.  of  the  water  ::  70,000  grs.  :  x 
x  =  Weight  of  an  imperial  gallon  of  the  water  in  grains. 

It  is  only  necessary,  therefore,  to  multiply  the  specific  gravity  by  70,000,  in 
order  to  obtain  the  weight  of  the  imperial  gallon  of  the  water  in  grains. 

Determination  of  the  Total  Weight  of  Solid  Matter. — About  4,000  grs.  of  the 
water  are  weighed  in  a  flask,  whence  they  are  transferred  to  a  beaker,  which  is 
covered  with  an  inverted  funnel,  and  heated  on  a  sand-bath  till  no  more  bubbles 
of  carbonic  acid  are  evolved.  The  water  is  then  evaporated,  by  successive  por- 
tions, in  a  weighed  platinum  dish  placed  in  an  air-bath ;  any  precipitate  which 
may  have  been  deposited  in  the  beaker  is  carefully  rinsed  out  into  the  dish ;  the 
evaporation  is  carried  to  dryness,  and  the  dry  residue  heated  to  about  320°  F. 
(160°  C.)  in  the  air-bath  till  its  weight  is  constant. 

Calculation. 

Weight  of  water  employed  :  Residue  obtained  : :  Weight  of  an  imp.  gall.  :  x 
x  =  Amount  of  solid  matter  in  an  imperial  gallon. 

Determination  of  Organic  Matter. — The  above  dry  residue  is  carefully  incine- 
rated, till  perfectly  white  (p.  573),  at  as  low  a  temperature  as  possible;  it  is  then 
moistened  with  carbonate  of  ammonia  (to  recarbonate  any  lime),  dried  in  the 
air-bath,  and  weighed.  The  loss  of  weight  represents  the  quantity  of  organic 
matter,  which  should  be  calculated  upon  a  gallon  of  the  water,  and  deducted 

1  In  order  to  dry  such  a  flask,  it  should  be  gently  heated,  and  the  contained  air  sucked 
out  repeatedly  with  a  tube. 


QUANTITATIVE   ANALYSIS   OF   WATERS.  631 

from  the  total  weight  of  solid  ingredients,  in  order  to  ascertain  the  amount  of 
inorganic  matter  contained  in  a  gallon. 

Determination  of  the  Lime,  Magnesia,  and  Iron. — About  12,000  grs.  of  the 
water  are  accurately  weighed,  introduced  into  a  large  flask,  and  heated  with  ex- 
cess of  nitric  acid  until  all  the  carbonic  acid  is  expelled.  The  solution  is  then 
evaporated  to  a  small  bulk  in  a  porcelain  dish  placed  upon  a  sand-bath,  trans- 
ferred to  a  small  dish,  and  the  evaporation  carried  to  perfect  dryness  in  an  air- 
bath.  The  dry  residue  is  digested  with  dilute  hydrochloric  acid,  the  residual 
silica  filtered  off,  well  washed,  dried,  ignited,  and  weighed.  The  iron  is  precipi- 
tated from  the  filtrate  (previously  concentrated)  by  ammonia,  the  lime  subse- 
quently, as  oxalate,  and  the  magnesia  determined  as  pyrophosphate.  The  filtrate 
should,  in  each  case,  be  concentrated  before  precipitation. 

The  amounts  of  lime  and  magnesia  are  calculated  for  an  imperial  gallon  of 
water. 

The  sesquioxide  of  iron  is  reckoned  as  protoxide,  and  calculated  for  an  impe- 
rial gallon  of  water. 

Determination  of  the  Lime,  Magnesia,  and  Iron,  in  the  Precipitate  produced 
by  Boiling. — About  12,000  grs.  of  the  water  are  accurately  weighed,  and  boiled, 
in  a  flask,  for  about  an  hour,  taking  care  to  preserve  the  same  quantity  of  water, 
by  adding  distilled  water  from  time  to  time,  so  that  no  sulphate  of  lime  may  be 
precipitated. 

The  solution  is  filtered  off,  the  precipitate  well  washed  upon  the  filter,  and 
dissolved  with  very  dilute  hydrochloric  acid,  which  should  be  also  rinsed  round 
the  flask,  to  dissolve  any  adhering  particles  of  the  precipitate. 

The  acid  solution  is  boiled  with  a  little  nitric  acid,  and  the  sesquioxide  of  iron, 
lime,  and  magnesia,  separated  and  determined  as  usual. 

The  amount  of  each  of  these  constituents  is  then  calculated  for  an  imperial 
gallon  of  the  water  (the  sesquioxide  of  iron  being  reduced  to  oxide),  and  deduct- 
ed from  the  total  amount  found  in  the  preceding  determination.  The  differences 
express  the  amounts  of  oxide  of  iron,  lime,  and  magnesia,  existing  in  the  water 
uncombined  with  carbonic  acid. 

The  quantities  of  carbonic  acid  required  by  the  oxide  of  iron,  lime,  and  mag- 
nesia, found  in  the  precipitate,  are  then  calculated,  and  added  to  the  weights  of 
the  three  oxides  existing  as  carbonates  in  the  imperial  gallon  ;  the  sums  repre- 
sent the  amounts  of  the  carbonates  of  oxide  of  iron,  lime,  and  magnesia,  existing 
in  an  imperial  gallon  of  water. 

Determination  of  Potassa  and  Soda. — About  9000  grs.  of  the  water  are  accu- 
rately weighed,  evaporated  in  a  beaker  to  about  J  of  their  bulk,  and  mixed  with 
a  little  chloride  of  barium  and  excess  of  baryta- water ;  the  solution  is  gently 
heated,  the  precipitate  allowed  to  subside,  filtered  off,  and  well  washed. 

The  filtrate  and  washings  are  again  evaporated  to  a  small  bulk,  and  gently 
heated  with  ammonia  and  carbonate  of  ammonia,  to  precipitate  the  baryta  and 
lime  which  are  filtered  off;  the  filtrate  is  then  evaporated  to  dryness  in  a  small 
weighed  dish,  and  carefully  ignited  to  expel  ammoniacal  salts.  The  residual 
chlorides  of  potassium  and  sodium  are  weighed,  and  separated  as  in  the  analysis 
of  Rochelle  salt  (p.  602).  The  amount  of  each  metal  is  then  calculated  for  an 
imperial  gallon  of  the  water. 

Determination  of  Sulphuric  Acid. — About  9000  grs.  of  the  original  water 
are  acidified  with  hydrochloric  acid,  and  the  sulphuric  acid  precipitated  as  sul- 
phate of  baryta,  which  is  allowed  24  hours  to  subside,  and  determined  as  directed 
at  p.  592.  Its  amount  is  then  calculated  for  an  imperial  gallon. 

Determination  of  Chlorine. — About  5000  grs.  of  the  water  are  acidulated 
with  nitric  acid,  and  the  chlorine  determined  as  chloride  of  silver  (p.  597).  The 
amount  of  chlorine  in  an  imperial  gallon  is  then  calculated. 

Determination  of  the  total  amount  of  Carbonic  Acid. — This  can  only  be 


632  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

effected  with  absolute  accuracy  when  the  analyst  has  access  to  the  source  of  the 
water. 

It  is  then  necessary  to  provide  himself,  beforehand,  with  the  following  appa- 
ratus, &c. 

A  glass  vessel,  of  suitable  form,  capable  of  containing  about  12  ounces;  its  capa- 
city must  be  accurately  known.  The  best  form  for  this  vessel  is  that  of  an  adapter 
(of  course  open -at  both  ends),  and  so  narrow  at  the  top  as  to  admit  of  its  being 
closed  with  the  thumb,  so  that  it  may  be  dipped  into  the  spring,  a  certain  quantity 
of  water  withdrawn  in  it,  by  closing  it  with  the  thumb,  and  the  water  allowed 
to  run  into  the  bottles  by  merely  removing  the  thumb  from  the  orifice.  This 
instrument  is  sold  under  the  rather  inappropriate  name  of  a  siphon  for  mineral 
waters. 

Four  or  five  stoppered  bottles,  capable  of  holding  about  16  ounces. 

A  few  ounces  of  a  clear  solution  of  chloride  of  calcium. 

A  small  quantity  of  ammonia  which  does  not  give  any  precipitate  with  chlo- 
ride of  calcium. 

When  at  the  spring,  the  operator  must  introduce  about  an  ounce  of  solution 
of  chloride  of  calcium,  and  an  ounce  of  ammonia,  into  each  of  the  bottles.  A 
siphon-full  of  water  is  then  placed  in  each  of  the  bottles,  which  are  then  closely 
stopped  and  removed  to  the  laboratory.  The  precipitates  are  collected  upon  a 
weighed  filter,  dried  at  212°  F.  and  weighed.  The  dry  precipitate  is  well 
mixed,  to  insure  its  uniformity,  and  the  carbonic  acid  in  a  weighed  portion  of  it 
determined  (p.  596).  Two  or  three  determinations  may  be  made,  to  control 
each  other. 

The  amount  of  carbonic  acid  is  then  calculated  for  the  whole  precipitate,  and 
subsequently  for  an  imperial  gallon  of  water. 

By  deducting,  from  the  total  quantity  of  carbonic  acid,  that  combined  with 
the  lime,  magnesia,  and  oxide  of  iron  (previously  determined),  we  ascertain  the 
amount  of  free  carbonic  acid  present  (unless  there  be  any  alkaline  carbonates). 

The  degree  of  hardness  of  a  mineral  water  is  determined  by  Claries  soap-tesf, 
which  consists  in  ascertaining  the  quantity  of  a  standard  solution  of  soap  in 
spirit,  required  to  produce  a  permanent  lather  with  a  given  quantity  of  the  water 
under  examination,  the  result  being  expressed  in  degrees  of  hardness,  each  of 
which  corresponds  to  one  grain  of  carbonate  of  lime  in  a  gallon  (=70,000  grs. 
of  distilled  water)  of  water. 

The  soap- solution  is  prepared  by  dissolving  curd  soap  (Hawes's  white-curd)  in 
proof  spirit,  in  the  proportion  of  about  120  grs.  to  a  pint.  In  order  to  graduate 
this  solution,  16  grs.  of  pure  carbonate  of  lime  (calcareous  spar,  white  marble) 
are  dissolved,  without  loss,  in  a  small  quantity  of  hydrochloric  acid;  the  solution 
is  very  carefully  evaporated  to  dryness  in  an  air-bath,  the  residue  redissolved  in 
water,  the  solution  again  evaporated,  and  these  operations  repeated  until  a  per- 
fectly neutral  solution  has  been  obtained. 

The  neutral  solution  of  chloride  of  calcium  thus  prepared  is  to  be  diluted  with 
so  much  distilled  water  as  will  make  up  a  gallon;  it  will  then  represent  a  water 
of  16°  hardness.  100  measures1  of  this  solution  are  introduced  into  a  stoppered 
bottle  capable  of  containing  2,000  grains,  and  the  soap-solution  is  very  gradually 
added  to  it  from  a  burette  (the  stopper  being  replaced,  and  the  solution  violently 
agitated  from  time  to  time),  until  a  lather  is  formed  which  remains  for  five 
minutes  over  the  whole  surface  of  the  liquid,  when  the  bottle  is  laid  down  upon 
the  table.  The  number  of  measures  of  soap-solution  used  is  then  noticed,  and 
the  strength  of  the  solution  altered,  if  necessary,  by  a  further  addition  either  of 
soap  or  spirit,  until  exactly  32  measures  of  the  liquid  are  required  for  100  mea- 
sures of  the  water  of  16°  hardness.3  The  trial  should  then  be  repeated,  in 

1  Each  measure  is  equal  to  10  grs.  of  distilled  water. 

2  This  standard  soap-solution  may  be  purchased  at  the  operative  chemist's. 


633 

exactly  the  same  way,  with  the  water  of  16°  hardness,  in  order  to  leave  no  doubt 
of  the  strength  of  the  soap-solution. 

To  apply  this  test,  the  water  to  be  examined  is  introduced  into  a  stoppered 
bottle,  which  should  be  half  filled  with  it,  and  violently  agitated,  in  order  to 
disengage  any  free  carbonic  acid,  which  would  increase  the  quantity  of  soap 
required  to  form  a  lather ;  the  air  in  the  bottle  is  then  sucked  out  through  a 
glass  tube,  and  these  operations  repeated  two  or  three  times,  until  it  is  judged 
that  the  free  carbonic  acid  is  entirely  removed.  100  measures  of  this  water  are 
then  introduced  into  a  stoppered  bottle  of  twice  that  capacity,  and  treated  as  in 
the  case  of  the  artificial  water  of  16°  hardness  (see  above),  except  that  the  car- 
bonic acid  should  be  sucked  out  at  intervals  from  the  upper  part  of  the  bottle. 
The  hardness  of  the  water  is  then  inferred  directly  from  the  number  of  measures 
of  soap-solution  employed,  by  reference  to  the  subjoined  table. 

If  the  water  is  so  hard  that  32  measures  of  the  soap-solution  do  not  yield  a 
permanent  lather,  100  measures  of  distilled  water  are  added,  and  the  experiment 
proceeded  with  in  the  usual  manner,  until  60  measures  of  soap-solution  have 
been  used.  Should  these  fail  to  produce  a  lather,  100  measures  of  distilled  water 
are  again  added,  and  the  operation  conducted  until  90  measures  of  soap-solution 
have  been  taken }  if  more  soap  is  even  then  necessary,  its  addition  must  be  pre- 
ceded by  that  of  100  measures  more  distilled  water.  When  a  lather  has  been 
obtained,  another  experiment  is  commenced  with  a  mixture  of  100  measures  of 
the  original  water,  with  the  total  quantity  of  distilled  water  added  in  the  pre- 
ceding determination.  The  number  of  measures  of  soap-solution  used,  must  be 
divided  by  the  number  of  100  measures  contained  in  the  mixture,  and  the  de- 
gree of  hardness  corresponding  to  the  quotient  having  been  found  by  reference  to 
the  table,  it  must  be  multiplied  by  the  former  divisor,  to  obtain  the  true  degree 
of  hardness.  Thus,  if  the  original  water  had  been  diluted  with  200  measures  of 
distilled  water,  and  had  then  required  96  measures  of  soap  solution,  it  would  be 
necessary  to  divide  96  by  3,  and  to  refer  the  quotient  32,  to  the  table,  where  it 
would  be  seen  to  correspond  to  16°,  which,  multiplied  by  3,  gives  48°  for  the 
actual  hardness  of  the  water. 

If  very  accurate  results  be  desired,  it  is  recommended  to  shake  the  water,  to 
which  a  sufficiency  of  soap-solution  has  been  added,  at  intervals  of  half  an  hour, 
and,  should  the  lather  not  then  continue  for  five  minutes,  to  add  as  much  more 
soap-solution  as  is  necessary  to  produce  that  effect,  even  after  standing  for  such 
a  period. 

Dearee  of  Measures  of  Diff^ 

1°  of  hardness. 

1.8 
2.2 
2.2 
2.0 
2.0 
2.0 
2.0 
1.9 
1.9 
1.9 
1.8 
1.8 
1.8 
1.8 
1.8 
l.T 


Degree  of 
hardness. 

0°  (Distilled  water) 

Measures  of                     Differe 
Soap-solution.                           1° 

1.4     

32         .     .     .     .     . 

2 

54     

3     

76     

4     

.       9.6     

5                        .     . 

11  6    

6     

.     13  6     

7     

.     15.6     

8 

.     17  5     

9         

.     19.4     

10     

.     21.3     

11 

.     23  1     

12     

.     24.9     

13     

.     26.7     

14                        .     . 

.     28  5     .              .     .     . 

15     

.    30.3     

16 

32.0 

634  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

When  the  number  of  measures  of  the  soap-solution  fall  between  any  two 
numbers  given  in  the  table,  the  hardness  will  be  expressed,  of  course,  by  an 
integer  and  a  fraction ;  the  integer  will  be  the  degree  of  hardness  corresponding 
to  the  next  lower  number  in  the  soap-test  column;  the  numerator  of  the  fraction 
will  be  found  by  subtracting  this  last  number  from  the  actual  number  of  mea- 
sures employed;  and  the  denominator  will  be  the  difference,  in  the  third  column, 
corresponding  to  the  number  above  referred  to  in  the  second  column;  thus,  if 
25.8  measures  of  the  soap-solution  have  been  employed,  the  number  12,  oppo- 
site to  the  next  lower  number,  24.9,  in  the  soap-test  column,  represents  the 
integral  part  of  the  hardness;  the  numerator  of  the  fractional  part  is  25.8-24.9 
=0.9,  and  the  denominator  is  1.8,  the  difference  corresponding  to  24.9;  the 
fraction,  then,  is  T9^=0.5,  and  12.5  is  the  hardness  required. 

According  to  Clark,  the  hardness  of  a  water  may  be  inferred  from  an  ordinary 
analysis,  by  calculating  the  total  amount,  in  grains,  of  carbonate  of  lime,  equi- 
valent to  the  lime,  magnesia,  oxides  of  lime,  and  alumina,  in  a  gallon  of  water; 
the  number  thus  obtained  will  represent  the  hardness,  in  degrees.1 

To  determine  the  amount  of  alkaline  carbonate  present  in  a  water,  the  following 
method  is  adopted :  About  5000  grains  of  water  are  boiled  for  a  considerable 
time,  the  precipitate  filtered  off,  and  well  washed.  The  filtrate  is  divided  into 
two  parts,  both  of  which  are  accurately  weighed.  In  the  one  portion,  the  chlorine . 
is  determined  as  usual.  The  other  is  acidified  with  hydrochloric  acid,  evaporated 
to  dryness,  gently  ignited,  and  the  chlorine  determined  in  the  aqueous  solution 
of  the  residue. 

The  difference  between  this  quantity  of  chlorine  and  the  former  (calculated 
upon  the  same  quantity  of  liquid)  expresses  the  amount  of  chlorine  correspond- 
ing, equivalent  for  equivalent,  to  the  alkali  present  in  the  form  of  carbonate. 

The  sulphuretted  hydrogen  contained  in  a  water  should,  if  possible,  be  de- 
termined at  the  spring. 

Three  or  four  stoppered  bottles  are  taken,  and  into  each  of  them  a  small  quantity 
of  a  solution  of  arsenious  acid  in  hydrochloric  acid  is  poured.  A  siphon-full  of  wa- 
ter is  then  introduced  into  each  bottle  (as  in  the  determination  of  carbonic  acid). 
In1  order  to  ascertain  the  amount  of  the  sulphuretted  hydrogen,  the  precipitated 
tersulphide  of  arsenic  is  collected  upon  a  filter  of  known  weight,  well  washed, 
dried  at  212°  F.,  and  weighed. 

The  amount  of  sulphuretted  hydrogen  is  then  calculated  for  an  imperial 
gallon. 

It  is  usual  to  arrange  the  results  of  the  analysis  of  a  water  according  to  the 
following  general  rules  (Fresenius);  the  equivalent  numbers  are,  of  course,  the 
data  for  the  calculations : — 

1.  The  lime,  magnesia,  and  protoxide  of  iron,  in  the  precipitate  by  boiling,  are 
calculated  and  stated  as  carbonates,  the  carbonic  acid  which  they  require  being 
calculated,  and  deducted  from  the  total  amount  of  carbonic  acid  present. 

The  remainder  is  stated  as  free  carbonic  acid  (unless  alkaline  carbonates  are 
present). 

2.  The  rest  of  the  lime  is  calculated  and  stated  as  sulphate.     The  sulphuric 
acid  which  it  requires  is  calculated  and  deducted  from  the  total  amount  of  sul- 
phuric acid;  the  remainder,  if  any,  is  calculated  as  sulphate  of  potassa,  and 
should  any  still  remain,  it  is  calculated  as  sulphate  of  soda. 

3.  The  rest  of  the  sodium  is  calculated  as  chloride. 

1  Campbell  has  made  some  experiments  on  the  action  of  the  soap-test  upon  waters  con- 
taining magnesia,  from  which  he  has  deduced  the  following  conclusions:  1.  That  the 
magnesia,  in  its  behavior  to  the  soap-test,  is  equivalent  to  lime,  only  when  its  amount 
does  not  correspond  to  more  than  six  grains  of  lime  in  a  gallon  of  water  2.  That,  for 
many  waters,  Clark's  rule  for  calculating  the  hardness  from  an  ordinary  analysis,  is  not 
accurate. 


ANALYSIS    OP   SOILS. 


635 


4.  The  remainder  of  the  chlorine  is  calculated  as  chloride  of  magnesium ; 
should  any  magnesium  remain,  it  must  exist  as  sulphate. 

It  is  obvious  that  this  method  of  calculation  will  afford  a  valuable  control  for 
the  analysis. 

Moreover,  the  sum  of  the  various  inorganic  constituents  (the  iron  being  calcu- 
lated as  sesquioxide)  should  be  nearly  equal  to  that  of  the  total  amount  of  inor- 
ganic matter  determined  by  evaporation. 

The  amount  of  alkali  existing  in  the  water  as  carbonate  has  been  determined 
previously. 


ANALYSIS   OF   SOILS. 


§  442.  The  following  substances 

Bases. 

Potassa 

Soda 

Ammonia  (rarely) 

Lime 

Magnesia 

Alumina 

Oxide  of  manganese 

Oxide  of  iron 

Sesquioxide  of  iron 


are  generally  found  in  soils : — 

Acids. 
Sulphuric 
Phosphoric 
Silicic 
Carbonic 
Hydrochloric 
Nitric  (rarely'} 
Hydrofluoric  (rarely) 


Organic  matter. 

Traces  of  copper,  arsenic,  &c.  have  occasionally  been  detected. 

The  specimens  of  soil  should  be  taken  at  different  depths,  and  from  different 
parts  of  the  field  ;  they  should  be  uniformly  mixed,  all  large  stones,  roots,  &c., 
picked  out,  and  the  soil  spread  upon  a  sheet  of  paper  and  allowed  to  dry  spontane- 
ously in  the  air  for  a  day  or  two ;  it  is  then  powdered  in  a  mortar,  and  rubbed, 
with  the  fingers,  through  a  piece  of  muslin  stretched  over  the  mouth  of  a  beaker. 

Preliminary  Examination  of  the  Soil. — 1.  A  portion  of  the  soil  is  heated 
on  platinum  to  ascertain  whether  much  organic  matter  is  present,  which  may  be 
known  by  the  carbonization,  and  whether  there  is  any  nitrogenized  organic  mat- 
ter, known  by  the  odor  of  burnt  hair  which  it  emits  when  heated. 

2.  Another  portion  is  mixed  with  hydrate  of  lime,  in  a  dish,  the  mixture 
moistened  with  water,  and  very  gently  heated,  to  test  for  ammonia. 

If  the  soil  be  found  to  contain  a  large  quantity  of  organic  matter,  it  should  be 
very  gently  ignited  previously  to  examination,  and,  in  this  case,  nitric  and  car- 
bonic acids  must  be  sought  in  the  unignited  soil;  after  ignition  we  must  expect 
to  find  some  of  the  sulphate  of  lime  reduced  to  sulphide  of  calcium,  and  the 
sesquioxide  of  iron  reduced  to  oxide. 

It  must  be  remembered  that  our  object  in  analyzing  a  soil  is  not  merely  to 
ascertain  what  substances  are  present,  but  also  to  determine  the  condition  in 
which  they  are  contained  in  the  soil,  whether  they  are  soluble  or  insoluble ; 
whether,  for  example,  the  lime  is  present  as  sulphate  or  as  carbonate ;  whether 
the  alkalies  are  soluble  and  ready  to  be  absorbed  by  the  plant,  or  whether  they 
exist  in  the  form  of  insoluble  silicates,  which  are,  at  present,  useless. 

The  examination  of  the  soil  must  therefore  be  divided  into  three  parts : — 

1.  Analysis  of  the  portion  soluble  in  water. 

2.  Analysis  of  the  portion  soluble  in  hydrochloric  acid. 

3.  Analysis  of  the  insoluble  residue. 


636  QUANTITATIVE  ANALYSIS;    SPECIAL  METHODS. 


QUALITATIVE  ANALYSIS. 

Examination  of  the  portion  soluble  in  Water. — About  eight  ounces  of  the 
soil  are  boiled,  in  a  dish,  with  a  pint  of  water,  for  half  an  hour,  and  filtered. 

The  filtrate  is  evaporated  to  about  one  ounce,  and  divided  into  two  parts. 

One  portion  is  examined  as  usual  for  bases. 

The  other  portion  is  tested  in  the  ordinary  manner,  for  sulphuric,  phosphoric, 
hydrochloric,  and  nitric  acids. 

Examination  of  the  portion  soluble  in  Hydrochloric  Acid.  About  \  of  the 
residue  left  by  water  is  introduced  into  a  flask,  and  boiled,  for  about  ten  minutes, 
with  concentrated  hydrochloric  acid;  water  is  then  added,  the  boiling  continued 
for  some  time,  and  the  solution  filtered.  (If  the  residue  effervesced  when  treated 
with  hydrochloric  acid,  it  indicates  the  presence  of  carbonic  acid.) 

A  small  portion  of  the  hydrochloric  solution  is  tested  with  chloride  of  barium, 
for  sulphuric  acid. 

Another  small  portion  is  set  aside. 

The  greater  part  of  the  hydrochloric  solution  is  examined  for  bases  and  for 
phosphoric  acid  according  to  the  general  process. 

Examination  of  the  insoluble  Residue. — This  residue  is  dried  and  divided  into 
two  parts. 

One  part  is  analyzed  according  to  Table  VIII. 

The  other  portion  is  examined  for  alkalies  according  to  Table  VIII. 

A  portion  of  the  original  soil  may  be  tested  for  hydrofluoric  acid  by  the 
terfluoride  of  silicon  test  (p.  536). 

A  portion  of  the  original  soil  should  be  ignited  and  tested  for  manganese,  by 
fusion  with  carbonate  of  soda  and  nitre. 

QUANTITATIVE  ANALYSIS. 

The  method  here  given  for  the  quantitative  analysis  of  soils,  will  include  the 
determination  of  the  following  substances  :  potassa,  soda,  lime,  magnesia,  alumina, 
oxide  of  manganese,  oxide  and  sesquioxide  of  iron,  sulphuric,  phosphoric,  silicic, 
carbonic,  and  hydrochloric  acids,  organic  matter,  and  water. 

Determination  of  Water. — About  250-300  grains  of  the  air-dried  soil,  are 
heated  in  a  water-bath  till  the  weight  is  constant.  The  loss  represents  the 
amount  of  water. 

Determination  of  Organic  Matter. — About  50  grains  of  the  perfectly  dried 
soil  are  introduced  into  a  platinum  crucible,  accurately  weighed,  and  completely 
incinerated  with  the  usual  precautions  (p.  573).  The  residue  is  allowed  to  cool, 
moistened  with  sesquicarbonate  of  ammonia  (to  recarbonate  any  caustic  lime), 
and  dried  in  an  air-bath,  at  a  little  above  212°  F.  till  its  weight  is  constant. 

The  loss  indicates  the  total  quantity  of  organic  matter  in  the  dry  soil,  which 
is  then  calculated  for  100  parts  of  air-dried  soil. 

Determination  of  the  total  amount  of  Carbonic  Acid. — About  50  grains  of 
the  air-dried  soil  are  employed  for  the  determination  of  carbonic  acid  by  the 
method  of  Fresenius  and  Will  (see  p.  596). 

Determination  of  the  total  amount  of  Constituents  soluble  in  Water. — From 
500  to  600  grains  9f  air-dried  soil  are  heated  with  four  or  five  ounces  of  water, 
in  a  beaker,  for  a  considerable  period,  nearly  to  ebullition  ;  the  residue  is  allowed 
to  subside  perfectly,  the  solution  poured  through  the  filter,  and  the  residue  again 
heated  with  water ;  this  operation  is  repeated,  till  a  few  drops  of  the  solution  do 
not  leave  any  considerable  residue  when  evaporated  on  platinum. 

The  residue  is  thrown  upon  a  weighed  filter,  washed  with  hot  water  till  the 
washings  leave  no  appreciable  residue  when  evaporated,  dried  in  a  water-bath, 
and  weighed. 


QUANTITATIVE   ANALYSIS   OF   SOILS.  637 

By  deducting  the  weight  of  this  residue  from  that  of  the  air-dried  soil  em- 
ployed, and  subtracting  from  the  result  the  amount  of  water  known  to  be 
present  in  the  air-dried  soil,  we  ascertain  the  total  quantity  of  the  soluble 
ingredients. 

It  is  well  to  control  this  result  by  evaporating  the  filtrate  and  washings,  first, 
in  a  porcelain  basin  upon  a  sand-bath,  then,  in  a  weighed  platinum  capsule, 
placed  on  a  water-bath,  to  dryness,  and  heating  the  residue  in  a  water-oven  till 
its  weight  is  constant.  The  total  quantity  of  soluble  matter  is  then  calculated 
for  100  parts  of  the  air-dried  soil. 

Determination  of  the  amount  of  Organic  Matter  soluble  in  Water. — The 
residue  obtained  in  the  above  experiment  is  gently  ignited  till  all  organic  matter 
is  burnt  off.  The  loss  of  weight  indicates  the  amount  of  soluble  organic  matter 
present. 

Determination  of  the  Individual  Constituents  soluble  in  Water. — (Should  a 
large  amount  of  organic  matter  be  present,  it  is  better  to  destroy  it  by  moderately 
heating  the  weighed  portion  of  the  soil,  before  proceeding  with  the  subsequent 
operations.) 

An  accurately  weighed1  quantity  of  the  soil  (which  must  be  varied  according 
to  the  number  of  constituents  to  be  determined  in  the  solution,  about  1500  grains 
being  usually  sufficient)  is  introduced  into  a  beaker,  and  treated  with  water  ex- 
actly as  directed  for  the  determination  of  the  total  amount  of  solid  matter,  except 
that  the  residue  may  be  collected  on  an  ordinary  (not  weighed)  filter. 

The  solution  and  washings  are  evaporated  till  they  do  not  measure  more  than 
10  or  12  ounces,  introduced  into  a  dry  weighed  flask,  and  accurately  weighed. 

Determination  of  the  Bases  (except  Alkalies) . — (It  very  rarely  happens  that  the 
aqueous  solution  contains  a  sufficient  quantity  of  alumina,  manganese,  iron,  or  of 
silica  or  phosphoric  acid,  for  quantitative  estimation ;  should  this,  however,  be 
the  case,  their  separation  and  determination  may  be  effected  by  the  ordinary 
methods.) 

About  one-fifth  of  the  aqueous  solution  is  poured  into  a  beaker,  and  the  flask 
afterwards  accurately  weighed  to  ascertain  the  amount  of  solution  which  has  been 
taken. 

The  lime  is  then  determined,  in  the  usual  manner,  as  oxalate,  and,  sub- 
sequently, the  magnesia  in  the  filtrate,  as  pyrophosphate. 

The  amounts  of  lime  and  magnesia  are  calculated  for  the  whole  of  the  solu- 
tion, and  thence,  for  100  parts  of  the  air-dried  soil. 

Determination  of  the  Alkalies. — The  alkalies  are  determined  in  two-fifths  of 
the  aqueous  solution  by  the  method  given  for  their  determination  in  waters,  p. 
631. 

Determination  of  Sulphuric  Acid. — The  sulphuric  acid  is  determined  in  an- 
other fifth  of  the  aqueous  solution,  as  sulphate  of  baryta. 

Determination  of  Chlorine. — The  remaining  fifth  of  the  solution  is  employed 
for  the  estimation  of  chlorine  as  chloride  of  silver. 

Determination  of  the  Constituents  soluble  in  Hydrochloric  Acid. — The  residue 
left  on  boiling  the  weighed  portion  of  soil  with  water  is  dried  on  the  filter  by 
exposure  in  a  warm  situation,  detached,  as  far  as  possible,  from  the  filter,  well 
powdered,  and  dried,  for  an  hour  or  two,  at  212°  F. 

About  500  grains  of  this  residue  (accurately  weighed)  are  introduced  into  a 
platinum  dish,  and  gently  ignited  till  all  organic  matter  is  perfectly  destroyed, 
and  the  mass  completely  incinerated.  The  residue  is  then  transferred  to  a  large 
flask,  covered  with  water,  and  concentrated  hydrochloric  acid  gradually  added 
till  all  effervescence  has  ceased;  a  little  more  hydrochloric  acid  is  then  added, 
the  mixture  boiled  for  about  an  hour,  upon  a  sand-bath,  allowed  to  subside,  the 

1  The  soil  may  be  conveniently  weighed  in  a  light  beaker. 


638  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

clear  liquid  carefully  poured  off  into  a  beaker,  and  the  residue  once  more  boiled, 
for  a  few  minutes,  with  a  fresh  portion  of  hydrochloric  acid.  The  clear  liquid 
is  again  decanted,  mixed  with  the  first  portion,  the  whole  diluted  with  water,  and 
filtered  through  a  weighed  filter.  The  residue  in  the  flask  is  thrown  on  to  the 
filter,  and  washed  till  the  washings  have  no  longer  an  acid  reaction. 

The  solution  and  washings  are  mixed  with  a  little  nitric  acid,  and  carefully 
evaporated  to  dryness,  in  an  air-bath,  the  residue  moistened  with  concentrated 
hydrochloric  acid,  then  digested  with  dilute  hydrochloric  acid  for  some  time.  The 
undissolved  silica  is  collected  upon  a  filter,  and  determined  in  the  usual  manner 
(p.  594). 

The  filtrate  and  washings  are  concentrated  by  evaporation,  introduced  into  a 
stoppered  bottle,  and  accurately  weighed. 

The  amount  of  silica  obtained  is  calculated  for  the  quantity  of  aqueous  residue 
employed,  and  subsequently,  for  the  quantity  of  this  residue  which  is  known  to 
correspond  to  100  parts  of  the  air-dried  soil. 

Determination  of  the  Bases  (except  the  Alkalies),  and  of  Phosphoric  Acid. — 
About  one-half  of  the  hydrochloric  solution  (accurately  weighed),  is  gradually 
mixed  with  ammonia,  with  constant  stirring,  until  a  precipitate  begins  to  appear, 
which  does  not  redissolve  entirely  on  stirring;  a  gentle  heat  is  then  applied,  and 
when  the  precipitate  has  redissolved,  some  acetate  of  potassa  is  added  until  the 
liquid  has  a  distinct  red  color  (should  there  be  not  enough  iron  for  this  purpose, 
a  little  sesquichloride  of  iron  should  be  added1).  The  mixture  is  introduced  into 
a  capacious  porcelain  dish,  and  boiled  till  the  liquid  portion  has  lost  its  red  color, 
denoting  that  all  the  acetate  of  sesquioxide  of  iron  is  decomposed ;  the  solution 
is  then  filtered  while  hot,  and  the  precipitate  washed  with  hot  water. 

The  precipitate,  which  contains  alumina,  sesquioxide  of  iron,  and  phosphoric 
acid,  is  dissolved  off  the  filter  in  warm  dilute  hydrochloric  acid  (the  filter  being 
well  washed);  the  solution  is  mixed  with  ammonia  till  a  permanent  precipitate 
begins  to  form,  and  sulphide  of  ammonium  added  in  excess.  The  mixture  is 
digested  for  an  hour  or  two  at  a  moderate  heat,  the  precipitate  (sulphide  of  iron 
and,  perhaps,  of  manganese  and  alumina,  with  a  little  phosphoric  acid)  filtered 
off  and  washed  with  water  containing  sulphide  of  ammonium. 

The  filtrate  and  washings  (containing  most  of  the  phosphoric  acid)  are  evapo- 
rated to  a  small  bulk,  acidulated  with  hydrochloric  acid,  and  heated  with  a  little 
concentrated  nitric  acid  to  oxidize  and  dissolve  the  separated  sulphur.  The 
phosphoric  acid  is  then  determined  in  the  solution  as  basic  perphosphate  of  iron 
(p.  593). 

The  precipitate,  containing  sulphide  of  iron,  and  perhaps,  of  manganese  and 
alumina,  is  dissolved  in  hydrochloric  acid,  the  solution  heated  till  all  sulphuretted 
hydrogen  is  expelled,  boiled  with  a  little  nitric  acid,  and  mixed  with  the  acetic 
solution  originally  filtered  off  from  the  precipitate  containing  phosphoric  acid. 

The  solution  is  concentrated,  if  necessary,  by  evaporation,  mixed  with  chloride 
of  ammonium  and  excess  of  ammonia,  heated,  and  filtered. 

The  lime  and  magnesia  in  the  filtrate  are  determined  as  usual. 

The  precipitate,  which  contains  alumina,  iron,  and  manganese,  is  treated  ex- 
actly as  in  the  analysis  of  clays  (p.  605);  the  ignited  precipitate,  containing  only 
iron  and  manganese,  is  subsequently  dissolved  in  hydrochloric  acid,  and  the  iron 
and  manganese  separated  and  determined  by  the  method  employed  in  the  analy- 
sis of  cast-iron  (p.  626). 

The  results  are  all  calculated  upon  100  parts  of  air-dried  soil,  the  iron  and 
manganese  being  calculated  as  peroxides. 

Determination  of  Alkalies. — About  one-fourth  of  the  hydrochloric  solution  is 

1  In  this  case,  which  seldom  occurs,  the  iron  must  of  course  be  determined  in  another 
portion. 


ANALYSIS   OF   THE   ASHES   OP   VEGETABLE   SUBSTANCES.       639 

evaporated  to  dryness  in  an  air-bath,  the  residue  stirred,  and  heated  with  water, 
an  excess  of  baryta-water  added,  the  solution  again  heated  for  some  time,  and 
filtered ;  the  filtrate  is  then  treated  as  directed  for  the  determination  of  alkalies 
in  the  aqueous  solution. 

The  alkalies  are  calculated  for  100  parts  of  air-dried  soil. 

Determination  of  Sulphuric  Acid. — This  acid  will  only  occur  in  the  hydro- 
chloric solution  when  the  washing  of  the  aqueous  residue  has  been  incomplete. 
It  is  determined  as  sulphate  of  baryta. 

Analysis  of  the  portion  insoluble  in  Water  and  Acids. — This  residue  is  dried 
in  the  water-bath,  till  its  weight  is  constant. 

Determination  of  Silicic  Acid  and  of  all  Bases  except  Alkalies.  This  is  con- 
ducted according  to  the  method  described  in  the  analysis  of  clays  (p.  605); 
about  15  or  20  grains  of  the  residue  are  fused  with  carbonate  of  potassa  and 
soda. 

Determination  of  Alkalies. — About  15  or  20  grains  of  the  residue  are  ignited 
with  three  or  four  parts  of  hydrate  of  baryta,  and  the  alkalies  estimated  as  in  the 
analysis  of  glass  (p.  624). 

The  results  of  the  analysis  of  the  insoluble  residue  are  also  calculated  upon 
100  parts  of  the  air-dried  soil. 

In  calculating  the  results  of  the  analysis  of  a  soil,  the  constituents  of  the 
aqueous  solution  should  be  arranged  upon  the  same  principles  as  in  the  analysis 
of  waters. 

The  whole  of  the  lime  and  magnesia  in  the  portion  soluble  in  hydrochloric 
acid  will  exist  as  carbonates,  unless  sulphuric  acid  be  present,  when  it  will  exist 
as  sulphate  of  lime.  The  determinations  of  the  carbonic  acid,  and  of  lime  and 
magnesia,  will  therefore  usually  check  each  other. 

If  there  be  an  excess  of  carbonic  acid,  it  must  exist  as  carbonate  of  iron  or 
manganese.  Unless  good  reason  is  seen  for  a  different  assumption,  the  iron  and 
manganese  are  calculated  as  sesquioxide  and  binoxide,  respectively. 

There  are  evidently  several  means  of  control  in  the  analysis  of  a  soil. 

The  amount  of  the  constituents  soluble  in  water,  found  by  direct  determina- 
tion, should  agree  with  that  determined  by  weighing  the  residue,  and  with  the 
joint  amount  of  the  various  substances  estimated  in  the  solution. 

The  sum  of  the  weights  of  the  substances  determined  in  the  hydrochloric 
solution  (plus  the  carbonic  acid)  should  coincide  (or  nearly  so)  with  the  amount 
ascertained  to  be  soluble  in  the  acid. 

In  this  calculation,  it  must  not  be  forgotten  that  the  organic  matter  has  been 
destroyed  before  dissolving  the  residue  in  hydrochloric  acid,  so  that  its  weight 
must  be  added  in  with  the  substances  determined  in  the  solution. 

Other  methods  of  control  will  readily  suggest  themselves  to  the  analyst. 


ANALYSIS  OF  THE  ASHES  OF  VEGETABLE 
SUBSTANCES. 

§  443.  It  would  be  very  desirable  to  ascertain  the  exact  forms  of  combination 
in  which  the  mineral  constituents  exist  in  vegetable  tissues,  but,  up  to  the  pre- 
sent time,  it  has  not  been  found  possible  to  determine  these  without  previously 
destroying  the  organic  matters  with  which  they  are  associated;  and  since  we 
can  never  be  sure  that  the  processes  employed  for  this  purpose  do  not  modify  or 
decompose  the  saline  combinations,  the  information  thus  acquired  can  only  pos- 
sess a  certain  relative  value,  enabling  us  to  compare,  with  considerable  accuracy, 
the  mineral  ingredients  of  plants  with  those  of  other  plants,  or  of  soils,  but  not 
to  be  regarded  in  the  light  of  an  actual  account  of  the  constitution  of  the  mineral 
portion  of  the  plant. 


640  QUANTITATIVE  ANALYSIS;    SPECIAL   METHODS. 

Much  attention  has  been  bestowed  by  analytical  chemists  upon  the  preparation 
of  the  ashes  of  vegetable  substances  for  analysis,  so  that  they  may  suffer  the  least 
possible  alteration,  but  nearly  every  method  which  has  at  present  been  used  for 
this  purpose,  is  based  upon  the  destruction  of  the  organic  matter  by  heat. 

When  we  remember  that  vegetable  tissues  generally  contain  compounds  of  the 
alkalies  and  alkaline  earths  with  organic  acids,  together  with  silicic  acid,  sul- 
phates, phosphates,  and  chlorides,  and  that,  in  the  destruction  of  the  organic 
matter  by  heat,  these  substances  are  exposed  to  a  high  temperature  in  contact 
with  charcoal  and  moisture,  we  are  not  surprised  that  a  considerable  alteration 
should  be  effected  in  these  constituents  by  the  incineration. 

Since  the  old  method  of  preparing  the  ashes  of  vegetables  is  by  far  the  sim- 
plest and  most  easy  of  execution,  and  has  not  yet  been  fairly  superseded  by  any 
other  which  lays  claim  to  very  superior  accuracy,  we  shall  here  consider  the 
analysis  of  ashes  prepared  by  that  method,  merely  suggesting,  that  if  all  ash- 
analyses  were  carefully  executed  by  one  standard  method,  the  purposes  of  com- 
parison would  be  fully  answered. 

INCINERATION  OF  VEGETABLE  SUBSTANCES. 

The  portion  of  the  plant  intended  for  incineration  must  be  thoroughly  cleansed 
with  a  dry  cloth. 

Roots  and  woods  may  be  cut  up  into  slices  or  fragments,  and  dried  in  an  oven. 
Fruits  are  also  cut  into  slices  and  dried  in  the  same  way.  Seeds,  leaves,  and 
flowers  are  simply  dried.  [Stalks,  straw,  &c.  may  be  conveniently  dried,  laid 
in  bunches,  and  kindled  at  a  flame,  the  ash  being  allowed  to  fall  into  a  dish,  and 
the  incineration  subsequently  completed  in  the  ordinary  way.  Or;  the  stalks, 
&c.  may  be  cut  into  small  pieces  and  incinerated.] 

The  substance,  thus  prepared,  is  placed  in  an  earthen  crucible,  or  in  a  porce- 
lain dish,  and  gradually  heated  over  a  charcoal  fire.  As  soon  as  the  matter  is 
thoroughly  carbonized,  and  no  more  fumes  are  evolved,  the  heat  is  somewhat 
raised,  and  continued  for  a  considerable  period  (several  hours  are  sometimes 
necessary),  until  all  or  the  greater  part  of  the  carbon  has  burnt  off;  the  heat 
must  not  be  sufficient  to  fuse  the  ash. 

If  a  large  quantity  of  carbon  still  remains  unburnt,  the  incineration  is  carried 
further  in  a  platinum  capsule,  over  a  gas-burner,  the  ashes  being  stirred  at 
intervals,  with  a  platinum  spatula. 

When  all  or  the  greater  part  of  the  carbon  is  consumed,  so  that  the  ashes 
appear  white  or  light  gray,  a  small  specimen  is  taken  out  and  treated  with  hydro- 
chloric acid;  if  any  hydrosulphuric  acid  is  evolved,  the  ash  must  be  mixed  (in 
a  mortar)  with  a  small  quantity  of  pure  red  oxide  of  mercury  (which  volatilizes 
without  residue)  and  heated  in  the  platinum  dish  (covered)  until  all  the  oxide  is 
volatilized.  (A  portion  of  the  ash  is  boiled  with  dilute  nitric  acid,  filtered,  and 
tested  with  hydrosulphuric  acid.)  In  this  way,  any  sulphide,  arising  from  the 
reduction  of  the  sulphates  by  the  charcoal,  is  oxidized  and  reconverted  into 
sulphate. 

The  ash  is  well  mixed  and  preserved  in  a  stoppered  bottle. 

Determination  of  the  total  amount  of  Ash. — A  quantity  of  the  vegetable  sub- 
stance varying  with  the  amount  of  ash  which  it  is  likely  to  yield,  is  dried  in  the 
water-oven  until  its  weight  is  constant.  It  is  then  very  carefully  incinerated  in 
a  platinum  crucible,  till  nearly  the  whole  of  the  carbon  has  burnt  off.  A  quan- 
tity of  pure  red  oxide  of  mercury  is  then  mixed  with  the  ash  in  the  crucible, 
and  the  mixture  very  strongly  ignited.  The  ash  is  afterwards  moistened  with 
carbonate  of  ammonia,  thoroughly  dried  in  an  air-bath,  and  weighed. 

In  very  accurate  determinations,  these  operations  should  be  repeated  until  the 
weight  is  constant. 


QUANTITATIVE  ANALYSIS.  641 

QUALITATIVE  ANALYSIS. 
The  following  constituents  are  usually  found  in  the  ashes  of  plants : — 

Acids. 
Sulphuric 
Phosphoric 
Hydrochloric 
Silicic 
Carbonic. 


Potassa 

Soda 

Lime 

Magnesia 

Alumina 

Protosesquioxide  of  manganese 

Sesquioxide  of  iron. 


In  marine  plants,  also,  bromine  and  iodine  should  be  sought. 

Fluorine  is  occasionally  found  in  ashes  of  plants. 

The  ashes  also  usually  contain  more  or  less  unconsumed  carbon,  and  some 
sand  mechanically  adhering  to  the  plant. 

A  portion  of  the  ash  is  boiled  with  water,  and  filtered. 

The  aqueous  solution  is  tested  in  the  usual  manner,  for  the  bases  and  acids 
mentioned  above. 

The  residue  insoluble  in  water  is  washed  and  boiled  with  dilute  hydrochloric  acid. 
Effervescence  of  course  indicates  carbonic  acid,  which  should  not  be  accompanied 
by  hydrosulphuric  acid,  if  the  preparation  of  the  ash  has  been  properly  effected. 

The  acid  solution  is  examined,  as  usual,  for  the  above  bases  and  acids  (except 
carbonic  and  hydrochloric). 

The  portion  insoluble  in  hydrochloric  acid  (which  most  frequently  consists  of 
sand  mechanically  adhering  to  the  plant,  and  of  unconsumed  carbon),  is  washed, 
dried,  ignited,  if  necessary,  to  burn  off  the  carbon,  and,  should  it  be  deemed  re- 
quisite, analyzed,  as  usual,  by  Table  VIII. 

It  is  only,  however,  in  the  case  of  ashes  very  rich  in  silicic  acid  (equisetaceze, 
&c.)  that  it  is  necessary  to  examine  this  residue. 

QUANTITATIVE  ANALYSIS. 

It  is  rarely  necessary,  except  for  some  special  purpose,  to  analyze  the  aqueous 
solution  separately. 

Determination  of  Carbonic  Acid. — About  30  or  40  grains  of  ash  are  employed 
for  the  estimation  of  the  carbonic  acid  according  to  the  method  of  Fresenius 
and  Will  (p.  617). 

Determination  of  Chlorine. — 15  or  20  grains  of  the  ash  are  boiled  in  a  flask, 
with  dilute  nitric  acid  (the  acid  being  gradually  added  to  water  previously  poured 
over  the  ash),  and  the  chlorine  determined,  in  the  filtered  solution,  as  chloride 
of  silver. 

Determination  of  the  Remaining  Constituents.  (The  manganese  and  alumina 
are  very  rarely  determined  in  ashes). — About  100  grs.  of  ash  are  introduced 
into  a  flask,  covered  with  water,  and  hydrochloric  acid  gradually  added  in  con- 
siderable excess.  The  contents  of  the  flask  are  then  boiled  for  some  time, 
thoroughly  rinsed  out  into  a  porcelain  dish,  and  evaporated  to  dryness  in  the 
air-bath.  The  residue  is  treated,  as  usual,  with  dilute  hydrochloric  acid,  the  in- 
soluble portion  (silicic  acid,  sand,  and  charcoal)  collected  on  a  weighed  filter 
containing  very  little  ash,  washed  till  the  washings  have  no  acid  reaction,  and 
dried. 

The  acid  filtrate  and  washings  are  evaporated  to  a  small  bulk,  and  accurately 
weighed  in  a  stoppered  bottle. 

Determination  of  Sulphuric  Acid. — About  |  of  the  solution  is  employed  for 
the  determination  of  sulphuric  acid  as  sulphate  of  baryta. 
41 


642  QUANTITATIVE   ANALYSIS;    SPECIAL   METHODS. 

Determination  of  Alkalies. — In  £  of  the  solution,  the  alkalies  are  determined, 
just  as  in  the  analysis  of  the  hydrochloric  solution  of  a  soil. 

Determination  of  Phosphoric  Acid,  Lime,  Magnesia,  and  Sesquioxide  of  Iron. — 
The  remaining  J  of  the  solution  (which  should  be  mixed  with  more  free  hydro- 
chloric acid)  is  treated  with  a  slight  excess  of  acetate  of  potassa ;  if  this  reagent 
should  produce  a  pink  color,  indicating  an  excess  of  sesquioxide  of  iron,  the  solu- 
tion is  boiled,  filtered,  and  the  phosphoric  acid  and  iron  determined  as  in  the 
analysis  of  soils ;  the  lime  and  magnesia  are  subsequently  determined  in  the 
filtrate. 

If,  however,  the  acetate  of  potassa  produces  merely  a  yellowish-white  precipi- 
tate, this  is  filtered  off,  washed,  dried,  ignited,  and  weighed  as  phosphate  of  ses- 
quioxide of  iron  (2Fe203.3P05). 

The  remainder  of  the  phosphoric  acid  is  then  separated  from  the  filtrate,  by 
adding  sesquichloride  of  iron  till  a  pink  color  is  produced,  boiling,  and  determin- 
ing the  phosphoric  acid  in  the  precipitate  as  at  p.  593. 

The  lime  and  magnesia  are  then  determined  in  the  filtrate  as  usual. 

Examination  of  the  residue  of  Silica,  Sand,  and  Charcoal. — If  this  residue 
consists,  as  is  generally  the  case,  of  the  above  substances  only,  it  is  (after  drying 
at  212°  F.  and  weighing)  transferred  from  the  filter  (which  is  afterwards  again 
weighed,  to  ascertain  how  much  of  the  residue  has  been  employed)  to  a  platinum 
dish,  and  boiled  with  a  dilute  solution  of  potassa  (free  from  alumina)  for  about 
30  minutes,  when  the  silica  is  entirely  dissolved.  The  residue  of  sand  and 
charcoal  is  collected  upon  a  weighed  filter,  well  washed,  dried  at  212°  F.,  and 
weighed.  The  filter  is  then  incinerated  as  usual,  and  the  weight  of  the  sand 
deducted  from  that  of  the  sand  and  charcoal,  in  order  to  obtain  the  amount  of 
the  latter. 

To  find  the  quantity  of  silica,  the  weight  of  the  sand  and  charcoal  must  be 
deducted  from  that  of  the  original  residue.  But  if  qualitative  analysis  has 
shown  that  other  constituents  are  to  be  determined  in  the  residue  left  by  hydro- 
chloric acid,  the  process  must  be  somewhat  modified. 

About  50  or  60  grains  of  the  residue  are  heated  with  solution  of  pure  potassa 
or  soda,  in  a  platinum  or  silver  dish.  The  mixture  is  afterwards  evaporated  to 
dryness,  the  residue  carefully  dissolved  in  an  excess  of  hydrochloric  acid,  and 
again  evaporated  to  dryness.  The  subsequent  process  is  then  conducted  exactly 
as  in  the  analysis  of  the  hydrochloric  solution  of  the  ash,  except  as  regards  the 
determination  of  alkalies. 

This  must  be  effected  in  another  portion  of  the  ash  or  residue,  by  heating  with 
hydrate  of  baryta,  as  in  the  analysis  of  glass  (p.  624). 

In  calculating  and  stating  the  results  of  an  analysis  of  a  vegetable  ash,  it 
must  be  remembered  that  the  carbonic  acid,  sand,  and  charcoal  are  not  essen- 
tially constituents  of  the  mineral  portion  of  the  plant,  but  may  be  said  to  be 
derived  from  extraneous  sources.  These  should  therefore  be  subtracted  from  the 
ash  employed,  and  the  other  ingredients  calculated  for  100  parts  of  ash,  free 
from  these  impurities. 

The  chlorine  should  be  calculated  as  chloride  of  sodium,  and  if  there  be  an 
excess,  as  chloride  of  potassium.  Any  excess  of  sodium  or  potassium  must  be 
stated  as  soda  or  potassa. 

It  is  also  usual  to  calculate  the  total  amount  of  oxygen  contained  in  the  bases 
present. 

ANALYSIS  OF  THE  ASHES  OF  ANIMAL  SUBSTANCES. 

§  444.  The  above  method  will  serve,  with  some  modifications,  for  the  analysis 
of  animal  ashes.  Since  these,  however,  are  generally  free  from  sand,  it  is 
unnecessary  to  digest  the  silica  with  potassa. 


ANALYSIS   OF   THE   ASHES    OF   ANIMAL   SUBSTANCES.  643 

It  is  advisable,  also,  in  the  analysis  of  animal  ashes,  to  determine  the  amount 
dissolved  by  water,  and  to  analyze  the  aqueous  solution  separately. 

In  these  ashes,  there  is  always  more  phosphoric  acid  than  corresponds  to  the 
iron  present.  It  will,  therefore,  be  necessary  to  adopt  the  second  of  the 
methods  given  in  the  analysis  of  ashes,  for  the  determination  of  phosphoric  acid 
and  iron. 


INDEX. 


ABSORBING  BALLS,  74 

Acetic  acid,  examination,  501 
reactions,  546 

Acid,  antimonic,  430 
antimonious,  431 
arsenic,  440 
arsenious,  438 
auric,  396 
bismuthic,  392 
boracic,  215 
carbonic^  197 

solvent  action,  199 
chloric,  139 
chlorocarbonic,  197 
chlorochloric,  140 
ehlorochromic,  334 
chloro  nitric,  143 
chloronitrous,  143 
chloroperchloric,  141 
chlorosulphuric,  276 
chlorous,  139 
chromic,  330 
common  phosphoric,  178 
croconic,  197 
cupric,  383 
definition,  40 
dimetaphosphoric,  178 
dithionic,  158 
ferric,  344 
fluoboric,  217 
glacial  phosphoric,  177 
hexametaphosphoric, 

178 

hydriodic,  150 
hydriodous,  150 
hydrobromic,  146 
hydrochloric,  142 
hydrofluoboracic,  217 
hydrofluoric,  153 
hydrofluosilicic,  227 
hydroselenic,  171 
hydrosulphuric,  165 
hydrosulphurous,  165 
hydrotelluric,  450 
hypochloric,  139 
hypochloronitric,  143 
hypochlorous,  137 
hyponitric,  127 
hyponitrous,  126 
hypophosphoric,  176 
hypophosphorous,  175 


Acid,  hypo  sulphuric,  158 
hyposulphurous,  156 
iodic,  149 
manganic,  359 
metantimonic,  431 
metaphosphoric,  177 
metastannic,  423 
molybdic,  447 
monometaphosphoric, 

177 
muriatic,  142 

of  commerce,  142 
niobic,  493 
nitric,  127 
nitromuriatic,  143 
nitrosulphuric,  166 
nitrous,  126 

commercial,  130 
osmic,  416 
osmious,  416 
pelopic,  494 
pentathionic,  164 
perchloric,  141 
perchromic,  333 
periodic,  150 
permanganic,  360 
phosphatic,  176 
phosphoric,  176 
phosphorous,  176 
pyro  phosphoric,  178 
rhodizonic,  197 
ruthenic,  418 
selenic,  170 
selenious,  170 
silicic,  219 
stannic,  423 
sulphantimonic,  435 
eulpharsenic,  442 
sulpharsenious,  442 
sulphocarbonic,  212 
sulphotungstic,  446 
sulphuric,  159 

distillation,  161 
sulphurous,  157 
tantalic,  493 
telluric,  449 
tellurous,  449 
tetrametaphosphoric, 

178 

tetrathionic,  164 
titanic,  451 


Acid,  tribasic  phosphoric,  173 
trimetaphosphoric,  173 
trithionic,  164 
tungstic,  445 
vanadic,  374 
Acidimetry,  619 
Acids,  general  examination 

for,  560 
inorganic,     analytical 

classification,  532 
mono-,  bi-,  and  tri-basic, 

40 

organic,  analytical,  clas- 
sification, 542 
preliminary  examination 

for,  559 

special  tests  for,  564 
Adapters,  78 
Adularia,  316 
Aeroliths,  349 
&tite,  349 
Affinity,  43 
After-damp,  202 
Agate,  219 
Agate  mortar,  106 
Air,  analysis  of,  130 
Air,  atmospheric,  130 
Air-baths,  95,  570,  571 
Alabaster,  296 
'Albite,  256 
AlMte,  potash-,  317 
Alcohol-potash,  232 
Alkali,  definition,  40 
Alkalies,   determination    in 

silicates,  623 
Alkalimetry,  616 
Allophane,  316 
Allotropy,  155 
Alloy,  defined,  229 
Alloy  for  musical  instru- 
ments, 387 

Alloys,  division  of,  84 
of  antimony,  436 
bismuth,  393 
copper  and  tin,  387 
copper  and  zinc,  387 
gold,  400 
lead,  481 
platinum,  410 
silver  and  copper,  492 
tin,  427 


646 


INDEX. 


Alloys,  qualitative  analysis, 

567 
Alum,  313 

ammonia-,  316 

analysis,  604 

burnt,  315 

chrome-,  329 

cubical,  315 

manganese-  (natural), 
357 

Roman,  313 
Alum-shale,  313 
Alum-slate,  313 
Alum,  soda-,  316 
Alum-stone,  313 
Alum,  uses,  316 
Alumen  ustum,  315 
Alumina,  310 

basic  sulphate,  312 

carbonate,  316 

determination,  585 

hydrates,  311 
Alumina-mordant,  312 
Alumina,  nitrate,  312 

phosphate,  316    - 
Alumina-potash-alum,  313 
Alumina,  reactions,  513 

silicates,  316 

sulphate,  312 
Aluminate  of  magnesia,  312 

potassa,  312 
Aluminite,  312 
Aluminum,  310 

and  sulphur,  321 

sesquichloride,  321 
Alums,  312 

Amalgamated  zinc,  465 
Amalgamation-process,  399 
Amalgam,  defined,  229 
Amalgams,  465 

qualitative  analysis,  567 
Amalgam,  quantitative  ana- 
lysis, 612 
Amethyst,  310 
jSmianth,  308 
Amides,  formation,  276 
Amidide  of  potassium,  132 
Amidogen,  132 
Ammonia,  133 
Ammonia- alum,  316 
Ammonia,  antimoniate,  431 

bicarbonate,  278 

bichromate,  333 

biinetantimoniate,  432 

bisulphate,  277 

bisulphite,  276 

carbonate,  278 

determination,  592 

examination,  503 

hydrosulphate,  280 

metantimoniate,  432 

muriate,  278 

nitrate,  276 

nitrite,  275 

phosphates,  277 

preparation,  133 


Ammonia,  reactions,  511 
sesquicarbonate,  277 

examination,  503 
solid,  133 
solution,  134 
sulphate,  276 
sulphite,  276 
Ammonias  aqua  f or tissima,  134 
Ammonium,  134,  275 
Ammonium-amalgam,  135, 

275 
Ammonium,  aurochloride, 

398 

bisulphide,  280 
bromide,  280 
chloride,  278 

examination,  503 
hydrosulphate   of    sul- 
phide, 280 
iodide,  280 
oxide,  275 
sulphide,  280 

examination,  503 
theory,  135 
Amorphous  bodies,  51 
Amphibole,  308 
Analcime,  256 
Analyses,  calculation,  600 
Analysis,  definition,  495,  496 
for  acids,  Tables  VI.  and 

VII.,  562,  563 
for  bases,  Tables  I.  to  V. 

551-556 
of  air,  130 
alloys,  567 
amalgams,  567,  612 
animal  ashes,  642 
alum,  604 
brass,  611 

Britannia-metal,  611 
bronze,  611 
calamine,  608 
cast-iron,  624 
chloride  of  sodium,  600 
chrome-iron  ore,  604 
clays,  605 
coal,  188 
coal-gas,  205 
copper-pyrites,  608 
crystallized  sulphate 

of  copper,  608 
fusible  alloy,  610*. 
German  silver,  611 
glass,  621 
gun-metal,  611 
gunpowder,  619 
heavy-spar,  601 
insoluble  silicates,  621 
insoluble  substances, 

567 

iron  ores,  606 
lead-glass,  624 
limestones,  602 
manganiferous  spathic 

iron-ore,  608 
marble,  602 


Analysis  of  mineral  waters, 

628 

pewter,  609 
platinum-ores,  418 
quartz,  594 
Bochelle  salt,  602 
Seignette  salt,  602 
silver-ores,  493 
soils,  635 
speiss-cobalt,  612 
standard  gold,  612 

silver,  612 

sulphate  of  baryta,  601 
tartar- emetic,  609 
tartrate  of  potassa  and 

soda,  602 
type-metal,  610 
ultramarine,  626 
vegetable  ashes,  640 
waters,  628 
wavellite,  606 
operations  in,  571 
preparation     of     sub- 
stances for,  546 
proximate,  495 
of  coal,  190 
qualitative,    apparatus 

for,  497 
quantitative,  apparatus 

for,  570 

reagents  for,  499 
systematic,  546 
ultimate,  495 
Anatase,  450 
Andalusite,  31.6 
Anhydrite,  296 
Anhydrous,  69 
Animal  charcoal,  193 

purification  of,  195 
Annealing,  223 
Anorthite,  311 
Anthosiderite,  344 
Anthracite,  187 
Antichlore,  259 
Antimonial  silver,  490 
Antimoniate  of  ammonia,  431 
potassa,  431 
teroxide   of  antimony, 

431 

Antimonic  acid,  430 
determination,  583 
reactions,  525 
Antimonious  acid,  431 
Antimoniuretted    hydrogen, 

432 

Antimony,  428 
alloys,  436 
antimoniate  of  teroxide, 

431 

basic  nitrate,  430 
butter,  433 
chlorosulphide,  434 
determination  in  alloys, 

583 

flowers,  430 
glass,  435 


INDEX. 


647 


Antimony,  golden  sulphuret,  Arsenite  of  copper,  440 


436 

liver,  435 
Antimonyle,  430 
Antimony,  metallurgy,  436 

native,  436 
Antimony-ochre,  436 
Antimony-ore,  gray,  434 
-    red,  434 

white,  429 

Antimony-ores,  assay,  437 
Antimony,    pentachloride, 
433 

pentasulphide,  435 

pharmaceutical  prepara- 
tions, 437 

purification,  428 

regulus,  428 

sesquichloride,  433 

sesquioxide,  429 

suboxide,  429 

sulphates,  430 

terbromide,  434 

terchloride,  433 

terfluoride,  434 

teriodide,  434 

teroxide,  429 

determination,  583 
reactions,  524 

tersulphide,  434 
Apatite,  298 
Apparatus    for    qualitative 

analysis,  497 
Aqua-fortis,  130 
Aqua  regia,  143 
Aqueous  fusion,  56 

vapor,  121 
Argand  lamp,  102 
Argentan,  389 
Arragonite,  299 
Arseniate  of  silver,  440 
Arseniates  of  potassa,  440 

soda,  440 
Arsenic,  437 
Arsenic  acid,  440 

determination,  584 

reactions,  530 
Arsenic  and  tin,  443 
Arsenical  caustic,  443 
Arsenical  iron,  443 
Arsenical  pyrites,  437 
Arsenic,  bisulphide,  442 

chlorosulphide,  441 

octodecasulphide,  443 

pentasulphide,  442 

pharmaceutical  prepara- 
tions, 443 

reduction-tubes,  112 

subsulphide,  442 

terchloride,  441 

tersulphide,  442 

white,  438 

w,ith  metals,  443 
Arsenide  of  manganese,  443 
Arsenides  of  copper,  443 

iron,  443 


potassa,  439 
Arsenious  acid,  438 

determination,  584 

reactions,  525 

Arseniuretted  hydrogen,  441 
Artificial  gems,  311 
Asbestos,  308 
Ashes,  animal,  analysis,  642 

vegetable,  analysis,  640 
Aspirator,  96 
j  Assay  of 

alloys  of  gold  by  cupel- 
lation,  401 

antimony-ores,  437 

auriferous  ores,  402 

bismuth-ores,  394 

copper-ores,  389 

galena,  482 

iron-ores,  355 

mercury-ores,  467 

silver-ores,  493 

tin-ores,  429 

zinc-ores,  366 
Atacamite,  384 
Atmospheric  air,  130 
Atomic  theory,  42 

weights,  41 
Augite,  308 
Aurate  of  potassa,  396 

soda,  396 
Auric  acid,  396 
Auriferous   ores,    assay  of, 
402 

valuation  of,  402 
Auriferous  sand,  examination 

by  washing,  402 
Aurosulphite  of  potassa,  396 
Aurum  musivum,  426 
Aurum potabile,  397 
Axes  of  crystals,  52 


BALANCES,  571 
Balling  process,  265 
Barilla,  263 
Bar-iron,  353 
Barium,  282 

binoxide,  285 

chloride,  286 

examination,  503 

fluoride,  286 

hydro  sulphate    of   sul- 
phide of,  287 

pentasulphide,  287 

silicofluoride,  287 

sulphide,  287 

tersulphide,  287 
Baryta,  282 

-biborate,  285 

bicarbonate,  285 

bisulphate,  284 

borate,  285 

carbonate,  285 

chlorate,  283 

determination,  588 

hydrate,  283 


Baryta,  hyposulphite,  287 

nitrate,  283 

permanganate,  361 

phosphate,  284 

reactions,  511 

seleniate,  284 

sesquicarbonate,  285 

sulphate,  284 

sulphite,  284 
Baryta-water,  283 
Basalt,  317 
Base,  definition,  40 
Bases,  preliminary  examina- 
tion for,  547 
Basic  salts,  49 

water,  56 
Bathgate  coal,  186 
Baum^'s  flux,  237 
Beakers,  87 
Bell-metal,  389 
Benzoic  acid,  reactions,  545 
Berlin  porcelain,  320 
Beryl,  321 
Beryllium,  320 
Berzelius's  lamp,  102 
Bibasic  acid,  definition,  40 
Biborate  of  soda,  269 
Bicarburetted  hydrogen,  207 

of  Faraday,  208 
Bimetantimoniate  of 

ammonia,  432 

potassa,  432 

soda,  432 

Binary  theory  of  acids.  163 
Bismuth,  390 
Bismuth-amalgam,  466 
Bismuth  arsenide,  392 

bisulphide,  392 
Bismuth-blende,  392 
Bismuth,  carbonate,  392 
Bismuth-glance,  392 
Bismuthic  acid,  392 
Bismuth,  metallurgy,  393 
Bismuth-minerals,  393 
Bismuth,  nitrate,  391 
Bismuth-ochre,  393 
Bismuth-ores,  assay,  394 
Bismuth,  oxy chloride,  391 

suboxide,  391 

sulphate,  392 

terchloride,  391 

teroxide,  391 

determination,  579 
reactions,  520 

tersulphide,  392 

trisnitrate,  391 
Bismuthum  album,  391 
Bismuth,  uses,  393 
Black  ash,  265 
Black-band,  350 
Black  flux,  99 
Black-jack,  366 
Black-lead,  185 
Black's  blowpipe,  105 
Black's  furnace,  104 
Blanquette,  263 


648 


INDEX. 


Blast-furnace,  350 
Bleaching,  295 
Bleaching-compounds,  138 
Bleaching  liquid   of  Labar- 

raque,  258 
Bleaching  powder,  294 

valuation,  616 
Bleaching  power  of  chlorine, 

136 

Block-tin,  427 
Blood-stone,  349 
Blowpipe-flame,  107 
Blowpipe-flames,  colored,  110 
Blowpipe-lamp,  106 
Blowpipe-reagents,  106 
Blowpipe-supports,  106 
Blowpipe,  use  of,  105 
Blue  copper,  385 

copperas,  380 

malachite,  382 

stone,  380 

verditer,  380 

vitriol,  380 

vitriol  of  commerce,  ex- 
amination of,  381 
Boiler-incrustations,  300 
Boiling-points,  determination 

of,  82 
Bole,  318 

Bologna  phosphorus,  287 
Bone-ash,  298 
Bone-black,  193 
Bone-earth,  298 

as  manure,  298 
Boracic  acid,  215 

determination,  593 

manufacture,  215 

reactions,  534 
Borate  of 

magnesia  and  soda,  308 

soda,  269 
Borates,  216 

of  baryta,  285 
Borax,  269 

for  blowpipe  reagent,  107 

octohedral,  269 

manufacture,  269 

uses,  270 

vitrified,  270 
Borofluoride    of    potassium, 

215 
Boron,  214 

and  nitrogen,  217 

and  sulphur,  217 

terchloride,  217 

terfluoride,  217 
Braunite,  358 
Bricks,  refractory,  319 
Brass,  387 

analysis,  611 
Britannia  metal,  427 

analysis,  611 
Brittle  silver  ore,  490 
Brochantite,  382 
Bromate  of  potassa,  249 
Bromates,  146 


Bromic  acid,  146 

Bromide  of  ammonium,  280 

antimony,  434 

lead,  470 

potassium,  252 

silicon,  227 

silver,  489 

sodium,  273 

sulphur,  168 
Bromides,  147 
Bromides  of 

iodine,  152 

iron,  346 

mercury,  463 

phosphorus,  183 

selenium,  171 

sulphur,  168 
Bromine,  145 

action  of,  upon  organic 
substances,  152 

chloride,  147 

determination,  597 

and  silica,  227 

hydrate,  146 
Bronze,  388 

analysis,  611 
Bronze-powder,  426 
Brookite,  450 
Brown  coal,  186 
Brown  iroh-ore,  compact,  342 

fibrous,  342 
Brucite,  304 
Brunner's    method    of   ana- 
lyzing silicates,  623 
Brunswick  green,  384 
Bude-light,  116 
Bulb  absorption-tubes,  74 
Bulb-tubes,  112 
Butter  of  antimony,  433 

zinc,  365 

CADMIUM,  376 

carbonate,  377 

chloride,  377 

nitrate,  377 

oxide,  376 

determination,  580 
reactions,  521 

"Bub sulphate,  377 

sulphate,  377 

sulphide,  377^ 
Caking  coal,  187. 
Calamine,  364 

analysis,  608 

electric,  365 
Calcareous  spar,  299 
Calcium,  289 

binoxide,  300 

bisulphide,  302 
Calcium,  chloride,  301 

examination,  504 
Calcium,  fluoride,  301 

oxychloride,  301 

oxysulphide,  302 

pentasulphide,  302 

phosphide,  303 


alcium,  sulphide,  302 
alomel,  459 
Cannel  coal,  186 
Canton's  phosphorus,  302 
Caoutchouc  joints,  65 
Capillary  pyrites,  369 
Carbamide,  276 
Carbides,  214 
Carbon,  184 
Carbonate  of 

alumina,  316 

baryta,  285 

bismuth,  392 

cadmium,  377 

glucina,  322 

iron,  342 

lime,  299 

lime  and  soda,  300 

lithia,  275 

manganese,  357 

potassa  and  soda,  268 

sesquioxide  of  chromium 
330 

silver,  487 

strontia,  288 

zinc,  364 
Carbonates,  200 

of  ammonia,  277 

cobalt,  371 

copper,  382 

lead,  473 

magnesia,  307 

mercury,  458 

potassa,  250 

soda,  263 

Carbon-batteries,  194 
Carbon,  bisulphide,  212 

chlorides,  210 

general    properties     of, 

193 
Carbonic  acid,  197 

composition,  199 

determination,  596 

liquefaction,  75 

liquid,  198 

reactions,  536 

solid,  198 

solidification,  76 

solvent  action,  199 
Carbonic  oxide,  195 
Carbonic  oxide  series,  197 

test  for,  197 
Carbon,  perchloride,  212 

protochloricle,  212 

sesquichloride,  212 

,uses,  194 
Carburets,  194 
Cast-iron,  352 

analysis,  624 

black,  353 

gray,  353 

impurities  in,  852 

white,  353 
Catalysis,  47 
Caustic  potassa,  232 

soda,  257 


INDEX. 


649 


Caustic  soda,  preparation  for 

soap-boiling,  257 
Celestine,  288 

Cement,  limestone  for,  exa- 
mination, 292 

Portland,  292 

Ransome's  vitrified,  293 

Roman,  292 

Cementation  process,  354 
Cerite,  324 
Cerium,  324 

oxide,  325 

reactions,  325 

salts,  325 

sesquioxide,  325 
Ceruse,  473 
Chalcedony,  219 
Chalcolite,  335 
Chalk,  precipitated,  299 
Chameleon-mineral,  359 
Charbon-roux,  192,  243 
Charcoal,  190 

absorption  of  gases  by, 
192 

burning,  190 

deoxidizing    properties 
of,  194 

for  fuel,  104 

properties  of,  192 
Charcoal  supports,  106 
Charring  by  steam,  192 
Chauffer,  104 
Chemistry,     definition    of, 

33 

Chili-saltpetre,  257  . 
China,  320 
China,  glazing,  320 
Chlorate  of 

baryta,  283 

potassa,  247 

soda,  258 
Chlorates,  140 

uses,  140 
Chloric  acid,  139 

determination,  599 

reactions,  542 
Chloride  of 

aluminum,  321 

ammonium,  278 

arsenic,  441 

barium,  286 

boron,  217 

bromine,  147 

cadmium,  377 

cerium,  325 

glucinum,  322 

lime,  valuation,  616 

magnesium,  309 

nickel,  369 

nitrogen,  144 

potassium,  251 

silicon,  226 

silver,  487 

soda,  258 

sodium,  271 

strontium,  288 


Chloride  of  tantalum,  493 

uranyle,  337 

vanadium,  374 

yttrium,  324 

zirconium,  326 
Chlorides,  144 
Chlorides  of 

antimony,  433 

bismuth,  391 

calcium,  301 

carbon,  210 

chromium,  333 

cobalt,  372 

copper,  383 

gold,  397 

iodine,  152 

iridium,  415 

iron,  345 

lead,  477 

lithium,  275 

manganese,  361 

mercury,  459 

molybdenum,  448 

niobium,  493 

osmium,  417 

palladium,  412 

phosphorus,  181 

platinum,  407 

rhodium,  413 

ruthenium,  418 

selenium,  171 

sulphur,  167 

tellurium,  450 

tin,  424 

titanium,  452 

tungsten,  445 

uranium,  337 

zinc,  365 
Chlorimetry,  615 
Chlorine,  136 

action  of,  upon  organic 
substances,  152 

determination,  597 

hydrate,  137 

peroxide,  139 
Chlorine- water,  136 
Chlorocarbonic  acid,  197 
Chlorochloric  acid,  140 
Chlorochromate  of  potassa, 

ooo 

OOO 

Chlorochromic  acid,  334 

Chloronitrie  acid,  143 

Chloronitrous  acid,  143 

Chloroperchloric  acid,  141 

Chlorophosphide  of  nitrogen, 
183 

Chlorostannates,  425 

Chlorosulphide   of  nitrogen, 
167 

Chlorosulphide   of  phospho- 
rus, 182 
silicon,  228 

Chlorosulphuric  acid,  277 

Chlorous  acid,  139 

Chromate  of 

ammonia,  333 


Chromate  of  soda,  333 

suboxide  of  mercury,  456 
Chromates,  331 

of  lead,  475 

potassa,  331 

sesquioxide  of  chromium, 

333 

Chrome-alum,  329 
Chrome-iron  ore,  327 

analysis,  604 
Chrome-yellow,  475 
Chromic  acid,  330 

determination,  595 

reactions,  535 
Chromium,  326 

brown  oxide,  327 

chloride,  333 

fluoride,  335 

nitride,  333 

oxide,  327 

oxychloride,  334 

protosesquioxide,  330 

sesquichloride,  334 

sesquioxide,  327 
carbonate,  330 
chromate,  333 
determination,  585 
nitrate,  329 
reactions,  514 
sulphate,  329 
Chromium,  sulphides,  335 
Chrysocolla,  383 
Chrysolite,  308 
Cinders,  187 
Cinnabar,  464 

valuation,  577 
Citric  acid,  reactions,  544 
Clark's  process  for  softening 
water,  122 

soap-test,  632 
Clay,  fire-  318 
Clay-ironstone,  349 
Clay,  pipe- 318 

potter's,  318 
Clays,  317 

analysis,  605      i 

chemical  characters,  318 
Cleavage,  52 
Coal,  185 

analysis,  188 

ash,  187 

Bathgate,  186 

black,  186 

brown,  186 

caking,  187 

cannel,  186 

cubical,  186 

decomposition,  187 

glance,  187 

peacock,  187 

pit,  187 

pitch,  186 

proximate  analysis,  190 

splint,  186 

Welsh,  187 
Coal-fires,  187 


650 


INDEX. 


Coal-gas,  203 

analysis,  205 

mines,  explosions  in,  203 

tar-naphtha,  205 
Cobalt,  370 

carbonates,  371 

chloride,  392 

double  sulphate,  371 

nitrate,  371 

nitrate,  for  blowpipe  re- 
agent, 107 
Cobalt-ore,  gray,  373 

white,  373 
Cobalt,  oxide,  370 

oxide,        determination, 
587 

oxide,  reactions,  516 

oxysulphide,  373 

protoxide,  370 
Cobalt-pyrites,  373 
Cobalt,  sesquichloride,  372 

sesquioxide,  371 

sesquisulphide,  373 

subarsenide,  443 

sulphate,  371 

sulphide,  373 

technical  history,  373 
Cobalt,  Tunaberg,  373 
Coke,  190 

hearths,  191 
Colcothar,  341,  342 
Colors  for  glass,  225 
Columbium,  493 
Combination,  44 

by  volume,  43 
Combining  proportions,  41 
Combustion-furnace,  104 

table,  103 

tubes,  112 
Common  phosphates,  179 

phosphoric  acid,  178 

salt,  271 

Composition  of  water  deter- 
mined, 120 

Condensation  of  gases,  74 
Condensing  apparatus,  80 
Condurrite,  443 
Constitutional  water,  56 
Copper,  377 
Copper-amalgam,  466 
Copper,      ammoniochlorides, 
384 

ammonio-nitrate,  380 

ammonio-sulphates,  382 

and  silver,  alloys,  466 

and  tin,  alloys,  387 
Copper  and  zinc,  alloys,  387 

arsenides,  433 

arsenite,  440 
Copperas,  340 

blue,  380 
Copper-Azure,  382 
Copper,  basic  nitrate,  380 

basic  sulphates,  382 

bibasic  carbonate,  382 

binoxide,  383 


Copper,  black  oxide,  379 
Copper,  blue  carbonate,  385 

carbonate,  382 

chloride,  384 

commercial,  purification, 
377 

determination,    in    ores, 
580 

double  carbonates,  382 

double  sulphates,  381 

engraving  on,  387 
Copper-glance,  384 
Copper,  hydrated  oxide,  380 

hydride,  383 

metallurgy,  385 
Copper-native,  385 
Copper-nickel,  369 
Copper,  nitrate,  380 

nitride,  383 
Copper-ore,  gray,  386 

red,  378 

variegated,  386 
Copper-ores,  assay,  389 
Copper,  oxide,  379 

determination,  579 
reactions,  520 

oxychlorides,  384 

oxysulphide,  385 

phosphides,  385 
Copper-pyrites,  385 

analysis,  608 
Copper,  red  oxide,  378 

silicates,  383 

subchloride,  383 

suboxide,  378 

subsulphate,  379 

subsulphide,  384 

sulphate,  380 
analysis,  608 
uses,  381 

sulphide,  385 

tinning,  389,  427 

uses,  387 
Coquimbite,  343 
Cork-borers,  61,  497 
Corks,  60 

perforation  of,  61 
Correction  of  gases  for  pres- 
sure, 38 
Correction  of  gases  for  tem- 
perature, 38 

Corrosive  sublimate,  460 
Corundum,  310 
Croconic  acid,  197 
Crocus,  435 
Crucible-jacket,  98 
Crucibles,  100 

composition,  319 

lined  with  charcoal   for 
iron  reductions,  100 

precautions   in  heating, 

98 

Crushing,  84 
Crushing  mortar,  8 
Crystals,  feeding,  97 

forms  of,  52 


Crystals    from     the    leaden 
chambers,  160 

Crystallization,  51,  96 
by  fusion,  97 
by  solution,  96 
by  vaporization,  97 
promoted,  97 
purification  by,  96 
water  of,  56 

Crystallography,  52 

Cubical  coal,  186 

Cubic  nitre,  257 

Cupel,  480 

Cupellation,  480 

Cupric  acid,  383 

Cyanite,  316 

Cyanogen,  209 

compounds,  210 
liquefaction  of,  209 

Cylinder-charcoal,  192 

DECANTATION,  92 

Decantation,  washing  by,  93 

Decoction,  90 

Decomposition,  46 

Decrepitation,  107 

Definition  of  chemical  terms, 
40 

Deflagration,  107 

Deflagrating-spoons,  71 

Deliquescence,  95 

Derbyshire  spar,  302 

Desiccating  tubes,  66 

Desiccation,  95 
in  vacuo,  94 
of  volatile  bodies,  95 

Desiccators,  95 

Destructive  distillation,  46 

Determination  of 

alkalies  in  silicates,  623 
alumina,  685 
ammonia,  592 
antimonic  acid,  683 
antimony  in  alloys,  683 
arsenic  acid,  684 
arsenious  acid,  684 
baryta,  588 
binoxide    of    platinum, 

681 

tin,  682 

boracic  acid,  593 
bromine,  597 
carbonic  acid,  596 
chloric  acid,  599 
chlorine,  597 
chromic  acid,  595 
copper  in  ores,  680 
fluorine,  595 
hydriodic  acid,  597 
hydrobromic  acid,  597 
hydrochloric  acid,  597 
hydrofluoric  acid,  595 
hydrosulphuric  acid,  598 
iodine,  597 
lime,  590 
magnesia,  590 


INDEX. 


651 


Determination  of 

nitric  acid,  599,  619 
oxalic  acid,  596 
oxide  of  cadmium,  680 
cobalt,  587 
copper,  579 
lead,  578 
manganese,  588 
mercury,  577 
nickel,  587 
silver,  576 
tin,  582 
zinc,  588 

phosphoric  acid,  593 
potassa,  590 
protoxide  of  iron,  586 
sesquioxide     of      chro- 
mium, 585 
iron,  58o 
silicic  acid,  594 
silver  by  standard  solu- 
tion, 612 
soda,  591 
stannic  acid,  582 
strength  of  commercial 

acids,  619 
strontia,  589 
suboxide  of  mercury, 

576 

sulphur,  598 
sulphuric  acid,  592 
sulphurous  acid,  595 
teroxide    of     antimony, 

683 

bismuth,  579 
gold,  681 

value  of  commercial  pot- 
ash, 616 

commercial  soda,  618 
manganese  ore,  614 
water    of    constitution, 

601 

crystallization,  601 
Detonation,  107 
Devitrification,  223 
Diamond,  184 
Diamond,  amorphous,  185 
Diaspore,  311 
Didymium,  224 

reactions,  325 
Diffusion  of  gases,  57 
Diffusion-tube,  57 
Digestion,  88 

Dimetaphosphoric  acid,  178 
Dimorphous  bodies,  51 
Dioptase,  383 
Diplatosarnine,  407 
Diplatosammonium,  407 
Dishes,  87 
Disinfectants,  295 
Disintegration,  84 
Displacement-apparatus,  90 
Disthene,  316 
Distillation,  77 

at  high  temperatures,  77 
at  lower  temperatures,  79 


Distillation,  at  temperatures 
below  212°  F.,  82 

connecting-tubes  in,  80 

dry,  77 

facilitation  of,  82 

fractional,  82 

on  a  small  scale,  80 
Distilled  water,  122 

for  analysis,  507 
Dithionates,  159 
Dithionic  acid,  158 
Dolomite,  308 
Double  decomposition,  47 
Drummond  light,  119 
Drying-closet,  103 
Drying-tiles,  96 
Dutch  liquid,  210 
Dutch  metal,  387 

EAGLE-STONE,  349 
Earthenware,  common,  321 

glaze  for,  320 
Eau  de  Javelle,  249 
Edulcoration,  92 

of  precipitates,  574 
Efflorescence,  56 
Elective  decomposition,  47 
Electrochemical  theory,  46 
Electro-gilding,  400 
Electrolysis,  46 
Electro-plating,  492 
Element,  definition,  113 
Elements,     classification,    of 
113 

table  of,  114 
Embolite,  489 
Emerald,  321 
Emerald  of  Limoges,  322 
Emery,  311 
Enamel,  225 
English  porcelain,  319 

glazing,  319 
Epsom  salts,  305 
Equations,  50 
Equivalent  volumes,  43 
Equivalents,  40 

table  of,  114 
Erbia,  324 

salts,  324 
Erbium,  323 
Ethiops  mineral,  464 
Euchlorine,  138 
Euclase,  322 
Eudiometer,  Ure's,  71 
Eudiometers,  71 
Eudiometry,  70 
Evaporation,  94 

at  the  boiling  tempera- 
ture, 94 

below  ebullition,  94 

in  quantitative  analysis. 
572 

in  vacuo,  94 

spontaneous,  94 

to  dryness,  94    • 


FARADAY'S    gas     condensing 

tube,  74 
Feldspar,  256,  316 

lime-  317 

lithia-  317 

potash-  316 

soda-  317 
Ferrate  of 

potassa,  344 

soda,  345 
Ferrates,  345 

Ferri  sulphas  exsiccalum,  341 
Ferric  acid,  344 
Ferroso-ferric  oxide,  344 
Filtering-paper,  91 

examination,  498 

quantitative,  570 
Filtering,  precautions  in,  91 
Filters,  91 
Filter-stands,  91 
Filtration,  90 
Fire-clay,  318 
Fire-damp,  201 
Flake-white,  391 
Flame,  structure  of,  108 
Flames,  luminous,  107 
Flasks,  drying,  630 

for  distillation,  80 

gas  evolution,  59 

solution,  88 
Fleitmann   and   Henneberg's 

phosphates,  179 
Fleitmann' s  test  for  arsenic, 

529 
Flint,  219 

and  steel,  330 
Florence  flasks,  57 
Fluoboric  acid,  217 
Fluoride  of 

aluminum,  321 

antimony,  434 

barium,  286 

boron,  217 

calcium,  301 

chromium,  335 

potassium,  253 

potassium  and  glucinum, 
323 

silicon,  227 

silver,  489 

sodium,  273 
Fluorides,  154 
Fluorine,  153 

Fluorine,  determination,  595 
Fluor-spar,  301 
Flux,  black,  90 

Baume"'s,  237 
Fluxes,  90 
Fly-powder,  438 
Formulae,  49 
Freezing  mixtures,  260 
French  chalk,  308 
Fresenius  and    Babo's   test, 

526 

Fuel,  patent,  188 
Fuel,  valuation,  188 


652 


INDEX. 


Fuller's  earth,  318 
Fulminating  gold,  396 

platinum,  406 

silver,  485 
Fuming  liquor   of  Libavius, 

425 

Funnel-bags,  90 
Funnel,  hot  water,  91 
Funnel-tubes,  60 
Funnels,  91 
Furnaces,  103 
Fusible  alloy,  393 

analysis,  610 
Fusion,  99 

aqueous,  56 

igneous,  56 

with  nitre,.  101 

precautions  in,  100 

Gadolinite,  324 
Galena,  471 

assay,  482 

Gallic  acid,  reactions,  544 
Garnet,  317 
Gas-bags,  67 
Gas-bladders,  67 
Gas-carbon,  190 
Gas-cylinders,  68 
Gases,  apparatus  for  collect- 
ing, 68 

collection,  67 

collection  of  by  displace- 
ment, 69 

combustion  of,  70 

combustion  in,  71 

condensation,  74 

detonation,  70 

diffusion,  57 

generation   of   at    ordi- 
nary temperatures,  64 

measurement,  72 

preparation  with  the  aid 
of  heat,  59 

purification,  64 

separation    by    absorp- 
tion, 74 

solution,  73 

transference,  72 
Gasholder,  Pepy's,  66 
Gas,  illuminating,  from  wa- 
ter, 207 
valuation,  204 
Gas-jars,  capped,  68 

stoppered,  68 
Gas-jets,  70 

lime,  205 
Gas,  defiant,  207 

used  as  fuel,  102 
Gauze  burners,  102 
Gaylussite,  300 
Gems,    artificial,    216,   226, 

311 
General  reagents,  treatment 

with,  550 
German  silver,  389 

analysis,  611 


Geyser,  220 

Gibbsite,  316 

Gilding,  400 

Glacial  phosphoric  acid,  177 

Glance-coal,  187 

Glance-cobalt,  373 

Glass,  221 

analysis,  621 

Bohemian,  224 
Glassblowing,  110 
Glass,  bottle-,  224 

colors  for,  225 

crown,  224 

flint,  225 

materials  for,  224 

paste,  225 

plate-,  224 

soluble,  222 
Glass-tubing,  German,  111 

operations  with,  61 
Glass,  window-  224 
Glauber's  salts,  259 
Glaze  for  earthenware,  319 
Glazes,  colored,  319 
Glazing  with    common   salt, 

273 
Glucina,  322 

carbonate,  322 

reactions,  322 

sulphates,  322 
Glucinum,  321 

and    potassium,    double 
fluoride,  323 

sesquichloride,  322 

sesquisulphide,  322 
Gneiss,  317 

Goadby's  solution,  461 
Gold,  394 

and  soda,  hyposulphite, 
395 

alloys,  400 

assay  by  cupellation,  401 

examination    by  touch- 
stone, 401 

alluvial,  398 
Gold-amalgam,  466 
Gold,  double  chlorides,  397 

dust,  399 

extraction,  399 

fulminating,  396 

jeweller's,  400 
Gold-leaf,  400 
Gold,  metallurgy,  398 

minerals,  398 

mosaic,  426 

native,  398 
Gold-ores,  fusion,  399 
Gold,  oxide,  395 

parting,  401 

powder,  466 

protochloride,  397 

quartation,  399 

refining,  399 

standard,  399 
analysis,  612 

sulphides,  398 


Gold,  terchloride,  397 

teroxide,  396 

determination,  681 
reactions,  521 

washing,  399 

wire,  400 
Goniometer,  56 
Grain-tin,  427 
Granite,  317 
Granulation,  86 
Graphite,  185 
Green  salt  of  ma  gnus,  407 
Green  vitriol,  340 

manufacture  of,  340 
Gray  antimony-ore,  434 
Gray  copper-ore,  386 
Gray  nickel-ore,  369 
Gros's  platinum-base,  408 
Guanite,  307 
Gun-metal,  388 

analysis,  611 
Gunpowder,  239 

analysis,  619 

composition  o*f  different 
varieties,  241 

manufacture,  242 

properties,  246 

white,  248 
Gypsum,  296 

Ilair-salt,  305 
Haloid  salts,  definition,  40 
Hannemann's    soluble    mer- 
cury, 456 
Hausmanite,  358 
Heating  arrangements,  102 
Heavy  lead-ore,  476 
Heavy-spar,  284 

analysis,  601 
Hemming's  jet,  120 
Hepar  sulphuris,  255 
Herapath's  blowpipe,  111 
Hexametaphosphoric  acid, 

178 

Hisingerite,  344 
Haematite  brown,  349 

red,  349 

Homberg's  phosphorus,  315 
Hornblende,  308,  317 
Horn-lead,  478 
Horn-mercury,  467 
Horn-silver,  487 
Hot  blast,  351 
Hyacinth,  326 
Hydrate  of 

baryta,  283 

bromine,  147 

chlorine,  136 

lime,  290 

magnesia,  304 

potassa,  232 

soda,  257 
Hydrates,  49,  121 

of  phosphoric  acid,  177 

silica,  219 
Hydration,  water,  56 


INDEX. 


653 


Hydraulic  mortars,  291 

of  Tournay,  293 
Hydriodate  of  potassa,  252 
.Hydriodic  acid,  150 

determination,  597 

reactions,  539 
Hydriodous  acid,  150 
Ilydroboracite,  308 
Hydrobromic  acid,  146 

determination,  597 

reactions,  538 
Hydrochloric  acid,  142 

determination,  597 

examination,  501 

reactions,  537 

solution,  142 
Hydrocyanic  acid,  reactions, 

540 

Hydroferricyanic  acid,  reac- 
tions, 541 

Hydroferrocyanic  acid,  reac- 
tions, 541 
Hydrofluoric  acid,  153 

determination,  595 

reactions,  536 
Hydrofluoboracic  acid,  217 
Hydrofluosilicic  acid,  227 
Hydrogen,  118 

and  platinum,  407 

and  silicon,  226 

antimoniuretted,  432 

arseniuretted,  441 

bicarburetted,  207 

binoxide,  123 

light  carburetted,  201 

pentasulphide,  165 

phosphides,  179 

phosphuretted,  179 

purification,  118 

seleniuretted,  171 

sulphuretted,  165 

telluretted,  450 

teroxide,  116 
Hydrometers,  35 
Hydroselenic  acid,  171 
Hydrosulphate  of 

ammonia,  280 

potassa,  253 

sulphide  of  ammonium, 
280 

sulphide  of  barium,  287 

sulphide  of  sodium,  273 
Hydrosulphocyanic  acid,  re- 
actions, 541 
Hydrosulphuric  acid,  165 

determination,  598 

hydrate,  166 

reactions,  539 
Hydrosulphurous  acid,  165 
Hydrotelluric  acid,  450 
Hygrometers,  131 
Hyperoxymuriate  of  potassa, 

247 

Hypochloric  acid,  139 
Hypochlorite  of 

lime,  294 


Hypochlorite  of 

magnesia,  305 

potassa,  249 

soda,  258 

Hypochloronitric  acid,  143 
Hypochlorous  acid,  137 

reactions,  542 
Hyponitric  acid,  127 
Hyponitrous  acid,  126 
Hypophosphites,  175 
Hypophosphoric  acid,  176 
Hypophosphorous  acid,  175 
Hyposulphates,  159 
Hyposulphite  of 

baryta,  287 

gold  and  soda,  395 

soda,  258 
Hyposulphites,  156 

of  silver,  486 
Hyposulphuric  acid,  158 
Hyposulphurous  acid,  156 

ICE,  120 
Iceland  spar,  299 
Igneous  fusion,  56 
Ignition,  93 

in  quantitative  analysis, 
573 

in  tubes,  99 

of  precipitates,  575 
Ilmenium,  494 
Incandescence,  107 
Incineration  in   quantitative 
analysis,  573 

of  vegetables,  640 
Incrustations,  109 

in  boilers,  121 
Indian  fire,  442 
Indigo  copper,  385 
Infusion,  88 
Ink,  sympathetic,  372 
Insoluble  silicates,  analysis, 

621 

Insoluble  substances,  analy- 
sis of,  566 
Intumescence,  107 
lodate  of  potassa,  249 
lodates,  149 
lodic  acid,  149 
Iodide  of 

ammonium,  280 

antimony,  434 

nitrogen,  151 

potassium,  252 

silver,  489 

sodium,  273 

sulphur,  168 
Iodides,  154 

of  iron,  346 
lead,  470 
mercury,  463 
phosphorus,  183 
Iodine,  148 

determination,  597 

action  of,  upon  organic 
substances,  152 


Iodine,  bromides,  152 

chloride,  152 

compound  solution  of,  252 

terchloride,  152 
Iridium,  414 

bichloride,  415 

binoxide,  414 
Iridium-black,  414 
Iridium,     double     chlorides, 
415 

oxide,  414 

protochloride,  415 

reactions,  415 

sesquichloride,  415 

sesquioxide,  414 

terchloride,  415 

teroxide,  414 
Iron,  338 

Iron-amalgam,  465 
Iron,  ammonio-chloride,  346 

ammonio-nitrate,  340 

arsenical,  443 

arsenides,  443 

bar-,  353 

bisulphide,  347 

black  oxide,  344 

bromides,  346 

carbonate,  342 

cast-,  353 
analysis,  624 

cold-short,  352 
Iron-glance,  349 
Iron,  iodide,  346 

magnetic  oxide,  344 

metallurgy,  349 

meteoric,  349 

nitrate,  340 

nitride,  345 
Iron-ore,  micaceous,  349 

oolitic,  349 

sparry,  350 

spathic,  350 
Iron-ores,  349 

analysis,  606 

assay,  355 

preparation,  350 

smelting,  350 
Iron,  oxide,  340 

determination,  586 
reactions,  515 

passive  state,  339 

peroxide,  342 

protochloride,  345 

proto-sesquioxide,  344 

protosulphate,  340 

protoxide,  340 

pure,  preparation,  338 

purification,  352 

oxides  of,  determination 
of  relative  quantities, 
587 

Iron-pyrites,  347 
Iron,  pyrophoric,  338 

refining,  352 

rusting,  339 
Iron- sand,  349 


654 


INDEX. 


Iron,  sesquichloride,  345 
sesqui-iodide,  346 
sesquioxide,  342 

basic  sulphates,  343 

determination,  585 

hydrate,  343 

nitrate,  343 

phosphate,  344 

reactions,  516 

silicates,  344 

sulphate,  343 
sesquisulphide,  347 
specular,  349 
Iron-stone,  magnetic,  349 
Iron,  subphosphide,  348 
subsulphide,  346 
sulphate,  340  ' 

uses,  341 
sulphide,  347 
sulphuret,  347 
tersulphide,  348 
tinned,  427 
titanic,  450 
with  boron,  349 

carbon,  348 

silicon,  349 
wrought,  353 
Isomerism,  49 
Isomorphism,  52 
Ivory-black,  193 

JASPER,  219 
Jet,  187 

Jeweller's  gold,  400 
Joints  in  distillation,  80 

Kaolin,  317 
Karstenite,  296 
Kelp,  263 

Kermes  mineral,  435 
King's  yellow,  442 
Kryolite,  256 

LABARRAQTTE'S  BLEACHING 

LIQUOR,  258 

Labrador,  256 
Labradorite,  317 
Lagoons,  215 
Lakes,  316 
Lampblack,  193 
Lanarkite,  475 
Lanthanium,  324 

oxide,  325 

reactions,  325 

salts,  325 
Lapis  lazuli,  273 
Laughing  gas,  124 
Law  of  definite  and  multiple 

proportions,  42 
Lead,  468 

alloys,  481 
Lead-amalgam,  466 
Lead,  basic  carbonate,  473 
nitrates,  471 
nitrites,  471 

binoxide,  476 


Lead,  bromide,  478 

carbonate,  473 

chloride,  477 

chlorosulphide,  479 

chromate,  uses,  475 

corrosion,  473 

dichromate,  475 
Lead-glass,  analysis,  624 
Leadhillite,  475  * 
Lead,  iodide,  479 

metallurgy,  479 
Lead-minerals,  479 
Lead,  neutral  chromate,  475 

nitrate,  471 

nitrite,  471 

oxide,  470 

determination,  578 
reactions,  530 

oxychlorides,  478 

oxy-iodide,  478 

peroxide,  476 

protoxide,  470 

puce  oxide,  476 

pure,  preparation,  468 
Lead,  pyrophorus,  468 
Lead,  selenide,  479 

silicates,  475 

solubility  in  water,  469 
Lead-spar,  473 
Lead,  subchromate,  475 

suboxide,  469 

sulphate,  472 

sulphide,  478 
Lead-tree,  469 
Lead,  uses,  481 
Lead-vitriol,  472 
Leblanc's  process,  264 
Lemery's  volcano,  347 
Lepidolite,  274 
Levigation,  86 

in  blowpipe  operations, 

109 
Liebig's  condenser,  78 

potassa-apparatus,  74 
Light  carburetted  hydrogen, 

201 

Lignite,  186 
Lime,  289 

acid  phosphate,  298 

agricultural  uses,  293 

and  soda,  double  carbon- 
ate, 300 

bicarbonate,  300 
Lime,  bisulphate,  289 
Lime-bleach,  294 
Lime  burning,  289 

carbonate,  299 
analysis,  590 

common  phosphate,  298 

determination,  590 
Lime-feldspar,  317 
Lime,  hydrate,  290 

hypochlorite,  294 
Lime-kilns,  289 
Lime,  milk,  291 

nitrate,  293 


Lime,  reactions,  512 

silicate,  as  manure,  219 
Limestone,  300 

for  cement,  examination^ 

292 

Limestones,  analysis,  602 
Lime,  sulphate,  296 

sulphite,  295 

superphosphate,  299 

triphosphate,  298 
Lime-water,  290 
Liquor  fumans  Boi/lii,  281 
Liquor  potassae,  233 
Litharge,  470 

reduction,  481 

uses,  471 
Lithia,  274 

carbonate,  275 
Lithia-feldspar,  317 
Lithia-mica,  274 
Lithia,  nitrate,  275 

phosphate,  275 

reactions,  275 

salts,  275 

sulphate,  275 
Lithium,  275 

chloride,  275 
Liver  of  sulphur,  255 
Lixiviation,  89 
Loadstone,  344 
Loam,  318 
Lucifer-matches,  248 
Lunar-caustic,  485 
Luting,  63 

MACERATION,  89 
Magnesia,  304 
Magnesia  alba,  307 
Magnesia,  aluminate,  312 

and  ammonia,  double 
sulphate,  306 

phosphate,  306 

and  potassa,  phosphate, 
307 

phosphate,  305 

and  soda,  borate,  308 

basic  carbonate,  307 

bicarbonate,  307 

calcinata  ponder osa,  304 

calcined,  304 

carbonate,  307 

common  phosphate,  306 

determination,  590 

heavy  carbonate,  308 

hydrate,  304 

hypochlorite,  305 

nitrate,  304 

pyrophosphate,  306,  307 

reactions,  513 

sulphate,  305 
Magnesia  usta,  304 
Magnesite,  307 
Magnesium,  303 

chloride,  309 

sulphide,  309 
Magnetic  iron-stone,  349 


INDEX. 


655 


Magnetic  pyrites,  348 
Malachite,  382 
Malachite,  blue,  382 
Manganate  of  potassa,  359 

soda,  360 
Manganese,  355 
Manganese- alum  (natural], 

357 

Manganese-alums,  357 
Manganese  arsenide,  443 

binoxide,  358 

uses,  359 

Manganese-blende,  361 
Manganese,  carbonate,  357 

chloride,  361 

double  sulphides,  361 
Manganese- ores,  valuation, 

614 
Manganese,  oxide,  356 

determination,  588 

reactions,  518 

oxysulphide,  361 

pel-chloride,  361 

peroxide,  358 

phosphate,  357 

protosesquioxide,  358 

red  oxide,  358 

sesquichloride,  361 

sesquioxide,  358 
sulphate,  358 

silicates,  357 

sulphate,  356 

sulphide,  361 
Manganic  acid,  359 
Manganiferous  spathic  iron- 
ore,  analysis,  608 
Many  anile,  358 
Marble,  299 
Marble,  analysis,  602 
Margueritte's  process,  606 
Marl,  318 
Marsh-gas,  202 
Marsh's  test,  528 
Mascagnine,  276 
Massicot,  470 
Meadow-ore,  349 
Meerschaum,  308 
Melanochroite,  476 
Mellon,  210 
Mendipite,  478 
Mercuramine,  462 
Mercurial-trough,  68 
Mercury,  454 

amido-subchloride,  460 

amm.oniated  oxide,  457 

ammoniated  subchloride, 
460 

basic  carbonates,  458 
nitrates,  458 
subnitrates,  456 

black  oxide,  456 

bromide,  463 

chloramidide,  462 

chloride,  460 
uses,  461 

double  chlorides,  461 


Mercury,    expansion   of,    by 
heat,  454 

extraction  from  its  ores, 
467 

iodide,  463 

manipulations  with,  69 

metallurgy,  467 

native,  467 

nitrate,  458 

nitric  oxide,  457 

nitride,  459 

Mercury-ores,  assay,  467 
Mercury-oxide,  457 

determination,  577 

reactions,  519 

oxyamidide,  457 

salts,  458 

oxybromide,  463 

oxychlorides,  462 

oxyiodide,  463 

pharmaceutical  prepara- 
tions, 467 

protonitrate,  456 

red  oxide,  457 

soluble,  Hannemann's, 
456 

subbromide,  463 

subchloride,  459 

subchromate,  456 

subiodide,  463 

sub  nitrate,  456 

suboxide,  456 

determination,  576 
reactions,  530 

subsulphate,  456 

subsulphide,  464 

sulphate,  458 

sulphide,  464 

double  compounds, 

465 

Metal,  definition,  113 
Metallic  powders,  prepara- 
tion, 86 

Metalloid  denned,  113 
Metallurgy  of 

antimony,  436 

bismuth,  393 

copper,  385 

gold,  398 

iron,  349 

lead,  479 

mercury,  467 

nickel,  369 

platinum,  410 

silver,  490 

tin,  426 

zinc,  366 

Metals,  analytical  classifica- 
tion, 507 

physical  properties,  494 
Metantimoniate  of 

ammonia,  432 

potassa,  431 
Metantimonic  acid,  431 
Metaphosphate  of  soda,  262 
Metaphosphates,  177 


Metaphosphoric  acid,  177 
Metastannate  of 

oxide  of  tin,  424 

potassa,  424 

soda,  424 

Metastannic  acid,  423 
Meteoric  iron,  349 

stones,  349 
Miasmata,  132 
Mica,  317 

Micaceous  iron-ore,  349 
Microcosmic  salt,  as  blow- 
pipe-reagent, 107 

preparation,  277 
Milk  of  lime,  291 
Milk  of  sulphur,  preparation, 

255 
Mineral,  chameleon,  359 

green,  384 

waters,  122 
analysis,  628 

yellow,  478 
Minerals  of  gold,  398 
Mine -tin,  426 
Minium,  477 

Mirrors,  manufacture,  466 
Mispickel,  437 
Mitscherlich's  lamp,  102 
Moire  metallique,  421 
Molybdates,  447 
Molybdena,  446 
Molybdenum,  446 

bichloride,  448 

binoxide,  447 

bisulphide,  448 

blue  oxide,  447 

green  oxide,  447 

oxide,  446 

oxychloride,  448 

protochloride,  448 

reactions,  448 
Molybdic  acid,  447 
Molybdic  ochre,  447 
Monobasic     acid,  definition, 
40 

Monometaphosphoric  acid, 

178 

Morass-ore,  349 
Mortar,  291 
Mortars  and  pestles,  85 
Mortars,  hydraulic,  291 

of  Tournay,  293 
Mosaic  gold,  425 
Mother-liquor,  96 
Mountain  blue,  382 
Muffle,  104 
Muriatic  acid,  142 

of  commerce,  142 
Mysorine,  382 

NASCENT  STATE,  45 
Natterer's  condensing  appa- 
ratus, 76 

Needle  iron-ore,  342 
Neutralization,  40 


656 


INDEX. 


Newton's  fusible  alloy,  393 

analysis,  610 
Nickel,  367 

Nickel-antimony,  369,  436 
Nickel,  arsenio- sulphide,  369 

basic  sulphate,  368 

chloride,  369 

double  sulphates,  368 
Nickel-glance,  369 
Nickel,  metallurgy,  369 

nitrate,  367 
Nickel-ore,  gray,  369 
Nickel,  oxide,  367 

determination,  587 
reactions,  517 

peroxide,  368 

sesquioxide,  368 

subsulphide,  369 

sulphate,  368 

sulphide,  369 
Niobic  acid,  493 
Niobium,  493 

chloride,  493 

sulphide,  493 
Nitrate  of 

alumina,  312 

ammonia,  276 

baryta,  283 

binoxide  of  platinum,  406 

cadmium,  377 

cobalt,  371 

lime,  293 

lithia,  27 

magnesia,  304 

nickel,  367 

oxide  of  iron,  340 

palladium,  411 

potassa,  234 

sesquioxide     of    chro- 
mium, 329 
iron,  343 
uranium,  336 

silver,  485 

soda,  257 

strontia,  288 

tin,  422 

zinc,  364 
Nitrates,  129 

of  bismuth,  391 
copper,  380 
lead,  471 
Nitrates  of  mercury,  458 

suboxide    of    mercury, 

456 
Nitre,  234 

cubic,  257 

Nitre-earth,  lixiviation,  235 
Nitre,  examination  of,  238 

for  blowpipe  reagent,  107 
Nitre-heaps,  128 
Nitre,  manufacture  of,  235 
Nitre-plantations,  235 
Nitre,  refining,  235 

refraction,  238 

uses,  237 


Nitric  acid,  127 

action  of,  upon  organic 
substances,  129 

anhydrous,  127 

determination,  599,  619 

examination,  501 

fuming,  130 

hydrated,  128 

preparation,  128 

reactions,  541 
Nitric  oxide,  125 
Nitride  of  chromium,  333 
Nitrification,  theory  of,  234 
Nitrite  of 

ammonia,  275 

potassa,  247 

silver,  485 
Nitrites  of  lead,  471 
Nitrogen,  123 

and  boron,  217 

and  sulphur,  166 

binoxide,  125 

chloride,  144 

chlorophosphide,  183 

chlorophosphite,  183 

chlorosulphide,  167 

iodide,  151 

peroxide,  127 

phosphides,  183 

protoxide,  124 

teroxide,  126 

tersulphide,  166 
Nitromuriatic  acid,  143 
Nitrosulphates,  166 
Nitrosulphuric  acid,  166 
Nitrous  acid,  126 

commercial,  130 
Nitrous  oxide,  124 
Nomenclature,  47 
Notation,  49 

Ochre,  yellow,  318 

Ochres,  318 

Octohedral  borax,  269 

Oil-bath,  82 

Oil-gas,  206 

Oil-lamp,  102 

Oil  of  vitriol,  160 

distillation,  82 
impurities  in,  161 

Olefiant  gas,  207 

Oligist,  349 

Olivine,  308 

Oolitic  iron-ore,  349 

Opal,  219 

Ores  of  iron,  349 
silver,  490 

Orpiment,  red,  442 
yellow,  442 

Orthite,  324 

Organic  acids,  analytical  clas- 
sification, 542 

Orthoclase,  316 

Osmic  acid,  416 

Osm-iridium,  415 

Osmious  acid,  416 


Osmites,  416 
Osmium,  415 

bichloride,  417 

binoxide,  416 

chloride,  417 

oxide,  416 

reactions,  417 

sesquioxide,  416 
Oxalic    acid,   determination, 

596 

reactions,  537 
Oxide,  carbonic,  195 
Oxide  of 

ammonium,  275 

antimonyle,  430 

cadmium,  376 

didymium,  325 

lanthanium,  325 

platosammonium,  407 

selenium,  169 

thorinum,  323 

uranyle,  336 
Oxides  of 

antimony,  429 

arsenic,  437 

barium,  282 

bismuth,  391 

calcium,  289 

carbon,  195 

cerium,  325 

chlorine,  137 

chromium,  327 

cobalt,  370 

copper,  378 

gold,  395 

hydrogen,  119 

iodine,  149 

indium,  414 

iron,  340 

lead,  469 

manganese,  356 

mercury,  455 

molybdenum,  446 

nickel,  367 

nitrogen,  124 

osmium,  416 

palladium,  411 

phosphorus,  175 

platinum,  405 

potassium,  231 

rhodium,  413 

ruthenium,  417 

selenium,  169 

silver,  484 

sodium,  257     . 

strontium,  288 

sulphur,  156 

tantalum,  493 

tellurium,  449 

tin,  422 

titanium,  451 

tungsten,  444 

uranium,  335 

vanadium,  374 

zinc,  363 
Oxy-amidide  of  mercury,  457 


INDEX. 


675 


Oxybromide  of  phosphorus, 

183 
Oxychloride   of  phosphorus, 

182 
Oxy  chlorides,  145 

of  zinc,  365 
Oxygen,  115 
Oxygen,  combustion  in,  71 

preparation,  115 
Oxyhydrogen  blowpipe,   119 
Oxysulphides,  168 
Ozone,  116 

tests  for,  117 

PACKFONG,  388 
Palladium,  411 

bichloride,  412 

binoxide,  411 

double-chlorides,  412 

nitrate,  411 

oxide,  411 

protochloride,  412 

reactions,  412 
Papin's  digester,  121 
Paracyanogen,  209 
Paris  yellow,  478 
Parting  of  gold,  399 
Patent  fuel,  188 
Pattinson's  process,  480 
Peacock  coal,  187 
Peacock-copper-ore,  385 
Pearlashes,  250 
Pearl-white,  392 
Peat,  186 
Pelopic  acid,  494 
Pelopium,  494 
Pentathionates,  164 
Pentathionic  acid,  164 
Perchlorate  of  potassa,  249 
Perchlorates,  141 
Perchloric  acid,  141 
Perchromic  acid,  333 
Percolators,  90 
Percussion-tube  composition, 

249 

Pericline,  317 
Peridote,  308 
Periodate  of  potassa,  249 
Periodates,  150 
Periodic  acid,  150 
Permanganate  of 

baryta,  361 

potassa,  360 

silver,  361 

Permanganic  acid,  360 
Petalite,  274,  317 
Petrifying  springs,  300 
Pewter,  427,  481 

analysis,  609 
Philosopher's  wool,  362 
Phosgene  gas,  197 
Phospharr,  183 
Phosphamide,  183 
Phosphate  of 

alumina,  316 

42 


Phosphate  of 

baryta,  284 

lithia,  275 

magnesia  and  ammonia, 
307 

manganese,  357 

sesquioxide  of  iron,  344 

soda  and  ammonia,  277 

Phosphates,    Fleitmann    and 

Henneberg's,  179,  263 

of  ammonia,  277 
lime,  298 
magnesia,  306 
soda,  260 

tribasic,  178 

triple,  307 
Phosphatic  acid,  176 
Phosphide  of 

calcium,  303 

iron,  348 
Phosphides,  184 

of  copper,  885 
hydrogen,  179 
nitrogen,  183 
tungsten,  446 
Phosphites,  176 
Phosphoric  acid,  176 

anhydrous,  177 

determination,  593 

hydrates,  177 

reactions,  532 
Phosphorous  acid,  176 
Phosphorus,  172 

allotropic  modifications, 
173 

amorphous,  174 

and  selenium,  184 
sulphur,  183 

chlorosulphide,  182 

impurities  in,  174 

iodides,  183 

oxy  bromide,  183 

oxychloride,  182 

pentabromide,  183 

pentachloride,  182 

red,  174 

Phosphorus-salt,    for    blow- 
pipe reagent,  109 
Phosphorus,  suboxide,  175 

terbromide,  183 
Phosphorus,  terchloride,  181 

white,  173 
Phosphuretted  hydrogen, 

gaseous,  180 

liquid,  180 

solid,  180 
Pig-iron,  351 
Pimclite,  370 
Pinchbeck,  387 
Pipe-clay,  318 

Pipette  for  eudiometrical  ex- 
periments, 74 
Pipettes,  93 
Pitch,  205 
Pitchblende,  335 


Pit-coal,  187 
Plaster  casts,  398 
Plaster  of  Paris,  397 
Platinates,  406 
Plating,  492 
Platinum,  403 

alloys,  410 

Platinum-amalgam,  466 
Platinum,  ammoniated  proto- 
chloride, 407 

ammonia-chloride,  409 
Platinum-bases,  407 
Platinum,  bichloride,  408 
double-salts,  409 

binoxide,  406 

determination,  681 
nitrate,  406 
reactions,  522 
sulphate,  406 

bisulphide,  410 
Platinum-black,  404 

_     action  on  gases,  404 
Platinum-foil,  106 
Platinum,  fulminating,  406 

metallurgy,  410 
Platinum-ores,  analysis,  418 
Platinum,  oxide,  405 

perchloride,  408 

potassio-chloride,  409 

protochloride,  407 

residues,  treatment,  408 

sodio-chloride,  409 

spongy,  403 

sulphide,  409 

uses  of,  410 

vessels,   precautions    in 
use,  404 

wire,  106 

Platosammonium,  oxide,  407 
Plumbago,  185 
Plumbates,  476 

of  potassa,  476 
Plumbites,  470 
Pneumatic  trough,  68 
Polymerism,  49 
Porcelain,  Berlin,  320 

English,  319 
Porcelain-painting,  319 
Porcelain,  Reaumur's,  223 
Porcelaine-tendre,  321 
Portland  cement,  292 
Potash,  231 
Potash-albite,  317 
Potash-feldspar,  316 
Potashes,  250 
Potash  valuation,  616 
Potassa,  231 

aluminate,  312 

antimoniate,  431 

arseniates,  440 

arsenite,  439 

aurate,  496 

aurosulphite,  496 

bicarbonate,  251 

bichromate,  332 


676 


INDEX. 


Potassa,  bimetantimoniate, 

432 

bisulphate,  250 
bromate,  249 
carbonate,  250 
caustic,  232 
chlorate,  247 
chlorochromate,  333 
chromate,  331 
determination,  590 
examination,  502 
ferrate,  344 
fusa,  233 
hydrate,  232 
hydriodate,  252 
hyperoxymuriate,  247 
hypochlorite,  249 
hyposulphite,  254 
iodate,  249 

Potassa-iron-alum,  344 
Potassa,  manganate,  359 
metantimoniate,  431 
metastannate,  424 
nitrate,  234 
nitrite,  247 
perchlorate,  249 
periodate,  249 
permanganate,  360 
plumbates,  476 
reactions,  510 
silicates,  251 
stannate,  423 
sulphate,  249 
sulphate    and    bichro- 
mate, 333 
terchromate,  333 
uranate,  337 
uses,  234 
Potassium,  230 
Potassium-amalgam,  465 
Potassium,  amidide,  132 
aurochloride,  397 
bisulphide,  255 
borofluoride,  215 
bromide,  252 
chloride,  251 
chloride,  combinations, 

252 

cyanide,  for  blowpipe- 
reagent,  107 
fluoride,  253 
hydrofluate  of  fluoride 

253 

hydrosulphate  of  sul- 
phide, 254 
iodide,  252 

impurities  in,  252 
valuation,  253 
pentasulphide,  255 
peroxide,  251 
polysulphides,  255 
silicofluoride,  255 
suboxide,  231 
sulphide,  254 


otassium,    sulphocarbonate 
of  sulphide,  254 

tersulphide,  255 
Potter's  day,  318 
3ottery,  SIS 

-'ouring,  directions  for,  86 
3owder  of  Algaroth,  433 
'recipitates,  edulcoration  of, 
574 

ignition  of,  575 
-*recipitation  defined,  51 

in  quantitative  analysis, 
.      574 
^recipitatum  per  se,  457 
'reliminary  examination  for 
acids,  559 

for  bases,  547 
J'silomelane,  358 
Cuddling  process,  352 
^Iverization,  85 
Pulvis  fulminans,  237 
Pumice  stone,  317 
3urple  of  Cassius,  395 
:>utty- powder,  423 
Puzzolano,  292 
Pyrites,  arsenical,  437 

capillary,  369 

cobalt,  373 

copper,  385 

cubical,  350 

iron,  347 

magnetic,  348 

martial,  347 

radiated,  350 

tin,  426 
Pyrochlorite,  323 
Pyrolusite,  358 
Pyrophorus,  Magnus's,  339 
Pyrophosphate  of  soda,  262 
Pyrophosphates,  178 
Pyrophosphoric  acid,  178 
Pyroxene,  317 

QUALITATIVE  analysis,  syste 

matic,  546 
apparatus  for,  570 
evaporation  in,  572 
ignition  in,  573 
operations  in,  571 
precipitation  in,  574 
solution  for,  572 

Quartation  of  gold,  401 

Quartz,  219 

analysis,  594 

Quicklime,  289 

RAEWSKY'S  platinum-base, 

408 

Rain-water,  121 
Ransome's  vitrified  cement, 

293 
Reactions  of 

acetic  acid,  546 
alumina,  513 
ammonia,  511 


leactions  of 

antimonic  acid,  525 
arsenic  acid,  529 
arsenious  acid,  525 
baryta,  511 
benzoic  acid,  545 
binoxide    of  platinum. 

522 

binoxide  of  tin,  523 
boracic  acid,  534 
carbonic  acid,  536 
cerium,  326 
chloric  acid,  542 
chromic  acid,  535 
citric  acid,  544 
didymium,  326 
erbium,  325 
gallic  acid,  544 
gluoina,  322 
hydriodic  acid,  539 
hydrobromic  acid,  538 
hydrochloric  acid,  537 
hydrocyanic  acid,  540 
hydroferricyanic  acid, 

541 
hydroferrocyanic  acid, 

541 

hydrofluoric  acid,  536 
hydrosulphocyanic  acid, 

541 

hydrosulphuric  acid,  539 
hypochlorous  acid,  512 
iridium,  415 
lanthanium,  325 
lime,  512 
lithia,  275 
magnesia,  513 
molybdenum,  448 
nitric  acid,  541 
osmium,  417 
oxalic  acid,  537 
oxide  of  cadmium,  521 
cobalt,  516 
copper,  520 
iron,  515 
lead,  530 
manganese,  518 
mercury,  519 
nickel,  517 
silver,  530 
tin,  523 
zinc,  518 
palladium,  412 
phosphoric  acid,  532 
potassa,  510 
rhodium,  413 
ruthenium,  418 
sesquioxide  of  chromi- 
um, 514 
iron,  514 
silicic  acid,  534 
soda,  511 
strontia,  512 
suboxide  of   mercury, 
530 


INDEX. 


677 


Reactions  of 

succinic  acid,  545 
sulphuric  acid,  532 
sulphurous  acid,  535 
tannic  acid,  543 
tartaric  acid,  543 
tellurium,  450 
terbium,  324 
teroxide  of  antimony, 

524 

bismuth,  520 
gold,  521 
thorina,  324 
titanium,  453 
tungsten,  446 
uranium,  337 
uric  acid,  544 
vanadium,  375 
yttria,  324 
zirconia,  328 
Reagents, 

definition,  499 

for  qualitative  analysis, 

499 

general  definition,  499 
examination,  500 
list,  499 

preparation,  500 
special,  definition,  499 
examination,  505 
list,  500 

preparation,  505 
Realgar,  442 
Reaumur's  alloy,  436 
Reaumur's  porcelain,  223 
Receivers,  78 
quilled,  78 
tubulated,  78 
Recrystallization,  96 
Red  antimony-ore,  436 
Red  copper-ore,  385 
Red  fire,  288 
Red-lead,  477 
Red  lead- ore,  475 
Red-lead,  uses  of,  477 
Red  orpiment,  442 
Red  silver-ore,  489 
Reduction,  by  fusion,  101 

on  charcoal,  109 
Reduction-tubes,  106 
Regulus  of  antimony,  428 
Reinsch's  test  for  arsenic, 

527 

Reiset's    platinum    com- 
pounds, 407 
Resin-gas,  207 
Retorts,  79 
filling,  79 
heating,  81 
iron,  59 
protection,  81 
tubulated,  79 
Rhodium,  412 

chlorides,  413 
oxide,  413 


Rhodium,  reactions,  413 

sesquioxide,  413 
Rhodizonic  acid,  197 
Ring-burner,  103 
River- water,  122 
Roasting  in  blowpipe-flame, 

109 

Rock  alum,  313 
Rochelle  salt,  analysis,  602 
Rock-crystal,  219 
Rock-salt,  271 

impurities  in,  272 
Roll  sulphur,  154 
Roman  alum,  313 
Roman  cement,  292 
Rose's  lamp,  102 
Ruby,  310,  326 
Rupert's  drop,  223 
Rust,  ammonia  in,  339 
Rusting  of  iron,  339 
Rutheniatos,  418 
Ruthenic  acid,  418 
Ruthenium,  417 

binoxide,  417 

bichloride,  418 

chloride,  418 

oxide,  417 

reactions,  418 

sesquichloride,  418 

sesquioxide,  417 
Rutile,  450 

SAFETY-LAMP,  Davy's,  202 
Safety-tubes,  60 
Sal-alembroth,  468 
Sal-ammoniac,  278 
Salicor,  263 
Sal-prunelle,  237 
Salt,  271 

definition,  40 

extraction,  272 
Salt-glazing,  273 

graduation,  271 

of  tartar,  250 
Saltpetre,  234 
Saltpetre-flour,  236 
Saltpetre-rot,  234 
Salt-radical,  definition,  40 
Salt,  schlotage,  272 

soccage,  272 
Sal  volatile,  277 
Sand,  219 

Sand  for  glass-making,  224 
Sand-trays,  69 
Sapphire,  310 
Saturation,  90 

defined,  51 

of  liquids  with  solids,  90 
Saturn's  tree,  469 
Scheele's-green,  440 
Schweinfurt-green,  440 
Sea-salt,  271 
Sea- water,  122 
Seignette  salt,  analysis,  602 
Seleniate  of  baryta,  284 


Selenic  acid,  170 
Selenide  of  lead,  479 
Selenides,  171 

of  phosphorus,  184 
Seleniferous  deposit,  169 
Selenious  acid,  170 
Selenite,  296 
Selenites,  170 
Selenium,  169 

bromides,  171 
chlorides,  171 
flowers,  169 
oxide,  169 
sulphides,  171 
Seleniuretted  hydrogen,  171 
Separating  funnel,  93 
Separation  of 

alumina  and  potassa,  604 
antimony,  lead,  and  bis- 
muth, 610 
arsenic,   cobalt,  nickel, 

and  iron,  612 
cadium  and  zinc,  608 
chlorine,  bromine,  and 

iodine,  627 

chromium  and  iron,  604 
copper  and  iron,  608 
copper  and  silver,  611 
copper,    tin,  antimony, 

and  lead,  611 
copper,  zinc,  and  nickel, 

611 
gold,  silver,  and  copper, 

612 
iron,  alumina,  silica,lime, 

and  magnesia,  605 
lime,  magnesia,  and  ses- 
quioxide of  iron,  602 
liquids,  93 

manganese  and  iron,  608 
mercury  and  tin,  612 
mercury  and  zinc,  612 
phosphoric  acid  and  alu- 
mina, 606 
potassium  and   sodium, 

602 
silicic  acid  and  alumina, 

602 

tin  and  antimony,  610 
tin,  antimony,  copper, 

and  bismuth,  609 
tin,   copper,  lead,  and 

zinc,  611 
tin,  lead,  and  bismuth, 

610 

Serpentine,  308 
Shear-steal,  354 
Shells,  299 

Shot,  manufacture,  482 
Sienna,  299 
Silica,  219 

hydrates,  219 
soluble,  natural  deposits, 
219 


678 


INDEX. 


Silicate  of  lime,  as  manure, 

219 

zirconia,  326 
Silicates,  221 

Brunner's    method   of 

analyzing,  623 
decomposition  of  by  chlo- 
ride of  barium,  286 
insoluble,  analysis,  621 
of  alumina,  316 
copper,  383 
lead,  475 
manganese,  357 
potassa,  251 
sesquioxide  of  iron, 

344 

soda,  270 

zinc,  365 

Silicic  acid,  219 

determination,  594 
reactions,  534 
Silicofluoride  of  barium,  287 

potassium,  255 
Silicon,  218 

and  bromine,  22-7 
hydrogen,  226 
sulphur,  228 
chlorosulphide,  228 
terchloride,  226 
terfluoride,  227 
tersulphide,  228 
Sillimanite,  316 
Silver,  482 
Silver-amalgams,  466 
Silver,  ammonio-chloride,488 
ammonio-nitrate,  486 
and  copper,  alloys,  492 
arseniate,  440 
binoxide,  487 
bromide,  489 
carbonate,  487 
chloride,  487 
chlorobromide,  489 
double    hyposulphites, 

487 

extraction,  by  amalga- 
mation, 490 
fluoride,  489 
fulminating,  485 
Silver-glance,  489 
Silver,  hyposulphite,  486 

iodide,  489 
Silver-lustre,  410 
Silver,  metallurgy,  490 
Silver,  native,  490 
nitrate,  485 
nitrite,  485 
Silver-ores,  490 
Silver,  oxide,  484 

determination,  576 
reactions,  530 
permanganate,  361 
pure,  preparation,  482 
residues,  treatment,  486 
standard,  analysis,  612 


Silver,  suboxide,  484 
sulphate,  487 
sulphide,  489 
technical  history,  492 
Silvering  on  glass,  492 
Slaked  lime,  290 
Smalt,  373 
Smelling-salts,  278 
Smithy-scales,  344 
Soapstone,  308 
Soap-test,  632 
Soda,  257 

acid  phosphate,  261 
acid  pyrophosphate,  262 
Soda-alum,  316 

arseniates,  440 
Soda,  artificial,  from  common 

salt,  264 
Soda-ash,  manufacture,  264 
Soda,  aurate,  396 
biborate,  209 
bicarbonate,  268 
bimetantimoniate,  432 
bisulpbate,  260 
bisulphite,  259 
borate,  269 
carbonate,  263 
examination,  502 
for  blowpipe  reagent, 

106 

impurities  in,  268 
uses,  268 
caustic,  257 
chlorate,  258 
chloride,  258 
chromate,  333 
common,  261 
common  phosphate,  260 

analysis,  601 
determination,  591 
dipyrophosphate,  262 
Soda-feldspar,  317 
Soda,  ferrate,  345 
hydrate,  257 
hypochlorite,  258 
hyposulphite,  258 
Soda-lakes,  263 
Soda-liver  of  sulphur,  273 
Soda,  manganate,  360 
manufacture  of,  264 
metaphosphate,  262 
nitrate,  257 
phosphates,  260 
Soda-process,    Tilghman's, 

267 

Soda,  pure  carbonate,  266 
pyrophosphate,  262 
reactions,  511 
sesquicarbonate,  268 
sesquisulphate,  260 
silicates,  270 
stannate,  423 
subphosphate,  260 
sulphate,  259 
sulphite,  259 


Soda,  triphosphate,  260 

valuation,  618 
Soda-waste,  266 
Sodium,  256 
Sodium-amalgam,  465 
Sodium,  aurochloride,  396 
bromide,  273 
chloride,  271 
analysis,  600 
uses,  272 
fluoride,  273  • 
hydrosulphate  of    sul- 
phide, 273 
iodide,  273 
oxide,  257 
suboxide,  257 
sulphides,  273 
peroxide,  271 
Soils,  analysis,  635 
Solder,  481 
Soldering,  270 
Solubility,  determination,  86 
Solution,  86 

at  ordinary  tempera- 
tures, apparatus  for, 
87 

by  the  aid  of  heat,  appa- 
ratus for,  87 
in  quantitative  analysis, 

572 

in  test-tubes,  88 
of  substances  for  analy- 
sis, 548,  560 
promoted,  88 
theory  of,  51 
Solvents,  87 
Soot,  187 
Spatulas,  85 
Specific  gravity,  833 
bottle,  35 
of  a  liquid,  35 
a  powder,  34 
a  solid,  34 

a  solid  soluble  in  wa- 
ter, 34 
gases,  36 
vapors,  36 
Specular  iron,  349 
Speculum-metal,  389 
Span,  370,  373 
Speiss  cobalt,  analysis,  612 
Spelter,  366 
Sphene,  450 
Spindle,  312 
Spirit-blowpipe,  111 
Spirit-lamps,  102 
Splint  coal,  186 
Spodumene,  274,  317 
Spring- water,  121 
Stalactites,  300 
Stalagmites,  300 
Standard  gold,  400 

analysis,  612 
Standard  silver,  492 
analysis,  612 


INDEX. 


679 


Stannate  of  oxide  of  tin,  423 

potassa,  423 

soda,  423 
Stannic  acid,  423 

determination,  582 
Steam,  121 
Steatite,  308 
Steel,  354 

blistered,  354 

cast,  354 

decarbonization,  355 

natural,  354 

properties,  354 

shear,  354 

tempering,  354 
Slilbite,  317 
Stills,  77 
Still-worm,  77 
Stirrers,  87 

Stoppers,  loosening,  68 
Straining,  92 
Strass,  225 
Stream-tin,  426 
Strontia,  288 

carbonate,  288 

determination,  589 

nitrate,  288 

reactions,  512 

sulphate,  288 
Strontianite,  288 
Strontium,  287 

binoxide,  288 

chloride,  288 

sulphides,  288 
Struvite,  307 
Stuccoes,  298 

Sublimation,  apparatus  for, 
84 

directions  for,  84 

described,  77 

Substitution-products,  152 
Succinic  acid,  reactions,  545 
Succussion,  prevention,  82 
Suffioni,  215 
Sugar-lime,  291 
Sulphamide,  276 
Sulphantimoniate  of  sulphide 

of  sodium,  435 
Sulphantimonic  acid,  435 
Sulpharseniates,  443 
Sulpharsenic  acid,  442 
Sulpharsenious  acid,  442 
Sulpharsenites,  442 
Sulphate  of  alumina,  312 

ammon,  276 

ammonia,  276 

baryta,  analysis,  601 

binoxide  of  platinum, 
406 

bismuth,  392 

copper.  380 

iron,  340 

lead,  472 

lithia,  275 

magnesia,  305 


Sulphate  of  manganese,  356 
mercury,  459 
nitric  oxide,  166 
oxide  of  chromium  and 

potassa,  333 
protoxide  of  iron,  340 
sesquioxide  of  chromi- 
um, 329 
iron,  343 
manganese,  358 
uranium,  337 
silver,  487 
strontia,  288 
suboxide  of  copper,  379 

mercury,  456 

tin,  422 

zinc,  364 
Sulphates,  162 

of  antimony,  430 

baryta,  284 

cadmium,  377 

cobalt,  371 

glucina,  322 

lime,  296 

nickel,  368 

potassa,  249 

soda,  259 
Sulphide  of 

aluminum,  321 
boron,  218 
cadmium,  377 
carbon,  212 
cerium,  325 
glucinum,  322 
lead,  478 
magnesium,  309 
molybdenum,  448 
niobium,  493 
nitrogen,  166 
silicon,  228 
silver,  489 
tantalum,  493 
titanium,  452 
vanadium,  374 
Sulphides,  168 
Sulphides  of 

ammonium,  280 
antimony,  435 
arsenic,  441 
barium,  286 
bismuth,  392 
calcium,  302 
chromium,  335 
cobalt,  373 
copper,  384 
gold,  398 
iron,  347 
manganese,  361 
mercury,  464 
nickel,  369 
phosphorus,  183 
platinum,  409 
potassium,  253 
selenium,  171 
sodium,  273 


Sulphides  of 

strontium,  288 
tellurium,  450 
tin,  425 
tungsten,  446 
uranium,  337 
zinc,  365 
Sulphites,  153 
Sulphocarbonate  of  potassa, 

255 

Sulphocarbonates,  214 
Sulphocarbonic  acid,  212 
Sulphophosphates,  132 
Sulphotungstic,  acid,  446 
Sulphur,  154 
Sulphur-acids,  168 
Sulphur  and  boron,  217 
and  nitrogen,  166 
and  silicon,  228 
and  bromine,  168 
and  chlorine,  168 
determination,  598 
Sulphuretted  hydrogen,  165 
Sulphur,  flowers,  154 

for  gunpowder,  242 
Sulphuric  acid,  159 
anhydrous,  159 
bihydrated,  162 
distillation,  161 
determination,  592 
examination,  500 
fuming,  160 
manufacture,  160 
monohydrated,  161 
reactions,  532 
Nordhausen,  160 
terhydrated,  162 
Sulphur,  iodide,  168 
milk  of,  154 

preparation,  255 
|  Sulphurous  acid,  157 

bleaching  action,  157 
determination,  595 
liquid,  157 
reactions,  535 
Sulphur-salts,  168 
Sulphur,  subchloride,  167 
Superphosphate  of  lime,  299 
Supports  for  dishes,  88 

funnels,  90 
Swamp-ore,  349 
Symbols,  49 

table,  114 
Syphon,  for  mineral  waters, 

632 

Syphons,  92 
Syringe-bottle,  92 

TABLE-BLOWPIPE,  111 
Talc,  308 

Tannic  acid,  reactions,  543 
Tantalic  acid,  493 
Tantalites,  494 
Tantalum,  493 
protoxide,  493 


680 


INDEX. 


Tantalum,  sesquichloride, 
493 

sesquioxide,  493 

sesquisulphide,  493 
Tartar-emetic,  analysis,  609 
Tartaric  acid,  reactions,  543 
Tartar,  salt,  250 
Tartrate  of  potassa  and  soda, 

analysis,  602 

Telluretted  hydrogen,  450 
Telluric  acid,  449 
Tellurides,  450 
Tellurium,  449 

bichloride,  450 

chloride,  450 

reactions,  450 

sulphides,  450 
Tellurous  acid,  449 
Tempering  of  steel,  354 
Terbia,  324 

salts,  324 
Terbium,  323 
Testae  preparatse,  300 
Test  for  hardness  of  water, 

632 

Testing,  definition,  496 
Tetrametaphosphoric  acid, 

178 

Tetrathionates  of  baryta,  165 
Tetrathionic  acid,  165 
Thenardite,  259 
ThSnard's  blue,  373 
Thermometric   degrees,  con- 
version of,  39 
Thilorier's  apparatus,  75 
Thorina,  323 

reactions,  323 
Thorinum,  323 
Thorite,  323 
Tin,  420 

Tin-amalgam,  466 
Tin  and  arsenic,  443 
Tin,  bichloride,  424 

binoxide,  423 

determination,  582 
reactions,  523 

bisulphide,  426 
Tincal,  269 

determination  of  value, 

270 
Tin,  chloride,  424 

valuation,  424 
Tinfoil,  427 
Tin,  metallurgy,  426 

metastannate  of  oxide, 

424 

Tinned  iron,  427 
Tinning  of  copper,  389,  427 

pins,  389 
Tin,  nitrate,  422 
Tin-ores,  assay,  427 
Tin,  oxide,  422 

determination,  582 
reactions,  523 

oxychloride,  424 


Tin,  perchloride,  424 

Tin-plate,  427 

Tin,  protoxide,  422 

Tin-pyrites,  426 

Tin,  refining,  by  liquation, 

426 
by  tossing,  427 

sesquioxide,  424 

sesquisulphide,  425 

stannate  of  oxide,  424 
Tin-stone,  423 
Tin,  sulphate,  422 

sulphide,  425 

uses,  427 
Titanic  acid,  451 
Titanic  iron,  450 
Titanite,  450 
Titanium,  450 

bichloride,  452 

bisulphide,  452 

nitrides,  452 

Oxide,  461 

reactions  of,  453 

sesquichloride,  452 

sesquioxide,  451 
Tombac,  387 

white,  443 
Top  ax,  310 
Touchstone,  401 
Triads  of  elements,  152 
Tribasic  acid,  definition,  40 

phosphates,  179 

phosphoric  acid,  178 
Trimetaphosphoric  acid,  178 
Triphane,  317 
Triphosphate  of  soda,  260 
Triple  phosphate,  307 
Tripoli,  219 
Trithionates,  164 
Trithionic  acid,  163 
Trona,  268 
Tube-holder,  88 
Tubes,  sealing  of,  112 
Tubing,  60 
Tunaberg  cobalt,  373 
Tungstates,  445 
Tungsten,  444 

bichloride,  445 

binoxide,  444 

bisulphide,  446 

phosphides,  446 

reactions,  445 

terchloride,  446 

tersulphide,  446 
Tungstic  acid,  445 
Turbith  mineral,  459 
Turner's  yellow,  478 
Type-metal,  481 

analysis,  610 

ULTRAMARINE,  ANALYSIS,  626 

artificial,  273 

green,  274 

natural,  273 
Umber,  318,  350 


Uranate  of  potassa,  337 
Uranite,  335 
Uranium,  335 

black  oxide,  336 

green  oxide,  336 
Uranium-ochre,  336 

oxide,  335 

oxychloride,  337 

peroxide,  336 

protochloride,  337 

protosesquioxides,  336 

reactions,  337 

sesquioxide,  336 
hydrates,  336 
nitrate,  336 
salts,  336 
sulphate,  337 

subchloride,  337 

suboxide,  835 

sulphides,  337 
Uranium-vitriol,  336 
Uran-mica,  335 
Uranyle,  336 

chloride,  337 

oxide,  -336 
Urao,  268 

Uric  acid,  reactions,  544 
Urinometer,  36 

VALUATION  OF  AURIFEROUS 

ORES,  402 
Vanadiates,  374 
Vanadic  acid,  374 
Vanadium,  374 

binoxide,  374 

bisulphide,  374 

protoxide,  374 

reactions,  375 

terchloride,  374 
Vapor-densities,  determina- 
tion of,  136 

Variegated  copper-ore,  385 
Vegetables,  incineration,  640 
Vermilion,  464 

impurities  in,  465 
Vesicular  vapor,  121 
Vitrified  borax,  270 
Vitriol,  blue,  380 
Vitriol-ochre,  343 

WASHING  BOTTLE,  92,  497 

Washing  by  decantation,  92 

Water,  119 

Water-bath,  82 

Water,  decomposition,  120 

at  high  temperatures, 

121 

formation,  119 
Water-gas,  207 
Water,  hard  and  soft,  122 
of  constitution,  56 

determination,  601 
of  crystallization,  56 
determination,  601 
of  hydration,  56 


INDEX. 


681 


Water-oven,  95 

Waters,  acidulous,  122 
analysis,  628 
carbonated,  122 
chalybeate,  122 
saline,  122 
sulphurous,  122 

Wavellite,  316 
analysis,  606 

Weighing,  571 

precipitates,  575 

Welsh  coal,  187 

Welter's  safety-tube,  60 

White  antimony-ore,  429 

White  lead,  473 

examination,  474 
manufacture,  473 

White  lead-ore,  473 

White  lead,  uses,  474 

White  precipitate,  462 

White  vitriol,  364 

Witherite,  285 


Wolfrqm,  445 
Wood-charcoal,  191 
Woulfe's  bottle,  64 
Wrought  iron,  353 

Yellow  orpiment,  442 
Yttria,  324 

reactions,  324 

salts,  324 
Yttrium,  323 
Yttrocerite,  324 
Yttrotantalite,  494 

ZAFFRE,  373 
Zeolites,  221 
Zinc,  362 

Zinc-amalgam,  465 
Zinc,  binoxide,  365 
Zinc-blende,  365 
Zinc,  butter,  365 

carbonate,  364 

double  compound! 


i,364 


Zinc,  chloride,  365 
Zinc-glance,  365 
Zinc,  metallurgy,  366 

nitrate,  364 
Zinc-ores,  assay,  366 
Zinc,  oxide,  368 

determination,  588 
reactions,  518 

oxychlorides,  365 

oxysulphide,  366 

silicate,  365 

suboxide,  363 

sulphate,  364 

sulphide,  365 

uses,  366 
Zinc-white,  363 
Zircon,  326 
Zirconia,  326 

reactions,  326 

salts,  326 

silicate,  326 
Zirconium,  326 


THE   END. 


-95m-7,'37 


: 03989 

&. 

A  a 


